GNAT User's Guide
GNAT, The GNU Ada Compiler
GCC version 4.4.7
AdaCore
--- The Detailed Node Listing ---
About This Guide
Getting Started with GNAT
The GNAT Compilation Model
Foreign Language Representation
Compiling Ada Programs With gcc
Switches for gcc
Binding Ada Programs With gnatbind
Switches for gnatbind
Linking Using gnatlink
The GNAT Make Program gnatmake
Improving Performance
Performance Considerations
Reducing Size of Ada Executables with gnatelim
Reducing Size of Executables with unused subprogram/data elimination
Renaming Files Using gnatchop
Configuration Pragmas
Handling Arbitrary File Naming Conventions Using gnatname
GNAT Project Manager
The Cross-Referencing Tools gnatxref and gnatfind
The GNAT Pretty-Printer gnatpp
The GNAT Metrics Tool gnatmetric
File Name Krunching Using gnatkr
Preprocessing Using gnatprep
The GNAT Library Browser gnatls
Cleaning Up Using gnatclean
GNAT and Libraries
Using the GNU make Utility
Memory Management Issues
Stack Related Facilities
Some Useful Memory Pools
The GNAT Debug Pool Facility
The gnatmem Tool
Verifying Properties Using gnatcheck
Sample Bodies Using gnatstub
Other Utility Programs
Code Coverage and Profiling
Running and Debugging Ada Programs
Platform-Specific Information for the Run-Time Libraries
Example of Binder Output File
Elaboration Order Handling in GNAT
Conditional Compilation
Inline Assembler
Compatibility and Porting Guide
Microsoft Windows Topics
This guide describes the use of GNAT, a compiler and software development toolset for the full Ada programming language. It documents the features of the compiler and tools, and explains how to use them to build Ada applications.
GNAT implements Ada 95 and Ada 2005, and it may also be invoked in Ada 83 compatibility mode. By default, GNAT assumes Ada 2005, but you can override with a compiler switch (see Compiling Different Versions of Ada) to explicitly specify the language version. Throughout this manual, references to “Ada” without a year suffix apply to both the Ada 95 and Ada 2005 versions of the language.
This guide contains the following chapters:
gnatbind, the GNAT binding
utility.
gnatchop, a utility that allows you to preprocess a file that
contains Ada source code, and split it into one or more new files, one
for each compilation unit.
gnatxref and gnatfind, two tools that provide an easy
way to navigate through sources.
gnatkr
file name krunching utility, used to handle shortened
file names on operating systems with a limit on the length of names.
gnatprep, a
preprocessor utility that allows a single source file to be used to
generate multiple or parameterized source files by means of macro
substitution.
gnatls, a
utility that displays information about compiled units, including dependences
on the corresponding sources files, and consistency of compilations.
gnatclean, a utility
to delete files that are produced by the compiler, binder and linker.
gnatcheck,
a utility that checks Ada code against a set of rules.
gnatstub,
a utility that generates empty but compilable bodies for library units.
gnathtml.
This guide assumes a basic familiarity with the Ada 95 language, as described in the International Standard ANSI/ISO/IEC-8652:1995, January 1995. It does not require knowledge of the new features introduced by Ada 2005, (officially known as ISO/IEC 8652:1995 with Technical Corrigendum 1 and Amendment 1). Both reference manuals are included in the GNAT documentation package.
For further information about related tools, refer to the following documents:
Following are examples of the typographical and graphic conventions used in this guide:
Functions, utility program names, standard names,
and classes.
Variables, environment variables, and metasyntactic
variables.
and then shown this way.
Commands that are entered by the user are preceded in this manual by the
characters “$ ” (dollar sign followed by space). If your system
uses this sequence as a prompt, then the commands will appear exactly as
you see them in the manual. If your system uses some other prompt, then
the command will appear with the $ replaced by whatever prompt
character you are using.
Full file names are shown with the “/” character
as the directory separator; e.g., parent-dir/subdir/myfile.adb.
If you are using GNAT on a Windows platform, please note that
the “\” character should be used instead.
This chapter describes some simple ways of using GNAT to build executable Ada programs. Running GNAT, through Using the gnatmake Utility, show how to use the command line environment. Introduction to GPS, provides a brief introduction to the GNAT Programming Studio, a visually-oriented Integrated Development Environment for GNAT. GPS offers a graphical “look and feel”, support for development in other programming languages, comprehensive browsing features, and many other capabilities. For information on GPS please refer to Using the GNAT Programming Studio.
Three steps are needed to create an executable file from an Ada source file:
All three steps are most commonly handled by using the gnatmake utility program that, given the name of the main program, automatically performs the necessary compilation, binding and linking steps.
Any text editor may be used to prepare an Ada program.
(If Emacs is
used, the optional Ada mode may be helpful in laying out the program.)
The
program text is a normal text file. We will assume in our initial
example that you have used your editor to prepare the following
standard format text file:
| with Ada.Text_IO; use Ada.Text_IO; procedure Hello is begin Put_Line ("Hello WORLD!"); end Hello; |
This file should be named hello.adb.
With the normal default file naming conventions, GNAT requires
that each file
contain a single compilation unit whose file name is the
unit name,
with periods replaced by hyphens; the
extension is ads for a
spec and adb for a body.
You can override this default file naming convention by use of the
special pragma Source_File_Name (see Using Other File Names).
Alternatively, if you want to rename your files according to this default
convention, which is probably more convenient if you will be using GNAT
for all your compilations, then the gnatchop utility
can be used to generate correctly-named source files
(see Renaming Files Using gnatchop).
You can compile the program using the following command ($ is used
as the command prompt in the examples in this document):
$ gcc -c hello.adb
gcc is the command used to run the compiler. This compiler is capable of compiling programs in several languages, including Ada and C. It assumes that you have given it an Ada program if the file extension is either .ads or .adb, and it will then call the GNAT compiler to compile the specified file.
The -c switch is required. It tells gcc to only do a compilation. (For C programs, gcc can also do linking, but this capability is not used directly for Ada programs, so the -c switch must always be present.)
This compile command generates a file
hello.o, which is the object
file corresponding to your Ada program. It also generates
an “Ada Library Information” file hello.ali,
which contains additional information used to check
that an Ada program is consistent.
To build an executable file,
use gnatbind to bind the program
and gnatlink to link it. The
argument to both gnatbind and gnatlink is the name of the
ALI file, but the default extension of .ali can
be omitted. This means that in the most common case, the argument
is simply the name of the main program:
$ gnatbind hello
$ gnatlink hello
A simpler method of carrying out these steps is to use gnatmake, a master program that invokes all the required compilation, binding and linking tools in the correct order. In particular, gnatmake automatically recompiles any sources that have been modified since they were last compiled, or sources that depend on such modified sources, so that “version skew” is avoided.
$ gnatmake hello.adb
The result is an executable program called hello, which can be run by entering:
$ hello
assuming that the current directory is on the search path for executable programs.
and, if all has gone well, you will see
Hello WORLD!
appear in response to this command.
Consider a slightly more complicated example that has three files: a main program, and the spec and body of a package:
|
package Greetings is procedure Hello; procedure Goodbye; end Greetings; with Ada.Text_IO; use Ada.Text_IO; package body Greetings is procedure Hello is begin Put_Line ("Hello WORLD!"); end Hello; procedure Goodbye is begin Put_Line ("Goodbye WORLD!"); end Goodbye; end Greetings; with Greetings; procedure Gmain is begin Greetings.Hello; Greetings.Goodbye; end Gmain; |
Following the one-unit-per-file rule, place this program in the following three separate files:
Greetings
Greetings
To build an executable version of this program, we could use four separate steps to compile, bind, and link the program, as follows:
$ gcc -c gmain.adb
$ gcc -c greetings.adb
$ gnatbind gmain
$ gnatlink gmain
Note that there is no required order of compilation when using GNAT. In particular it is perfectly fine to compile the main program first. Also, it is not necessary to compile package specs in the case where there is an accompanying body; you only need to compile the body. If you want to submit these files to the compiler for semantic checking and not code generation, then use the -gnatc switch:
$ gcc -c greetings.ads -gnatc
Although the compilation can be done in separate steps as in the above example, in practice it is almost always more convenient to use the gnatmake tool. All you need to know in this case is the name of the main program's source file. The effect of the above four commands can be achieved with a single one:
$ gnatmake gmain.adb
In the next section we discuss the advantages of using gnatmake in more detail.
If you work on a program by compiling single components at a time using gcc, you typically keep track of the units you modify. In order to build a consistent system, you compile not only these units, but also any units that depend on the units you have modified. For example, in the preceding case, if you edit gmain.adb, you only need to recompile that file. But if you edit greetings.ads, you must recompile both greetings.adb and gmain.adb, because both files contain units that depend on greetings.ads.
gnatbind will warn you if you forget one of these compilation
steps, so that it is impossible to generate an inconsistent program as a
result of forgetting to do a compilation. Nevertheless it is tedious and
error-prone to keep track of dependencies among units.
One approach to handle the dependency-bookkeeping is to use a
makefile. However, makefiles present maintenance problems of their own:
if the dependencies change as you change the program, you must make
sure that the makefile is kept up-to-date manually, which is also an
error-prone process.
The gnatmake utility takes care of these details automatically. Invoke it using either one of the following forms:
$ gnatmake gmain.adb
$ gnatmake gmain
The argument is the name of the file containing the main program; you may omit the extension. gnatmake examines the environment, automatically recompiles any files that need recompiling, and binds and links the resulting set of object files, generating the executable file, gmain. In a large program, it can be extremely helpful to use gnatmake, because working out by hand what needs to be recompiled can be difficult.
Note that gnatmake takes into account all the Ada rules that establish dependencies among units. These include dependencies that result from inlining subprogram bodies, and from generic instantiation. Unlike some other Ada make tools, gnatmake does not rely on the dependencies that were found by the compiler on a previous compilation, which may possibly be wrong when sources change. gnatmake determines the exact set of dependencies from scratch each time it is run.
Although the command line interface (gnatmake, etc.) alone is sufficient, a graphical Interactive Development Environment can make it easier for you to compose, navigate, and debug programs. This section describes the main features of GPS (“GNAT Programming Studio”), the GNAT graphical IDE. You will see how to use GPS to build and debug an executable, and you will also learn some of the basics of the GNAT “project” facility.
GPS enables you to do much more than is presented here; e.g., you can produce a call graph, interface to a third-party Version Control System, and inspect the generated assembly language for a program. Indeed, GPS also supports languages other than Ada. Such additional information, and an explanation of all of the GPS menu items. may be found in the on-line help, which includes a user's guide and a tutorial (these are also accessible from the GNAT startup menu).
GPS invokes the GNAT compilation tools using information contained in a project (also known as a project file): a collection of properties such as source directories, identities of main subprograms, tool switches, etc., and their associated values. See GNAT Project Manager for details. In order to run GPS, you will need to either create a new project or else open an existing one.
This section will explain how you can use GPS to create a project, to associate Ada source files with a project, and to build and run programs.
Invoke GPS, either from the command line or the platform's IDE. After it starts, GPS will display a “Welcome” screen with three radio buttons:
Start with default project in directory
Create new project with wizard
Open existing project
Select Create new project with wizard and press OK.
A new window will appear. In the text box labeled with
Enter the name of the project to create, type sample
as the project name.
In the next box, browse to choose the directory in which you
would like to create the project file.
After selecting an appropriate directory, press Forward.
A window will appear with the title
Version Control System Configuration.
Simply press Forward.
A window will appear with the title
Please select the source directories for this project.
The directory that you specified for the project file will be selected
by default as the one to use for sources; simply press Forward.
A window will appear with the title
Please select the build directory for this project.
The directory that you specified for the project file will be selected
by default for object files and executables;
simply press Forward.
A window will appear with the title
Please select the main units for this project.
You will supply this information later, after creating the source file.
Simply press Forward for now.
A window will appear with the title
Please select the switches to build the project.
Press Apply. This will create a project file named
sample.prj in the directory that you had specified.
After you create the new project, a GPS window will appear, which is partitioned into two main sections:
Select File on the menu bar, and then the New command.
The Workspace area will become white, and you can now
enter the source program explicitly.
Type the following text
with Ada.Text_IO; use Ada.Text_IO;
procedure Hello is
begin
Put_Line("Hello from GPS!");
end Hello;
Select File, then Save As, and enter the source file name
hello.adb.
The file will be saved in the same directory you specified as the
location of the default project file.
You need to add the new source file to the project.
To do this, select
the Project menu and then Edit project properties.
Click the Main files tab on the left, and then the
Add button.
Choose hello.adb from the list, and press Open.
The project settings window will reflect this action.
Click OK.
In the main GPS window, now choose the Build menu, then Make,
and select hello.adb.
The Messages window will display the resulting invocations of gcc,
gnatbind, and gnatlink
(reflecting the default switch settings from the
project file that you created) and then a “successful compilation/build”
message.
To run the program, choose the Build menu, then Run, and
select hello.
An Arguments Selection window will appear.
There are no command line arguments, so just click OK.
The Messages window will now display the program's output (the string
Hello from GPS), and at the bottom of the GPS window a status
update is displayed (Run: hello).
Close the GPS window (or select File, then Exit) to
terminate this GPS session.
This section illustrates basic debugging techniques (setting breakpoints, examining/modifying variables, single stepping).
Start GPS and select Open existing project; browse to
specify the project file sample.prj that you had created in the
earlier example.
Select File, then New, and type in the following program:
with Ada.Text_IO; use Ada.Text_IO;
procedure Example is
Line : String (1..80);
N : Natural;
begin
Put_Line("Type a line of text at each prompt; an empty line to exit");
loop
Put(": ");
Get_Line (Line, N);
Put_Line (Line (1..N) );
exit when N=0;
end loop;
end Example;
Select File, then Save as, and enter the file name
example.adb.
Add Example as a new main unit for the project:
Project, then Edit Project Properties.
Main files tab, click Add, then
select the file example.adb from the list, and
click Open.
You will see the file name appear in the list of main units
OK
To build the executable
select Build, then Make, and then choose example.adb.
Run the program to see its effect (in the Messages area). Each line that you enter is displayed; an empty line will cause the loop to exit and the program to terminate.
Note that the -g switches to gcc and gnatlink, which are required for debugging, are on by default when you create a new project. Thus unless you intentionally remove these settings, you will be able to debug any program that you develop using GPS.
Select Debug, then Initialize, then example
After performing the initialization step, you will observe a small icon to the right of each line number. This serves as a toggle for breakpoints; clicking the icon will set a breakpoint at the corresponding line (the icon will change to a red circle with an “x”), and clicking it again will remove the breakpoint / reset the icon.
For purposes of this example, set a breakpoint at line 10 (the
statement Put_Line (Line (1..N));
Select Debug, then Run. When the
Program Arguments window appears, click OK.
A console window will appear; enter some line of text,
e.g. abcde, at the prompt.
The program will pause execution when it gets to the
breakpoint, and the corresponding line is highlighted.
Move the mouse over one of the occurrences of the variable N.
You will see the value (5) displayed, in “tool tip” fashion.
Right click on N, select Debug, then select Display N.
You will see information about N appear in the Debugger Data
pane, showing the value as 5.
Right click on the N in the Debugger Data pane, and
select Set value of N.
When the input window appears, enter the value 4 and click
OK.
This value does not automatically appear in the Debugger Data
pane; to see it, right click again on the N in the
Debugger Data pane and select Update value.
The new value, 4, will appear in red.
Select Debug, then Next.
This will cause the next statement to be executed, in this case the
call of Put_Line with the string slice.
Notice in the console window that the displayed string is simply
abcd and not abcde which you had entered.
This is because the upper bound of the slice is now 4 rather than 5.
Toggle the breakpoint icon at line 10.
Select Debug, then Continue.
The program will reach the next iteration of the loop, and
wait for input after displaying the prompt.
This time, just hit the Enter key.
The value of N will be 0, and the program will terminate.
The console window will disappear.
This chapter describes the compilation model used by GNAT. Although similar to that used by other languages, such as C and C++, this model is substantially different from the traditional Ada compilation models, which are based on a library. The model is initially described without reference to the library-based model. If you have not previously used an Ada compiler, you need only read the first part of this chapter. The last section describes and discusses the differences between the GNAT model and the traditional Ada compiler models. If you have used other Ada compilers, this section will help you to understand those differences, and the advantages of the GNAT model.
Ada source programs are represented in standard text files, using Latin-1 coding. Latin-1 is an 8-bit code that includes the familiar 7-bit ASCII set, plus additional characters used for representing foreign languages (see Foreign Language Representation for support of non-USA character sets). The format effector characters are represented using their standard ASCII encodings, as follows:
VT16#0B#
HT16#09#
CR16#0D#
LF16#0A#
FF16#0C#
Source files are in standard text file format. In addition, GNAT will
recognize a wide variety of stream formats, in which the end of
physical lines is marked by any of the following sequences:
LF, CR, CR-LF, or LF-CR. This is useful
in accommodating files that are imported from other operating systems.
The end of a source file is normally represented by the physical end of
file. However, the control character 16#1A# (SUB) is also
recognized as signalling the end of the source file. Again, this is
provided for compatibility with other operating systems where this
code is used to represent the end of file.
Each file contains a single Ada compilation unit, including any pragmas associated with the unit. For example, this means you must place a package declaration (a package spec) and the corresponding body in separate files. An Ada compilation (which is a sequence of compilation units) is represented using a sequence of files. Similarly, you will place each subunit or child unit in a separate file.
GNAT supports the standard character sets defined in Ada as well as several other non-standard character sets for use in localized versions of the compiler (see Character Set Control).
The basic character set is Latin-1. This character set is defined by ISO
standard 8859, part 1. The lower half (character codes 16#00#
... 16#7F#) is identical to standard ASCII coding, but the upper half
is used to represent additional characters. These include extended letters
used by European languages, such as French accents, the vowels with umlauts
used in German, and the extra letter A-ring used in Swedish.
For a complete list of Latin-1 codes and their encodings, see the source
file of library unit Ada.Characters.Latin_1 in file
a-chlat1.ads.
You may use any of these extended characters freely in character or
string literals. In addition, the extended characters that represent
letters can be used in identifiers.
GNAT also supports several other 8-bit coding schemes:
For precise data on the encodings permitted, and the uppercase and lowercase equivalences that are recognized, see the file csets.adb in the GNAT compiler sources. You will need to obtain a full source release of GNAT to obtain this file.
GNAT allows wide character codes to appear in character and string literals, and also optionally in identifiers, by means of the following possible encoding schemes:
ESC a b c d
Where a, b, c, d are the four hexadecimal
characters (using uppercase letters) of the wide character code. For
example, ESC A345 is used to represent the wide character with code
16#A345#.
This scheme is compatible with use of the full Wide_Character set.
16#abcd# where the upper bit is on
(in other words, “a” is in the range 8-F) is represented as two bytes,
16#ab# and 16#cd#. The second byte cannot be a format control
character, but is not required to be in the upper half. This method can
be also used for shift-JIS or EUC, where the internal coding matches the
external coding.
16#ab# and
16#cd#, with the restrictions described for upper-half encoding as
described above. The internal character code is the corresponding JIS
character according to the standard algorithm for Shift-JIS
conversion. Only characters defined in the JIS code set table can be
used with this encoding method.
16#ab# and
16#cd#, with both characters being in the upper half. The internal
character code is the corresponding JIS character according to the EUC
encoding algorithm. Only characters defined in the JIS code set table
can be used with this encoding method.
16#0000#-16#007f#: 2#0xxxxxxx#
16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx#
16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
where the xxx bits correspond to the left-padded bits of the
16-bit character value. Note that all lower half ASCII characters
are represented as ASCII bytes and all upper half characters and
other wide characters are represented as sequences of upper-half
(The full UTF-8 scheme allows for encoding 31-bit characters as
6-byte sequences, but in this implementation, all UTF-8 sequences
of four or more bytes length will be treated as illegal).
[ " a b c d " ]
Where a, b, c, d are the four hexadecimal
characters (using uppercase letters) of the wide character code. For
example, [“A345”] is used to represent the wide character with code
16#A345#. It is also possible (though not required) to use the
Brackets coding for upper half characters. For example, the code
16#A3# can be represented as [``A3''].
This scheme is compatible with use of the full Wide_Character set, and is also the method used for wide character encoding in the standard ACVC (Ada Compiler Validation Capability) test suite distributions.
Note: Some of these coding schemes do not permit the full use of the Ada character set. For example, neither Shift JIS, nor EUC allow the use of the upper half of the Latin-1 set.
The default file name is determined by the name of the unit that the file contains. The name is formed by taking the full expanded name of the unit and replacing the separating dots with hyphens and using lowercase for all letters.
An exception arises if the file name generated by the above rules starts with one of the characters ‘a’, ‘g’, ‘i’, or ‘s’, and the second character is a minus. In this case, the character tilde is used in place of the minus. The reason for this special rule is to avoid clashes with the standard names for child units of the packages System, Ada, Interfaces, and GNAT, which use the prefixes ‘s-’, ‘a-’, ‘i-’, and ‘g-’, respectively.
The file extension is .ads for a spec and .adb for a body. The following list shows some examples of these rules.
Following these rules can result in excessively long file names if corresponding unit names are long (for example, if child units or subunits are heavily nested). An option is available to shorten such long file names (called file name “krunching”). This may be particularly useful when programs being developed with GNAT are to be used on operating systems with limited file name lengths. See Using gnatkr.
Of course, no file shortening algorithm can guarantee uniqueness over all possible unit names; if file name krunching is used, it is your responsibility to ensure no name clashes occur. Alternatively you can specify the exact file names that you want used, as described in the next section. Finally, if your Ada programs are migrating from a compiler with a different naming convention, you can use the gnatchop utility to produce source files that follow the GNAT naming conventions. (For details see Renaming Files Using gnatchop.)
Note: in the case of Windows NT/XP or OpenVMS operating
systems, case is not significant. So for example on Windows XP
if the canonical name is main-sub.adb, you can use the file name
Main-Sub.adb instead. However, case is significant for other
operating systems, so for example, if you want to use other than
canonically cased file names on a Unix system, you need to follow
the procedures described in the next section.
In the previous section, we have described the default rules used by GNAT to determine the file name in which a given unit resides. It is often convenient to follow these default rules, and if you follow them, the compiler knows without being explicitly told where to find all the files it needs.
However, in some cases, particularly when a program is imported from another Ada compiler environment, it may be more convenient for the programmer to specify which file names contain which units. GNAT allows arbitrary file names to be used by means of the Source_File_Name pragma. The form of this pragma is as shown in the following examples:
| pragma Source_File_Name (My_Utilities.Stacks, Spec_File_Name => "myutilst_a.ada"); pragma Source_File_name (My_Utilities.Stacks, Body_File_Name => "myutilst.ada"); |
As shown in this example, the first argument for the pragma is the unit name (in this example a child unit). The second argument has the form of a named association. The identifier indicates whether the file name is for a spec or a body; the file name itself is given by a string literal.
The source file name pragma is a configuration pragma, which means that
normally it will be placed in the gnat.adc
file used to hold configuration
pragmas that apply to a complete compilation environment.
For more details on how the gnat.adc file is created and used
see Handling of Configuration Pragmas.
GNAT allows completely arbitrary file names to be specified using the
source file name pragma. However, if the file name specified has an
extension other than .ads or .adb it is necessary to use
a special syntax when compiling the file. The name in this case must be
preceded by the special sequence -x followed by a space and the name
of the language, here ada, as in:
$ gcc -c -x ada peculiar_file_name.sim
gnatmake handles non-standard file names in the usual manner (the non-standard file name for the main program is simply used as the argument to gnatmake). Note that if the extension is also non-standard, then it must be included in the gnatmake command, it may not be omitted.
In the previous section, we described the use of the Source_File_Name
pragma to allow arbitrary names to be assigned to individual source files.
However, this approach requires one pragma for each file, and especially in
large systems can result in very long gnat.adc files, and also create
a maintenance problem.
GNAT also provides a facility for specifying systematic file naming schemes
other than the standard default naming scheme previously described. An
alternative scheme for naming is specified by the use of
Source_File_Name pragmas having the following format:
pragma Source_File_Name (
Spec_File_Name => FILE_NAME_PATTERN
[,Casing => CASING_SPEC]
[,Dot_Replacement => STRING_LITERAL]);
pragma Source_File_Name (
Body_File_Name => FILE_NAME_PATTERN
[,Casing => CASING_SPEC]
[,Dot_Replacement => STRING_LITERAL]);
pragma Source_File_Name (
Subunit_File_Name => FILE_NAME_PATTERN
[,Casing => CASING_SPEC]
[,Dot_Replacement => STRING_LITERAL]);
FILE_NAME_PATTERN ::= STRING_LITERAL
CASING_SPEC ::= Lowercase | Uppercase | Mixedcase
The FILE_NAME_PATTERN string shows how the file name is constructed.
It contains a single asterisk character, and the unit name is substituted
systematically for this asterisk. The optional parameter
Casing indicates
whether the unit name is to be all upper-case letters, all lower-case letters,
or mixed-case. If no
Casing parameter is used, then the default is all
lower-case.
The optional Dot_Replacement string is used to replace any periods
that occur in subunit or child unit names. If no Dot_Replacement
argument is used then separating dots appear unchanged in the resulting
file name.
Although the above syntax indicates that the
Casing argument must appear
before the Dot_Replacement argument, but it
is also permissible to write these arguments in the opposite order.
As indicated, it is possible to specify different naming schemes for
bodies, specs, and subunits. Quite often the rule for subunits is the
same as the rule for bodies, in which case, there is no need to give
a separate Subunit_File_Name rule, and in this case the
Body_File_name rule is used for subunits as well.
The separate rule for subunits can also be used to implement the rather unusual case of a compilation environment (e.g. a single directory) which contains a subunit and a child unit with the same unit name. Although both units cannot appear in the same partition, the Ada Reference Manual allows (but does not require) the possibility of the two units coexisting in the same environment.
The file name translation works in the following steps:
Source_File_Name pragma for the given unit,
then this is always used, and any general pattern rules are ignored.
Source_File_Name pragma that applies to
the unit, then the resulting file name will be used if the file exists. If
more than one pattern matches, the latest one will be tried first, and the
first attempt resulting in a reference to a file that exists will be used.
Source_File_Name pragma that applies to the unit
for which the corresponding file exists, then the standard GNAT default
naming rules are used.
As an example of the use of this mechanism, consider a commonly used scheme in which file names are all lower case, with separating periods copied unchanged to the resulting file name, and specs end with .1.ada, and bodies end with .2.ada. GNAT will follow this scheme if the following two pragmas appear:
pragma Source_File_Name
(Spec_File_Name => "*.1.ada");
pragma Source_File_Name
(Body_File_Name => "*.2.ada");
The default GNAT scheme is actually implemented by providing the following default pragmas internally:
pragma Source_File_Name
(Spec_File_Name => "*.ads", Dot_Replacement => "-");
pragma Source_File_Name
(Body_File_Name => "*.adb", Dot_Replacement => "-");
Our final example implements a scheme typically used with one of the Ada 83 compilers, where the separator character for subunits was “__” (two underscores), specs were identified by adding _.ADA, bodies by adding .ADA, and subunits by adding .SEP. All file names were upper case. Child units were not present of course since this was an Ada 83 compiler, but it seems reasonable to extend this scheme to use the same double underscore separator for child units.
pragma Source_File_Name
(Spec_File_Name => "*_.ADA",
Dot_Replacement => "__",
Casing = Uppercase);
pragma Source_File_Name
(Body_File_Name => "*.ADA",
Dot_Replacement => "__",
Casing = Uppercase);
pragma Source_File_Name
(Subunit_File_Name => "*.SEP",
Dot_Replacement => "__",
Casing = Uppercase);
An Ada program consists of a set of source files, and the first step in compiling the program is to generate the corresponding object files. These are generated by compiling a subset of these source files. The files you need to compile are the following:
The preceding rules describe the set of files that must be compiled to generate the object files for a program. Each object file has the same name as the corresponding source file, except that the extension is .o as usual.
You may wish to compile other files for the purpose of checking their syntactic and semantic correctness. For example, in the case where a package has a separate spec and body, you would not normally compile the spec. However, it is convenient in practice to compile the spec to make sure it is error-free before compiling clients of this spec, because such compilations will fail if there is an error in the spec.
GNAT provides an option for compiling such files purely for the purposes of checking correctness; such compilations are not required as part of the process of building a program. To compile a file in this checking mode, use the -gnatc switch.
A given object file clearly depends on the source file which is compiled
to produce it. Here we are using depends in the sense of a typical
make utility; in other words, an object file depends on a source
file if changes to the source file require the object file to be
recompiled.
In addition to this basic dependency, a given object may depend on
additional source files as follows:
with's a unit X, the object file
depends on the file containing the spec of unit X. This includes
files that are with'ed implicitly either because they are parents
of with'ed child units or they are run-time units required by the
language constructs used in a particular unit.
Inline applies and inlining is activated with the
-gnatn switch, the object file depends on the file containing the
body of this subprogram as well as on the file containing the spec. Note
that for inlining to actually occur as a result of the use of this switch,
it is necessary to compile in optimizing mode.
The use of -gnatN activates inlining optimization that is performed by the front end of the compiler. This inlining does not require that the code generation be optimized. Like -gnatn, the use of this switch generates additional dependencies. Note that -gnatN automatically implies -gnatn so it is not necessary to specify both options.
When using a gcc-based back end (in practice this means using any version of GNAT other than the JGNAT, .NET or GNAAMP versions), then the use of -gnatN is deprecated, and the use of -gnatn is preferred. Historically front end inlining was more extensive than the gcc back end inlining, but that is no longer the case.
These rules are applied transitively: if unit A with's
unit B, whose elaboration calls an inlined procedure in package
C, the object file for unit A will depend on the body of
C, in file c.adb.
The set of dependent files described by these rules includes all the files on which the unit is semantically dependent, as dictated by the Ada language standard. However, it is a superset of what the standard describes, because it includes generic, inline, and subunit dependencies.
An object file must be recreated by recompiling the corresponding source
file if any of the source files on which it depends are modified. For
example, if the make utility is used to control compilation,
the rule for an Ada object file must mention all the source files on
which the object file depends, according to the above definition.
The determination of the necessary
recompilations is done automatically when one uses gnatmake.
Each compilation actually generates two output files. The first of these is the normal object file that has a .o extension. The second is a text file containing full dependency information. It has the same name as the source file, but an .ali extension. This file is known as the Ada Library Information (ALI) file. The following information is contained in the ALI file.
Pure).
with'ed units, including presence of
Elaborate or Elaborate_All pragmas.
Linker_Options pragmas used in the unit
Body_Version or Version
attributes in the unit.
gnatxref and gnatfind to
provide cross-reference information.
For a full detailed description of the format of the ALI file,
see the source of the body of unit Lib.Writ, contained in file
lib-writ.adb in the GNAT compiler sources.
When using languages such as C and C++, once the source files have been compiled the only remaining step in building an executable program is linking the object modules together. This means that it is possible to link an inconsistent version of a program, in which two units have included different versions of the same header.
The rules of Ada do not permit such an inconsistent program to be built. For example, if two clients have different versions of the same package, it is illegal to build a program containing these two clients. These rules are enforced by the GNAT binder, which also determines an elaboration order consistent with the Ada rules.
The GNAT binder is run after all the object files for a program have been created. It is given the name of the main program unit, and from this it determines the set of units required by the program, by reading the corresponding ALI files. It generates error messages if the program is inconsistent or if no valid order of elaboration exists.
If no errors are detected, the binder produces a main program, in Ada by default, that contains calls to the elaboration procedures of those compilation unit that require them, followed by a call to the main program. This Ada program is compiled to generate the object file for the main program. The name of the Ada file is b~xxx.adb (with the corresponding spec b~xxx.ads) where xxx is the name of the main program unit.
Finally, the linker is used to build the resulting executable program, using the object from the main program from the bind step as well as the object files for the Ada units of the program.
This section describes how to develop a mixed-language program, specifically one that comprises units in both Ada and C.
Interfacing Ada with a foreign language such as C involves using
compiler directives to import and/or export entity definitions in each
language—using extern statements in C, for instance, and the
Import, Export, and Convention pragmas in Ada.
A full treatment of these topics is provided in Appendix B, section 1
of the Ada Reference Manual.
There are two ways to build a program using GNAT that contains some Ada sources and some foreign language sources, depending on whether or not the main subprogram is written in Ada. Here is a source example with the main subprogram in Ada:
/* file1.c */
#include <stdio.h>
void print_num (int num)
{
printf ("num is %d.\n", num);
return;
}
/* file2.c */
/* num_from_Ada is declared in my_main.adb */
extern int num_from_Ada;
int get_num (void)
{
return num_from_Ada;
}
-- my_main.adb
procedure My_Main is
-- Declare then export an Integer entity called num_from_Ada
My_Num : Integer := 10;
pragma Export (C, My_Num, "num_from_Ada");
-- Declare an Ada function spec for Get_Num, then use
-- C function get_num for the implementation.
function Get_Num return Integer;
pragma Import (C, Get_Num, "get_num");
-- Declare an Ada procedure spec for Print_Num, then use
-- C function print_num for the implementation.
procedure Print_Num (Num : Integer);
pragma Import (C, Print_Num, "print_num");
begin
Print_Num (Get_Num);
end My_Main;
gcc -c file1.c
gcc -c file2.c
gnatmake -c my_main.adb
gnatbind my_main.ali
gnatlink my_main.ali file1.o file2.o
The last three steps can be grouped in a single command:
gnatmake my_main.adb -largs file1.o file2.o
If the main program is in a language other than Ada, then you may have more than one entry point into the Ada subsystem. You must use a special binder option to generate callable routines that initialize and finalize the Ada units (see Binding with Non-Ada Main Programs). Calls to the initialization and finalization routines must be inserted in the main program, or some other appropriate point in the code. The call to initialize the Ada units must occur before the first Ada subprogram is called, and the call to finalize the Ada units must occur after the last Ada subprogram returns. The binder will place the initialization and finalization subprograms into the b~xxx.adb file where they can be accessed by your C sources. To illustrate, we have the following example:
/* main.c */
extern void adainit (void);
extern void adafinal (void);
extern int add (int, int);
extern int sub (int, int);
int main (int argc, char *argv[])
{
int a = 21, b = 7;
adainit();
/* Should print "21 + 7 = 28" */
printf ("%d + %d = %d\n", a, b, add (a, b));
/* Should print "21 - 7 = 14" */
printf ("%d - %d = %d\n", a, b, sub (a, b));
adafinal();
}
-- unit1.ads
package Unit1 is
function Add (A, B : Integer) return Integer;
pragma Export (C, Add, "add");
end Unit1;
-- unit1.adb
package body Unit1 is
function Add (A, B : Integer) return Integer is
begin
return A + B;
end Add;
end Unit1;
-- unit2.ads
package Unit2 is
function Sub (A, B : Integer) return Integer;
pragma Export (C, Sub, "sub");
end Unit2;
-- unit2.adb
package body Unit2 is
function Sub (A, B : Integer) return Integer is
begin
return A - B;
end Sub;
end Unit2;
gcc -c main.c
gnatmake -c unit1.adb
gnatmake -c unit2.adb
gnatbind -n unit1.ali unit2.ali
gnatlink unit2.ali main.o -o exec_file
This procedure yields a binary executable called exec_file.
Depending on the circumstances (for example when your non-Ada main object
does not provide symbol main), you may also need to instruct the
GNAT linker not to include the standard startup objects by passing the
-nostartfiles switch to gnatlink.
GNAT follows standard calling sequence conventions and will thus interface to any other language that also follows these conventions. The following Convention identifiers are recognized by GNAT:
AdaNote that in the case of GNAT running on a platform that supports HP Ada 83, a higher degree of compatibility can be guaranteed, and in particular records are layed out in an identical manner in the two compilers. Note also that if output from two different compilers is mixed, the program is responsible for dealing with elaboration issues. Probably the safest approach is to write the main program in the version of Ada other than GNAT, so that it takes care of its own elaboration requirements, and then call the GNAT-generated adainit procedure to ensure elaboration of the GNAT components. Consult the documentation of the other Ada compiler for further details on elaboration.
However, it is not possible to mix the tasking run time of GNAT and HP Ada 83, All the tasking operations must either be entirely within GNAT compiled sections of the program, or entirely within HP Ada 83 compiled sections of the program.
AssemblerAsmCOBOLCA note on interfacing to a C “varargs” function:
varargs allows a function to take a variable number of
arguments. There is no direct equivalent in this to Ada. One
approach that can be used is to create a C wrapper for each
different profile and then interface to this C wrapper. For
example, to print an int value using printf,
create a C function printfi that takes two arguments, a
pointer to a string and an int, and calls printf.
Then in the Ada program, use pragma Import to
interface to printfi.
varargs function by providing a specific Ada profile
for a particular call. However, this does not work on
all platforms, since there is no guarantee that the
calling sequence for a two argument normal C function
is the same as for calling a varargs C function with
the same two arguments.
DefaultExternalC_Plus_Plus (or CPP)FortranIntrinsic type Distance is new Long_Float;
type Time is new Long_Float;
type Velocity is new Long_Float;
function "/" (D : Distance; T : Time)
return Velocity;
pragma Import (Intrinsic, "/");
This common idiom is often programmed with a generic definition and an explicit body. The pragma makes it simpler to introduce such declarations. It incurs no overhead in compilation time or code size, because it is implemented as a single machine instruction.
function builtin_sqrt (F : Float) return Float;
pragma Import (Intrinsic, builtin_sqrt, "__builtin_sqrtf");
Most of the GCC builtins are accessible this way, and as for other import conventions (e.g. C), it is the user's responsibility to ensure that the Ada subprogram profile matches the underlying builtin expectations.
StdcallStdcall calling sequence will be used,
as defined by the NT API. Nevertheless, to ease building
cross-platform bindings this convention will be handled as a C calling
convention on non-Windows platforms.
DLLStdcall.
Win32Stdcall.
StubbedProgram_Error.
GNAT additionally provides a useful pragma Convention_Identifier
that can be used to parametrize conventions and allow additional synonyms
to be specified. For example if you have legacy code in which the convention
identifier Fortran77 was used for Fortran, you can use the configuration
pragma:
pragma Convention_Identifier (Fortran77, Fortran);
And from now on the identifier Fortran77 may be used as a convention
identifier (for example in an Import pragma) with the same
meaning as Fortran.
A programmer inexperienced with mixed-language development may find that building an application containing both Ada and C++ code can be a challenge. This section gives a few hints that should make this task easier. The first section addresses the differences between interfacing with C and interfacing with C++. The second section looks into the delicate problem of linking the complete application from its Ada and C++ parts. The last section gives some hints on how the GNAT run-time library can be adapted in order to allow inter-language dispatching with a new C++ compiler.
GNAT supports interfacing with the G++ compiler (or any C++ compiler generating code that is compatible with the G++ Application Binary Interface —see http://www.codesourcery.com/archives/cxx-abi).
Interfacing can be done at 3 levels: simple data, subprograms, and
classes. In the first two cases, GNAT offers a specific Convention
C_Plus_Plus (or CPP) that behaves exactly like Convention C.
Usually, C++ mangles the names of subprograms, and currently, GNAT does
not provide any help to solve the demangling problem. This problem can be
addressed in two ways:
extern "C" syntax.
Interfacing at the class level can be achieved by using the GNAT specific
pragmas such as CPP_Constructor. See Interfacing to C++, for additional information.
Usually the linker of the C++ development system must be used to link mixed applications because most C++ systems will resolve elaboration issues (such as calling constructors on global class instances) transparently during the link phase. GNAT has been adapted to ease the use of a foreign linker for the last phase. Three cases can be considered:
c++. Note that this setup is not very common because it
may involve recompiling the whole GCC tree from sources, which makes it
harder to upgrade the compilation system for one language without
destabilizing the other.
$ c++ -c file1.C
$ c++ -c file2.C
$ gnatmake ada_unit -largs file1.o file2.o --LINK=c++
$ gnatbind ada_unit
$ gnatlink -v -v ada_unit file1.o file2.o --LINK=c++
If there is a problem due to interfering environment variables, it can be worked around by using an intermediate script. The following example shows the proper script to use when GNAT has not been installed at its default location and g++ has been installed at its default location:
$ cat ./my_script
#!/bin/sh
unset BINUTILS_ROOT
unset GCC_ROOT
c++ $*
$ gnatlink -v -v ada_unit file1.o file2.o --LINK=./my_script
If the setjmp/longjmp exception mechanism is used, only the paths
to the libgcc libraries are required:
$ cat ./my_script
#!/bin/sh
CC $* `gcc -print-file-name=libgcc.a` `gcc -print-file-name=libgcc_eh.a`
$ gnatlink ada_unit file1.o file2.o --LINK=./my_script
Where CC is the name of the non-GNU C++ compiler.
If the zero cost exception mechanism is used, and the platform
supports automatic registration of exception tables (e.g. Solaris or IRIX),
paths to more objects are required:
$ cat ./my_script
#!/bin/sh
CC `gcc -print-file-name=crtbegin.o` $* \
`gcc -print-file-name=libgcc.a` `gcc -print-file-name=libgcc_eh.a` \
`gcc -print-file-name=crtend.o`
$ gnatlink ada_unit file1.o file2.o --LINK=./my_script
If the zero cost exception mechanism is used, and the platform
doesn't support automatic registration of exception tables (e.g. HP-UX,
Tru64 or AIX), the simple approach described above will not work and
a pre-linking phase using GNAT will be necessary.
The following example, provided as part of the GNAT examples, shows how to achieve procedural interfacing between Ada and C++ in both directions. The C++ class A has two methods. The first method is exported to Ada by the means of an extern C wrapper function. The second method calls an Ada subprogram. On the Ada side, The C++ calls are modelled by a limited record with a layout comparable to the C++ class. The Ada subprogram, in turn, calls the C++ method. So, starting from the C++ main program, the process passes back and forth between the two languages.
Here are the compilation commands:
$ gnatmake -c simple_cpp_interface
$ c++ -c cpp_main.C
$ c++ -c ex7.C
$ gnatbind -n simple_cpp_interface
$ gnatlink simple_cpp_interface -o cpp_main --LINK=$(CPLUSPLUS)
-lstdc++ ex7.o cpp_main.o
Here are the corresponding sources:
//cpp_main.C
#include "ex7.h"
extern "C" {
void adainit (void);
void adafinal (void);
void method1 (A *t);
}
void method1 (A *t)
{
t->method1 ();
}
int main ()
{
A obj;
adainit ();
obj.method2 (3030);
adafinal ();
}
//ex7.h
class Origin {
public:
int o_value;
};
class A : public Origin {
public:
void method1 (void);
void method2 (int v);
A();
int a_value;
};
//ex7.C
#include "ex7.h"
#include <stdio.h>
extern "C" { void ada_method2 (A *t, int v);}
void A::method1 (void)
{
a_value = 2020;
printf ("in A::method1, a_value = %d \n",a_value);
}
void A::method2 (int v)
{
ada_method2 (this, v);
printf ("in A::method2, a_value = %d \n",a_value);
}
A::A(void)
{
a_value = 1010;
printf ("in A::A, a_value = %d \n",a_value);
}
-- Ada sources
package body Simple_Cpp_Interface is
procedure Ada_Method2 (This : in out A; V : Integer) is
begin
Method1 (This);
This.A_Value := V;
end Ada_Method2;
end Simple_Cpp_Interface;
with System;
package Simple_Cpp_Interface is
type A is limited
record
Vptr : System.Address;
O_Value : Integer;
A_Value : Integer;
end record;
pragma Convention (C, A);
procedure Method1 (This : in out A);
pragma Import (C, Method1);
procedure Ada_Method2 (This : in out A; V : Integer);
pragma Export (C, Ada_Method2);
end Simple_Cpp_Interface;
In this section we demonstrate the GNAT features for interfacing with C++ by means of an example making use of Ada 2005 abstract interface types. This example consists of a classification of animals; classes have been used to model our main classification of animals, and interfaces provide support for the management of secondary classifications. We first demonstrate a case in which the types and constructors are defined on the C++ side and imported from the Ada side, and latter the reverse case.
The root of our derivation will be the Animal class, with a
single private attribute (the Age of the animal) and two public
primitives to set and get the value of this attribute.
class Animal {
public:
virtual void Set_Age (int New_Age);
virtual int Age ();
private:
int Age_Count;
};
Abstract interface types are defined in C++ by means of classes with pure
virtual functions and no data members. In our example we will use two
interfaces that provide support for the common management of Carnivore
and Domestic animals:
class Carnivore {
public:
virtual int Number_Of_Teeth () = 0;
};
class Domestic {
public:
virtual void Set_Owner (char* Name) = 0;
};
Using these declarations, we can now say that a Dog is an animal that is
both Carnivore and Domestic, that is:
class Dog : Animal, Carnivore, Domestic {
public:
virtual int Number_Of_Teeth ();
virtual void Set_Owner (char* Name);
Dog(); // Constructor
private:
int Tooth_Count;
char *Owner;
};
In the following examples we will assume that the previous declarations are
located in a file named animals.h. The following package demonstrates
how to import these C++ declarations from the Ada side:
with Interfaces.C.Strings; use Interfaces.C.Strings;
package Animals is
type Carnivore is interface;
pragma Convention (C_Plus_Plus, Carnivore);
function Number_Of_Teeth (X : Carnivore)
return Natural is abstract;
type Domestic is interface;
pragma Convention (C_Plus_Plus, Set_Owner);
procedure Set_Owner
(X : in out Domestic;
Name : Chars_Ptr) is abstract;
type Animal is tagged record
Age : Natural := 0;
end record;
pragma Import (C_Plus_Plus, Animal);
procedure Set_Age (X : in out Animal; Age : Integer);
pragma Import (C_Plus_Plus, Set_Age);
function Age (X : Animal) return Integer;
pragma Import (C_Plus_Plus, Age);
type Dog is new Animal and Carnivore and Domestic with record
Tooth_Count : Natural;
Owner : String (1 .. 30);
end record;
pragma Import (C_Plus_Plus, Dog);
function Number_Of_Teeth (A : Dog) return Integer;
pragma Import (C_Plus_Plus, Number_Of_Teeth);
procedure Set_Owner (A : in out Dog; Name : Chars_Ptr);
pragma Import (C_Plus_Plus, Set_Owner);
function New_Dog return Dog'Class;
pragma CPP_Constructor (New_Dog);
pragma Import (CPP, New_Dog, "_ZN3DogC2Ev");
end Animals;
Thanks to the compatibility between GNAT run-time structures and the C++ ABI, interfacing with these C++ classes is easy. The only requirement is that all the primitives and components must be declared exactly in the same order in the two languages.
Regarding the abstract interfaces, we must indicate to the GNAT compiler by
means of a pragma Convention (C_Plus_Plus), the convention used to pass
the arguments to the called primitives will be the same as for C++. For the
imported classes we use pragma Import with convention C_Plus_Plus
to indicate that they have been defined on the C++ side; this is required
because the dispatch table associated with these tagged types will be built
in the C++ side and therefore will not contain the predefined Ada primitives
which Ada would otherwise expect.
As the reader can see there is no need to indicate the C++ mangled names
associated with each subprogram because it is assumed that all the calls to
these primitives will be dispatching calls. The only exception is the
constructor, which must be registered with the compiler by means of
pragma CPP_Constructor and needs to provide its associated C++
mangled name because the Ada compiler generates direct calls to it.
With the above packages we can now declare objects of type Dog on the Ada side and dispatch calls to the corresponding subprograms on the C++ side. We can also extend the tagged type Dog with further fields and primitives, and override some of its C++ primitives on the Ada side. For example, here we have a type derivation defined on the Ada side that inherits all the dispatching primitives of the ancestor from the C++ side.
with Animals; use Animals;
package Vaccinated_Animals is
type Vaccinated_Dog is new Dog with null record;
function Vaccination_Expired (A : Vaccinated_Dog) return Boolean;
end Vaccinated_Animals;
It is important to note that, because of the ABI compatibility, the programmer does not need to add any further information to indicate either the object layout or the dispatch table entry associated with each dispatching operation.
Now let us define all the types and constructors on the Ada side and export them to C++, using the same hierarchy of our previous example:
with Interfaces.C.Strings;
use Interfaces.C.Strings;
package Animals is
type Carnivore is interface;
pragma Convention (C_Plus_Plus, Carnivore);
function Number_Of_Teeth (X : Carnivore)
return Natural is abstract;
type Domestic is interface;
pragma Convention (C_Plus_Plus, Set_Owner);
procedure Set_Owner
(X : in out Domestic;
Name : Chars_Ptr) is abstract;
type Animal is tagged record
Age : Natural := 0;
end record;
pragma Convention (C_Plus_Plus, Animal);
procedure Set_Age (X : in out Animal; Age : Integer);
pragma Export (C_Plus_Plus, Set_Age);
function Age (X : Animal) return Integer;
pragma Export (C_Plus_Plus, Age);
type Dog is new Animal and Carnivore and Domestic with record
Tooth_Count : Natural;
Owner : String (1 .. 30);
end record;
pragma Convention (C_Plus_Plus, Dog);
function Number_Of_Teeth (A : Dog) return Integer;
pragma Export (C_Plus_Plus, Number_Of_Teeth);
procedure Set_Owner (A : in out Dog; Name : Chars_Ptr);
pragma Export (C_Plus_Plus, Set_Owner);
function New_Dog return Dog'Class;
pragma Export (C_Plus_Plus, New_Dog);
end Animals;
Compared with our previous example the only difference is the use of
pragma Export to indicate to the GNAT compiler that the primitives will
be available to C++. Thanks to the ABI compatibility, on the C++ side there is
nothing else to be done; as explained above, the only requirement is that all
the primitives and components are declared in exactly the same order.
For completeness, let us see a brief C++ main program that uses the
declarations available in animals.h (presented in our first example) to
import and use the declarations from the Ada side, properly initializing and
finalizing the Ada run-time system along the way:
#include "animals.h"
#include <iostream>
using namespace std;
void Check_Carnivore (Carnivore *obj) {...}
void Check_Domestic (Domestic *obj) {...}
void Check_Animal (Animal *obj) {...}
void Check_Dog (Dog *obj) {...}
extern "C" {
void adainit (void);
void adafinal (void);
Dog* new_dog ();
}
void test ()
{
Dog *obj = new_dog(); // Ada constructor
Check_Carnivore (obj); // Check secondary DT
Check_Domestic (obj); // Check secondary DT
Check_Animal (obj); // Check primary DT
Check_Dog (obj); // Check primary DT
}
int main ()
{
adainit (); test(); adafinal ();
return 0;
}
The GNAT model of compilation is close to the C and C++ models. You can
think of Ada specs as corresponding to header files in C. As in C, you
don't need to compile specs; they are compiled when they are used. The
Ada with is similar in effect to the #include of a C
header.
One notable difference is that, in Ada, you may compile specs separately to check them for semantic and syntactic accuracy. This is not always possible with C headers because they are fragments of programs that have less specific syntactic or semantic rules.
The other major difference is the requirement for running the binder, which performs two important functions. First, it checks for consistency. In C or C++, the only defense against assembling inconsistent programs lies outside the compiler, in a makefile, for example. The binder satisfies the Ada requirement that it be impossible to construct an inconsistent program when the compiler is used in normal mode.
The other important function of the binder is to deal with elaboration
issues. There are also elaboration issues in C++ that are handled
automatically. This automatic handling has the advantage of being
simpler to use, but the C++ programmer has no control over elaboration.
Where gnatbind might complain there was no valid order of
elaboration, a C++ compiler would simply construct a program that
malfunctioned at run time.
This section is intended for Ada programmers who have used an Ada compiler implementing the traditional Ada library model, as described in the Ada Reference Manual.
In GNAT, there is no “library” in the normal sense. Instead, the set of source files themselves acts as the library. Compiling Ada programs does not generate any centralized information, but rather an object file and a ALI file, which are of interest only to the binder and linker. In a traditional system, the compiler reads information not only from the source file being compiled, but also from the centralized library. This means that the effect of a compilation depends on what has been previously compiled. In particular:
with'ed, the unit seen by the compiler corresponds
to the version of the unit most recently compiled into the library.
In GNAT, compiling one unit never affects the compilation of any other units because the compiler reads only source files. Only changes to source files can affect the results of a compilation. In particular:
with'ed, the unit seen by the compiler corresponds
to the source version of the unit that is currently accessible to the
compiler.
The most important result of these differences is that order of compilation is never significant in GNAT. There is no situation in which one is required to do one compilation before another. What shows up as order of compilation requirements in the traditional Ada library becomes, in GNAT, simple source dependencies; in other words, there is only a set of rules saying what source files must be present when a file is compiled.
This chapter discusses how to compile Ada programs using the gcc command. It also describes the set of switches that can be used to control the behavior of the compiler.
The first step in creating an executable program is to compile the units of the program using the gcc command. You must compile the following files:
You need not compile the following files
because they are compiled as part of compiling related units. GNAT package specs when the corresponding body is compiled, and subunits when the parent is compiled.
If you attempt to compile any of these files, you will get one of the following error messages (where fff is the name of the file you compiled):
cannot generate code for file fff (package spec)
to check package spec, use -gnatc
cannot generate code for file fff (missing subunits)
to check parent unit, use -gnatc
cannot generate code for file fff (subprogram spec)
to check subprogram spec, use -gnatc
cannot generate code for file fff (subunit)
to check subunit, use -gnatc
As indicated by the above error messages, if you want to submit one of these files to the compiler to check for correct semantics without generating code, then use the -gnatc switch.
The basic command for compiling a file containing an Ada unit is
$ gcc -c [switches] file name
where file name is the name of the Ada file (usually having an extension .ads for a spec or .adb for a body). You specify the -c switch to tell gcc to compile, but not link, the file. The result of a successful compilation is an object file, which has the same name as the source file but an extension of .o and an Ada Library Information (ALI) file, which also has the same name as the source file, but with .ali as the extension. GNAT creates these two output files in the current directory, but you may specify a source file in any directory using an absolute or relative path specification containing the directory information.
gcc is actually a driver program that looks at the extensions of the file arguments and loads the appropriate compiler. For example, the GNU C compiler is cc1, and the Ada compiler is gnat1. These programs are in directories known to the driver program (in some configurations via environment variables you set), but need not be in your path. The gcc driver also calls the assembler and any other utilities needed to complete the generation of the required object files.
It is possible to supply several file names on the same gcc command. This causes gcc to call the appropriate compiler for each file. For example, the following command lists three separate files to be compiled:
$ gcc -c x.adb y.adb z.c
calls gnat1 (the Ada compiler) twice to compile x.adb and
y.adb, and cc1 (the C compiler) once to compile z.c.
The compiler generates three object files x.o, y.o and
z.o and the two ALI files x.ali and y.ali from the
Ada compilations. Any switches apply to all the files listed,
except for
-gnatx switches, which apply only to Ada compilations.
The gcc command accepts switches that control the compilation process. These switches are fully described in this section. First we briefly list all the switches, in alphabetical order, then we describe the switches in more detail in functionally grouped sections.
More switches exist for GCC than those documented here, especially for specific targets. However, their use is not recommended as they may change code generation in ways that are incompatible with the Ada run-time library, or can cause inconsistencies between compilation units.
gnat1, the Ada compiler)
from dir instead of the default location. Only use this switch
when multiple versions of the GNAT compiler are available.
See Options for Directory Search, for further details. You would normally
use the -b or -V switch instead.
Note: for some other languages when using gcc, notably in
the case of C and C++, it is possible to use
use gcc without a -c switch to
compile and link in one step. In the case of GNAT, you
cannot use this approach, because the binder must be run
and gcc cannot be used to run the GNAT binder.
Inline_Always.
Any occurrences of pragma Inline or Inline_Always
are ignored, and -gnatn and -gnatN have no
effect if this switch is present.
Pragma Assert and pragma Debug to be
activated. Note that these pragmas can also be controlled using the
configuration pragmas Assertion_Policy and Debug_Policy.
It also activates pragmas Check, Precondition, and
Postcondition. Note that these pragmas can also be controlled
using the configuration pragma Check_Policy.
k = krunch).
inline is specified. This inlining is performed
by the GCC back-end.
Inline is specified. This inlining is performed
by the front end and will be visible in the
-gnatG output.
In some cases, this has proved more effective than the back end
inlining resulting from the use of
-gnatn.
Note that
-gnatN automatically implies
-gnatn so it is not necessary
to specify both options. There are a few cases that the back-end inlining
catches that cannot be dealt with in the front-end.
case statements.
This may result in less efficient code, but is sometimes necessary
(for example on HP-UX targets)
in order to compile large and/or nested case statements.
See also Optimization Levels.
You may combine a sequence of GNAT switches into a single switch. For example, the combined switch
-gnatofi3
is equivalent to specifying the following sequence of switches:
-gnato -gnatf -gnati3
The following restrictions apply to the combination of switches in this manner:
The standard default format for error messages is called “brief format”. Brief format messages are written to stderr (the standard error file) and have the following form:
e.adb:3:04: Incorrect spelling of keyword "function"
e.adb:4:20: ";" should be "is"
The first integer after the file name is the line number in the file,
and the second integer is the column number within the line.
GPS can parse the error messages
and point to the referenced character.
The following switches provide control over the error message
format:
| 3. funcion X (Q : Integer) | >>> Incorrect spelling of keyword "function" 4. return Integer; | >>> ";" should be "is" |
The vertical bar indicates the location of the error, and the ‘>>>’
prefix can be used to search for error messages. When this switch is
used the only source lines output are those with errors.
l stands for list.
This switch causes a full listing of
the file to be generated. In the case where a body is
compiled, the corresponding spec is also listed, along
with any subunits. Typical output from compiling a package
body p.adb might look like:
| Compiling: p.adb 1. package body p is 2. procedure a; 3. procedure a is separate; 4. begin 5. null | >>> missing ";" 6. end; Compiling: p.ads 1. package p is 2. pragma Elaborate_Body | >>> missing ";" 3. end p; Compiling: p-a.adb 1. separate p | >>> missing "(" 2. procedure a is 3. begin 4. null | >>> missing ";" 5. end; |
When you specify the -gnatv or -gnatl switches and
standard output is redirected, a brief summary is written to
stderr (standard error) giving the number of error messages and
warning messages generated.
b stands for brief.
This switch causes GNAT to generate the
brief format error messages to stderr (the standard error
file) as well as the verbose
format message or full listing (which as usual is written to
stdout (the standard output file).
m stands for maximum.
n is a decimal integer in the
range of 1 to 999 and limits the number of error messages to be
generated. For example, using -gnatm2 might yield
e.adb:3:04: Incorrect spelling of keyword "function"
e.adb:5:35: missing ".."
fatal error: maximum errors reached
compilation abandoned
Note that the equal sign is optional, so the switches
-gnatm2 and -gnatm=2 are equivalent.
f stands for full.
Normally, the compiler suppresses error messages that are likely to be
redundant. This switch causes all error
messages to be generated. In particular, in the case of
references to undefined variables. If a given variable is referenced
several times, the normal format of messages is
e.adb:7:07: "V" is undefined (more references follow)
where the parenthetical comment warns that there are additional
references to the variable V. Compiling the same program with the
-gnatf switch yields
e.adb:7:07: "V" is undefined
e.adb:8:07: "V" is undefined
e.adb:8:12: "V" is undefined
e.adb:8:16: "V" is undefined
e.adb:9:07: "V" is undefined
e.adb:9:12: "V" is undefined
The -gnatf switch also generates additional information for some error messages. Some examples are:
If the -gnatjnn switch is used with a positive value for nn, then
messages are output in a different manner. A message and all its continuation
lines are treated as a unit, and count as only one warning or message in the
statistics totals. Furthermore, the message is reformatted so that no line
is longer than nn characters.
q stands for quit (really “don't quit”).
In normal operation mode, the compiler first parses the program and
determines if there are any syntax errors. If there are, appropriate
error messages are generated and compilation is immediately terminated.
This switch tells
GNAT to continue with semantic analysis even if syntax errors have been
found. This may enable the detection of more errors in a single run. On
the other hand, the semantic analyzer is more likely to encounter some
internal fatal error when given a syntactically invalid tree.
In addition, if -gnatt is also specified, then the tree file is generated even if there are illegalities. It may be useful in this case to also specify -gnatq to ensure that full semantic processing occurs. The resulting tree file can be processed by ASIS, for the purpose of providing partial information about illegal units, but if the error causes the tree to be badly malformed, then ASIS may crash during the analysis.
When -gnatQ is used and the generated ALI file is marked as being in error, gnatmake will attempt to recompile the source when it finds such an ALI file, including with switch -gnatc.
Note that -gnatQ has no effect if -gnats is specified, since ALI files are never generated if -gnats is set.
In addition to error messages, which correspond to illegalities as defined in the Ada Reference Manual, the compiler detects two kinds of warning situations.
First, the compiler considers some constructs suspicious and generates a warning message to alert you to a possible error. Second, if the compiler detects a situation that is sure to raise an exception at run time, it generates a warning message. The following shows an example of warning messages:
e.adb:4:24: warning: creation of object may raise Storage_Error
e.adb:10:17: warning: static value out of range
e.adb:10:17: warning: "Constraint_Error" will be raised at run time
GNAT considers a large number of situations as appropriate
for the generation of warning messages. As always, warnings are not
definite indications of errors. For example, if you do an out-of-range
assignment with the deliberate intention of raising a
Constraint_Error exception, then the warning that may be
issued does not indicate an error. Some of the situations for which GNAT
issues warnings (at least some of the time) are given in the following
list. This list is not complete, and new warnings are often added to
subsequent versions of GNAT. The list is intended to give a general idea
of the kinds of warnings that are generated.
accept statement
select
return statement along some execution path in a function
with clauses
Bit_Order usage that does not have any effect
Standard.Duration used to resolve universal fixed expression
with'ed by application unit
for loop that is known to be null or might be null
The following section lists compiler switches that are available to control the handling of warning messages. It is also possible to exercise much finer control over what warnings are issued and suppressed using the GNAT pragma Warnings, See Pragma Warnings.
This warning option also activates a special test for comparisons using
the operators “>=” and“ <=”.
If the compiler can tell that only the equality condition is possible,
then it will warn that the “>” or “<” part of the test
is useless and that the operator could be replaced by “=”.
An example would be comparing a Natural variable <= 0.
This warning option also generates warnings if one or both tests is optimized away in a membership test for integer values if the result can be determined at compile time. Range tests on enumeration types are not included, since it is common for such tests to include an end point.
This warning can also be turned on using -gnatwa.
This warning can also be turned on using -gnatwa.
.all will generate a warning. With this warning
enabled, access checks occur only at points where an explicit
.all appears in the source code (assuming no warnings are
generated as a result of this switch). The default is that such
warnings are not generated.
Note that -gnatwa does not affect the setting of
this warning option.
-gnatwa.
with of an internal GNAT
implementation unit, defined as any unit from the Ada,
Interfaces, GNAT,
or System
hierarchies that is not
documented in either the Ada Reference Manual or the GNAT
Programmer's Reference Manual. Such units are intended only
for internal implementation purposes and should not be with'ed
by user programs. The default is that such warnings are generated
This warning can also be turned on using -gnatwa.
with of an internal GNAT
implementation unit.
pragma Obsolescent and
for use of features in Annex J of the Ada Reference Manual. In the
case of Annex J, not all features are flagged. In particular use
of the renamed packages (like Text_IO) and use of package
ASCII are not flagged, since these are very common and
would generate many annoying positive warnings. The default is that
such warnings are not generated. This warning is also turned on by
the use of -gnatwa.
In addition to the above cases, warnings are also generated for
GNAT features that have been provided in past versions but which
have been superseded (typically by features in the new Ada standard).
For example, pragma Ravenscar will be flagged since its
function is replaced by pragma Profile(Ravenscar).
Note that this warning option functions differently from the
restriction No_Obsolescent_Features in two respects.
First, the restriction applies only to annex J features.
Second, the restriction does flag uses of package ASCII.
Elaborate_All and Elaborate pragmas.
See the section in this guide on elaboration checking for details on
when such pragmas should be used. In dynamic elaboration mode, this switch
generations warnings about the need to add elaboration pragmas. Note however,
that if you blindly follow these warnings, and add Elaborate_All
warnings wherever they are recommended, you basically end up with the
equivalent of the static elaboration model, which may not be what you want for
legacy code for which the static model does not work.
For the static model, the messages generated are labeled "info:" (for information messages). They are not warnings to add elaboration pragmas, merely informational messages showing what implicit elaboration pragmas have been added, for use in analyzing elaboration circularity problems.
Warnings are also generated if you
are using the static mode of elaboration, and a pragma Elaborate
is encountered. The default is that such warnings
are not generated.
This warning is not automatically turned on by the use of -gnatwa.
Base where typ'Base is the same
as typ.
Pack when all components are placed by a record
representation clause.
This warning can also be turned on using -gnatwa.
The default is that warnings for redundant constructs are not given.
with'ed
and not
referenced. In the case of packages, a warning is also generated if
no entities in the package are referenced. This means that if the package
is referenced but the only references are in use
clauses or renames
declarations, a warning is still generated. A warning is also generated
for a generic package that is with'ed but never instantiated.
In the case where a package or subprogram body is compiled, and there
is a with on the corresponding spec
that is only referenced in the body,
a warning is also generated, noting that the
with can be moved to the body. The default is that
such warnings are not generated.
This switch also activates warnings on unreferenced formals
(it includes the effect of -gnatwf).
This warning can also be turned on using -gnatwa.
Tab : Table := (others => <>);
will suppress warnings on subsequent statements that access components
of variable Tab.
procedure K (S : String) is
pragma Assert (S'First = 1);
...
pragma Warnings (Off, entity
where either the pragma is entirely useless (because it suppresses no
warnings), or it could be replaced by pragma Unreferenced or
pragma Unmodified.The default is that these warnings are not given.
Note that this warning is not included in -gnatwa, it must be
activated explicitly.
pragma Warnings (Off, entity.
interface is now a reserved word in Ada 2005). This
switch activates several warnings to help in identifying
and correcting such incompatibilities. The default is that
these warnings are generated. Note that at one point Ada 2005
was called Ada 0Y, hence the choice of character.
This warning can also be turned on using -gnatwa.
A string of warning parameters can be used in the same parameter. For example:
-gnatwaLe
will turn on all optional warnings except for elaboration pragma warnings, and also specify that warnings should be treated as errors. When no switch -gnatw is used, this is equivalent to:
Assert and Debug normally have no effect and
are ignored. This switch, where ‘a’ stands for assert, causes
Assert and Debug pragmas to be activated.
The pragmas have the form:
| pragma Assert (Boolean-expression [, static-string-expression]) pragma Debug (procedure call) |
The Assert pragma causes Boolean-expression to be tested.
If the result is True, the pragma has no effect (other than
possible side effects from evaluating the expression). If the result is
False, the exception Assert_Failure declared in the package
System.Assertions is
raised (passing static-string-expression, if present, as the
message associated with the exception). If no string expression is
given the default is a string giving the file name and line number
of the pragma.
The Debug pragma causes procedure to be called. Note that
pragma Debug may appear within a declaration sequence, allowing
debugging procedures to be called between declarations.
The Ada Reference Manual has specific requirements for checking for invalid values. In particular, RM 13.9.1 requires that the evaluation of invalid values (for example from unchecked conversions), not result in erroneous execution. In GNAT, the result of such an evaluation in normal default mode is to either use the value unmodified, or to raise Constraint_Error in those cases where use of the unmodified value would cause erroneous execution. The cases where unmodified values might lead to erroneous execution are case statements (where a wild jump might result from an invalid value), and subscripts on the left hand side (where memory corruption could occur as a result of an invalid value).
The -gnatVx switch allows more control over the validity
checking mode.
The x argument is a string of letters that
indicate validity checks that are performed or not performed in addition
to the default checks described above.
in should be validity checked.
in mode parameters
Arguments for parameters of mode in are validity checked in function
and procedure calls at the point of call.
in out mode parameters.
Arguments for parameters of mode in out are validity checked in
procedure calls at the point of call. The 'm' here stands for
modify, since this concerns parameters that can be modified by the call.
Note that there is no specific option to test out parameters,
but any reference within the subprogram will be tested in the usual
manner, and if an invalid value is copied back, any reference to it
will be subject to validity checking.
Standard,
the shift operators defined as intrinsic in package Interfaces
and operands for attributes such as Pos. Checks are also made
on individual component values for composite comparisons, and on the
expressions in type conversions and qualified expressions. Checks are
also made on explicit ranges using ‘..’ (e.g. slices, loops etc).
return statements in functions is validity
checked.
if, while or exit
statements are checked, as well as guard expressions in entry calls.
The -gnatV switch may be followed by
a string of letters
to turn on a series of validity checking options.
For example,
-gnatVcr
specifies that in addition to the default validity checking, copies and
function return expressions are to be validity checked.
In order to make it easier
to specify the desired combination of effects,
the upper case letters CDFIMORST may
be used to turn off the corresponding lower case option.
Thus
-gnatVaM
turns on all validity checking options except for
checking of in out procedure arguments.
The specification of additional validity checking generates extra code (and
in the case of -gnatVa the code expansion can be substantial).
However, these additional checks can be very useful in detecting
uninitialized variables, incorrect use of unchecked conversion, and other
errors leading to invalid values. The use of pragma Initialize_Scalars
is useful in conjunction with the extra validity checking, since this
ensures that wherever possible uninitialized variables have invalid values.
See also the pragma Validity_Checks which allows modification of
the validity checking mode at the program source level, and also allows for
temporary disabling of validity checks.
The -gnatyx switch causes the compiler to enforce specified style rules. A limited set of style rules has been used in writing the GNAT sources themselves. This switch allows user programs to activate all or some of these checks. If the source program fails a specified style check, an appropriate warning message is given, preceded by the character sequence “(style)”. The string x is a sequence of letters or digits indicating the particular style checks to be performed. The following checks are defined:
-- starting on a column that is a multiple of
the alignment level, or they may be aligned the same way as the following
non-blank line (this is useful when full line comments appear in the middle
of a statement.
digits
used as attributes names, must be written in mixed case, that is, the
initial letter and any letter following an underscore must be uppercase.
All other letters must be lowercase.
--” that starts the column must either start in column one,
or else at least one blank must precede this sequence.
--” at the start of the comment.
--” that
starts the comment, with the following exceptions.
--” characters, possibly preceded
by blanks is permitted.
--x” where x is a special character
is permitted.
This allows proper processing of the output generated by specialized tools
including gnatprep (where “--!” is used) and the SPARK
annotation
language (where “--#” is used). For the purposes of this rule, a
special character is defined as being in one of the ASCII ranges
16#21#...16#2F# or 16#3A#...16#3F#.
Note that this usage is not permitted
in GNAT implementation units (i.e., when -gnatg is used).
--” is permitted as long as at
least one blank follows the initial “--”. Together with the preceding
rule, this allows the construction of box comments, as shown in the following
example:
---------------------------
-- This is a box comment --
-- with two text lines. --
---------------------------
end statements ending subprograms and on
exit statements exiting named loops, are required to be present.
then must appear either on the same
line as corresponding if, or on a line on its own, lined
up under the if with at least one non-blank line in between
containing all or part of the condition to be tested.
in (the default mode) is not
allowed to be given explicitly. in out is fine,
but not in on its own.
digits used as attribute names to which this check
does not apply).
else keyword must
be lined up with the corresponding if keyword.
There are two respects in which the style rule enforced by this check
option are more liberal than those in the Ada Reference Manual. First
in the case of record declarations, it is permissible to put the
record keyword on the same line as the type keyword, and
then the end in end record must line up under type.
This is also permitted when the type declaration is split on two lines.
For example, any of the following three layouts is acceptable:
| type q is record a : integer; b : integer; end record; type q is record a : integer; b : integer; end record; type q is record a : integer; b : integer; end record; |
Second, in the case of a block statement, a permitted alternative
is to put the block label on the same line as the declare or
begin keyword, and then line the end keyword up under
the block label. For example both the following are permitted:
| Block : declare A : Integer := 3; begin Proc (A, A); end Block; Block : declare A : Integer := 3; begin Proc (A, A); end Block; |
The same alternative format is allowed for loops. For example, both of the following are permitted:
| Clear : while J < 10 loop A (J) := 0; end loop Clear; Clear : while J < 10 loop A (J) := 0; end loop Clear; |
Integer and ASCII.NUL).
=> must be surrounded by spaces.
<> must be preceded by a space or a left parenthesis.
** must be surrounded by spaces.
There is no restriction on the layout of the ** binary operator.
if statements, while statements and
exit statements.
gnaty3aAbcefhiklmnprst, that is all checking
options enabled with the exception of -gnatyo, -gnatyI,
-gnatyS, -gnatyLnnn,
-gnatyd, -gnatyu, and -gnatyx.
In the above rules, appearing in column one is always permitted, that is, counts as meeting either a requirement for a required preceding space, or as meeting a requirement for no preceding space.
Appearing at the end of a line is also always permitted, that is, counts as meeting either a requirement for a following space, or as meeting a requirement for no following space.
If any of these style rules is violated, a message is generated giving
details on the violation. The initial characters of such messages are
always “(style)”. Note that these messages are treated as warning
messages, so they normally do not prevent the generation of an object
file. The -gnatwe switch can be used to treat warning messages,
including style messages, as fatal errors.
The switch -gnaty on its own (that is not followed by any letters or digits), then the effect is equivalent to the use of -gnatyy, as described above, that is all built-in standard style check options are enabled.
The switch -gnatyN clears any previously set style checks.
By default, the following checks are suppressed: integer overflow checks, stack overflow checks, and checks for access before elaboration on subprogram calls. All other checks, including range checks and array bounds checks, are turned on by default. The following gcc switches refine this default behavior.
pragma Suppress (All_checks)
had been present in the source. Validity checks are also suppressed (in
other words -gnatp also implies -gnatVn.
Use this switch to improve the performance
of the code at the expense of safety in the presence of invalid data or
program bugs.
Note that when checks are suppressed, the compiler is allowed, but not required, to omit the checking code. If the run-time cost of the checking code is zero or near-zero, the compiler will generate it even if checks are suppressed. In particular, if the compiler can prove that a certain check will necessarily fail, it will generate code to do an unconditional “raise”, even if checks are suppressed. The compiler warns in this case.
Of course, run-time checks are omitted whenever the compiler can prove that they will not fail, whether or not checks are suppressed.
Note that if you suppress a check that would have failed, program
execution is erroneous, which means the behavior is totally
unpredictable. The program might crash, or print wrong answers, or
do anything else. It might even do exactly what you wanted it to do
(and then it might start failing mysteriously next week or next
year). The compiler will generate code based on the assumption that
the condition being checked is true, which can result in disaster if
that assumption is wrong.
Constraint_Error as required by standard Ada
semantics). These overflow checks correspond to situations in which
the true value of the result of an operation may be outside the base
range of the result type. The following example shows the distinction:
X1 : Integer := "Integer'Last";
X2 : Integer range 1 .. 5 := "5";
X3 : Integer := "Integer'Last";
X4 : Integer range 1 .. 5 := "5";
F : Float := "2.0E+20";
...
X1 := X1 + 1;
X2 := X2 + 1;
X3 := Integer (F);
X4 := Integer (F);
Note that if explicit values are assigned at compile time, the compiler may be able to detect overflow at compile time, in which case no actual run-time checking code is required, and Constraint_Error will be raised unconditionally, with or without -gnato. That's why the assigned values in the above fragment are in quotes, the meaning is "assign a value not known to the compiler that happens to be equal to ...". The remaining discussion assumes that the compiler cannot detect the values at compile time.
Here the first addition results in a value that is outside the base range
of Integer, and hence requires an overflow check for detection of the
constraint error. Thus the first assignment to X1 raises a
Constraint_Error exception only if -gnato is set.
The second increment operation results in a violation of the explicit range constraint; such range checks are performed by default, and are unaffected by -gnato.
The two conversions of F both result in values that are outside
the base range of type Integer and thus will raise
Constraint_Error exceptions only if -gnato is used.
The fact that the result of the second conversion is assigned to
variable X4 with a restricted range is irrelevant, since the problem
is in the conversion, not the assignment.
Basically the rule is that in the default mode (-gnato not used), the generated code assures that all integer variables stay within their declared ranges, or within the base range if there is no declared range. This prevents any serious problems like indexes out of range for array operations.
What is not checked in default mode is an overflow that results in
an in-range, but incorrect value. In the above example, the assignments
to X1, X2, X3 all give results that are within the
range of the target variable, but the result is wrong in the sense that
it is too large to be represented correctly. Typically the assignment
to X1 will result in wrap around to the largest negative number.
The conversions of F will result in some Integer value
and if that integer value is out of the X4 range then the
subsequent assignment would generate an exception.
Note that the -gnato switch does not affect the code generated
for any floating-point operations; it applies only to integer
semantics).
For floating-point, GNAT has the Machine_Overflows
attribute set to False and the normal mode of operation is to
generate IEEE NaN and infinite values on overflow or invalid operations
(such as dividing 0.0 by 0.0).
The reason that we distinguish overflow checking from other kinds of range constraint checking is that a failure of an overflow check, unlike for example the failure of a range check, can result in an incorrect value, but cannot cause random memory destruction (like an out of range subscript), or a wild jump (from an out of range case value). Overflow checking is also quite expensive in time and space, since in general it requires the use of double length arithmetic.
Note again that -gnato is off by default, so overflow checking is
not performed in default mode. This means that out of the box, with the
default settings, GNAT does not do all the checks expected from the
language description in the Ada Reference Manual. If you want all constraint
checks to be performed, as described in this Manual, then you must
explicitly use the -gnato switch either on the gnatmake or
gcc command.
The setting of these switches only controls the default setting of the
checks. You may modify them using either Suppress (to remove
checks) or Unsuppress (to add back suppressed checks) pragmas in
the program source.
s stands for “syntax”.
Run GNAT in syntax checking only mode. For example, the command
$ gcc -c -gnats x.adb
compiles file x.adb in syntax-check-only mode. You can check a series of files in a single command , and can use wild cards to specify such a group of files. Note that you must specify the -c (compile only) flag in addition to the -gnats flag. . You may use other switches in conjunction with -gnats. In particular, -gnatl and -gnatv are useful to control the format of any generated error messages.
When the source file is empty or contains only empty lines and/or comments, the output is a warning:
$ gcc -c -gnats -x ada toto.txt
toto.txt:1:01: warning: empty file, contains no compilation units
$
Otherwise, the output is simply the error messages, if any. No object file or
ALI file is generated by a syntax-only compilation. Also, no units other
than the one specified are accessed. For example, if a unit X
with's a unit Y, compiling unit X in syntax
check only mode does not access the source file containing unit
Y.
Normally, GNAT allows only a single unit in a source file. However, this
restriction does not apply in syntax-check-only mode, and it is possible
to check a file containing multiple compilation units concatenated
together. This is primarily used by the gnatchop utility
(see Renaming Files Using gnatchop).
c stands for “check”.
Causes the compiler to operate in semantic check mode,
with full checking for all illegalities specified in the
Ada Reference Manual, but without generation of any object code
(no object file is generated).
Because dependent files must be accessed, you must follow the GNAT semantic restrictions on file structuring to operate in this mode:
The output consists of error messages as appropriate. No object file is generated. An ALI file is generated for use in the context of cross-reference tools, but this file is marked as not being suitable for binding (since no object file is generated). The checking corresponds exactly to the notion of legality in the Ada Reference Manual.
Any unit can be compiled in semantics-checking-only mode, including units that would not normally be compiled (subunits, and specifications where a separate body is present).
The switches described in this section allow you to explicitly specify the version of the Ada language that your programs are written in. By default GNAT assumes Ada 2005, but you can also specify Ada 95 or indicate Ada 83 compatibility mode.
With few exceptions (most notably the need to use <> on
unconstrained generic formal parameters, the use of the new Ada 95 / Ada 2005
reserved words, and the use of packages
with optional bodies), it is not necessary to specify the
-gnat83 switch when compiling Ada 83 programs, because, with rare
exceptions, Ada 95 and Ada 2005 are upwardly compatible with Ada 83. Thus
a correct Ada 83 program is usually also a correct program
in these later versions of the language standard.
For further information, please refer to Compatibility and Porting Guide.
This switch also can be used to cancel the effect of a previous
-gnat83 or -gnat05 switch earlier in the command line.
For information about the approved “Ada Issues” that have been incorporated into Ada 2005, see http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs. Included with GNAT releases is a file features-ada0y that describes the set of implemented Ada 2005 features.
123459p8fnwSee Foreign Language Representation, for full details on the
implementation of these character sets.
huse8bIf no -gnatW? parameter is present, then the default representation is normally Brackets encoding only. However, if the first three characters of the file are 16#EF# 16#BB# 16#BF# (the standard byte order mark or BOM for UTF-8), then these three characters are skipped and the default representation for the file is set to UTF-8.
Note that the wide character representation that is specified (explicitly or by default) for the main program also acts as the default encoding used for Wide_Text_IO files if not specifically overridden by a WCEM form parameter.
For the source file naming rules, See File Naming Rules.
n here is intended to suggest the first syllable of the
word “inline”.
GNAT recognizes and processes Inline pragmas. However, for the
inlining to actually occur, optimization must be enabled. To enable
inlining of subprograms specified by pragma Inline,
you must also specify this switch.
In the absence of this switch, GNAT does not attempt
inlining and does not need to access the bodies of
subprograms for which pragma Inline is specified if they are not
in the current unit.
If you specify this switch the compiler will access these bodies,
creating an extra source dependency for the resulting object file, and
where possible, the call will be inlined.
For further details on when inlining is possible
see Inlining of Subprograms.
When -pass-exit-codes is used, gcc exits with an extended exit status and allows an integrated development environment to better react to a compilation failure. Those exit status are:
Debug unit in the compiler source
file debug.adb.
The format of the output is very similar to standard Ada source, and is
easily understood by an Ada programmer. The following special syntactic
additions correspond to low level features used in the generated code that
do not have any exact analogies in pure Ada source form. The following
is a partial list of these special constructions. See the spec
of package Sprint in file sprint.ads for a full list.
If the switch -gnatL is used in conjunction with -gnatG, then the original source lines are interspersed in the expanded source (as comment lines with the original line number).
new xxx [storage_pool = yyy]at end procedure-name;(if expr then expr else expr)x?y:z construction in C.
^(source)?(source)?^(source) #/ y #mod y #* y #rem yfree expr [storage_pool = xxx]free statement.
[subtype or type declaration]freeze type-name [actions]reference itype! (arg, arg, arg) : label#$ subprogram-name && expr && expr ... && expr[constraint_error]Constraint_Error exception.
'reference!(source-expression)[numerator/denominator]Note that -gnatD actually implies -gnatG automatically, so it is not necessary to give both options. In other words -gnatD is equivalent to -gnatDG).
If the switch -gnatL is used in conjunction with
-gnatDG, then the original source lines are interspersed
in the expanded source (as comment lines with the original line number).
GNAT sources for full details on the format of -gnatR3
output. If the switch is followed by an s (e.g. -gnatR2s), then
the output is to a file with the name file.rep where
file is the name of the corresponding source file.
Note that it is possible for record components to have zero size. In
this case, the component clause uses an obvious extension of permitted
Ada syntax, for example at 0 range 0 .. -1.
Representation information requires that code be generated (since it is the
code generator that lays out complex data structures). If an attempt is made
to output representation information when no code is generated, for example
when a subunit is compiled on its own, then no information can be generated
and the compiler outputs a message to this effect.
gnatfind and gnatxref. The -gnatx switch
suppresses this information. This saves some space and may slightly
speed up compilation, but means that these tools cannot be used.
GNAT uses two methods for handling exceptions at run-time. The
setjmp/longjmp method saves the context when entering
a frame with an exception handler. Then when an exception is
raised, the context can be restored immediately, without the
need for tracing stack frames. This method provides very fast
exception propagation, but introduces significant overhead for
the use of exception handlers, even if no exception is raised.
The other approach is called “zero cost” exception handling. With this method, the compiler builds static tables to describe the exception ranges. No dynamic code is required when entering a frame containing an exception handler. When an exception is raised, the tables are used to control a back trace of the subprogram invocation stack to locate the required exception handler. This method has considerably poorer performance for the propagation of exceptions, but there is no overhead for exception handlers if no exception is raised. Note that in this mode and in the context of mixed Ada and C/C++ programming, to propagate an exception through a C/C++ code, the C/C++ code must be compiled with the -funwind-tables GCC's option.
The following switches may be used to control which of the two exception handling methods is used.
The same option --RTS must be used both for gcc and gnatbind. Passing this option to gnatmake (see Switches for gnatmake) will ensure the required consistency through the compilation and binding steps.
The use of mapping files is not required for correct operation of the compiler, but mapping files can improve efficiency, particularly when sources are read over a slow network connection. In normal operation, you need not be concerned with the format or use of mapping files, and the -gnatem switch is not a switch that you would use explicitly. it is intended only for use by automatic tools such as gnatmake running under the project file facility. The description here of the format of mapping files is provided for completeness and for possible use by other tools.
A mapping file is a sequence of sets of three lines. In each set,
the first line is the unit name, in lower case, with “%s”
appended for
specs and “%b” appended for bodies; the second line is the
file name; and the third line is the path name.
Example:
main%b
main.2.ada
/gnat/project1/sources/main.2.ada
When the switch -gnatem is specified, the compiler will create in memory the two mappings from the specified file. If there is any problem (nonexistent file, truncated file or duplicate entries), no mapping will be created.
Several -gnatem switches may be specified; however, only the last one on the command line will be taken into account.
When using a project file, gnatmake create a temporary mapping file and communicates it to the compiler using this switch.
GNAT sources may be preprocessed immediately before compilation. In this case, the actual text of the source is not the text of the source file, but is derived from it through a process called preprocessing. Integrated preprocessing is specified through switches -gnatep and/or -gnateD. -gnatep indicates, through a text file, the preprocessing data to be used. -gnateD specifies or modifies the values of preprocessing symbol.
Note that when integrated preprocessing is used, the output from the preprocessor is not written to any external file. Instead it is passed internally to the compiler. If you need to preserve the result of preprocessing in a file, then you should use gnatprep to perform the desired preprocessing in stand-alone mode.
It is recommended that gnatmake switch -s should be used when Integrated Preprocessing is used. The reason is that preprocessing with another Preprocessing Data file without changing the sources will not trigger recompilation without this switch.
Note that gnatmake switch -m will almost always trigger recompilation for sources that are preprocessed, because gnatmake cannot compute the checksum of the source after preprocessing.
The actual preprocessing function is described in details in section Preprocessing Using gnatprep. This section only describes how integrated preprocessing is triggered and parameterized.
-gnatep=fileA preprocessing data file is a text file with significant lines indicating how should be preprocessed either a specific source or all sources not mentioned in other lines. A significant line is a nonempty, non-comment line. Comments are similar to Ada comments.
Each significant line starts with either a literal string or the character '*'. A literal string is the file name (without directory information) of the source to preprocess. A character '*' indicates the preprocessing for all the sources that are not specified explicitly on other lines (order of the lines is not significant). It is an error to have two lines with the same file name or two lines starting with the character '*'.
After the file name or the character '*', another optional literal string indicating the file name of the definition file to be used for preprocessing (see Form of Definitions File). The definition files are found by the compiler in one of the source directories. In some cases, when compiling a source in a directory other than the current directory, if the definition file is in the current directory, it may be necessary to add the current directory as a source directory through switch -I., otherwise the compiler would not find the definition file.
Then, optionally, switches similar to those of gnatprep may
be found. Those switches are:
-b-c--! ”.
-Dsymbol=valueif,
else, elsif, end, and, or and then.
value is either a literal string, an Ada identifier or any Ada reserved
word. A symbol declared with this switch replaces a symbol with the
same name defined in a definition file.
-s-uFALSE
in the context
of a preprocessor test. In the absence of this option, an undefined symbol in
a #if or #elsif test will be treated as an error.
Examples of valid lines in a preprocessor data file:
"toto.adb" "prep.def" -u
-- preprocess "toto.adb", using definition file "prep.def",
-- undefined symbol are False.
* -c -DVERSION=V101
-- preprocess all other sources without a definition file;
-- suppressed lined are commented; symbol VERSION has the value V101.
"titi.adb" "prep2.def" -s
-- preprocess "titi.adb", using definition file "prep2.def";
-- list all symbols with their values.
-gnateDsymbol[=value]True.
A symbol is an identifier, following normal Ada (case-insensitive)
rules for its syntax, and value is any sequence (including an empty sequence)
of characters from the set (letters, digits, period, underline).
Ada reserved words may be used as symbols, with the exceptions of if,
else, elsif, end, and, or and then.
A symbol declared with this switch on the command line replaces a symbol with the same name either in a definition file or specified with a switch -D in the preprocessor data file.
This switch is similar to switch -D of gnatprep.
-gnateGThe GCC technology provides a wide range of target dependent -m switches for controlling details of code generation with respect to different versions of architectures. This includes variations in instruction sets (e.g. different members of the power pc family), and different requirements for optimal arrangement of instructions (e.g. different members of the x86 family). The list of available -m switches may be found in the GCC documentation.
Use of these -m switches may in some cases result in improved code performance.
The GNAT Pro technology is tested and qualified without any -m switches, so generally the most reliable approach is to avoid the use of these switches. However, we generally expect most of these switches to work successfully with GNAT Pro, and many customers have reported successful use of these options.
Our general advice is to avoid the use of -m switches unless special needs lead to requirements in this area. In particular, there is no point in using -m switches to improve performance unless you actually see a performance improvement.
With the GNAT source-based library system, the compiler must be able to find source files for units that are needed by the unit being compiled. Search paths are used to guide this process.
The compiler compiles one source file whose name must be given explicitly on the command line. In other words, no searching is done for this file. To find all other source files that are needed (the most common being the specs of units), the compiler examines the following directories, in the following order:
ADA_PRJ_INCLUDE_FILE is normally set by gnatmake or by the gnat driver when project files are used. It should not normally be set by other means.
Specifying the switch -I- inhibits the use of the directory containing the source file named in the command line. You can still have this directory on your search path, but in this case it must be explicitly requested with a -I switch.
Specifying the switch -nostdinc inhibits the search of the default location for the GNAT Run Time Library (RTL) source files.
The compiler outputs its object files and ALI files in the current
working directory.
Caution: The object file can be redirected with the -o switch;
however, gcc and gnat1 have not been coordinated on this
so the ALI file will not go to the right place. Therefore, you should
avoid using the -o switch.
The packages Ada, System, and Interfaces and their
children make up the GNAT RTL, together with the simple System.IO
package used in the "Hello World" example. The sources for these units
are needed by the compiler and are kept together in one directory. Not
all of the bodies are needed, but all of the sources are kept together
anyway. In a normal installation, you need not specify these directory
names when compiling or binding. Either the environment variables or
the built-in defaults cause these files to be found.
In addition to the language-defined hierarchies (System, Ada and
Interfaces), the GNAT distribution provides a fourth hierarchy,
consisting of child units of GNAT. This is a collection of generally
useful types, subprograms, etc. See GNAT Reference Manual, for further details.
Besides simplifying access to the RTL, a major use of search paths is in compiling sources from multiple directories. This can make development environments much more flexible.
If, in our earlier example, there was a spec for the hello
procedure, it would be contained in the file hello.ads; yet this
file would not have to be explicitly compiled. This is the result of the
model we chose to implement library management. Some of the consequences
of this model are as follows:
with's, all its subunits, and the bodies of any generics it
instantiates must be available (reachable by the search-paths mechanism
described above), or you will receive a fatal error message.
The following are some typical Ada compilation command line examples:
$ gcc -c xyz.adb$ gcc -c -O2 -gnata xyz-def.adbAssert/Debug statements
enabled.
$ gcc -c -gnatc abc-def.adbgnatbindThis chapter describes the GNAT binder, gnatbind, which is used
to bind compiled GNAT objects.
Note: to invoke gnatbind with a project file, use the gnat
driver (see The GNAT Driver and Project Files).
The gnatbind program performs four separate functions:
gnatbindThe form of the gnatbind command is
$ gnatbind [switches] mainprog[.ali] [switches]
where mainprog.adb is the Ada file containing the main program
unit body. If no switches are specified, gnatbind constructs an Ada
package in two files whose names are
b~mainprog.ads, and b~mainprog.adb.
For example, if given the
parameter hello.ali, for a main program contained in file
hello.adb, the binder output files would be b~hello.ads
and b~hello.adb.
When doing consistency checking, the binder takes into consideration
any source files it can locate. For example, if the binder determines
that the given main program requires the package Pack, whose
.ALI
file is pack.ali and whose corresponding source spec file is
pack.ads, it attempts to locate the source file pack.ads
(using the same search path conventions as previously described for the
gcc command). If it can locate this source file, it checks that
the time stamps
or source checksums of the source and its references to in ALI files
match. In other words, any ALI files that mentions this spec must have
resulted from compiling this version of the source file (or in the case
where the source checksums match, a version close enough that the
difference does not matter).
The effect of this consistency checking, which includes source files, is that the binder ensures that the program is consistent with the latest version of the source files that can be located at bind time. Editing a source file without compiling files that depend on the source file cause error messages to be generated by the binder.
For example, suppose you have a main program hello.adb and a
package P, from file p.ads and you perform the following
steps:
gcc -c hello.adb to compile the main program.
gcc -c p.ads to compile package P.
gnatbind hello.
At this point, the file p.ali contains an out-of-date time stamp because the file p.ads has been edited. The attempt at binding fails, and the binder generates the following error messages:
error: "hello.adb" must be recompiled ("p.ads" has been modified)
error: "p.ads" has been modified and must be recompiled
Now both files must be recompiled as indicated, and then the bind can succeed, generating a main program. You need not normally be concerned with the contents of this file, but for reference purposes a sample binder output file is given in Example of Binder Output File.
In most normal usage, the default mode of gnatbind which is to generate the main package in Ada, as described in the previous section. In particular, this means that any Ada programmer can read and understand the generated main program. It can also be debugged just like any other Ada code provided the -g switch is used for gnatbind and gnatlink.
However for some purposes it may be convenient to generate the main
program in C rather than Ada. This may for example be helpful when you
are generating a mixed language program with the main program in C. The
GNAT compiler itself is an example.
The use of the -C switch
for both gnatbind and gnatlink will cause the program to
be generated in C (and compiled using the gnu C compiler).
The following switches are available with gnatbind; details will
be presented in subsequent sections.
pragma Storage_Size (nn);
When they do not already have such a pragma.
The secondary stack is used to deal with functions that return a variable sized result, for example a function returning an unconstrained String. There are two ways in which this secondary stack is allocated.
For most targets, the secondary stack is growing on demand and is allocated as a chain of blocks in the heap. The -D option is not very relevant. It only give some control over the size of the allocated blocks (whose size is the minimum of the default secondary stack size value, and the actual size needed for the current allocation request).
For certain targets, notably VxWorks 653,
the secondary stack is allocated by carving off a fixed ratio chunk of the
primary task stack. The -D option is used to define the
size of the environment task's secondary stack.
GNAT.Traceback and
GNAT.Traceback.Symbolic for more information.
Note that on x86 ports, you must not use -fomit-frame-pointer
gcc option.
gnatbind was
invoked, and do not look for ALI files in the directory containing the
ALI file named in the gnatbind command line.
16#xx# (i.e., xx is a string of two hexadecimal digits).
In addition, you can specify -Sev to indicate that the value is
to be set at run time. In this case, the program will look for an environment
variable of the form GNAT_INIT_SCALARS=xx, where xx is one
of in/lo/hi/xx with the same meanings as above.
If no environment variable is found, or if it does not have a valid value,
then the default is in (invalid values).
A value of zero is treated specially. It turns off time
slicing, and in addition, indicates to the tasking run time that the
semantics should match as closely as possible the Annex D
requirements of the Ada RM, and in particular sets the default
scheduling policy to FIFO_Within_Priorities.
Ada.Calendar and its children.
You may obtain this listing of switches by running gnatbind with
no arguments.
As described earlier, by default gnatbind checks
that object files are consistent with one another and are consistent
with any source files it can locate. The following switches control binder
access to sources.
The following switches provide control over the generation of error messages from the binder:
main to xxx.
This is useful in the case of some cross-building environments, where
the actual main program is separate from the one generated
by gnatbind.
GNAT were used for compilation
Normally failure of such checks, in accordance with the consistency requirements of the Ada Reference Manual, causes error messages to be generated which abort the binder and prevent the output of a binder file and subsequent link to obtain an executable.
The -t switch converts these error messages into warnings, so that binding and linking can continue to completion even in the presence of such errors. The result may be a failed link (due to missing symbols), or a non-functional executable which has undefined semantics. This means that -t should be used only in unusual situations, with extreme care.
The following switches provide additional control over the elaboration order. For full details see Elaboration Order Handling in GNAT.
Program_Error exception. This switch reverses the
action of the binder, and requests that it deliberately choose an order
that is likely to maximize the likelihood of an elaboration error.
This is useful in ensuring portability and avoiding dependence on
accidental fortuitous elaboration ordering.
Normally it only makes sense to use the -p
switch if dynamic
elaboration checking is used (-gnatE switch used for compilation).
This is because in the default static elaboration mode, all necessary
Elaborate and Elaborate_All pragmas are implicitly inserted.
These implicit pragmas are still respected by the binder in
-p mode, so a
safe elaboration order is assured.
The following switches allow additional control over the output generated by the binder.
gnatbind option.
gnatbind
option.
gnatbind.
pragma Restrictions that could be applied to
the current unit. This is useful for code audit purposes, and also may
be used to improve code generation in some cases.
In our description so far we have assumed that the main
program is in Ada, and that the task of the binder is to generate a
corresponding function main that invokes this Ada main
program. GNAT also supports the building of executable programs where
the main program is not in Ada, but some of the called routines are
written in Ada and compiled using GNAT (see Mixed Language Programming).
The following switch is used in this situation:
In this case, most of the functions of the binder are still required, but instead of generating a main program, the binder generates a file containing the following callable routines:
adainitadainit is
required before the first call to an Ada subprogram.
Note that it is assumed that the basic execution environment must be setup
to be appropriate for Ada execution at the point where the first Ada
subprogram is called. In particular, if the Ada code will do any
floating-point operations, then the FPU must be setup in an appropriate
manner. For the case of the x86, for example, full precision mode is
required. The procedure GNAT.Float_Control.Reset may be used to ensure
that the FPU is in the right state.
adafinaladafinal is required
after the last call to an Ada subprogram, and before the program
terminates.
If the -n switch
is given, more than one ALI file may appear on
the command line for gnatbind. The normal closure
calculation is performed for each of the specified units. Calculating
the closure means finding out the set of units involved by tracing
with references. The reason it is necessary to be able to
specify more than one ALI file is that a given program may invoke two or
more quite separate groups of Ada units.
The binder takes the name of its output file from the last specified ALI file, unless overridden by the use of the -o file. The output is an Ada unit in source form that can be compiled with GNAT unless the -C switch is used in which case the output is a C source file, which must be compiled using the C compiler. This compilation occurs automatically as part of the gnatlink processing.
Currently the GNAT run time requires a FPU using 80 bits mode precision. Under targets where this is not the default it is required to call GNAT.Float_Control.Reset before using floating point numbers (this include float computation, float input and output) in the Ada code. A side effect is that this could be the wrong mode for the foreign code where floating point computation could be broken after this call.
It is possible to have an Ada program which does not have a main subprogram. This program will call the elaboration routines of all the packages, then the finalization routines.
The following switch is used to bind programs organized in this manner:
The package Ada.Command_Line provides access to the command-line
arguments and program name. In order for this interface to operate
correctly, the two variables
int gnat_argc;
char **gnat_argv;
are declared in one of the GNAT library routines. These variables must
be set from the actual argc and argv values passed to the
main program. With no n present, gnatbind
generates the C main program to automatically set these variables.
If the n switch is used, there is no automatic way to
set these variables. If they are not set, the procedures in
Ada.Command_Line will not be available, and any attempt to use
them will raise Constraint_Error. If command line access is
required, your main program must set gnat_argc and
gnat_argv from the argc and argv values passed to
it.
gnatbindThe binder takes the name of an ALI file as its argument and needs to locate source files as well as other ALI files to verify object consistency.
For source files, it follows exactly the same search rules as gcc (see Search Paths and the Run-Time Library (RTL)). For ALI files the directories searched are:
gnatbind
command line, in the order given.
ADA_PRJ_OBJECTS_FILE is normally set by gnatmake or by the gnat driver when project files are used. It should not normally be set by other means.
In the binder the switch -I is used to specify both source and library file paths. Use -aI instead if you want to specify source paths only, and -aO if you want to specify library paths only. This means that for the binder -Idir is equivalent to -aIdir -aOdir. The binder generates the bind file (a C language source file) in the current working directory.
The packages Ada, System, and Interfaces and their
children make up the GNAT Run-Time Library, together with the package
GNAT and its children, which contain a set of useful additional
library functions provided by GNAT. The sources for these units are
needed by the compiler and are kept together in one directory. The ALI
files and object files generated by compiling the RTL are needed by the
binder and the linker and are kept together in one directory, typically
different from the directory containing the sources. In a normal
installation, you need not specify these directory names when compiling
or binding. Either the environment variables or the built-in defaults
cause these files to be found.
Besides simplifying access to the RTL, a major use of search paths is in compiling sources from multiple directories. This can make development environments much more flexible.
gnatbind UsageThis section contains a number of examples of using the GNAT binding
utility gnatbind.
gnatbind helloHello (source program in hello.adb) is
bound using the standard switch settings. The generated main program is
b~hello.adb. This is the normal, default use of the binder.
gnatbind hello -o mainprog.adbHello (source program in hello.adb) is
bound using the standard switch settings. The generated main program is
mainprog.adb with the associated spec in
mainprog.ads. Note that you must specify the body here not the
spec, in the case where the output is in Ada. Note that if this option
is used, then linking must be done manually, since gnatlink will not
be able to find the generated file.
gnatbind main -C -o mainprog.c -xMain (source program in
main.adb) is bound, excluding source files from the
consistency checking, generating
the file mainprog.c.
gnatbind -x main_program -C -o mainprog.cgnatbind -n math dbase -C -o ada-control.cMath and Dbase appear. This call
to gnatbind generates the file ada-control.c containing
the adainit and adafinal routines to be called before and
after accessing the Ada units.
This chapter discusses gnatlink, a tool that links an Ada program and builds an executable file. This utility invokes the system linker (via the gcc command) with a correct list of object files and library references. gnatlink automatically determines the list of files and references for the Ada part of a program. It uses the binder file generated by the gnatbind to determine this list.
Note: to invoke gnatlink with a project file, use the gnat
driver (see The GNAT Driver and Project Files).
The form of the gnatlink command is
$ gnatlink [switches] mainprog[.ali] [non-Ada objects] [linker options]
The arguments of gnatlink (switches, main ALI file, non-Ada objects or linker options) may be in any order, provided that no non-Ada object may be mistaken for a main ALI file. Any file name F without the .ali extension will be taken as the main ALI file if a file exists whose name is the concatenation of F and .ali.
mainprog.ali references the ALI file of the main program. The .ali extension of this file can be omitted. From this reference, gnatlink locates the corresponding binder file b~mainprog.adb and, using the information in this file along with the list of non-Ada objects and linker options, constructs a linker command file to create the executable.
The arguments other than the gnatlink switches and the main
ALI file are passed to the linker uninterpreted.
They typically include the names of
object files for units written in other languages than Ada and any library
references required to resolve references in any of these foreign language
units, or in Import pragmas in any Ada units.
linker options is an optional list of linker specific switches. The default linker called by gnatlink is gcc which in turn calls the appropriate system linker. Standard options for the linker such as -lmy_lib or -Ldir can be added as is. For options that are not recognized by gcc as linker options, use the gcc switches -Xlinker or -Wl,. Refer to the GCC documentation for details. Here is an example showing how to generate a linker map:
$ gnatlink my_prog -Wl,-Map,MAPFILE
Using linker options it is possible to set the program stack and heap size. See Setting Stack Size from gnatlink and Setting Heap Size from gnatlink.
gnatlink determines the list of objects required by the Ada
program and prepends them to the list of objects passed to the linker.
gnatlink also gathers any arguments set by the use of
pragma Linker_Options and adds them to the list of arguments
presented to the linker.
The following switches are available with the gnatlink utility:
gnatbind option, in this case the filenames
are b_mainprog.c and b_mainprog.o.
gnatlink try.ali creates
an executable called try.
gnat1, the Ada compiler)
from dir instead of the default location. Only use this switch
when multiple versions of the GNAT compiler are available.
See Directory Options,
for further details. You would normally use the -b or
-V switch instead.
compiler_name contains spaces or other separator characters.
As an example --GCC="foo -x -y" will instruct gnatlink to
use foo -x -y as your compiler. Note that switch -c is always
inserted after your command name. Thus in the above example the compiler
command that will be used by gnatlink will be foo -c -x -y.
A limitation of this syntax is that the name and path name of the executable
itself must not include any embedded spaces. If the compiler executable is
different from the default one (gcc or <prefix>-gcc), then the back-end
switches in the ALI file are not used to compile the binder generated source.
For example, this is the case with --GCC="foo -x -y". But the back end
switches will be used for --GCC="gcc -gnatv". If several
--GCC=compiler_name are used, only the last compiler_name
is taken into account. However, all the additional switches are also taken
into account. Thus,
--GCC="foo -x -y" --GCC="bar -z -t" is equivalent to
--GCC="bar -x -y -z -t".
The third step can be tricky, because not only do the modified files
have to be compiled, but any files depending on these files must also be
recompiled. The dependency rules in Ada can be quite complex, especially
in the presence of overloading, use clauses, generics and inlined
subprograms.
gnatmake automatically takes care of the third and fourth steps of this process. It determines which sources need to be compiled, compiles them, and binds and links the resulting object files.
Unlike some other Ada make programs, the dependencies are always accurately recomputed from the new sources. The source based approach of the GNAT compilation model makes this possible. This means that if changes to the source program cause corresponding changes in dependencies, they will always be tracked exactly correctly by gnatmake.
The usual form of the gnatmake command is
$ gnatmake [switches] file_name [file_names] [mode_switches]
The only required argument is one file_name, which specifies
a compilation unit that is a main program. Several file_names can be
specified: this will result in several executables being built.
If switches are present, they can be placed before the first
file_name, between file_names or after the last file_name.
If mode_switches are present, they must always be placed after
the last file_name and all switches.
If you are using standard file extensions (.adb and .ads), then the extension may be omitted from the file_name arguments. However, if you are using non-standard extensions, then it is required that the extension be given. A relative or absolute directory path can be specified in a file_name, in which case, the input source file will be searched for in the specified directory only. Otherwise, the input source file will first be searched in the directory where gnatmake was invoked and if it is not found, it will be search on the source path of the compiler as described in Search Paths and the Run-Time Library (RTL).
All gnatmake output (except when you specify -M) is to stderr. The output produced by the -M switch is send to stdout.
You may specify any of the following switches to gnatmake:
compiler_name contains
spaces or other separator characters. As an example --GCC="foo -x
-y" will instruct gnatmake to use foo -x -y as your
compiler. A limitation of this syntax is that the name and path name of
the executable itself must not include any embedded spaces. Note that
switch -c is always inserted after your command name. Thus in the
above example the compiler command that will be used by gnatmake
will be foo -c -x -y. If several --GCC=compiler_name are
used, only the last compiler_name is taken into account. However,
all the additional switches are also taken into account. Thus,
--GCC="foo -x -y" --GCC="bar -z -t" is equivalent to
--GCC="bar -x -y -z -t".
gnatbind'. You need to
use quotes around binder_name if binder_name contains spaces
or other separator characters. As an example --GNATBIND="bar -x
-y" will instruct gnatmake to use bar -x -y as your
binder. Binder switches that are normally appended by gnatmake
to `gnatbind' are now appended to the end of bar -x -y.
A limitation of this syntax is that the name and path name of the executable
itself must not include any embedded spaces.
lan -x -y as your
linker. Linker switches that are normally appended by gnatmake to
`gnatlink' are now appended to the end of lan -x -y.
A limitation of this syntax is that the name and path name of the executable
itself must not include any embedded spaces.
Normalize_Scalars pragma.
By default
gnatmake -a compiles all GNAT
internal files with
gcc -c -gnatpg rather than gcc -c.
completed x out of y (zz%)
If the file needs to be compiled this is displayed after the invocation of
the compiler. These lines are displayed even in quiet output mode.
This switch cannot be used when using a project file.
If gnatmake is invoked with several file_names and with this
switch, if there are compilation errors when building an executable,
gnatmake will not attempt to build the following executables.
gnatmake -M
-q
(see below), only the source file names,
without relative paths, are output. If you just specify the
-M
switch, dependencies of the GNAT internal system files are omitted. This
is typically what you want. If you also specify
the -a switch,
dependencies of the GNAT internal files are also listed. Note that
dependencies of the objects in external Ada libraries (see switch
-aLdir in the following list)
are never reported.
This switch cannot be used when invoking gnatmake with several
file_names.
This switch is recommended when Integrated Preprocessing is used.
external(name) when parsing the project file.
See Switches Related to Project Files.
Source and library search path switches:
The selected path is handled like a normal RTS path.
The mode switches (referred to as mode_switches) allow the
inclusion of switches that are to be passed to the compiler itself, the
binder or the linker. The effect of a mode switch is to cause all
subsequent switches up to the end of the switch list, or up to the next
mode switch, to be interpreted as switches to be passed on to the
designated component of GNAT.
gnatbind. They will be passed on to
all bind steps performed by gnatmake.
This section contains some additional useful notes on the operation of the gnatmake command.
gnatmake file.adb, where file.adb
is a subunit or body of a generic unit, gnatmake recompiles
file.adb (because it finds no ALI) and stops, issuing a
warning.
main.adb, which uses this Ada library you would just type
$ gnatmake -aIinclude-dir -aLobj-dir main
Generally gnatmake automatically performs all necessary recompilations and you don't need to worry about how it works. However, it may be useful to have some basic understanding of the gnatmake approach and in particular to understand how it uses the results of previous compilations without incorrectly depending on them.
First a definition: an object file is considered up to date if the corresponding ALI file exists and if all the source files listed in the dependency section of this ALI file have time stamps matching those in the ALI file. This means that neither the source file itself nor any files that it depends on have been modified, and hence there is no need to recompile this file.
gnatmake works by first checking if the specified main unit is up to date. If so, no compilations are required for the main unit. If not, gnatmake compiles the main program to build a new ALI file that reflects the latest sources. Then the ALI file of the main unit is examined to find all the source files on which the main program depends, and gnatmake recursively applies the above procedure on all these files.
This process ensures that gnatmake only trusts the dependencies in an existing ALI file if they are known to be correct. Otherwise it always recompiles to determine a new, guaranteed accurate set of dependencies. As a result the program is compiled “upside down” from what may be more familiar as the required order of compilation in some other Ada systems. In particular, clients are compiled before the units on which they depend. The ability of GNAT to compile in any order is critical in allowing an order of compilation to be chosen that guarantees that gnatmake will recompute a correct set of new dependencies if necessary.
When invoking gnatmake with several file_names, if a unit is imported by several of the executables, it will be recompiled at most once.
Note: when using non-standard naming conventions (see Using Other File Names), changing through a configuration pragmas file the version of a source and invoking gnatmake to recompile may have no effect, if the previous version of the source is still accessible by gnatmake. It may be necessary to use the switch -f.
gnatmake hello.adbHello) and bind and link the
resulting object files to generate an executable file hello.
gnatmake main1 main2 main3Main1), main2.adb
(containing unit Main2) and main3.adb
(containing unit Main3) and bind and link the resulting object files
to generate three executable files main1,
main2
and main3.
gnatmake -q Main_Unit -cargs -O2 -bargs -lMain_Unit (from file main_unit.adb). All compilations will
be done with optimization level 2 and the order of elaboration will be
listed by the binder. gnatmake will operate in quiet mode, not
displaying commands it is executing.
This chapter presents several topics related to program performance. It first describes some of the tradeoffs that need to be considered and some of the techniques for making your program run faster. It then documents the gnatelim tool and unused subprogram/data elimination feature, which can reduce the size of program executables.
Note: to invoke gnatelim with a project file, use the gnat
driver (see The GNAT Driver and Project Files).
The GNAT system provides a number of options that allow a trade-off between
The defaults (if no options are selected) aim at improving the speed of compilation and minimizing dependences, at the expense of performance of the generated code:
These options are suitable for most program development purposes. This chapter describes how you can modify these choices, and also provides some guidelines on debugging optimized code.
By default, GNAT generates all run-time checks, except integer overflow checks, stack overflow checks, and checks for access before elaboration on subprogram calls. The latter are not required in default mode, because all necessary checking is done at compile time. Two gnat switches, -gnatp and -gnato allow this default to be modified. See Run-Time Checks.
Our experience is that the default is suitable for most development purposes.
We treat integer overflow specially because these are quite expensive and in our experience are not as important as other run-time checks in the development process. Note that division by zero is not considered an overflow check, and divide by zero checks are generated where required by default.
Elaboration checks are off by default, and also not needed by default, since GNAT uses a static elaboration analysis approach that avoids the need for run-time checking. This manual contains a full chapter discussing the issue of elaboration checks, and if the default is not satisfactory for your use, you should read this chapter.
For validity checks, the minimal checks required by the Ada Reference Manual (for case statements and assignments to array elements) are on by default. These can be suppressed by use of the -gnatVn switch. Note that in Ada 83, there were no validity checks, so if the Ada 83 mode is acceptable (or when comparing GNAT performance with an Ada 83 compiler), it may be reasonable to routinely use -gnatVn. Validity checks are also suppressed entirely if -gnatp is used.
Note that the setting of the switches controls the default setting of
the checks. They may be modified using either pragma Suppress (to
remove checks) or pragma Unsuppress (to add back suppressed
checks) in the program source.
The use of pragma Restrictions allows you to control which features are permitted in your program. Apart from the obvious point that if you avoid relatively expensive features like finalization (enforceable by the use of pragma Restrictions (No_Finalization), the use of this pragma does not affect the generated code in most cases.
One notable exception to this rule is that the possibility of task abort results in some distributed overhead, particularly if finalization or exception handlers are used. The reason is that certain sections of code have to be marked as non-abortable.
If you use neither the abort statement, nor asynchronous transfer
of control (select ... then abort), then this distributed overhead
is removed, which may have a general positive effect in improving
overall performance. Especially code involving frequent use of tasking
constructs and controlled types will show much improved performance.
The relevant restrictions pragmas are
pragma Restrictions (No_Abort_Statements);
pragma Restrictions (Max_Asynchronous_Select_Nesting => 0);
It is recommended that these restriction pragmas be used if possible. Note that this also means that you can write code without worrying about the possibility of an immediate abort at any point.
Without any optimization option, the compiler's goal is to reduce the cost of compilation and to make debugging produce the expected results. Statements are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the subprogram and get exactly the results you would expect from the source code.
Turning on optimization makes the compiler attempt to improve the performance and/or code size at the expense of compilation time and possibly the ability to debug the program.
If you use multiple -O options, with or without level numbers, the last such option is the one that is effective.
The default is optimization off. This results in the fastest compile times, but GNAT makes absolutely no attempt to optimize, and the generated programs are considerably larger and slower than when optimization is enabled. You can use the -O switch (the permitted forms are -O0, -O1 -O2, -O3, and -Os) to gcc to control the optimization level:
Note that many other compilers do fairly extensive optimization
even if “no optimization” is specified. With gcc, it is
very unusual to use -O0 for production if
execution time is of any concern, since -O0
really does mean no optimization at all. This difference between
gcc and other compilers should be kept in mind when doing
performance comparisons.
Higher optimization levels perform more global transformations on the program and apply more expensive analysis algorithms in order to generate faster and more compact code. The price in compilation time, and the resulting improvement in execution time, both depend on the particular application and the hardware environment. You should experiment to find the best level for your application.
Since the precise set of optimizations done at each level will vary from release to release (and sometime from target to target), it is best to think of the optimization settings in general terms. See Options That Control Optimization, for details about the -O settings and a number of -f options that individually enable or disable specific optimizations.
Unlike some other compilation systems, gcc has been tested extensively at all optimization levels. There are some bugs which appear only with optimization turned on, but there have also been bugs which show up only in unoptimized code. Selecting a lower level of optimization does not improve the reliability of the code generator, which in practice is highly reliable at all optimization levels.
Note regarding the use of -O3: The use of this optimization level is generally discouraged with GNAT, since it often results in larger executables which run more slowly. See further discussion of this point in Inlining of Subprograms.
Although it is possible to do a reasonable amount of debugging at nonzero optimization levels, the higher the level the more likely that source-level constructs will have been eliminated by optimization. For example, if a loop is strength-reduced, the loop control variable may be completely eliminated and thus cannot be displayed in the debugger. This can only happen at -O2 or -O3. Explicit temporary variables that you code might be eliminated at level -O1 or higher.
The use of the -g switch, which is needed for source-level debugging, affects the size of the program executable on disk, and indeed the debugging information can be quite large. However, it has no effect on the generated code (and thus does not degrade performance)
Since the compiler generates debugging tables for a compilation unit before it performs optimizations, the optimizing transformations may invalidate some of the debugging data. You therefore need to anticipate certain anomalous situations that may arise while debugging optimized code. These are the most common cases:
step or next
commands show
the PC bouncing back and forth in the code. This may result from any of
the following optimizations:
goto, a return, or
a break in a C switch statement.
In general, when an unexpected value appears for a local variable or parameter you should first ascertain if that value was actually computed by your program, as opposed to being incorrectly reported by the debugger. Record fields or array elements in an object designated by an access value are generally less of a problem, once you have ascertained that the access value is sensible. Typically, this means checking variables in the preceding code and in the calling subprogram to verify that the value observed is explainable from other values (one must apply the procedure recursively to those other values); or re-running the code and stopping a little earlier (perhaps before the call) and stepping to better see how the variable obtained the value in question; or continuing to step from the point of the strange value to see if code motion had simply moved the variable's assignments later.
In light of such anomalies, a recommended technique is to use -O0 early in the software development cycle, when extensive debugging capabilities are most needed, and then move to -O1 and later -O2 as the debugger becomes less critical. Whether to use the -g switch in the release version is a release management issue. Note that if you use -g you can then use the strip program on the resulting executable, which removes both debugging information and global symbols.
A call to a subprogram in the current unit is inlined if all the following conditions are met:
pragma Inline applies to the subprogram, or it is local
to the unit and called once from within it, or it is small and automatic
inlining (optimization level -O3) is specified.
Calls to subprograms in with'ed units are normally not inlined.
To achieve actual inlining (that is, replacement of the call by the code
in the body of the subprogram), the following conditions must all be true.
pragma Inline for the subprogram.
Even if all these conditions are met, it may not be possible for the compiler to inline the call, due to the length of the body, or features in the body that make it impossible for the compiler to do the inlining.
Note that specifying the -gnatn switch causes additional compilation dependencies. Consider the following:
| package R is procedure Q; pragma Inline (Q); end R; package body R is ... end R; with R; procedure Main is begin ... R.Q; end Main; |
With the default behavior (no -gnatn switch specified), the
compilation of the Main procedure depends only on its own source,
main.adb, and the spec of the package in file r.ads. This
means that editing the body of R does not require recompiling
Main.
On the other hand, the call R.Q is not inlined under these
circumstances. If the -gnatn switch is present when Main
is compiled, the call will be inlined if the body of Q is small
enough, but now Main depends on the body of R in
r.adb as well as on the spec. This means that if this body is edited,
the main program must be recompiled. Note that this extra dependency
occurs whether or not the call is in fact inlined by gcc.
The use of front end inlining with -gnatN generates similar additional dependencies.
Note: The -fno-inline switch can be used to prevent all inlining. This switch overrides all other conditions and ensures that no inlining occurs. The extra dependences resulting from -gnatn will still be active, even if this switch is used to suppress the resulting inlining actions.
Note: The -fno-inline-functions switch can be used to prevent automatic inlining of small subprograms if -O3 is used.
Note: The -fno-inline-functions-called-once switch can be used to prevent inlining of subprograms local to the unit and called once from within it if -O1 is used.
Note regarding the use of -O3: There is no difference in inlining
behavior between -O2 and -O3 for subprograms with an explicit
pragma Inline assuming the use of -gnatn
or -gnatN (the switches that activate inlining). If you have used
pragma Inline in appropriate cases, then it is usually much better
to use -O2 and -gnatn and avoid the use of -O3 which
in this case only has the effect of inlining subprograms you did not
think should be inlined. We often find that the use of -O3 slows
down code by performing excessive inlining, leading to increased instruction
cache pressure from the increased code size. So the bottom line here is
that you should not automatically assume that -O3 is better than
-O2, and indeed you should use -O3 only if tests show that
it actually improves performance.
Since GNAT uses the gcc back end, all the specialized
gcc optimization switches are potentially usable. These switches
have not been extensively tested with GNAT but can generally be expected
to work. Examples of switches in this category are
-funroll-loops and
the various target-specific -m options (in particular, it has been
observed that -march=pentium4 can significantly improve performance
on appropriate machines). For full details of these switches, see
Hardware Models and Configurations.
The strong typing capabilities of Ada allow an optimizer to generate efficient code in situations where other languages would be forced to make worst case assumptions preventing such optimizations. Consider the following example:
| procedure R is type Int1 is new Integer; type Int2 is new Integer; type Int1A is access Int1; type Int2A is access Int2; Int1V : Int1A; Int2V : Int2A; ... begin ... for J in Data'Range loop if Data (J) = Int1V.all then Int2V.all := Int2V.all + 1; end if; end loop; ... end R; |
In this example, since the variable Int1V can only access objects
of type Int1, and Int2V can only access objects of type
Int2, there is no possibility that the assignment to
Int2V.all affects the value of Int1V.all. This means that
the compiler optimizer can "know" that the value Int1V.all is constant
for all iterations of the loop and avoid the extra memory reference
required to dereference it each time through the loop.
This kind of optimization, called strict aliasing analysis, is
triggered by specifying an optimization level of -O2 or
higher and allows GNAT to generate more efficient code
when access values are involved.
However, although this optimization is always correct in terms of
the formal semantics of the Ada Reference Manual, difficulties can
arise if features like Unchecked_Conversion are used to break
the typing system. Consider the following complete program example:
| package p1 is type int1 is new integer; type int2 is new integer; type a1 is access int1; type a2 is access int2; end p1; with p1; use p1; package p2 is function to_a2 (Input : a1) return a2; end p2; with Unchecked_Conversion; package body p2 is function to_a2 (Input : a1) return a2 is function to_a2u is new Unchecked_Conversion (a1, a2); begin return to_a2u (Input); end to_a2; end p2; with p2; use p2; with p1; use p1; with Text_IO; use Text_IO; procedure m is v1 : a1 := new int1; v2 : a2 := to_a2 (v1); begin v1.all := 1; v2.all := 0; put_line (int1'image (v1.all)); end; |
This program prints out 0 in -O0 or -O1
mode, but it prints out 1 in -O2 mode. That's
because in strict aliasing mode, the compiler can and
does assume that the assignment to v2.all could not
affect the value of v1.all, since different types
are involved.
This behavior is not a case of non-conformance with the standard, since
the Ada RM specifies that an unchecked conversion where the resulting
bit pattern is not a correct value of the target type can result in an
abnormal value and attempting to reference an abnormal value makes the
execution of a program erroneous. That's the case here since the result
does not point to an object of type int2. This means that the
effect is entirely unpredictable.
However, although that explanation may satisfy a language lawyer, in practice an applications programmer expects an unchecked conversion involving pointers to create true aliases and the behavior of printing 1 seems plain wrong. In this case, the strict aliasing optimization is unwelcome.
Indeed the compiler recognizes this possibility, and the unchecked conversion generates a warning:
p2.adb:5:07: warning: possible aliasing problem with type "a2"
p2.adb:5:07: warning: use -fno-strict-aliasing switch for references
p2.adb:5:07: warning: or use "pragma No_Strict_Aliasing (a2);"
Unfortunately the problem is recognized when compiling the body of
package p2, but the actual "bad" code is generated while
compiling the body of m and this latter compilation does not see
the suspicious Unchecked_Conversion.
As implied by the warning message, there are approaches you can use to avoid the unwanted strict aliasing optimization in a case like this.
One possibility is to simply avoid the use of -O2, but that is a bit drastic, since it throws away a number of useful optimizations that do not involve strict aliasing assumptions.
A less drastic approach is to compile the program using the
option -fno-strict-aliasing. Actually it is only the
unit containing the dereferencing of the suspicious pointer
that needs to be compiled. So in this case, if we compile
unit m with this switch, then we get the expected
value of zero printed. Analyzing which units might need
the switch can be painful, so a more reasonable approach
is to compile the entire program with options -O2
and -fno-strict-aliasing. If the performance is
satisfactory with this combination of options, then the
advantage is that the entire issue of possible "wrong"
optimization due to strict aliasing is avoided.
To avoid the use of compiler switches, the configuration
pragma No_Strict_Aliasing with no parameters may be
used to specify that for all access types, the strict
aliasing optimization should be suppressed.
However, these approaches are still overkill, in that they causes all manipulations of all access values to be deoptimized. A more refined approach is to concentrate attention on the specific access type identified as problematic.
First, if a careful analysis of uses of the pointer shows
that there are no possible problematic references, then
the warning can be suppressed by bracketing the
instantiation of Unchecked_Conversion to turn
the warning off:
pragma Warnings (Off);
function to_a2u is
new Unchecked_Conversion (a1, a2);
pragma Warnings (On);
Of course that approach is not appropriate for this particular example, since indeed there is a problematic reference. In this case we can take one of two other approaches.
The first possibility is to move the instantiation of unchecked
conversion to the unit in which the type is declared. In
this example, we would move the instantiation of
Unchecked_Conversion from the body of package
p2 to the spec of package p1. Now the
warning disappears. That's because any use of the
access type knows there is a suspicious unchecked
conversion, and the strict aliasing optimization
is automatically suppressed for the type.
If it is not practical to move the unchecked conversion to the same unit
in which the destination access type is declared (perhaps because the
source type is not visible in that unit), you may use pragma
No_Strict_Aliasing for the type. This pragma must occur in the
same declarative sequence as the declaration of the access type:
type a2 is access int2;
pragma No_Strict_Aliasing (a2);
Here again, the compiler now knows that the strict aliasing optimization
should be suppressed for any reference to type a2 and the
expected behavior is obtained.
Finally, note that although the compiler can generate warnings for simple cases of unchecked conversions, there are tricker and more indirect ways of creating type incorrect aliases which the compiler cannot detect. Examples are the use of address overlays and unchecked conversions involving composite types containing access types as components. In such cases, no warnings are generated, but there can still be aliasing problems. One safe coding practice is to forbid the use of address clauses for type overlaying, and to allow unchecked conversion only for primitive types. This is not really a significant restriction since any possible desired effect can be achieved by unchecked conversion of access values.
Text_IO Suggestions
The Ada.Text_IO package has fairly high overheads due in part to
the requirement of maintaining page and line counts. If performance
is critical, a recommendation is to use Stream_IO instead of
Text_IO for volume output, since this package has less overhead.
If Text_IO must be used, note that by default output to the standard
output and standard error files is unbuffered (this provides better
behavior when output statements are used for debugging, or if the
progress of a program is observed by tracking the output, e.g. by
using the Unix tail -f command to watch redirected output.
If you are generating large volumes of output with Text_IO and
performance is an important factor, use a designated file instead
of the standard output file, or change the standard output file to
be buffered using Interfaces.C_Streams.setvbuf.
gnatelimThis section describes gnatelim, a tool which detects unused subprograms and helps the compiler to create a smaller executable for your program.
gnatelimWhen a program shares a set of Ada packages with other programs, it may happen that this program uses only a fraction of the subprograms defined in these packages. The code created for these unused subprograms increases the size of the executable.
gnatelim tracks unused subprograms in an Ada program and
outputs a list of GNAT-specific pragmas Eliminate marking all the
subprograms that are declared but never called. By placing the list of
Eliminate pragmas in the GNAT configuration file gnat.adc and
recompiling your program, you may decrease the size of its executable,
because the compiler will not generate the code for 'eliminated' subprograms.
See Pragma Eliminate, for more
information about this pragma.
gnatelim needs as its input data the name of the main subprogram
and a bind file for a main subprogram.
To create a bind file for gnatelim, run gnatbind for
the main subprogram. gnatelim can work with both Ada and C
bind files; when both are present, it uses the Ada bind file.
The following commands will build the program and create the bind file:
$ gnatmake -c Main_Prog
$ gnatbind main_prog
Note that gnatelim needs neither object nor ALI files.
gnatelimgnatelim has the following command-line interface:
$ gnatelim [options] name
name should be a name of a source file that contains the main subprogram
of a program (partition).
gnatelim has the following switches:
gnatelim outputs to the standard error
stream the number of program units left to be processed. This option turns
this trace off.
gnatelim version information is printed as Ada
comments to the standard output stream. Also, in addition to the number of
program units left gnatelim will output the name of the current unit
being processed.
gnatelim not to look for
sources in the current directory.
gnatelim to use specific gcc compiler instead of one
available on the path.
gnatelim to use specific gnatmake instead of one
available on the path.
gnatelim sends its output to the standard output stream, and all the
tracing and debug information is sent to the standard error stream.
In order to produce a proper GNAT configuration file
gnat.adc, redirection must be used:
$ gnatelim main_prog.adb > gnat.adc
or
$ gnatelim main_prog.adb >> gnat.adc
in order to append the gnatelim output to the existing contents of
gnat.adc.
In some rare cases gnatelim may try to eliminate
subprograms that are actually called in the program. In this case, the
compiler will generate an error message of the form:
file.adb:106:07: cannot call eliminated subprogram "My_Prog"
You will need to manually remove the wrong Eliminate pragmas from
the gnat.adc file. You should recompile your program
from scratch after that, because you need a consistent gnat.adc file
during the entire compilation.
In order to get a smaller executable for your program you now have to
recompile the program completely with the new gnat.adc file
created by gnatelim in your current directory:
$ gnatmake -f main_prog
(Use the -f option for gnatmake to
recompile everything
with the set of pragmas Eliminate that you have obtained with
gnatelim).
Be aware that the set of Eliminate pragmas is specific to each
program. It is not recommended to merge sets of Eliminate
pragmas created for different programs in one gnat.adc file.
Here is a quick summary of the steps to be taken in order to reduce
the size of your executables with gnatelim. You may use
other GNAT options to control the optimization level,
to produce the debugging information, to set search path, etc.
$ gnatmake -c main_prog
$ gnatbind main_prog
Eliminate pragmas
$ gnatelim main_prog >[>] gnat.adc
$ gnatmake -f main_prog
This section describes how you can eliminate unused subprograms and data from your executable just by setting options at compilation time.
By default, an executable contains all code and data of its composing objects (directly linked or coming from statically linked libraries), even data or code never used by this executable.
This feature will allow you to eliminate such unused code from your executable, making it smaller (in disk and in memory).
This functionality is available on all Linux platforms except for the IA-64 architecture and on all cross platforms using the ELF binary file format. In both cases GNU binutils version 2.16 or later are required to enable it.
The operation of eliminating the unused code and data from the final executable is directly performed by the linker.
In order to do this, it has to work with objects compiled with the following options: -ffunction-sections -fdata-sections. These options are usable with C and Ada files. They will place respectively each function or data in a separate section in the resulting object file.
Once the objects and static libraries are created with these options, the linker can perform the dead code elimination. You can do this by setting the -Wl,--gc-sections option to gcc command or in the -largs section of gnatmake. This will perform a garbage collection of code and data never referenced.
If the linker performs a partial link (-r ld linker option), then you will need to provide one or several entry point using the -e / --entry ld option.
Note that objects compiled without the -ffunction-sections and -fdata-sections options can still be linked with the executable. However, no dead code elimination will be performed on those objects (they will be linked as is).
The GNAT static library is now compiled with -ffunction-sections and -fdata-sections on some platforms. This allows you to eliminate the unused code and data of the GNAT library from your executable.
Here is a simple example:
with Aux;
procedure Test is
begin
Aux.Used (10);
end Test;
package Aux is
Used_Data : Integer;
Unused_Data : Integer;
procedure Used (Data : Integer);
procedure Unused (Data : Integer);
end Aux;
package body Aux is
procedure Used (Data : Integer) is
begin
Used_Data := Data;
end Used;
procedure Unused (Data : Integer) is
begin
Unused_Data := Data;
end Unused;
end Aux;
Unused and Unused_Data are never referenced in this code
excerpt, and hence they may be safely removed from the final executable.
$ gnatmake test
$ nm test | grep used
020015f0 T aux__unused
02005d88 B aux__unused_data
020015cc T aux__used
02005d84 B aux__used_data
$ gnatmake test -cargs -fdata-sections -ffunction-sections \
-largs -Wl,--gc-sections
$ nm test | grep used
02005350 T aux__used
0201ffe0 B aux__used_data
It can be observed that the procedure Unused and the object
Unused_Data are removed by the linker when using the
appropriate options.
gnatchop
This chapter discusses how to handle files with multiple units by using
the gnatchop utility. This utility is also useful in renaming
files to meet the standard GNAT default file naming conventions.
The basic compilation model of GNAT requires that a file submitted to the compiler have only one unit and there be a strict correspondence between the file name and the unit name.
The gnatchop utility allows both of these rules to be relaxed,
allowing GNAT to process files which contain multiple compilation units
and files with arbitrary file names. gnatchop
reads the specified file and generates one or more output files,
containing one unit per file. The unit and the file name correspond,
as required by GNAT.
If you want to permanently restructure a set of “foreign” files so that they match the GNAT rules, and do the remaining development using the GNAT structure, you can simply use gnatchop once, generate the new set of files and work with them from that point on.
Alternatively, if you want to keep your files in the “foreign” format, perhaps to maintain compatibility with some other Ada compilation system, you can set up a procedure where you use gnatchop each time you compile, regarding the source files that it writes as temporary files that you throw away.
The basic function of gnatchop is to take a file with multiple units
and split it into separate files. The boundary between files is reasonably
clear, except for the issue of comments and pragmas. In default mode, the
rule is that any pragmas between units belong to the previous unit, except
that configuration pragmas always belong to the following unit. Any comments
belong to the following unit. These rules
almost always result in the right choice of
the split point without needing to mark it explicitly and most users will
find this default to be what they want. In this default mode it is incorrect to
submit a file containing only configuration pragmas, or one that ends in
configuration pragmas, to gnatchop.
However, using a special option to activate “compilation mode”,
gnatchop
can perform another function, which is to provide exactly the semantics
required by the RM for handling of configuration pragmas in a compilation.
In the absence of configuration pragmas (at the main file level), this
option has no effect, but it causes such configuration pragmas to be handled
in a quite different manner.
First, in compilation mode, if gnatchop is given a file that consists of
only configuration pragmas, then this file is appended to the
gnat.adc file in the current directory. This behavior provides
the required behavior described in the RM for the actions to be taken
on submitting such a file to the compiler, namely that these pragmas
should apply to all subsequent compilations in the same compilation
environment. Using GNAT, the current directory, possibly containing a
gnat.adc file is the representation
of a compilation environment. For more information on the
gnat.adc file, see Handling of Configuration Pragmas.
Second, in compilation mode, if gnatchop
is given a file that starts with
configuration pragmas, and contains one or more units, then these
configuration pragmas are prepended to each of the chopped files. This
behavior provides the required behavior described in the RM for the
actions to be taken on compiling such a file, namely that the pragmas
apply to all units in the compilation, but not to subsequently compiled
units.
Finally, if configuration pragmas appear between units, they are appended to the previous unit. This results in the previous unit being illegal, since the compiler does not accept configuration pragmas that follow a unit. This provides the required RM behavior that forbids configuration pragmas other than those preceding the first compilation unit of a compilation.
For most purposes, gnatchop will be used in default mode. The
compilation mode described above is used only if you need exactly
accurate behavior with respect to compilations, and you have files
that contain multiple units and configuration pragmas. In this
circumstance the use of gnatchop with the compilation mode
switch provides the required behavior, and is for example the mode
in which GNAT processes the ACVC tests.
gnatchopThe gnatchop command has the form:
$ gnatchop switches file name [file name ...] [directory]
The only required argument is the file name of the file to be chopped. There are no restrictions on the form of this file name. The file itself contains one or more Ada units, in normal GNAT format, concatenated together. As shown, more than one file may be presented to be chopped.
When run in default mode, gnatchop generates one output file in
the current directory for each unit in each of the files.
directory, if specified, gives the name of the directory to which the output files will be written. If it is not specified, all files are written to the current directory.
For example, given a file called hellofiles containing
| procedure hello; with Text_IO; use Text_IO; procedure hello is begin Put_Line ("Hello"); end hello; |
the command
$ gnatchop hellofiles
generates two files in the current directory, one called hello.ads containing the single line that is the procedure spec, and the other called hello.adb containing the remaining text. The original file is not affected. The generated files can be compiled in the normal manner.
When gnatchop is invoked on a file that is empty or that contains only empty lines and/or comments, gnatchop will not fail, but will not produce any new sources.
For example, given a file called toto.txt containing
| -- Just a comment |
the command
$ gnatchop toto.txt
will not produce any new file and will result in the following warnings:
toto.txt:1:01: warning: empty file, contains no compilation units
no compilation units found
no source files written
gnatchopgnatchop recognizes the following switches:
gnatchop to operate in compilation mode, in which
configuration pragmas are handled according to strict RM rules. See
previous section for a full description of this mode.
gnat which is
used to parse the given file. Not all xxx options make sense,
but for example, the use of -gnati2 allows gnatchop to
process a source file that uses Latin-2 coding for identifiers.
gnatchop to generate a brief help summary to the standard
output file showing usage information.
mm
of characters.
This is useful if the
resulting set of files is required to be interoperable with systems
which limit the length of file names.
No space is allowed between the -k and the numeric value. The numeric
value may be omitted in which case a default of -k8,
suitable for use
with DOS-like file systems, is used. If no -k switch
is present then
there is no limit on the length of file names.
gnatchop is used as part of a standard build process.
Source_Reference pragmas. Use this switch if the output
files are regarded as temporary and development is to be done in terms
of the original unchopped file. This switch causes
Source_Reference pragmas to be inserted into each of the
generated files to refers back to the original file name and line number.
The result is that all error messages refer back to the original
unchopped file.
In addition, the debugging information placed into the object file (when
the -g switch of gcc or gnatmake is
specified)
also refers back to this original file so that tools like profilers and
debuggers will give information in terms of the original unchopped file.
If the original file to be chopped itself contains
a Source_Reference
pragma referencing a third file, then gnatchop respects
this pragma, and the generated Source_Reference pragmas
in the chopped file refer to the original file, with appropriate
line numbers. This is particularly useful when gnatchop
is used in conjunction with gnatprep to compile files that
contain preprocessing statements and multiple units.
gnatchop to operate in verbose mode. The version
number and copyright notice are output, as well as exact copies of
the gnat1 commands spawned to obtain the chop control information.
gnatchop regards it as a
fatal error if there is already a file with the same name as a
file it would otherwise output, in other words if the files to be
chopped contain duplicated units. This switch bypasses this
check, and causes all but the last instance of such duplicated
units to be skipped.
gnatchop Usagegnatchop -w hello_s.ada prerelease/filesgnatchop archivegnatchop is in sending sets of sources
around, for example in email messages. The required sources are simply
concatenated (for example, using a Unix cat
command), and then
gnatchop is used at the other end to reconstitute the original
file names.
gnatchop file1 file2 file3 direc
Configuration pragmas include those pragmas described as
such in the Ada Reference Manual, as well as
implementation-dependent pragmas that are configuration pragmas.
See Implementation Defined Pragmas,
for details on these additional GNAT-specific configuration pragmas.
Most notably, the pragma Source_File_Name, which allows
specifying non-default names for source files, is a configuration
pragma. The following is a complete list of configuration pragmas
recognized by GNAT:
Ada_83
Ada_95
Ada_05
Ada_2005
Assertion_Policy
C_Pass_By_Copy
Check_Name
Check_Policy
Compile_Time_Error
Compile_Time_Warning
Compiler_Unit
Component_Alignment
Debug_Policy
Detect_Blocking
Discard_Names
Elaboration_Checks
Eliminate
Extend_System
External_Name_Casing
Fast_Math
Favor_Top_Level
Float_Representation
Implicit_Packing
Initialize_Scalars
Interrupt_State
License
Locking_Policy
Long_Float
No_Run_Time
No_Strict_Aliasing
Normalize_Scalars
Optimize_Alignment
Persistent_BSS
Polling
Priority_Specific_Dispatching
Profile
Profile_Warnings
Propagate_Exceptions
Queuing_Policy
Ravenscar
Restricted_Run_Time
Restrictions
Restrictions_Warnings
Reviewable
Source_File_Name
Source_File_Name_Project
Style_Checks
Suppress
Suppress_Exception_Locations
Task_Dispatching_Policy
Universal_Data
Unsuppress
Use_VADS_Size
Validity_Checks
Warnings
Wide_Character_Encoding
Configuration pragmas may either appear at the start of a compilation unit, in which case they apply only to that unit, or they may apply to all compilations performed in a given compilation environment.
GNAT also provides the gnatchop utility to provide an automatic
way to handle configuration pragmas following the semantics for
compilations (that is, files with multiple units), described in the RM.
See Operating gnatchop in Compilation Mode for details.
However, for most purposes, it will be more convenient to edit the
gnat.adc file that contains configuration pragmas directly,
as described in the following section.
In GNAT a compilation environment is defined by the current directory at the time that a compile command is given. This current directory is searched for a file whose name is gnat.adc. If this file is present, it is expected to contain one or more configuration pragmas that will be applied to the current compilation. However, if the switch -gnatA is used, gnat.adc is not considered.
Configuration pragmas may be entered into the gnat.adc file
either by running gnatchop on a source file that consists only of
configuration pragmas, or more conveniently by
direct editing of the gnat.adc file, which is a standard format
source file.
In addition to gnat.adc, additional files containing configuration pragmas may be applied to the current compilation using the switch -gnatecpath. path must designate an existing file that contains only configuration pragmas. These configuration pragmas are in addition to those found in gnat.adc (provided gnat.adc is present and switch -gnatA is not used).
It is allowed to specify several switches -gnatec, all of which will be taken into account.
If you are using project file, a separate mechanism is provided using project attributes, see Specifying Configuration Pragmas for more details.
gnatnameThe GNAT compiler must be able to know the source file name of a compilation
unit. When using the standard GNAT default file naming conventions
(.ads for specs, .adb for bodies), the GNAT compiler
does not need additional information.
When the source file names do not follow the standard GNAT default file naming
conventions, the GNAT compiler must be given additional information through
a configuration pragmas file (see Configuration Pragmas)
or a project file.
When the non-standard file naming conventions are well-defined,
a small number of pragmas Source_File_Name specifying a naming pattern
(see Alternative File Naming Schemes) may be sufficient. However,
if the file naming conventions are irregular or arbitrary, a number
of pragma Source_File_Name for individual compilation units
must be defined.
To help maintain the correspondence between compilation unit names and
source file names within the compiler,
GNAT provides a tool gnatname to generate the required pragmas for a
set of files.
gnatnameThe usual form of the gnatname command is
$ gnatname [switches] naming_pattern [naming_patterns] [--and [switches] naming_pattern [naming_patterns]]
All of the arguments are optional. If invoked without any argument,
gnatname will display its usage.
When used with at least one naming pattern, gnatname will attempt to
find all the compilation units in files that follow at least one of the
naming patterns. To find these compilation units,
gnatname will use the GNAT compiler in syntax-check-only mode on all
regular files.
One or several Naming Patterns may be given as arguments to gnatname.
Each Naming Pattern is enclosed between double quotes.
A Naming Pattern is a regular expression similar to the wildcard patterns
used in file names by the Unix shells or the DOS prompt.
gnatname may be called with several sections of directories/patterns.
Sections are separated by switch --and. In each section, there must be
at least one pattern. If no directory is specified in a section, the current
directory (or the project directory is -P is used) is implied.
The options other that the directory switches and the patterns apply globally
even if they are in different sections.
Examples of Naming Patterns are
"*.[12].ada"
"*.ad[sb]*"
"body_*" "spec_*"
For a more complete description of the syntax of Naming Patterns, see the second kind of regular expressions described in g-regexp.ads (the “Glob” regular expressions).
When invoked with no switch -P, gnatname will create a
configuration pragmas file gnat.adc in the current working directory,
with pragmas Source_File_Name for each file that contains a valid Ada
unit.
gnatnameSwitches for gnatname must precede any specified Naming Pattern.
You may specify any of the following switches to gnatname:
gnatname -Pprj -f"*.c" "*.ada"
will look for Ada units in all files with the .ada extension,
and will add to the list of file for project prj.gpr the C files
with extension .c.
gnatname -x "*_nt.ada" "*.ada"
will look for Ada units in all files with the .ada extension, except those whose names end with _nt.ada.
gnatname Usage$ gnatname -c /home/me/names.adc -d sources "[a-z]*.ada*"
In this example, the directory /home/me must already exist and be writable. In addition, the directory /home/me/sources (specified by -d sources) must exist and be readable.
Note the optional spaces after -c and -d.
$ gnatname -P/home/me/proj -x "*_nt_body.ada"
-dsources -dsources/plus -Dcommon_dirs.txt "body_*" "spec_*"
Note that several switches -d may be used, even in conjunction with one or several switches -D. Several Naming Patterns and one excluded pattern are used in this example.
This chapter describes GNAT's Project Manager, a facility that allows you to manage complex builds involving a number of source files, directories, and compilation options for different system configurations. In particular, project files allow you to specify:
gnatls, gnatxref,
gnatfind); you can apply these settings either globally or to individual
compilation units.
Project files are written in a syntax close to that of Ada, using familiar notions such as packages, context clauses, declarations, default values, assignments, and inheritance. Finally, project files can be built hierarchically from other project files, simplifying complex system integration and project reuse.
A project is a specific set of values for various compilation properties. The settings for a given project are described by means of a project file, which is a text file written in an Ada-like syntax. Property values in project files are either strings or lists of strings. Properties that are not explicitly set receive default values. A project file may interrogate the values of external variables (user-defined command-line switches or environment variables), and it may specify property settings conditionally, based on the value of such variables.
In simple cases, a project's source files depend only on other source files
in the same project, or on the predefined libraries. (Dependence is
used in
the Ada technical sense; as in one Ada unit withing another.) However,
the Project Manager also allows more sophisticated arrangements,
where the source files in one project depend on source files in other
projects:
More generally, the Project Manager lets you structure large development efforts into hierarchical subsystems, where build decisions are delegated to the subsystem level, and thus different compilation environments (switch settings) used for different subsystems.
The Project Manager is invoked through the -Pprojectfile switch to gnatmake or to the gnat front driver. There may be zero, one or more spaces between -P and projectfile. If you want to define (on the command line) an external variable that is queried by the project file, you must use the -Xvbl=value switch. The Project Manager parses and interprets the project file, and drives the invoked tool based on the project settings.
The Project Manager supports a wide range of development strategies, for systems of all sizes. Here are some typical practices that are easily handled:
The destination of an executable can be controlled inside a project file
using the -o
switch.
In the absence of such a switch either inside
the project file or on the command line, any executable files generated by
gnatmake are placed in the directory Exec_Dir specified
in the project file. If no Exec_Dir is specified, they will be placed
in the object directory of the project.
You can use project files to achieve some of the effects of a source versioning system (for example, defining separate projects for the different sets of sources that comprise different releases) but the Project Manager is independent of any source configuration management tools that might be used by the developers.
The next section introduces the main features of GNAT's project facility through a sequence of examples; subsequent sections will present the syntax and semantics in more detail. A more formal description of the project facility appears in Project File Reference.
This section illustrates some of the typical uses of project files and explains their basic structure and behavior.
Suppose that the Ada source files pack.ads, pack.adb, and
proc.adb are in the /common directory. The file
proc.adb contains an Ada main subprogram Proc that withs
package Pack. We want to compile these source files under two sets
of switches:
The GNAT project files shown below, respectively debug.gpr and release.gpr in the /common directory, achieve these effects.
Schematically:
/common
debug.gpr
release.gpr
pack.ads
pack.adb
proc.adb
/common/debug
proc.ali, proc.o
pack.ali, pack.o
/common/release
proc.ali, proc.o
pack.ali, pack.o
Here are the corresponding project files:
project Debug is
for Object_Dir use "debug";
for Main use ("proc");
package Builder is
for Default_Switches ("Ada")
use ("-g");
for Executable ("proc.adb") use "proc1";
end Builder;
package Compiler is
for Default_Switches ("Ada")
use ("-fstack-check",
"-gnata",
"-gnato",
"-gnatE");
end Compiler;
end Debug;
project Release is
for Object_Dir use "release";
for Exec_Dir use ".";
for Main use ("proc");
package Compiler is
for Default_Switches ("Ada")
use ("-O2");
end Compiler;
end Release;
The name of the project defined by debug.gpr is "Debug" (case
insensitive), and analogously the project defined by release.gpr is
"Release". For consistency the file should have the same name as the
project, and the project file's extension should be "gpr". These
conventions are not required, but a warning is issued if they are not followed.
If the current directory is /temp, then the command
gnatmake -P/common/debug.gpr
generates object and ALI files in /common/debug,
as well as the proc1 executable,
using the switch settings defined in the project file.
Likewise, the command
gnatmake -P/common/release.gpr
generates object and ALI files in /common/release,
and the proc
executable in /common,
using the switch settings from the project file.
If a project file does not explicitly specify a set of source directories or a set of source files, then by default the project's source files are the Ada source files in the project file directory. Thus pack.ads, pack.adb, and proc.adb are the source files for both projects.
Several project properties are modeled by Ada-style attributes;
a property is defined by supplying the equivalent of an Ada attribute
definition clause in the project file.
A project's object directory is another such a property; the corresponding
attribute is Object_Dir, and its value is also a string expression,
specified either as absolute or relative. In the later case,
it is relative to the project file directory. Thus the compiler's
output is directed to /common/debug
(for the Debug project)
and to /common/release
(for the Release project).
If Object_Dir is not specified, then the default is the project file
directory itself.
A project's exec directory is another property; the corresponding
attribute is Exec_Dir, and its value is also a string expression,
either specified as relative or absolute. If Exec_Dir is not specified,
then the default is the object directory (which may also be the project file
directory if attribute Object_Dir is not specified). Thus the executable
is placed in /common/debug
for the Debug project (attribute Exec_Dir not specified)
and in /common for the Release project.
A GNAT tool that is integrated with the Project Manager is modeled by a
corresponding package in the project file. In the example above,
The Debug project defines the packages Builder
(for gnatmake) and Compiler;
the Release project defines only the Compiler package.
The Ada-like package syntax is not to be taken literally. Although packages in project files bear a surface resemblance to packages in Ada source code, the notation is simply a way to convey a grouping of properties for a named entity. Indeed, the package names permitted in project files are restricted to a predefined set, corresponding to the project-aware tools, and the contents of packages are limited to a small set of constructs. The packages in the example above contain attribute definitions.
Switch settings for a project-aware tool can be specified through
attributes in the package that corresponds to the tool.
The example above illustrates one of the relevant attributes,
Default_Switches, which is defined in packages
in both project files.
Unlike simple attributes like Source_Dirs,
Default_Switches is
known as an associative array. When you define this attribute, you must
supply an “index” (a literal string), and the effect of the attribute
definition is to set the value of the array at the specified index.
For the Default_Switches attribute,
the index is a programming language (in our case, Ada),
and the value specified (after use) must be a list
of string expressions.
The attributes permitted in project files are restricted to a predefined set. Some may appear at project level, others in packages. For any attribute that is an associative array, the index must always be a literal string, but the restrictions on this string (e.g., a file name or a language name) depend on the individual attribute. Also depending on the attribute, its specified value will need to be either a string or a string list.
In the Debug project, we set the switches for two tools,
gnatmake and the compiler, and thus we include the two corresponding
packages; each package defines the Default_Switches
attribute with index "Ada".
Note that the package corresponding to
gnatmake is named Builder. The Release project is
similar, but only includes the Compiler package.
In project Debug above, the switches starting with
-gnat that are specified in package Compiler
could have been placed in package Builder, since gnatmake
transmits all such switches to the compiler.
One of the specifiable properties of a project is a list of files that contain
main subprograms. This property is captured in the Main attribute,
whose value is a list of strings. If a project defines the Main
attribute, it is not necessary to identify the main subprogram(s) when
invoking gnatmake (see gnatmake and Project Files).
By default, the executable file name corresponding to a main source is
deduced from the main source file name. Through the attributes
Executable and Executable_Suffix of package Builder,
it is possible to change this default.
In project Debug above, the executable file name
for main source proc.adb is
proc1.
Attribute Executable_Suffix, when specified, may change the suffix
of the executable files, when no attribute Executable applies:
its value replace the platform-specific executable suffix.
Attributes Executable and Executable_Suffix are the only ways to
specify a non-default executable file name when several mains are built at once
in a single gnatmake command.
Since the project files above do not specify any source file naming
conventions, the GNAT defaults are used. The mechanism for defining source
file naming conventions – a package named Naming –
is described below (see Naming Schemes).
Since the project files do not specify a Languages attribute, by
default the GNAT tools assume that the language of the project file is Ada.
More generally, a project can comprise source files
in Ada, C, and/or other languages.
Instead of supplying different project files for debug and release, we can
define a single project file that queries an external variable (set either
on the command line or via an environment variable) in order to
conditionally define the appropriate settings. Again, assume that the
source files pack.ads, pack.adb, and proc.adb are
located in directory /common. The following project file,
build.gpr, queries the external variable named STYLE and
defines an object directory and switch settings based on whether
the value is "deb" (debug) or "rel" (release), and where
the default is "deb".
project Build is
for Main use ("proc");
type Style_Type is ("deb", "rel");
Style : Style_Type := external ("STYLE", "deb");
case Style is
when "deb" =>
for Object_Dir use "debug";
when "rel" =>
for Object_Dir use "release";
for Exec_Dir use ".";
end case;
package Builder is
case Style is
when "deb" =>
for Default_Switches ("Ada")
use ("-g");
for Executable ("proc") use "proc1";
when others =>
null;
end case;
end Builder;
package Compiler is
case Style is
when "deb" =>
for Default_Switches ("Ada")
use ("-gnata",
"-gnato",
"-gnatE");
when "rel" =>
for Default_Switches ("Ada")
use ("-O2");
end case;
end Compiler;
end Build;
Style_Type is an example of a string type, which is the project
file analog of an Ada enumeration type but whose components are string literals
rather than identifiers. Style is declared as a variable of this type.
The form external("STYLE", "deb") is known as an
external reference; its first argument is the name of an
external variable, and the second argument is a default value to be
used if the external variable doesn't exist. You can define an external
variable on the command line via the -X switch,
or you can use an environment variable
as an external variable.
Each case construct is expanded by the Project Manager based on the
value of Style. Thus the command
gnatmake -P/common/build.gpr -XSTYLE=deb
is equivalent to the gnatmake invocation using the project file debug.gpr in the earlier example. So is the command
gnatmake -P/common/build.gpr
since "deb" is the default for STYLE.
Analogously,
gnatmake -P/common/build.gpr -XSTYLE=rel
is equivalent to the gnatmake invocation using the project file release.gpr in the earlier example.
A compilation unit in a source file in one project may depend on compilation
units in source files in other projects. To compile this unit under
control of a project file, the
dependent project must import the projects containing the needed source
files.
This effect is obtained using syntax similar to an Ada with clause,
but where withed entities are strings that denote project files.
As an example, suppose that the two projects GUI_Proj and
Comm_Proj are defined in the project files gui_proj.gpr and
comm_proj.gpr in directories /gui
and /comm, respectively.
Suppose that the source files for GUI_Proj are
gui.ads and gui.adb, and that the source files for
Comm_Proj are comm.ads and comm.adb, where each set of
files is located in its respective project file directory. Schematically:
/gui
gui_proj.gpr
gui.ads
gui.adb
/comm
comm_proj.gpr
comm.ads
comm.adb
We want to develop an application in directory /app that
with the packages GUI and Comm, using the properties of
the corresponding project files (e.g. the switch settings
and object directory).
Skeletal code for a main procedure might be something like the following:
with GUI, Comm;
procedure App_Main is
...
begin
...
end App_Main;
Here is a project file, app_proj.gpr, that achieves the desired effect:
with "/gui/gui_proj", "/comm/comm_proj";
project App_Proj is
for Main use ("app_main");
end App_Proj;
Building an executable is achieved through the command:
gnatmake -P/app/app_proj
which will generate the app_main executable
in the directory where app_proj.gpr resides.
If an imported project file uses the standard extension (gpr) then
(as illustrated above) the with clause can omit the extension.
Our example specified an absolute path for each imported project file. Alternatively, the directory name of an imported object can be omitted if either
ADA_PROJECT_PATH is the same as
the syntax of ADA_INCLUDE_PATH and ADA_OBJECTS_PATH: a list of
directory names separated by colons (semicolons on Windows).
Thus, if we define ADA_PROJECT_PATH to include /gui and
/comm, then our project file app_proj.gpr can be written
as follows:
with "gui_proj", "comm_proj";
project App_Proj is
for Main use ("app_main");
end App_Proj;
Importing other projects can create ambiguities. For example, the same unit might be present in different imported projects, or it might be present in both the importing project and in an imported project. Both of these conditions are errors. Note that in the current version of the Project Manager, it is illegal to have an ambiguous unit even if the unit is never referenced by the importing project. This restriction may be relaxed in a future release.
In large software systems it is common to have multiple implementations of a common interface; in Ada terms, multiple versions of a package body for the same spec. For example, one implementation might be safe for use in tasking programs, while another might only be used in sequential applications. This can be modeled in GNAT using the concept of project extension. If one project (the “child”) extends another project (the “parent”) then by default all source files of the parent project are inherited by the child, but the child project can override any of the parent's source files with new versions, and can also add new files. This facility is the project analog of a type extension in Object-Oriented Programming. Project hierarchies are permitted (a child project may be the parent of yet another project), and a project that inherits one project can also import other projects.
As an example, suppose that directory /seq contains the project file seq_proj.gpr as well as the source files pack.ads, pack.adb, and proc.adb:
/seq
pack.ads
pack.adb
proc.adb
seq_proj.gpr
Note that the project file can simply be empty (that is, no attribute or package is defined):
project Seq_Proj is
end Seq_Proj;
implying that its source files are all the Ada source files in the project directory.
Suppose we want to supply an alternate version of pack.adb, in
directory /tasking, but use the existing versions of
pack.ads and proc.adb. We can define a project
Tasking_Proj that inherits Seq_Proj:
/tasking
pack.adb
tasking_proj.gpr
project Tasking_Proj extends "/seq/seq_proj" is
end Tasking_Proj;
The version of pack.adb used in a build depends on which project file is specified.
Note that we could have obtained the desired behavior using project import
rather than project inheritance; a base project would contain the
sources for pack.ads and proc.adb, a sequential project would
import base and add pack.adb, and likewise a tasking project
would import base and add a different version of pack.adb. The
choice depends on whether other sources in the original project need to be
overridden. If they do, then project extension is necessary, otherwise,
importing is sufficient.
In a project file that extends another project file, it is possible to indicate that an inherited source is not part of the sources of the extending project. This is necessary sometimes when a package spec has been overloaded and no longer requires a body: in this case, it is necessary to indicate that the inherited body is not part of the sources of the project, otherwise there will be a compilation error when compiling the spec.
For that purpose, the attribute Excluded_Source_Files is used.
Its value is a string list: a list of file names. It is also possible to use
attribute Excluded_Source_List_File. Its value is a single string:
the file name of a text file containing a list of file names, one per line.
project B extends "a" is
for Source_Files use ("pkg.ads");
-- New spec of Pkg does not need a completion
for Excluded_Source_Files use ("pkg.adb");
end B;
Attribute Excluded_Source_Files may also be used to check if a source
is still needed: if it is possible to build using gnatmake when such
a source is put in attribute Excluded_Source_Files of a project P, then
it is possible to remove the source completely from a system that includes
project P.
This section describes the structure of project files.
A project may be an independent project, entirely defined by a single project file. Any Ada source file in an independent project depends only on the predefined library and other Ada source files in the same project.
A project may also depend on other projects, in either or both of the following ways:
The dependence relation is a directed acyclic graph (the subgraph reflecting the “extends” relation is a tree).
A project's immediate sources are the source files directly defined by that project, either implicitly by residing in the project file's directory, or explicitly through any of the source-related attributes described below. More generally, a project proj's sources are the immediate sources of proj together with the immediate sources (unless overridden) of any project on which proj depends (either directly or indirectly).
As seen in the earlier examples, project files have an Ada-like syntax. The minimal project file is:
project Empty is
end Empty;
The identifier Empty is the name of the project.
This project name must be present after the reserved
word end at the end of the project file, followed by a semi-colon.
Any name in a project file, such as the project name or a variable name, has the same syntax as an Ada identifier.
The reserved words of project files are the Ada 95 reserved words plus
extends, external, and project. Note that the only Ada
reserved words currently used in project file syntax are:
all
at
case
end
for
is
limited
null
others
package
renames
type
use
when
with
Comments in project files have the same syntax as in Ada, two consecutive hyphens through the end of the line.
Before the reserved project, there may be one or two "qualifiers", that
is identifiers or other reserved words, to qualify the project.
The current list of qualifiers is:
abstract: qualify a project with no sources. An abstract project must
have a declaration specifying that there are no sources in the project, and,
if it extends another project, the project it extends must also be a qualified
abstract project.
standard: a standard project is a non library project with sources.
aggregate: for future extension
aggregate library: for future extension
library: a library project must declare both attributes
Library_Name and Library_Dir.
configuration: a configuration project cannot be in a project tree.
A project file may contain packages. The name of a package must be one of the identifiers from the following list. A package with a given name may only appear once in a project file. Package names are case insensitive. The following package names are legal:
Naming
Builder
Compiler
Binder
Linker
Finder
Cross_Reference
Eliminate
Pretty_Printer
Metrics
gnatls
gnatstub
IDE
Language_Processing
In its simplest form, a package may be empty:
project Simple is
package Builder is
end Builder;
end Simple;
A package may contain attribute declarations, variable declarations and case constructions, as will be described below.
When there is ambiguity between a project name and a package name,
the name always designates the project. To avoid possible confusion, it is
always a good idea to avoid naming a project with one of the
names allowed for packages or any name that starts with gnat.
An expression is either a string expression or a string list expression.
A string expression is either a simple string expression or a compound string expression.
A simple string expression is one of the following:
"comm/my_proj.gpr"
A compound string expression is a concatenation of string expressions,
using the operator "&"
Path & "/" & File_Name & ".ads"
A string list expression is either a simple string list expression or a compound string list expression.
A simple string list expression is one of the following:
File_Names := (File_Name, "gnat.adc", File_Name & ".orig");
Empty_List := ();
A compound string list expression is the concatenation (using
"&") of a simple string list expression and an expression. Note that
each term in a compound string list expression, except the first, may be
either a string expression or a string list expression.
File_Name_List := () & File_Name; -- One string in this list
Extended_File_Name_List := File_Name_List & (File_Name & ".orig");
-- Two strings
Big_List := File_Name_List & Extended_File_Name_List;
-- Concatenation of two string lists: three strings
Illegal_List := "gnat.adc" & Extended_File_Name_List;
-- Illegal: must start with a string list
A string type declaration introduces a discrete set of string literals. If a string variable is declared to have this type, its value is restricted to the given set of literals.
Here is an example of a string type declaration:
type OS is ("NT", "nt", "Unix", "GNU/Linux", "other OS");
Variables of a string type are called typed variables; all other
variables are called untyped variables. Typed variables are
particularly useful in case constructions, to support conditional
attribute declarations.
(see case Constructions).
The string literals in the list are case sensitive and must all be different. They may include any graphic characters allowed in Ada, including spaces.
A string type may only be declared at the project level, not inside a package.
A string type may be referenced by its name if it has been declared in the same project file, or by an expanded name whose prefix is the name of the project in which it is declared.
A variable may be declared at the project file level, or within a package. Here are some examples of variable declarations:
This_OS : OS := external ("OS"); -- a typed variable declaration
That_OS := "GNU/Linux"; -- an untyped variable declaration
The syntax of a typed variable declaration is identical to the Ada syntax for an object declaration. By contrast, the syntax of an untyped variable declaration is identical to an Ada assignment statement. In fact, variable declarations in project files have some of the characteristics of an assignment, in that successive declarations for the same variable are allowed. Untyped variable declarations do establish the expected kind of the variable (string or string list), and successive declarations for it must respect the initial kind.
A string variable declaration (typed or untyped) declares a variable whose value is a string. This variable may be used as a string expression.
File_Name := "readme.txt";
Saved_File_Name := File_Name & ".saved";
A string list variable declaration declares a variable whose value is a list of strings. The list may contain any number (zero or more) of strings.
Empty_List := ();
List_With_One_Element := ("-gnaty");
List_With_Two_Elements := List_With_One_Element & "-gnatg";
Long_List := ("main.ada", "pack1_.ada", "pack1.ada", "pack2_.ada"
"pack2.ada", "util_.ada", "util.ada");
The same typed variable may not be declared more than once at project level, and it may not be declared more than once in any package; it is in effect a constant.
The same untyped variable may be declared several times. Declarations are elaborated in the order in which they appear, so the new value replaces the old one, and any subsequent reference to the variable uses the new value. However, as noted above, if a variable has been declared as a string, all subsequent declarations must give it a string value. Similarly, if a variable has been declared as a string list, all subsequent declarations must give it a string list value.
A variable reference may take several forms:
A context may be one of the following:
A variable reference may be used in an expression.
A project (and its packages) may have attributes that define the project's properties. Some attributes have values that are strings; others have values that are string lists.
There are two categories of attributes: simple attributes and associative arrays (see Associative Array Attributes).
Legal project attribute names, and attribute names for each legal package are listed below. Attributes names are case-insensitive.
The following attributes are defined on projects (all are simple attributes):
| Attribute Name | Value
|
Source_Files
| string list
|
Source_Dirs
| string list
|
Source_List_File
| string
|
Object_Dir
| string
|
Exec_Dir
| string
|
Excluded_Source_Dirs
| string list
|
Excluded_Source_Files
| string list
|
Excluded_Source_List_File
| string
|
Languages
| string list
|
Main
| string list
|
Library_Dir
| string
|
Library_Name
| string
|
Library_Kind
| string
|
Library_Version
| string
|
Library_Interface
| string
|
Library_Auto_Init
| string
|
Library_Options
| string list
|
Library_Src_Dir
| string
|
Library_ALI_Dir
| string
|
Library_GCC
| string
|
Library_Symbol_File
| string
|
Library_Symbol_Policy
| string
|
Library_Reference_Symbol_File
| string
|
Externally_Built
| string
|
The following attributes are defined for package Naming
(see Naming Schemes):
| Attribute Name | Category | Index | Value
|
Spec_Suffix
| associative array | language name | string
|
Body_Suffix
| associative array | language name | string
|
Separate_Suffix
| simple attribute | n/a | string
|
Casing
| simple attribute | n/a | string
|
Dot_Replacement
| simple attribute | n/a | string
|
Spec
| associative array | Ada unit name | string
|
Body
| associative array | Ada unit name | string
|
Specification_Exceptions
| associative array | language name | string list
|
Implementation_Exceptions
| associative array | language name | string list
|
The following attributes are defined for packages Builder,
Compiler, Binder,
Linker, Cross_Reference, and Finder
(see Switches and Project Files).
| Attribute Name | Category | Index | Value
|
Default_Switches
| associative array | language name | string list
|
Switches
| associative array | file name | string list
|
In addition, package Compiler has a single string attribute
Local_Configuration_Pragmas and package Builder has a single
string attribute Global_Configuration_Pragmas.
Each simple attribute has a default value: the empty string (for string-valued attributes) and the empty list (for string list-valued attributes).
An attribute declaration defines a new value for an attribute.
Examples of simple attribute declarations:
for Object_Dir use "objects";
for Source_Dirs use ("units", "test/drivers");
The syntax of a simple attribute declaration is similar to that of an attribute definition clause in Ada.
Attributes references may be appear in expressions.
The general form for such a reference is <entity>'<attribute>:
Associative array attributes are functions. Associative
array attribute references must have an argument that is a string literal.
Examples are:
project'Object_Dir
Naming'Dot_Replacement
Imported_Project'Source_Dirs
Imported_Project.Naming'Casing
Builder'Default_Switches("Ada")
The prefix of an attribute may be:
project for an attribute of the current project
Example:
project Prj is
for Source_Dirs use project'Source_Dirs & "units";
for Source_Dirs use project'Source_Dirs & "test/drivers"
end Prj;
In the first attribute declaration, initially the attribute Source_Dirs
has the default value: an empty string list. After this declaration,
Source_Dirs is a string list of one element: "units".
After the second attribute declaration Source_Dirs is a string list of
two elements: "units" and "test/drivers".
Note: this example is for illustration only. In practice, the project file would contain only one attribute declaration:
for Source_Dirs use ("units", "test/drivers");
Some attributes are defined as associative arrays. An associative array may be regarded as a function that takes a string as a parameter and delivers a string or string list value as its result.
Here are some examples of single associative array attribute associations:
for Body ("main") use "Main.ada";
for Switches ("main.ada")
use ("-v",
"-gnatv");
for Switches ("main.ada")
use Builder'Switches ("main.ada")
& "-g";
Like untyped variables and simple attributes, associative array attributes may be declared several times. Each declaration supplies a new value for the attribute, and replaces the previous setting.
An associative array attribute may be declared as a full associative array declaration, with the value of the same attribute in an imported or extended project.
package Builder is
for Default_Switches use Default.Builder'Default_Switches;
end Builder;
In this example, Default must be either a project imported by the
current project, or the project that the current project extends. If the
attribute is in a package (in this case, in package Builder), the same
package needs to be specified.
A full associative array declaration replaces any other declaration for the attribute, including other full associative array declaration. Single associative array associations may be declare after a full associative declaration, modifying the value for a single association of the attribute.
case ConstructionsA case construction is used in a project file to effect conditional
behavior.
Here is a typical example:
project MyProj is
type OS_Type is ("GNU/Linux", "Unix", "NT", "VMS");
OS : OS_Type := external ("OS", "GNU/Linux");
package Compiler is
case OS is
when "GNU/Linux" | "Unix" =>
for Default_Switches ("Ada")
use ("-gnath");
when "NT" =>
for Default_Switches ("Ada")
use ("-gnatP");
when others =>
end case;
end Compiler;
end MyProj;
The syntax of a case construction is based on the Ada case statement
(although there is no null construction for empty alternatives).
The case expression must be a typed string variable.
Each alternative comprises the reserved word when, either a list of
literal strings separated by the "|" character or the reserved word
others, and the "=>" token.
Each literal string must belong to the string type that is the type of the
case variable.
An others alternative, if present, must occur last.
After each =>, there are zero or more constructions. The only
constructions allowed in a case construction are other case constructions,
attribute declarations and variable declarations. String type declarations and
package declarations are not allowed. Variable declarations are restricted to
variables that have already been declared before the case construction.
The value of the case variable is often given by an external reference (see External References in Project Files).
Each project has exactly one object directory and one or more source directories. The source directories must contain at least one source file, unless the project file explicitly specifies that no source files are present (see Source File Names).
The object directory for a project is the directory containing the compiler's output (such as ALI files and object files) for the project's immediate sources.
The object directory is given by the value of the attribute Object_Dir
in the project file.
for Object_Dir use "objects";
The attribute Object_Dir has a string value, the path name of the object
directory. The path name may be absolute or relative to the directory of the
project file. This directory must already exist, and be readable and writable.
By default, when the attribute Object_Dir is not given an explicit value
or when its value is the empty string, the object directory is the same as the
directory containing the project file.
The exec directory for a project is the directory containing the executables for the project's main subprograms.
The exec directory is given by the value of the attribute Exec_Dir
in the project file.
for Exec_Dir use "executables";
The attribute Exec_Dir has a string value, the path name of the exec
directory. The path name may be absolute or relative to the directory of the
project file. This directory must already exist, and be writable.
By default, when the attribute Exec_Dir is not given an explicit value
or when its value is the empty string, the exec directory is the same as the
object directory of the project file.
The source directories of a project are specified by the project file
attribute Source_Dirs.
This attribute's value is a string list. If the attribute is not given an explicit value, then there is only one source directory, the one where the project file resides.
A Source_Dirs attribute that is explicitly defined to be the empty list,
as in
for Source_Dirs use ();
indicates that the project contains no source files.
Otherwise, each string in the string list designates one or more source directories.
for Source_Dirs use ("sources", "test/drivers");
If a string in the list ends with "/**", then the directory whose path
name precedes the two asterisks, as well as all its subdirectories
(recursively), are source directories.
for Source_Dirs use ("/system/sources/**");
Here the directory /system/sources and all of its subdirectories
(recursively) are source directories.
To specify that the source directories are the directory of the project file
and all of its subdirectories, you can declare Source_Dirs as follows:
for Source_Dirs use ("./**");
Each of the source directories must exist and be readable.
In a project that contains source files, their names may be specified by the
attributes Source_Files (a string list) or Source_List_File
(a string). Source file names never include any directory information.
If the attribute Source_Files is given an explicit value, then each
element of the list is a source file name.
for Source_Files use ("main.adb");
for Source_Files use ("main.adb", "pack1.ads", "pack2.adb");
If the attribute Source_Files is not given an explicit value,
but the attribute Source_List_File is given a string value,
then the source file names are contained in the text file whose path name
(absolute or relative to the directory of the project file) is the
value of the attribute Source_List_File.
Each line in the file that is not empty or is not a comment contains a source file name.
for Source_List_File use "source_list.txt";
By default, if neither the attribute Source_Files nor the attribute
Source_List_File is given an explicit value, then each file in the
source directories that conforms to the project's naming scheme
(see Naming Schemes) is an immediate source of the project.
A warning is issued if both attributes Source_Files and
Source_List_File are given explicit values. In this case, the attribute
Source_Files prevails.
Each source file name must be the name of one existing source file in one of the source directories.
A Source_Files attribute whose value is an empty list
indicates that there are no source files in the project.
If the order of the source directories is known statically, that is if
"/**" is not used in the string list Source_Dirs, then there may
be several files with the same source file name. In this case, only the file
in the first directory is considered as an immediate source of the project
file. If the order of the source directories is not known statically, it is
an error to have several files with the same source file name.
Projects can be specified to have no Ada source
files: the value of (Source_Dirs or Source_Files may be an empty
list, or the "Ada" may be absent from Languages:
for Source_Dirs use ();
for Source_Files use ();
for Languages use ("C", "C++");
Otherwise, a project must contain at least one immediate source.
Projects with no source files are useful as template packages
(see Packages in Project Files) for other projects; in particular to
define a package Naming (see Naming Schemes).
An immediate source of a project P may depend on source files that are neither immediate sources of P nor in the predefined library. To get this effect, P must import the projects that contain the needed source files.
with "project1", "utilities.gpr";
with "/namings/apex.gpr";
project Main is
...
As can be seen in this example, the syntax for importing projects is similar
to the syntax for importing compilation units in Ada. However, project files
use literal strings instead of names, and the with clause identifies
project files rather than packages.
Each literal string is the file name or path name (absolute or relative) of a
project file. If a string corresponds to a file name, with no path or a
relative path, then its location is determined by the project path. The
latter can be queried using gnatls -v. It contains:
If a relative pathname is used, as in
with "tests/proj";
then the full path for the project is constructed by concatenating this relative path to those in the project path, in order, until a matching file is found. Any symbolic link will be fully resolved in the directory of the importing project file before the imported project file is examined.
If the with'ed project file name does not have an extension,
the default is .gpr. If a file with this extension is not found,
then the file name as specified in the with clause (no extension) will
be used. In the above example, if a file project1.gpr is found, then it
will be used; otherwise, if a file project1 exists
then it will be used; if neither file exists, this is an error.
A warning is issued if the name of the project file does not match the name of the project; this check is case insensitive.
Any source file that is an immediate source of the imported project can be
used by the immediate sources of the importing project, transitively. Thus
if A imports B, and B imports C, the immediate
sources of A may depend on the immediate sources of C, even if
A does not import C explicitly. However, this is not recommended,
because if and when B ceases to import C, some sources in
A will no longer compile.
A side effect of this capability is that normally cyclic dependencies are not
permitted: if A imports B (directly or indirectly) then B
is not allowed to import A. However, there are cases when cyclic
dependencies would be beneficial. For these cases, another form of import
between projects exists, the limited with: a project A that
imports a project B with a straight with may also be imported,
directly or indirectly, by B on the condition that imports from B
to A include at least one limited with.
with "../b/b.gpr";
with "../c/c.gpr";
project A is
end A;
limited with "../a/a.gpr";
project B is
end B;
with "../d/d.gpr";
project C is
end C;
limited with "../a/a.gpr";
project D is
end D;
In the above legal example, there are two project cycles:
In each of these cycle there is one limited with: import of A
from B and import of A from D.
The difference between straight with and limited with is that
the name of a project imported with a limited with cannot be used in the
project that imports it. In particular, its packages cannot be renamed and
its variables cannot be referred to.
An exception to the above rules for limited with is that for the main
project specified to gnatmake or to the GNAT driver a
limited with is equivalent to a straight with. For example,
in the example above, projects B and D could not be main
projects for gnatmake or to the GNAT driver, because they
each have a limited with that is the only one in a cycle of importing
projects.
During development of a large system, it is sometimes necessary to use modified versions of some of the source files, without changing the original sources. This can be achieved through the project extension facility.
project Modified_Utilities extends "/baseline/utilities.gpr" is ...
A project extension declaration introduces an extending project (the child) and a project being extended (the parent).
By default, a child project inherits all the sources of its parent. However, inherited sources can be overridden: a unit in a parent is hidden by a unit of the same name in the child.
Inherited sources are considered to be sources (but not immediate sources) of the child project; see Project File Syntax.
An inherited source file retains any switches specified in the parent project.
For example if the project Utilities contains the spec and the
body of an Ada package Util_IO, then the project
Modified_Utilities can contain a new body for package Util_IO.
The original body of Util_IO will not be considered in program builds.
However, the package spec will still be found in the project
Utilities.
A child project can have only one parent, except when it is qualified as abstract. But it may import any number of other projects.
A project is not allowed to import directly or indirectly at the same time a child project and any of its ancestors.
When extending a large system spanning multiple projects, it is often
inconvenient to extend every project in the hierarchy that is impacted by a
small change introduced. In such cases, it is possible to create a virtual
extension of entire hierarchy using extends all relationship.
When the project is extended using extends all inheritance, all projects
that are imported by it, both directly and indirectly, are considered virtually
extended. That is, the Project Manager creates "virtual projects"
that extend every project in the hierarchy; all these virtual projects have
no sources of their own and have as object directory the object directory of
the root of "extending all" project.
It is possible to explicitly extend one or more projects in the hierarchy in order to modify the sources. These extending projects must be imported by the "extending all" project, which will replace the corresponding virtual projects with the explicit ones.
When building such a project hierarchy extension, the Project Manager will ensure that both modified sources and sources in virtual extending projects that depend on them, are recompiled.
By means of example, consider the following hierarchy of projects.
We want to modify packages P1 and P3.
This project hierarchy will need to be extended as follows:
project A1 extends "(...)/A" is
end A1;
with "(...)/A1";
project C1 extends all "(...)/C" is
end C1;
When you build project C1, your entire modified project space will be recompiled, including the virtual project B1 that has been impacted by the "extending all" inheritance of project C.
Note that if a Library Project in the hierarchy is virtually extended, the virtual project that extends the Library Project is not a Library Project.
A project file may contain references to external variables; such references are called external references.
An external variable is either defined as part of the environment (an environment variable in Unix, for example) or else specified on the command line via the -Xvbl=value switch. If both, then the command line value is used.
The value of an external reference is obtained by means of the built-in
function external, which returns a string value.
This function has two forms:
external (external_variable_name)
external (external_variable_name, default_value)
Each parameter must be a string literal. For example:
external ("USER")
external ("OS", "GNU/Linux")
In the form with one parameter, the function returns the value of the external variable given as parameter. If this name is not present in the environment, the function returns an empty string.
In the form with two string parameters, the second argument is
the value returned when the variable given as the first argument is not
present in the environment. In the example above, if "OS" is not
the name of an environment variable and is not passed on
the command line, then the returned value is "GNU/Linux".
An external reference may be part of a string expression or of a string list expression, and can therefore appear in a variable declaration or an attribute declaration.
type Mode_Type is ("Debug", "Release");
Mode : Mode_Type := external ("MODE");
case Mode is
when "Debug" =>
...
A package defines the settings for project-aware tools within a project. For each such tool one can declare a package; the names for these packages are preset (see Packages). A package may contain variable declarations, attribute declarations, and case constructions.
project Proj is
package Builder is -- used by gnatmake
for Default_Switches ("Ada")
use ("-v",
"-g");
end Builder;
end Proj;
The syntax of package declarations mimics that of package in Ada.
Most of the packages have an attribute
Default_Switches.
This attribute is an associative array, and its value is a string list.
The index of the associative array is the name of a programming language (case
insensitive). This attribute indicates the switch
or switches to be used
with the corresponding tool.
Some packages also have another attribute, Switches,
an associative array whose value is a string list.
The index is the name of a source file.
This attribute indicates the switch
or switches to be used by the corresponding
tool when dealing with this specific file.
Further information on these switch-related attributes is found in Switches and Project Files.
A package may be declared as a renaming of another package; e.g., from the project file for an imported project.
with "/global/apex.gpr";
project Example is
package Naming renames Apex.Naming;
...
end Example;
Packages that are renamed in other project files often come from project files that have no sources: they are just used as templates. Any modification in the template will be reflected automatically in all the project files that rename a package from the template.
In addition to the tool-oriented packages, you can also declare a package
named Naming to establish specialized source file naming conventions
(see Naming Schemes).
An attribute or variable defined in an imported or parent project can be used in expressions in the importing / extending project. Such an attribute or variable is denoted by an expanded name whose prefix is either the name of the project or the expanded name of a package within a project.
with "imported";
project Main extends "base" is
Var1 := Imported.Var;
Var2 := Base.Var & ".new";
package Builder is
for Default_Switches ("Ada")
use Imported.Builder'Ada_Switches &
"-gnatg" &
"-v";
end Builder;
package Compiler is
for Default_Switches ("Ada")
use Base.Compiler'Ada_Switches;
end Compiler;
end Main;
In this example:
Var1 is a copy of the variable Var defined
in the project file "imported.gpr"
Var2 is a copy of the value of variable Var
defined in the project file base.gpr, concatenated with ".new"
Default_Switches ("Ada") in package
Builder is a string list that includes in its value a copy of the value
of Ada_Switches defined in the Builder package
in project file imported.gpr plus two new elements:
"-gnatg"
and "-v";
Default_Switches ("Ada") in package
Compiler is a copy of the variable Ada_Switches
defined in the Compiler package in project file base.gpr,
the project being extended.
Sometimes an Ada software system is ported from a foreign compilation
environment to GNAT, and the file names do not use the default GNAT
conventions. Instead of changing all the file names (which for a variety
of reasons might not be possible), you can define the relevant file
naming scheme in the Naming package in your project file.
Note that the use of pragmas described in Alternative File Naming Schemes by mean of a configuration pragmas file is not supported when using project files. You must use the features described in this paragraph. You can however use specify other configuration pragmas (see Specifying Configuration Pragmas).
For example, the following package models the Apex file naming rules:
package Naming is
for Casing use "lowercase";
for Dot_Replacement use ".";
for Spec_Suffix ("Ada") use ".1.ada";
for Body_Suffix ("Ada") use ".2.ada";
end Naming;
You can define the following attributes in package Naming:
Casing"lowercase",
"uppercase" or "mixedcase"; these strings are case insensitive.
If Casing is not specified, then the default is "lowercase".
Dot_Replacement'.' except if the entire string
is "."
If Dot_Replacement is not specified, then the default is "-".
Spec_SuffixSpec_Suffix ("Ada") is not specified, then the default is
".ads".
Body_SuffixSpec_Suffix ("Ada")
Body_Suffix ("Ada") and Spec_Suffix ("Ada") end with the
same string, then a file name that ends with the longest of these two suffixes
will be a body if the longest suffix is Body_Suffix ("Ada") or a spec
if the longest suffix is Spec_Suffix ("Ada").
If Body_Suffix ("Ada") is not specified, then the default is
".adb".
Separate_SuffixBody_Suffix. The same "longest suffix" rules apply.
If Separate_Suffix ("Ada") is not specified, then it defaults to same
value as Body_Suffix ("Ada").
SpecSpec to define
the source file name for an individual Ada compilation unit's spec. The array
index must be a string literal that identifies the Ada unit (case insensitive).
The value of this attribute must be a string that identifies the file that
contains this unit's spec (case sensitive or insensitive depending on the
operating system).
for Spec ("MyPack.MyChild") use "mypack.mychild.spec";
BodyBody to
define the source file name for an individual Ada compilation unit's body
(possibly a subunit). The array index must be a string literal that identifies
the Ada unit (case insensitive). The value of this attribute must be a string
that identifies the file that contains this unit's body or subunit (case
sensitive or insensitive depending on the operating system).
for Body ("MyPack.MyChild") use "mypack.mychild.body";
Library projects are projects whose object code is placed in a library. (Note that this facility is not yet supported on all platforms)
To create a library project, you need to define in its project file
two project-level attributes: Library_Name and Library_Dir.
Additionally, you may define other library-related attributes such as
Library_Kind, Library_Version, Library_Interface,
Library_Auto_Init, Library_Options and Library_GCC.
The Library_Name attribute has a string value. There is no restriction
on the name of a library. It is the responsibility of the developer to
choose a name that will be accepted by the platform. It is recommended to
choose names that could be Ada identifiers; such names are almost guaranteed
to be acceptable on all platforms.
The Library_Dir attribute has a string value that designates the path
(absolute or relative) of the directory where the library will reside.
It must designate an existing directory, and this directory must be writable,
different from the project's object directory and from any source directory
in the project tree.
If both Library_Name and Library_Dir are specified and
are legal, then the project file defines a library project. The optional
library-related attributes are checked only for such project files.
The Library_Kind attribute has a string value that must be one of the
following (case insensitive): "static", "dynamic" or
"relocatable" (which is a synonym for "dynamic"). If this
attribute is not specified, the library is a static library, that is
an archive of object files that can be potentially linked into a
static executable. Otherwise, the library may be dynamic or
relocatable, that is a library that is loaded only at the start of execution.
If you need to build both a static and a dynamic library, you should use two different object directories, since in some cases some extra code needs to be generated for the latter. For such cases, it is recommended to either use two different project files, or a single one which uses external variables to indicate what kind of library should be build.
The Library_ALI_Dir attribute may be specified to indicate the
directory where the ALI files of the library will be copied. When it is
not specified, the ALI files are copied to the directory specified in
attribute Library_Dir. The directory specified by Library_ALI_Dir
must be writable and different from the project's object directory and from
any source directory in the project tree.
The Library_Version attribute has a string value whose interpretation
is platform dependent. It has no effect on VMS and Windows. On Unix, it is
used only for dynamic/relocatable libraries as the internal name of the
library (the "soname"). If the library file name (built from the
Library_Name) is different from the Library_Version, then the
library file will be a symbolic link to the actual file whose name will be
Library_Version.
Example (on Unix):
project Plib is
Version := "1";
for Library_Dir use "lib_dir";
for Library_Name use "dummy";
for Library_Kind use "relocatable";
for Library_Version use "libdummy.so." & Version;
end Plib;
Directory lib_dir will contain the internal library file whose name will be libdummy.so.1, and libdummy.so will be a symbolic link to libdummy.so.1.
When gnatmake detects that a project file is a library project file, it will check all immediate sources of the project and rebuild the library if any of the sources have been recompiled.
Standard project files can import library project files. In such cases, the libraries will only be rebuilt if some of its sources are recompiled because they are in the closure of some other source in an importing project. Sources of the library project files that are not in such a closure will not be checked, unless the full library is checked, because one of its sources needs to be recompiled.
For instance, assume the project file A imports the library project file
L. The immediate sources of A are a1.adb, a2.ads and
a2.adb. The immediate sources of L are l1.ads, l1.adb,
l2.ads, l2.adb.
If l1.adb has been modified, then the library associated with L
will be rebuilt when compiling all the immediate sources of A only
if a1.ads, a2.ads or a2.adb includes a statement
"with L1;".
To be sure that all the sources in the library associated with L are
up to date, and that all the sources of project A are also up to date,
the following two commands needs to be used:
gnatmake -Pl.gpr
gnatmake -Pa.gpr
When a library is built or rebuilt, an attempt is made first to delete all files in the library directory. All ALI files will also be copied from the object directory to the library directory. To build executables, gnatmake will use the library rather than the individual object files.
It is also possible to create library project files for third-party libraries
that are precompiled and cannot be compiled locally thanks to the
externally_built attribute. (See Installing a library).
A Stand-alone Library is a library that contains the necessary code to elaborate the Ada units that are included in the library. A Stand-alone Library is suitable to be used in an executable when the main is not in Ada. However, Stand-alone Libraries may also be used with an Ada main subprogram.
A Stand-alone Library Project is a Library Project where the library is a Stand-alone Library.
To be a Stand-alone Library Project, in addition to the two attributes
that make a project a Library Project (Library_Name and
Library_Dir, see Library Projects), the attribute
Library_Interface must be defined.
for Library_Dir use "lib_dir";
for Library_Name use "dummy";
for Library_Interface use ("int1", "int1.child");
Attribute Library_Interface has a nonempty string list value,
each string in the list designating a unit contained in an immediate source
of the project file.
When a Stand-alone Library is built, first the binder is invoked to build a package whose name depends on the library name (b~dummy.ads/b in the example above). This binder-generated package includes initialization and finalization procedures whose names depend on the library name (dummyinit and dummyfinal in the example above). The object corresponding to this package is included in the library.
A dynamic or relocatable Stand-alone Library is automatically initialized
if automatic initialization of Stand-alone Libraries is supported on the
platform and if attribute Library_Auto_Init is not specified or
is specified with the value "true". A static Stand-alone Library is never
automatically initialized.
Single string attribute Library_Auto_Init may be specified with only
two possible values: "false" or "true" (case-insensitive). Specifying
"false" for attribute Library_Auto_Init will prevent automatic
initialization of dynamic or relocatable libraries.
When a non-automatically initialized Stand-alone Library is used in an executable, its initialization procedure must be called before any service of the library is used. When the main subprogram is in Ada, it may mean that the initialization procedure has to be called during elaboration of another package.
For a Stand-Alone Library, only the ALI files of the Interface Units
(those that are listed in attribute Library_Interface) are copied to
the Library Directory. As a consequence, only the Interface Units may be
imported from Ada units outside of the library. If other units are imported,
the binding phase will fail.
When a Stand-Alone Library is bound, the switches that are specified in
the attribute Default_Switches ("Ada") in package Binder are
used in the call to gnatbind.
The string list attribute Library_Options may be used to specified
additional switches to the call to gcc to link the library.
The attribute Library_Src_Dir, may be specified for a
Stand-Alone Library. Library_Src_Dir is a simple attribute that has a
single string value. Its value must be the path (absolute or relative to the
project directory) of an existing directory. This directory cannot be the
object directory or one of the source directories, but it can be the same as
the library directory. The sources of the Interface
Units of the library, necessary to an Ada client of the library, will be
copied to the designated directory, called Interface Copy directory.
These sources includes the specs of the Interface Units, but they may also
include bodies and subunits, when pragmas Inline or Inline_Always
are used, or when there is a generic units in the spec. Before the sources
are copied to the Interface Copy directory, an attempt is made to delete all
files in the Interface Copy directory.
The following switches are used by GNAT tools that support project files:
There must be only one -P switch on the command line.
Since the Project Manager parses the project file only after all the switches
on the command line are checked, the order of the switches
-P,
-vPx
or -X is not significant.
external(name) when parsing the project file.
If name or value includes a space, then name=value should be put between quotes.
-XOS=NT
-X"user=John Doe"
Several -X switches can be used simultaneously. If several -X switches specify the same name, only the last one is used.
An external variable specified with a -X switch
takes precedence over the value of the same name in the environment.
-vP0 means Default; -vP1 means Medium; -vP2 means High.
The default is Default: no output for syntactically correct
project files.
If several -vPx switches are present,
only the last one is used.
This section covers several topics related to gnatmake and
project files: defining switches for gnatmake
and for the tools that it invokes; specifying configuration pragmas;
the use of the Main attribute; building and rebuilding library project
files.
For each of the packages Builder, Compiler, Binder, and
Linker, you can specify a Default_Switches
attribute, a Switches attribute, or both;
as their names imply, these switch-related
attributes affect the switches that are used for each of these GNAT
components when
gnatmake is invoked. As will be explained below, these
component-specific switches precede
the switches provided on the gnatmake command line.
The Default_Switches attribute is an associative
array indexed by language name (case insensitive) whose value is a string list.
For example:
package Compiler is
for Default_Switches ("Ada")
use ("-gnaty",
"-v");
end Compiler;
The Switches attribute is also an associative array,
indexed by a file name (which may or may not be case sensitive, depending
on the operating system) whose value is a string list. For example:
package Builder is
for Switches ("main1.adb")
use ("-O2");
for Switches ("main2.adb")
use ("-g");
end Builder;
For the Builder package, the file names must designate source files
for main subprograms. For the Binder and Linker packages, the
file names must designate ALI or source files for main subprograms.
In each case just the file name without an explicit extension is acceptable.
For each tool used in a program build (gnatmake, the compiler, the binder, and the linker), the corresponding package contributes a set of switches for each file on which the tool is invoked, based on the switch-related attributes defined in the package. In particular, the switches that each of these packages contributes for a given file f comprise:
Switches (f),
if it is specified in the package for the given file,
Default_Switches ("Ada"),
if it is specified in the package.
If neither of these attributes is defined in the package, then the package does not contribute any switches for the given file.
When gnatmake is invoked on a file, the switches comprise
two sets, in the following order: those contributed for the file
by the Builder package;
and the switches passed on the command line.
When gnatmake invokes a tool (compiler, binder, linker) on a file, the switches passed to the tool comprise three sets, in the following order:
Builder package in the project file supplied on the command line;
The term applicable switches reflects the fact that gnatmake switches may or may not be passed to individual tools, depending on the individual switch.
gnatmake may invoke the compiler on source files from different
projects. The Project Manager will use the appropriate project file to
determine the Compiler package for each source file being compiled.
Likewise for the Binder and Linker packages.
As an example, consider the following package in a project file:
project Proj1 is
package Compiler is
for Default_Switches ("Ada")
use ("-g");
for Switches ("a.adb")
use ("-O1");
for Switches ("b.adb")
use ("-O2",
"-gnaty");
end Compiler;
end Proj1;
If gnatmake is invoked with this project file, and it needs to compile, say, the files a.adb, b.adb, and c.adb, then a.adb will be compiled with the switch -O1, b.adb with switches -O2 and -gnaty, and c.adb with -g.
The following example illustrates the ordering of the switches contributed by different packages:
project Proj2 is
package Builder is
for Switches ("main.adb")
use ("-g",
"-O1",
"-f");
end Builder;
package Compiler is
for Switches ("main.adb")
use ("-O2");
end Compiler;
end Proj2;
If you issue the command:
gnatmake -Pproj2 -O0 main
then the compiler will be invoked on main.adb with the following sequence of switches
-g -O1 -O2 -O0
with the last -O switch having precedence over the earlier ones; several other switches (such as -c) are added implicitly.
The switches
-g
and -O1 are contributed by package
Builder, -O2 is contributed
by the package Compiler
and -O0 comes from the command line.
The -g switch will also be passed in the invocation of Gnatlink.
A final example illustrates switch contributions from packages in different project files:
project Proj3 is
for Source_Files use ("pack.ads", "pack.adb");
package Compiler is
for Default_Switches ("Ada")
use ("-gnata");
end Compiler;
end Proj3;
with "Proj3";
project Proj4 is
for Source_Files use ("foo_main.adb", "bar_main.adb");
package Builder is
for Switches ("foo_main.adb")
use ("-s",
"-g");
end Builder;
end Proj4;
-- Ada source file:
with Pack;
procedure Foo_Main is
...
end Foo_Main;
If the command is
gnatmake -PProj4 foo_main.adb -cargs -gnato
then the switches passed to the compiler for foo_main.adb are
-g (contributed by the package Proj4.Builder) and
-gnato (passed on the command line).
When the imported package Pack is compiled, the switches used
are -g from Proj4.Builder,
-gnata (contributed from package Proj3.Compiler,
and -gnato from the command line.
When using gnatmake with project files, some switches or
arguments may be expressed as relative paths. As the working directory where
compilation occurs may change, these relative paths are converted to absolute
paths. For the switches found in a project file, the relative paths
are relative to the project file directory, for the switches on the command
line, they are relative to the directory where gnatmake is invoked.
The switches for which this occurs are:
-I,
-A,
-L,
-aO,
-aL,
-aI, as well as all arguments that are not switches (arguments to
switch
-o, object files specified in package Linker or after
-largs on the command line). The exception to this rule is the switch
–RTS= for which a relative path argument is never converted.
When using gnatmake with project files, if there exists a file gnat.adc that contains configuration pragmas, this file will be ignored.
Configuration pragmas can be defined by means of the following attributes in
project files: Global_Configuration_Pragmas in package Builder
and Local_Configuration_Pragmas in package Compiler.
Both these attributes are single string attributes. Their values is the path name of a file containing configuration pragmas. If a path name is relative, then it is relative to the project directory of the project file where the attribute is defined.
When compiling a source, the configuration pragmas used are, in order,
those listed in the file designated by attribute
Global_Configuration_Pragmas in package Builder of the main
project file, if it is specified, and those listed in the file designated by
attribute Local_Configuration_Pragmas in package Compiler of
the project file of the source, if it exists.
When using a project file, you can invoke gnatmake with one or several main subprograms, by specifying their source files on the command line.
gnatmake -Pprj main1 main2 main3
Each of these needs to be a source file of the same project, except when the switch -u is used.
When -u is not used, all the mains need to be sources of the
same project, one of the project in the tree rooted at the project specified
on the command line. The package Builder of this common project, the
"main project" is the one that is considered by gnatmake.
When -u is used, the specified source files may be in projects
imported directly or indirectly by the project specified on the command line.
Note that if such a source file is not part of the project specified on the
command line, the switches found in package Builder of the
project specified on the command line, if any, that are transmitted
to the compiler will still be used, not those found in the project file of
the source file.
When using a project file, you can also invoke gnatmake without
explicitly specifying any main, and the effect depends on whether you have
defined the Main attribute. This attribute has a string list value,
where each element in the list is the name of a source file (the file
extension is optional) that contains a unit that can be a main subprogram.
If the Main attribute is defined in a project file as a non-empty
string list and the switch -u is not used on the command
line, then invoking gnatmake with this project file but without any
main on the command line is equivalent to invoking gnatmake with all
the file names in the Main attribute on the command line.
Example:
project Prj is
for Main use ("main1", "main2", "main3");
end Prj;
With this project file, "gnatmake -Pprj"
is equivalent to
"gnatmake -Pprj main1 main2 main3".
When the project attribute Main is not specified, or is specified
as an empty string list, or when the switch -u is used on the command
line, then invoking gnatmake with no main on the command line will
result in all immediate sources of the project file being checked, and
potentially recompiled. Depending on the presence of the switch -u,
sources from other project files on which the immediate sources of the main
project file depend are also checked and potentially recompiled. In other
words, the -u switch is applied to all of the immediate sources of the
main project file.
When no main is specified on the command line and attribute Main exists
and includes several mains, or when several mains are specified on the
command line, the default switches in package Builder will
be used for all mains, even if there are specific switches
specified for one or several mains.
But the switches from package Binder or Linker will be
the specific switches for each main, if they are specified.
When gnatmake is invoked with a main project file that is a library project file, it is not allowed to specify one or more mains on the command line.
When a library project file is specified, switches -b and -l have special meanings.
A number of GNAT tools, other than gnatmake can benefit from project files: gnatbind, gnatcheck), gnatclean), gnatelim, gnatfind, gnatlink, gnatls, gnatmetric, gnatpp, gnatstub, and gnatxref. However, none of these tools can be invoked directly with a project file switch (-P). They must be invoked through the gnat driver.
The gnat driver is a wrapper that accepts a number of commands and calls the corresponding tool. It was designed initially for VMS platforms (to convert VMS qualifiers to Unix-style switches), but it is now available on all GNAT platforms.
On non-VMS platforms, the gnat driver accepts the following commands (case insensitive):
(note that the compiler is invoked using the command gnatmake -f -u -c).
On non-VMS platforms, between gnat and the command, two special switches may be used:
The command may be followed by switches and arguments for the invoked tool.
gnat bind -C main.ali
gnat ls -a main
gnat chop foo.txt
Switches may also be put in text files, one switch per line, and the text files may be specified with their path name preceded by '@'.
gnat bind @args.txt main.ali
In addition, for commands BIND, COMP or COMPILE, FIND, ELIM, LS or LIST, LINK, METRIC, PP or PRETTY, STUB and XREF, the project file related switches (-P, -X and -vPx) may be used in addition to the switches of the invoking tool.
When GNAT PP or GNAT PRETTY is used with a project file, but with no source specified on the command line, it invokes gnatpp with all the immediate sources of the specified project file.
When GNAT METRIC is used with a project file, but with no source specified on the command line, it invokes gnatmetric with all the immediate sources of the specified project file and with -d with the parameter pointing to the object directory of the project.
In addition, when GNAT PP, GNAT PRETTY or GNAT METRIC is used with a project file, no source is specified on the command line and switch -U is specified on the command line, then the underlying tool (gnatpp or gnatmetric) is invoked for all sources of all projects, not only for the immediate sources of the main project. (-U stands for Universal or Union of the project files of the project tree)
For each of the following commands, there is optionally a corresponding package in the main project.
Binder for command BIND (invoking gnatbind)
Check for command CHECK (invoking
gnatcheck)
Compiler for command COMP or COMPILE (invoking the compiler)
Cross_Reference for command XREF (invoking
gnatxref)
Eliminate for command ELIM (invoking
gnatelim)
Finder for command FIND (invoking gnatfind)
Gnatls for command LS or LIST (invoking gnatls)
Gnatstub for command STUB
(invoking gnatstub)
Linker for command LINK (invoking gnatlink)
Metrics for command METRIC
(invoking gnatmetric)
Pretty_Printer for command PP or PRETTY
(invoking gnatpp)
Package Gnatls has a unique attribute Switches,
a simple variable with a string list value. It contains switches
for the invocation of gnatls.
project Proj1 is
package gnatls is
for Switches
use ("-a",
"-v");
end gnatls;
end Proj1;
All other packages have two attribute Switches and
Default_Switches.
Switches is an associative array attribute, indexed by the
source file name, that has a string list value: the switches to be
used when the tool corresponding to the package is invoked for the specific
source file.
Default_Switches is an associative array attribute,
indexed by the programming language that has a string list value.
Default_Switches ("Ada") contains the
switches for the invocation of the tool corresponding
to the package, except if a specific Switches attribute
is specified for the source file.
project Proj is
for Source_Dirs use ("./**");
package gnatls is
for Switches use
("-a",
"-v");
end gnatls;
package Compiler is
for Default_Switches ("Ada")
use ("-gnatv",
"-gnatwa");
end Binder;
package Binder is
for Default_Switches ("Ada")
use ("-C",
"-e");
end Binder;
package Linker is
for Default_Switches ("Ada")
use ("-C");
for Switches ("main.adb")
use ("-C",
"-v",
"-v");
end Linker;
package Finder is
for Default_Switches ("Ada")
use ("-a",
"-f");
end Finder;
package Cross_Reference is
for Default_Switches ("Ada")
use ("-a",
"-f",
"-d",
"-u");
end Cross_Reference;
end Proj;
With the above project file, commands such as
gnat comp -Pproj main
gnat ls -Pproj main
gnat xref -Pproj main
gnat bind -Pproj main.ali
gnat link -Pproj main.ali
will set up the environment properly and invoke the tool with the switches
found in the package corresponding to the tool:
Default_Switches ("Ada") for all tools,
except Switches ("main.adb")
for gnatlink.
It is also possible to invoke some of the tools,
gnatcheck),
gnatmetric),
and gnatpp)
on a set of project units thanks to the combination of the switches
-P, -U and possibly the main unit when one is interested
in its closure. For instance,
gnat metric -Pproj
will compute the metrics for all the immediate units of project
proj.
gnat metric -Pproj -U
will compute the metrics for all the units of the closure of projects
rooted at proj.
gnat metric -Pproj -U main_unit
will compute the metrics for the closure of units rooted at
main_unit. This last possibility relies implicitly
on gnatbind's option -R.
Suppose that we have two programs, prog1 and prog2, whose sources are in corresponding directories. We would like to build them with a single gnatmake command, and we want to place their object files into build subdirectories of the source directories. Furthermore, we want to have to have two separate subdirectories in build – release and debug – which will contain the object files compiled with different set of compilation flags.
In other words, we have the following structure:
main
|- prog1
| |- build
| | debug
| | release
|- prog2
|- build
| debug
| release
Here are the project files that we must place in a directory main to maintain this structure:
Common project with a package Compiler that
specifies the compilation switches:
File "common.gpr":
project Common is
for Source_Dirs use (); -- No source files
type Build_Type is ("release", "debug");
Build : Build_Type := External ("BUILD", "debug");
package Compiler is
case Build is
when "release" =>
for Default_Switches ("Ada")
use ("-O2");
when "debug" =>
for Default_Switches ("Ada")
use ("-g");
end case;
end Compiler;
end Common;
File "prog1.gpr":
with "common";
project Prog1 is
for Source_Dirs use ("prog1");
for Object_Dir use "prog1/build/" & Common.Build;
package Compiler renames Common.Compiler;
end Prog1;
File "prog2.gpr":
with "common";
project Prog2 is
for Source_Dirs use ("prog2");
for Object_Dir use "prog2/build/" & Common.Build;
package Compiler renames Common.Compiler;
end Prog2;
Main:
File "main.gpr":
with "common";
with "prog1";
with "prog2";
project Main is
package Compiler renames Common.Compiler;
end Main;
withs (either
explicitly or implicitly) all the sources of our two programs.
Now we can build the programs using the command
gnatmake -Pmain dummy
for the Debug mode, or
gnatmake -Pmain -XBUILD=release
for the Release mode.
project ::=
context_clause project_declaration
context_clause ::=
{with_clause}
with_clause ::=
with path_name { , path_name } ;
path_name ::=
string_literal
project_declaration ::=
simple_project_declaration | project_extension
simple_project_declaration ::=
project <project_>simple_name is
{declarative_item}
end <project_>simple_name;
project_extension ::=
project <project_>simple_name extends path_name is
{declarative_item}
end <project_>simple_name;
declarative_item ::=
package_declaration |
typed_string_declaration |
other_declarative_item
package_declaration ::=
package_spec | package_renaming
package_spec ::=
package package_identifier is
{simple_declarative_item}
end package_identifier ;
package_identifier ::=
Naming | Builder | Compiler | Binder |
Linker | Finder | Cross_Reference |
gnatls | IDE | Pretty_Printer
package_renaming ::==
package package_identifier renames
<project_>simple_name.package_identifier ;
typed_string_declaration ::=
type <typed_string_>_simple_name is
( string_literal {, string_literal} );
other_declarative_item ::=
attribute_declaration |
typed_variable_declaration |
variable_declaration |
case_construction
attribute_declaration ::=
full_associative_array_declaration |
for attribute_designator use expression ;
full_associative_array_declaration ::=
for <associative_array_attribute_>simple_name use
<project_>simple_name [ . <package_>simple_Name ] ' <attribute_>simple_name ;
attribute_designator ::=
<simple_attribute_>simple_name |
<associative_array_attribute_>simple_name ( string_literal )
typed_variable_declaration ::=
<typed_variable_>simple_name : <typed_string_>name := string_expression ;
variable_declaration ::=
<variable_>simple_name := expression;
expression ::=
term {& term}
term ::=
literal_string |
string_list |
<variable_>name |
external_value |
attribute_reference
string_literal ::=
(same as Ada)
string_list ::=
( <string_>expression { , <string_>expression } )
external_value ::=
external ( string_literal [, string_literal] )
attribute_reference ::=
attribute_prefix ' <simple_attribute_>simple_name [ ( literal_string ) ]
attribute_prefix ::=
project |
<project_>simple_name | package_identifier |
<project_>simple_name . package_identifier
case_construction ::=
case <typed_variable_>name is
{case_item}
end case ;
case_item ::=
when discrete_choice_list =>
{case_construction | attribute_declaration}
discrete_choice_list ::=
string_literal {| string_literal} |
others
name ::=
simple_name {. simple_name}
simple_name ::=
identifier (same as Ada)
gnatxref and gnatfindThe compiler generates cross-referencing information (unless you set the ‘-gnatx’ switch), which are saved in the .ali files. This information indicates where in the source each entity is declared and referenced. Note that entities in package Standard are not included, but entities in all other predefined units are included in the output.
Before using any of these two tools, you need to compile successfully your application, so that GNAT gets a chance to generate the cross-referencing information.
The two tools gnatxref and gnatfind take advantage of this
information to provide the user with the capability to easily locate the
declaration and references to an entity. These tools are quite similar,
the difference being that gnatfind is intended for locating
definitions and/or references to a specified entity or entities, whereas
gnatxref is oriented to generating a full report of all
cross-references.
To use these tools, you must not compile your application using the -gnatx switch on the gnatmake command line (see The GNAT Make Program gnatmake). Otherwise, cross-referencing information will not be generated.
Note: to invoke gnatxref or gnatfind with a project file,
use the gnat driver (see The GNAT Driver and Project Files).
gnatxref SwitchesThe command invocation for gnatxref is:
$ gnatxref [switches] sourcefile1 [sourcefile2 ...]
where
These file names are considered to be regular expressions, so for instance specifying source*.adb is the same as giving every file in the current directory whose name starts with source and whose extension is adb.
You shouldn't specify any directory name, just base names. gnatxref and gnatfind will be able to locate these files by themselves using the source path. If you specify directories, no result is produced.
The switches can be:
gnatfind and gnatxref will parse
the read-only files found in the library search path. Otherwise, these files
will be ignored. This option can be used to protect Gnat sources or your own
libraries from being parsed, thus making gnatfind and gnatxref
much faster, and their output much smaller. Read-only here refers to access
or permissions status in the file system for the current user.
gnatxref will output the parent type
reference for each matching derived types.
gnatfind and gnatxref.
By default, gnatxref and gnatfind will try to locate a
project file in the current directory.
If a project file is either specified or found by the tools, then the content
of the source directory and object directory lines are added as if they
had been specified respectively by ‘-aI’
and ‘-aO’.
gnatxref will then
display every unused entity and 'with'ed package.
gnatxref will generate a
tags file that can be used by vi. For examples how to use this
feature, see Examples of gnatxref Usage. The tags file is output
to the standard output, thus you will have to redirect it to a file.
All these switches may be in any order on the command line, and may even appear after the file names. They need not be separated by spaces, thus you can say ‘gnatxref -ag’ instead of ‘gnatxref -a -g’.
gnatfind SwitchesThe command line for gnatfind is:
$ gnatfind [switches] pattern[:sourcefile[:line[:column]]] [file1 file2 ...]
where
Omitting the pattern is equivalent to specifying ‘*’, which will match any entity. Note that if you do not provide a pattern, you have to provide both a sourcefile and a line.
Entity names are given in Latin-1, with uppercase/lowercase equivalence
for matching purposes. At the current time there is no support for
8-bit codes other than Latin-1, or for wide characters in identifiers.
gnatfind will look for references, bodies or declarations
of symbols referenced in sourcefile, at line line
and column column. See Examples of gnatfind Usage
for syntax examples.
These file names are considered to be regular expressions, so for instance specifying source*.adb is the same as giving every file in the current directory whose name starts with source and whose extension is adb.
The location of the spec of the entity will always be displayed, even if it isn't in one of file1, file2,... The occurrences of the entity in the separate units of the ones given on the command line will also be displayed.
Note that if you specify at least one file in this part, gnatfind may
sometimes not be able to find the body of the subprograms.
At least one of 'sourcefile' or 'pattern' has to be present on the command line.
The following switches are available:
Display Copyright and version, then exit disregarding all other options.
gnatfind and gnatxref will parse
the read-only files found in the library search path. Otherwise, these files
will be ignored. This option can be used to protect Gnat sources or your own
libraries from being parsed, thus making gnatfind and gnatxref
much faster, and their output much smaller. Read-only here refers to access
or permission status in the file system for the current user.
gnatfind will output the parent type
reference for each matching derived types.
gnatfind accept the simple regular expression set for
‘pattern’. If this switch is set, then the pattern will be
considered as full Unix-style regular expression.
gnatfind and gnatxref.
gnatxref and gnatfind will try to locate a
project file in the current directory.
If a project file is either specified or found by the tools, then the content
of the source directory and object directory lines are added as if they
had been specified respectively by ‘-aI’ and
‘-aO’.
gnatfind will output only the information about the
declaration, body or type completion of the entities. If this switch is
set, the gnatfind will locate every reference to the entities in
the files specified on the command line (or in every file in the search
path if no file is given on the command line).
gnatfind will output the content
of the Ada source file lines were the entity was found.
gnatfind will output the type hierarchy for
the specified type. It act like -d option but recursively from parent
type to parent type. When this switch is set it is not possible to
specify more than one file.
All these switches may be in any order on the command line, and may even appear after the file names. They need not be separated by spaces, thus you can say ‘gnatxref -ag’ instead of ‘gnatxref -a -g’.
As stated previously, gnatfind will search in every directory in the
search path. You can force it to look only in the current directory if
you specify * at the end of the command line.
Project files allow a programmer to specify how to compile its
application, where to find sources, etc. These files are used
primarily by GPS, but they can also be used
by the two tools
gnatxref and gnatfind.
A project file name must end with .gpr. If a single one is
present in the current directory, then gnatxref and gnatfind will
extract the information from it. If multiple project files are found, none of
them is read, and you have to use the ‘-p’ switch to specify the one
you want to use.
The following lines can be included, even though most of them have default values which can be used in most cases. The lines can be entered in any order in the file. Except for src_dir and obj_dir, you can only have one instance of each line. If you have multiple instances, only the last one is taken into account.
src_dir=DIR"./"]
specifies a directory where to look for source files. Multiple src_dir
lines can be specified and they will be searched in the order they
are specified.
obj_dir=DIR"./"]
specifies a directory where to look for object and library files. Multiple
obj_dir lines can be specified, and they will be searched in the order
they are specified
comp_opt=SWITCHES""]
creates a variable which can be referred to subsequently by using
the ${comp_opt} notation. This is intended to store the default
switches given to gnatmake and gcc.
bind_opt=SWITCHES""]
creates a variable which can be referred to subsequently by using
the ‘${bind_opt}’ notation. This is intended to store the default
switches given to gnatbind.
link_opt=SWITCHES""]
creates a variable which can be referred to subsequently by using
the ‘${link_opt}’ notation. This is intended to store the default
switches given to gnatlink.
main=EXECUTABLE""]
specifies the name of the executable for the application. This variable can
be referred to in the following lines by using the ‘${main}’ notation.
comp_cmd=COMMAND"gcc -c -I${src_dir} -g -gnatq"]
specifies the command used to compile a single file in the application.
make_cmd=COMMAND"gnatmake ${main} -aI${src_dir}
-aO${obj_dir} -g -gnatq -cargs ${comp_opt}
-bargs ${bind_opt} -largs ${link_opt}"]
specifies the command used to recompile the whole application.
run_cmd=COMMAND"${main}"]
specifies the command used to run the application.
debug_cmd=COMMAND"gdb ${main}"]
specifies the command used to debug the application
gnatxref and gnatfind only take into account the
src_dir and obj_dir lines, and ignore the others.
gnatfind and gnatxrefAs specified in the section about gnatfind, the pattern can be a regular expression. Actually, there are to set of regular expressions which are recognized by the program:
globbing patternsHere is a more formal grammar:
regexp ::= term
term ::= elmt -- matches elmt
term ::= elmt elmt -- concatenation (elmt then elmt)
term ::= * -- any string of 0 or more characters
term ::= ? -- matches any character
term ::= [char {char}] -- matches any character listed
term ::= [char - char] -- matches any character in range
full regular expressionThe following is the form of a regular expression, expressed in Ada reference manual style BNF is as follows
regexp ::= term {| term} -- alternation (term or term ...)
term ::= item {item} -- concatenation (item then item)
item ::= elmt -- match elmt
item ::= elmt * -- zero or more elmt's
item ::= elmt + -- one or more elmt's
item ::= elmt ? -- matches elmt or nothing
elmt ::= nschar -- matches given character
elmt ::= [nschar {nschar}] -- matches any character listed
elmt ::= [^ nschar {nschar}] -- matches any character not listed
elmt ::= [char - char] -- matches chars in given range
elmt ::= \ char -- matches given character
elmt ::= . -- matches any single character
elmt ::= ( regexp ) -- parens used for grouping
char ::= any character, including special characters
nschar ::= any character except ()[].*+?^
Following are a few examples:
gnatxref UsageFor the following examples, we will consider the following units:
| main.ads: 1: with Bar; 2: package Main is 3: procedure Foo (B : in Integer); 4: C : Integer; 5: private 6: D : Integer; 7: end Main; main.adb: 1: package body Main is 2: procedure Foo (B : in Integer) is 3: begin 4: C := B; 5: D := B; 6: Bar.Print (B); 7: Bar.Print (C); 8: end Foo; 9: end Main; bar.ads: 1: package Bar is 2: procedure Print (B : Integer); 3: end bar; |
gnatxref main.adbgnatxref generates cross-reference information for main.adb
and every unit 'with'ed by main.adb.
The output would be:
B Type: Integer
Decl: bar.ads 2:22
B Type: Integer
Decl: main.ads 3:20
Body: main.adb 2:20
Ref: main.adb 4:13 5:13 6:19
Bar Type: Unit
Decl: bar.ads 1:9
Ref: main.adb 6:8 7:8
main.ads 1:6
C Type: Integer
Decl: main.ads 4:5
Modi: main.adb 4:8
Ref: main.adb 7:19
D Type: Integer
Decl: main.ads 6:5
Modi: main.adb 5:8
Foo Type: Unit
Decl: main.ads 3:15
Body: main.adb 2:15
Main Type: Unit
Decl: main.ads 2:9
Body: main.adb 1:14
Print Type: Unit
Decl: bar.ads 2:15
Ref: main.adb 6:12 7:12
that is the entity Main is declared in main.ads, line 2, column 9,
its body is in main.adb, line 1, column 14 and is not referenced any where.
The entity Print is declared in bar.ads, line 2, column 15 and it
it referenced in main.adb, line 6 column 12 and line 7 column 12.
gnatxref package1.adb package2.adsgnatxref will generates cross-reference information for
package1.adb, package2.ads and any other package 'with'ed by any
of these.
gnatxref can generate a tags file output, which can be used
directly from vi. Note that the standard version of vi
will not work properly with overloaded symbols. Consider using another
free implementation of vi, such as vim.
$ gnatxref -v gnatfind.adb > tags
will generate the tags file for gnatfind itself (if the sources
are in the search path!).
From vi, you can then use the command ‘:tag entity’ (replacing entity by whatever you are looking for), and vi will display a new file with the corresponding declaration of entity.
gnatfind Usagegnatfind -f xyz:main.adbThe directories will be printed as well (as the ‘-f’ switch is set)
The output will look like:
directory/main.ads:106:14: xyz <= declaration
directory/main.adb:24:10: xyz <= body
directory/foo.ads:45:23: xyz <= declaration
that is to say, one of the entities xyz found in main.adb is declared at
line 12 of main.ads (and its body is in main.adb), and another one is
declared at line 45 of foo.ads
gnatfind -fs xyz:main.adbgnatfind will
display the content of the Ada source file lines.
The output will look like:
directory/main.ads:106:14: xyz <= declaration
procedure xyz;
directory/main.adb:24:10: xyz <= body
procedure xyz is
directory/foo.ads:45:23: xyz <= declaration
xyz : Integer;
This can make it easier to find exactly the location your are looking
for.
gnatfind -r "*x*":main.ads:123 foo.adbgnatfind main.ads:123This is the same as gnatfind "*":main.adb:123.
gnatfind mydir/main.adb:123:45The column has to be the beginning of the identifier, and should not point to any character in the middle of the identifier.
The gnatpp tool is an ASIS-based utility for source reformatting / pretty-printing. It takes an Ada source file as input and generates a reformatted version as output. You can specify various style directives via switches; e.g., identifier case conventions, rules of indentation, and comment layout.
To produce a reformatted file, gnatpp generates and uses the ASIS tree for the input source and thus requires the input to be syntactically and semantically legal. If this condition is not met, gnatpp will terminate with an error message; no output file will be generated.
If the source files presented to gnatpp contain preprocessing directives, then the output file will correspond to the generated source after all preprocessing is carried out. There is no way using gnatpp to obtain pretty printed files that include the preprocessing directives.
If the compilation unit contained in the input source depends semantically upon units located outside the current directory, you have to provide the source search path when invoking gnatpp, if these units are contained in files with names that do not follow the GNAT file naming rules, you have to provide the configuration file describing the corresponding naming scheme; see the description of the gnatpp switches below. Another possibility is to use a project file and to call gnatpp through the gnat driver
The gnatpp command has the form
$ gnatpp [switches] filename
where
The following subsections describe the various switches accepted by gnatpp, organized by category.
You specify a switch by supplying a name and generally also a value. In many cases the values for a switch with a given name are incompatible with each other (for example the switch that controls the casing of a reserved word may have exactly one value: upper case, lower case, or mixed case) and thus exactly one such switch can be in effect for an invocation of gnatpp. If more than one is supplied, the last one is used. However, some values for the same switch are mutually compatible. You may supply several such switches to gnatpp, but then each must be specified in full, with both the name and the value. Abbreviated forms (the name appearing once, followed by each value) are not permitted. For example, to set the alignment of the assignment delimiter both in declarations and in assignment statements, you must write -A2A3 (or -A2 -A3), but not -A23.
In most cases, it is obvious whether or not the values for a switch with a given name are compatible with each other. When the semantics might not be evident, the summaries below explicitly indicate the effect.
Programs can be easier to read if certain constructs are vertically aligned. By default all alignments are set ON. Through the -A0 switch you may reset the default to OFF, and then use one or more of the other -An switches to activate alignment for specific constructs.
: in declarations
:= in initializations in declarations
:= in assignment statements
=> in associations
at keywords in the component clauses in record
representation clauses
The -A switches are mutually compatible; any combination is allowed.
gnatpp allows you to specify the casing for reserved words, pragma names, attribute designators and identifiers. For identifiers you may define a general rule for name casing but also override this rule via a set of dictionary files.
Three types of casing are supported: lower case, upper case, and mixed case. Lower and upper case are self-explanatory (but since some letters in Latin1 and other GNAT-supported character sets exist only in lower-case form, an upper case conversion will have no effect on them.) “Mixed case” means that the first letter, and also each letter immediately following an underscore, are converted to their uppercase forms; all the other letters are converted to their lowercase forms.
gnatpp implicitly uses a default dictionary file
to define the casing for the Ada predefined names and
the names declared in the GNAT libraries.
The structure of a dictionary file, and details on the conventions used in the default dictionary file, are defined in Name Casing.
The -D- and -Dfile switches are mutually compatible.
This group of gnatpp switches controls the layout of comments and complex syntactic constructs. See Formatting Comments for details on their effect.
Reformat comment blocks
is on a separate line in a subprogram body in
case if the spec occupies more then one line.
loop in FOR and WHILE loop statements and the
keyword then in IF statements on a separate line.
loop in FOR and WHILE loop statements and the
keyword then in IF statements on a separate line. This option is
incompatible with --separate-loop-then option.
The -c1 and -c2 switches are incompatible. The -c3 and -c4 switches are compatible with each other and also with -c1 and -c2. The -c0 switch disables all the other comment formatting switches.
The -l1, -l2, and -l3 switches are incompatible.
These switches allow control over line length and indentation.
These switches control the inclusion of missing end/exit labels, and the indentation level in case statements.
To define the search path for the input source file, gnatpp uses the same switches as the GNAT compiler, with the same effects.
By default the output is sent to the file whose name is obtained by appending the .pp suffix to the name of the input file (if the file with this name already exists, it is unconditionally overwritten). Thus if the input file is my_ada_proc.adb then gnatpp will produce my_ada_proc.adb.pp as output file. The output may be redirected by the following switches:
Standard_Output
Options -pipe, -o and -of are allowed only if the call to gnatpp contains only one file to reformat. Option --eol and -W cannot be used together with -pipe option.
gnatpp SwitchesThe additional gnatpp switches are defined in this subsection.
The following subsections show how gnatpp treats “white space”, comments, program layout, and name casing. They provide the detailed descriptions of the switches shown above.
gnatpp does not have an option to control space characters. It will add or remove spaces according to the style illustrated by the examples in the Ada Reference Manual.
The only format effectors
(see Ada Reference Manual, paragraph 2.1(13))
that will appear in the output file are platform-specific line breaks,
and also format effectors within (but not at the end of) comments.
In particular, each horizontal tab character that is not inside
a comment will be treated as a space and thus will appear in the
output file as zero or more spaces depending on
the reformatting of the line in which it appears.
The only exception is a Form Feed character, which is inserted after a
pragma Page when -ff is set.
The output file will contain no lines with trailing “white space” (spaces, format effectors).
Empty lines in the original source are preserved only if they separate declarations or statements. In such contexts, a sequence of two or more empty lines is replaced by exactly one empty line. Note that a blank line will be removed if it separates two “comment blocks” (a comment block is a sequence of whole-line comments). In order to preserve a visual separation between comment blocks, use an “empty comment” (a line comprising only hyphens) rather than an empty line. Likewise, if for some reason you wish to have a sequence of empty lines, use a sequence of empty comments instead.
Comments in Ada code are of two kinds:
The indentation of a whole-line comment is that of either the preceding or following line in the formatted source, depending on switch settings as will be described below.
For an end-of-line comment, gnatpp leaves the same number of spaces between the end of the preceding Ada lexical element and the beginning of the comment as appear in the original source, unless either the comment has to be split to satisfy the line length limitation, or else the next line contains a whole line comment that is considered a continuation of this end-of-line comment (because it starts at the same position). In the latter two cases, the start of the end-of-line comment is moved right to the nearest multiple of the indentation level. This may result in a “line overflow” (the right-shifted comment extending beyond the maximum line length), in which case the comment is split as described below.
There is a difference between -c1 (GNAT-style comment line indentation) and -c2 (reference-manual comment line indentation). With reference-manual style, a whole-line comment is indented as if it were a declaration or statement at the same place (i.e., according to the indentation of the preceding line(s)). With GNAT style, a whole-line comment that is immediately followed by an if or case statement alternative, a record variant, or the reserved word begin, is indented based on the construct that follows it.
For example:
| if A then null; -- some comment else null; end if; |
Reference-manual indentation produces:
| if A then null; -- some comment else null; end if; |
while GNAT-style indentation produces:
| if A then null; -- some comment else null; end if; |
The -c3 switch (GNAT style comment beginning) has the following effect:
For an end-of-line comment, if in the original source the next line is a whole-line comment that starts at the same position as the end-of-line comment, then the whole-line comment (and all whole-line comments that follow it and that start at the same position) will start at this position in the output file.
That is, if in the original source we have:
| begin A := B + C; -- B must be in the range Low1..High1 -- C must be in the range Low2..High2 --B+C will be in the range Low1+Low2..High1+High2 X := X + 1; |
Then in the formatted source we get
| begin A := B + C; -- B must be in the range Low1..High1 -- C must be in the range Low2..High2 -- B+C will be in the range Low1+Low2..High1+High2 X := X + 1; |
A comment that exceeds the line length limit will be split. Unless switch -c4 (reformat comment blocks) is set and the line belongs to a reformattable block, splitting the line generates a gnatpp warning. The -c4 switch specifies that whole-line comments may be reformatted in typical word processor style (that is, moving words between lines and putting as many words in a line as possible).
The -c5 switch specifies, that comments
that has a special format (that is, a character that is neither a letter nor digit
not white space nor line break immediately following the leading -- of
the comment) should be without any change moved from the argument source
into reformatted source. This switch allows to preserve comments that are used
as a special marks in the code (e.g. SPARK annotation).
In several cases the suggested layout in the Ada Reference Manual includes an extra level of indentation that many programmers prefer to avoid. The affected cases include:
In compact mode (when GNAT style layout or compact layout is set),
the pretty printer uses one level of indentation instead
of two. This is achieved in the record definition and record representation
clause cases by putting the record keyword on the same line as the
start of the declaration or representation clause, and in the block and loop
case by putting the block or loop header on the same line as the statement
identifier.
The difference between GNAT style -l1 and compact -l2 layout on the one hand, and uncompact layout -l3 on the other hand, can be illustrated by the following examples:
| GNAT style, compact layout Uncompact layout type q is record type q is a : integer; record b : integer; a : integer; end record; b : integer; end record; for q use record for q use a at 0 range 0 .. 31; record b at 4 range 0 .. 31; a at 0 range 0 .. 31; end record; b at 4 range 0 .. 31; end record; Block : declare Block : A : Integer := 3; declare begin A : Integer := 3; Proc (A, A); begin end Block; Proc (A, A); end Block; Clear : for J in 1 .. 10 loop Clear : A (J) := 0; for J in 1 .. 10 loop end loop Clear; A (J) := 0; end loop Clear; |
A further difference between GNAT style layout and compact layout is that GNAT style layout inserts empty lines as separation for compound statements, return statements and bodies.
Note that the layout specified by --separate-stmt-name for named block and loop statements overrides the layout defined by these constructs by -l1, -l2 or -l3 option.
gnatpp always converts the usage occurrence of a (simple) name to the same casing as the corresponding defining identifier.
You control the casing for defining occurrences via the -n switch. With -nD (“as declared”, which is the default), defining occurrences appear exactly as in the source file where they are declared. The other values for this switch — -nU, -nL, -nM — result in upper, lower, or mixed case, respectively. If gnatpp changes the casing of a defining occurrence, it analogously changes the casing of all the usage occurrences of this name.
If the defining occurrence of a name is not in the source compilation unit currently being processed by gnatpp, the casing of each reference to this name is changed according to the value of the -n switch (subject to the dictionary file mechanism described below). Thus gnatpp acts as though the -n switch had affected the casing for the defining occurrence of the name.
Some names may need to be spelled with casing conventions that are not covered by the upper-, lower-, and mixed-case transformations. You can arrange correct casing by placing such names in a dictionary file, and then supplying a -D switch. The casing of names from dictionary files overrides any -n switch.
To handle the casing of Ada predefined names and the names from GNAT libraries, gnatpp assumes a default dictionary file. The name of each predefined entity is spelled with the same casing as is used for the entity in the Ada Reference Manual. The name of each entity in the GNAT libraries is spelled with the same casing as is used in the declaration of that entity.
The -D- switch suppresses the use of the
default dictionary file.
Instead, the casing for predefined and GNAT-defined names will be established
by the -n switch or explicit dictionary files.
For example, by default the names Ada.Text_IO and GNAT.OS_Lib
will appear as just shown,
even in the presence of a -nU switch.
To ensure that even such names are rendered in uppercase,
additionally supply the -D- switch
(or else, less conveniently, place these names in upper case in a dictionary
file).
A dictionary file is a plain text file; each line in this file can be either a blank line (containing only space characters and ASCII.HT characters), an Ada comment line, or the specification of exactly one casing schema.
A casing schema is a string that has the following syntax:
| casing_schema ::= identifier | *simple_identifier* simple_identifier ::= letter{letter_or_digit} |
(See Ada Reference Manual, Section 2.3) for the definition of the identifier lexical element and the letter_or_digit category.)
The casing schema string can be followed by white space and/or an Ada-style comment; any amount of white space is allowed before the string.
If a dictionary file is passed as the value of a -Dfile switch then for every simple name and every identifier, gnatpp checks if the dictionary defines the casing for the name or for some of its parts (the term “subword” is used below to denote the part of a name which is delimited by “_” or by the beginning or end of the word and which does not contain any “_” inside):
*simple_identifier*,
and if it does, the casing of this simple_identifier is used
for this subword
For example, suppose we have the following source to reformat:
| procedure test is name1 : integer := 1; name4_name3_name2 : integer := 2; name2_name3_name4 : Boolean; name1_var : Float; begin name2_name3_name4 := name4_name3_name2 > name1; end; |
And suppose we have two dictionaries:
| dict1: NAME1 *NaMe3* *Name1* |
| dict2: *NAME3* |
If gnatpp is called with the following switches:
gnatpp -nM -D dict1 -D dict2 test.adb
then we will get the following name casing in the gnatpp output:
| procedure Test is NAME1 : Integer := 1; Name4_NAME3_Name2 : Integer := 2; Name2_NAME3_Name4 : Boolean; Name1_Var : Float; begin Name2_NAME3_Name4 := Name4_NAME3_Name2 > NAME1; end Test; |
The gnatmetric tool is an ASIS-based utility for computing various program metrics. It takes an Ada source file as input and generates a file containing the metrics data as output. Various switches control which metrics are computed and output.
gnatmetric generates and uses the ASIS tree for the input source and thus requires the input to be syntactically and semantically legal. If this condition is not met, gnatmetric will generate an error message; no metric information for this file will be computed and reported.
If the compilation unit contained in the input source depends semantically upon units in files located outside the current directory, you have to provide the source search path when invoking gnatmetric. If it depends semantically upon units that are contained in files with names that do not follow the GNAT file naming rules, you have to provide the configuration file describing the corresponding naming scheme (see the description of the gnatmetric switches below.) Alternatively, you may use a project file and invoke gnatmetric through the gnat driver.
The gnatmetric command has the form
$ gnatmetric [switches] {filename} [-cargs gcc_switches]
where
The following subsections describe the various switches accepted by gnatmetric, organized by category.
gnatmetric has two output formats. It can generate a textual (human-readable) form, and also XML. By default only textual output is generated.
When generating the output in textual form, gnatmetric creates for each Ada source file a corresponding text file containing the computed metrics, except for the case when the set of metrics specified by gnatmetric parameters consists only of metrics that are computed for the whole set of analyzed sources, but not for each Ada source. By default, this file is placed in the same directory as where the source file is located, and its name is obtained by appending the .metrix suffix to the name of the input file.
All the output information generated in XML format is placed in a single file. By default this file is placed in the current directory and has the name metrix.xml.
Some of the computed metrics are summed over the units passed to gnatmetric; for example, the total number of lines of code. By default this information is sent to stdout, but a file can be specified with the -og switch.
The following switches control the gnatmetric output:
gnatmetric relies on the GNAT compilation model − one compilation unit per one source file. It computes line metrics for the whole source file, and it also computes syntax and complexity metrics for the file's outermost unit.
By default, gnatmetric will also compute all metrics for certain kinds of locally declared program units:
These kinds of entities will be referred to as eligible local program units, or simply eligible local units, in the discussion below.
Note that a subprogram declaration, generic instantiation, or renaming declaration only receives metrics computation when it appear as the outermost entity in a source file.
Suppression of metrics computation for eligible local units can be obtained via the following switch:
By default all the metrics are computed and reported. The switches described in this subsection allow you to control, on an individual basis, whether metrics are computed and reported. If at least one positive metric switch is specified (that is, a switch that defines that a given metric or set of metrics is to be computed), then only explicitly specified metrics are reported.
For any (legal) source file, and for each of its eligible local program units, gnatmetric computes the following metrics:
gnatmetric sums the values of the line metrics for all the files being processed and then generates the cumulative results. The tool also computes for all the files being processed the average number of code lines in bodies.
You can use the following switches to select the specific line metrics to be computed and reported.
gnatmetric computes various syntactic metrics for the outermost unit and for each eligible local unit:
For the outermost unit in the file, gnatmetric additionally computes the following metrics:
Along with the total number of public types, the following types are counted and reported separately:
By default, all the syntax metrics are computed and reported. You can use the following switches to select specific syntax metrics.
For a program unit that is an executable body (a subprogram body (including generic bodies), task body, entry body or a package body containing its own statement sequence) gnatmetric computes the following complexity metrics:
The McCabe complexity metrics are defined in http://www.mccabe.com/pdf/nist235r.pdf
According to McCabe, both control statements and short-circuit control forms should be taken into account when computing cyclomatic complexity. For each body, we compute three metric values:
When computing cyclomatic and essential complexity, gnatmetric skips the code in the exception handlers and in all the nested program units.
By default, all the complexity metrics are computed and reported. For more fine-grained control you can use the following switches:
exit statements as gotos when
computing Essential Complexity
Coupling metrics are object-oriented metrics that measure the dependencies between a given class (or a group of classes) and the “external world” (that is, the other classes in the program). In this subsection the term “class” is used in its traditional object-oriented programming sense (an instantiable module that contains data and/or method members). A category (of classes) is a group of closely related classes that are reused and/or modified together.
A class K's efferent coupling is the number of classes
that K depends upon.
A category's efferent coupling is the number of classes outside the
category that the classes inside the category depend upon.
A class K's afferent coupling is the number of classes
that depend upon K.
A category's afferent coupling is the number of classes outside the
category that depend on classes belonging to the category.
Ada's implementation of the object-oriented paradigm does not use the traditional class notion, so the definition of the coupling metrics for Ada maps the class and class category notions onto Ada constructs.
For the coupling metrics, several kinds of modules – a library package, a library generic package, and a library generic package instantiation – that define a tagged type or an interface type are considered to be a class. A category consists of a library package (or a library generic package) that defines a tagged or an interface type, together with all its descendant (generic) packages that define tagged or interface types. For any package counted as a class, its body (if any) is considered together with its spec when counting the dependencies. For dependencies between classes, the Ada semantic dependencies are considered. For coupling metrics, only dependencies on units that are considered as classes, are considered.
When computing coupling metrics, gnatmetric counts only dependencies between units that are arguments of the gnatmetric call. Coupling metrics are program-wide (or project-wide) metrics, so to get a valid result, you should call gnatmetric for the whole set of sources that make up your program. It can be done by calling gnatmetric from the GNAT driver with -U option (see See The GNAT Driver and Project Files for details.
By default, all the coupling metrics are disabled. You can use the following switches to specify the coupling metrics to be computed and reported:
gnatmetric SwitchesAdditional gnatmetric switches are as follows:
In order to compute metrics on all units of a given project, you can use the gnat driver along with the -P option:
gnat metric -Pproj
If the project proj depends upon other projects, you can compute
the metrics on the project closure using the -U option:
gnat metric -Pproj -U
Finally, if not all the units are relevant to a particular main program in the project closure, you can generate metrics for the set of units needed to create a given main program (unit closure) using the -U option followed by the name of the main unit:
gnat metric -Pproj -U main
gnatkr
This chapter discusses the method used by the compiler to shorten
the default file names chosen for Ada units so that they do not
exceed the maximum length permitted. It also describes the
gnatkr utility that can be used to determine the result of
applying this shortening.
gnatkrThe default file naming rule in GNAT is that the file name must be derived from the unit name. The exact default rule is as follows:
The -gnatknn switch of the compiler activates a “krunching” circuit that limits file names to nn characters (where nn is a decimal integer). For example, using OpenVMS, where the maximum file name length is 39, the value of nn is usually set to 39, but if you want to generate a set of files that would be usable if ported to a system with some different maximum file length, then a different value can be specified. The default value of 39 for OpenVMS need not be specified.
The gnatkr utility can be used to determine the krunched name for
a given file, when krunched to a specified maximum length.
gnatkrThe gnatkr command has the form
$ gnatkr name [length]
name is the uncrunched file name, derived from the name of the unit in the standard manner described in the previous section (i.e., in particular all dots are replaced by hyphens). The file name may or may not have an extension (defined as a suffix of the form period followed by arbitrary characters other than period). If an extension is present then it will be preserved in the output. For example, when krunching hellofile.ads to eight characters, the result will be hellofil.ads.
Note: for compatibility with previous versions of gnatkr dots may
appear in the name instead of hyphens, but the last dot will always be
taken as the start of an extension. So if gnatkr is given an argument
such as Hello.World.adb it will be treated exactly as if the first
period had been a hyphen, and for example krunching to eight characters
gives the result hellworl.adb.
Note that the result is always all lower case (except on OpenVMS where it is all upper case). Characters of the other case are folded as required.
length represents the length of the krunched name. The default when no argument is given is 8 characters. A length of zero stands for unlimited, in other words do not chop except for system files where the implied crunching length is always eight characters.
The output is the krunched name. The output has an extension only if the original argument was a file name with an extension.
The initial file name is determined by the name of the unit that the file
contains. The name is formed by taking the full expanded name of the
unit and replacing the separating dots with hyphens and
using lowercase
for all letters, except that a hyphen in the second character position is
replaced by a tilde if the first character is
‘a’, ‘i’, ‘g’, or ‘s’.
The extension is .ads for a
spec and .adb for a body.
Krunching does not affect the extension, but the file name is shortened to
the specified length by following these rules:
As an example, consider the krunching of
our-strings-wide_fixed.adb
to fit the name into 8 characters as required by some operating systems.
our-strings-wide_fixed 22
our strings wide fixed 19
our string wide fixed 18
our strin wide fixed 17
our stri wide fixed 16
our stri wide fixe 15
our str wide fixe 14
our str wid fixe 13
our str wid fix 12
ou str wid fix 11
ou st wid fix 10
ou st wi fix 9
ou st wi fi 8
Final file name: oustwifi.adb
These system files have a hyphen in the second character position. That is why normal user files replace such a character with a tilde, to avoid confusion with system file names.
As an example of this special rule, consider
ada-strings-wide_fixed.adb, which gets krunched as follows:
ada-strings-wide_fixed 22
a- strings wide fixed 18
a- string wide fixed 17
a- strin wide fixed 16
a- stri wide fixed 15
a- stri wide fixe 14
a- str wide fixe 13
a- str wid fixe 12
a- str wid fix 11
a- st wid fix 10
a- st wi fix 9
a- st wi fi 8
Final file name: a-stwifi.adb
Of course no file shortening algorithm can guarantee uniqueness over all
possible unit names, and if file name krunching is used then it is your
responsibility to ensure that no name clashes occur. The utility
program gnatkr is supplied for conveniently determining the
krunched name of a file.
gnatkr Usage $ gnatkr very_long_unit_name.ads --> velounna.ads
$ gnatkr grandparent-parent-child.ads --> grparchi.ads
$ gnatkr Grandparent.Parent.Child.ads --> grparchi.ads
$ gnatkr grandparent-parent-child --> grparchi
$ gnatkr very_long_unit_name.ads/count=6 --> vlunna.ads
$ gnatkr very_long_unit_name.ads/count=0 --> very_long_unit_name.ads
gnatprep
This chapter discusses how to use GNAT's gnatprep utility for simple
preprocessing.
Although designed for use with GNAT, gnatprep does not depend on any
special GNAT features.
For further discussion of conditional compilation in general, see
Conditional Compilation.
Preprocessing symbols are defined in definition files and referred to in sources to be preprocessed. A Preprocessing symbol is an identifier, following normal Ada (case-insensitive) rules for its syntax, with the restriction that all characters need to be in the ASCII set (no accented letters).
gnatprepTo call gnatprep use
$ gnatprep [switches] infile outfile [deffile]
where
gnatprep"--! ". This option will result in line numbers
being preserved in the output file.
True. This switch
can be used in place of a definition file.
Source_Reference pragma to be generated that
references the original input file, so that error messages will use
the file name of this original file. The use of this switch implies
that preprocessor lines are not to be removed from the file, so its
use will force -b mode if
-c
has not been specified explicitly.
Note that if the file to be preprocessed contains multiple units, then
it will be necessary to gnatchop the output file from
gnatprep. If a Source_Reference pragma is present
in the preprocessed file, it will be respected by
gnatchop -r
so that the final chopped files will correctly refer to the original
input source file for gnatprep.
#if or #elsif test will be treated as an error.
Note: if neither -b nor -c is present, then preprocessor lines and deleted lines are completely removed from the output, unless -r is specified, in which case -b is assumed.
The definitions file contains lines of the form
symbol := value
where symbol is a preprocessing symbol, and value is one of the following:
Comment lines may also appear in the definitions file, starting with
the usual --,
and comments may be added to the definitions lines.
gnatprepThe input text may contain preprocessor conditional inclusion lines, as well as general symbol substitution sequences.
The preprocessor conditional inclusion commands have the form
| #if expression [then] lines #elsif expression [then] lines #elsif expression [then] lines ... #else lines #end if; |
In this example, expression is defined by the following grammar:
expression ::= <symbol>
expression ::= <symbol> = "<value>"
expression ::= <symbol> = <symbol>
expression ::= <symbol> 'Defined
expression ::= not expression
expression ::= expression and expression
expression ::= expression or expression
expression ::= expression and then expression
expression ::= expression or else expression
expression ::= ( expression )
The following restriction exists: it is not allowed to have "and" or "or" following "not" in the same expression without parentheses. For example, this is not allowed:
not X or Y
This should be one of the following:
(not X) or Y
not (X or Y)
For the first test (expression ::= <symbol>) the symbol must have
either the value true or false, that is to say the right-hand of the
symbol definition must be one of the (case-insensitive) literals
True or False. If the value is true, then the
corresponding lines are included, and if the value is false, they are
excluded.
The test (expression ::= <symbol> 'Defined) is true only if
the symbol has been defined in the definition file or by a -D
switch on the command line. Otherwise, the test is false.
The equality tests are case insensitive, as are all the preprocessor lines.
If the symbol referenced is not defined in the symbol definitions file,
then the effect depends on whether or not switch -u
is specified. If so, then the symbol is treated as if it had the value
false and the test fails. If this switch is not specified, then
it is an error to reference an undefined symbol. It is also an error to
reference a symbol that is defined with a value other than True
or False.
The use of the not operator inverts the sense of this logical test.
The not operator cannot be combined with the or or and
operators, without parentheses. For example, "if not X or Y then" is not
allowed, but "if (not X) or Y then" and "if not (X or Y) then" are.
The then keyword is optional as shown
The # must be the first non-blank character on a line, but
otherwise the format is free form. Spaces or tabs may appear between
the # and the keyword. The keywords and the symbols are case
insensitive as in normal Ada code. Comments may be used on a
preprocessor line, but other than that, no other tokens may appear on a
preprocessor line. Any number of elsif clauses can be present,
including none at all. The else is optional, as in Ada.
The # marking the start of a preprocessor line must be the first
non-blank character on the line, i.e., it must be preceded only by
spaces or horizontal tabs.
Symbol substitution outside of preprocessor lines is obtained by using the sequence
$symbol
anywhere within a source line, except in a comment or within a
string literal. The identifier
following the $ must match one of the symbols defined in the symbol
definition file, and the result is to substitute the value of the
symbol in place of $symbol in the output file.
Note that although the substitution of strings within a string literal
is not possible, it is possible to have a symbol whose defined value is
a string literal. So instead of setting XYZ to hello and writing:
Header : String := "$XYZ";
you should set XYZ to "hello" and write:
Header : String := $XYZ;
and then the substitution will occur as desired.
gnatls
gnatls is a tool that outputs information about compiled
units. It gives the relationship between objects, unit names and source
files. It can also be used to check the source dependencies of a unit
as well as various characteristics.
Note: to invoke gnatls with a project file, use the gnat
driver (see The GNAT Driver and Project Files).
gnatlsThe gnatls command has the form
$ gnatls switches object_or_ali_file
The main argument is the list of object or ali files (see The Ada Library Information Files) for which information is requested.
In normal mode, without additional option, gnatls produces a
four-column listing. Each line represents information for a specific
object. The first column gives the full path of the object, the second
column gives the name of the principal unit in this object, the third
column gives the status of the source and the fourth column gives the
full path of the source representing this unit.
Here is a simple example of use:
$ gnatls *.o
./demo1.o demo1 DIF demo1.adb
./demo2.o demo2 OK demo2.adb
./hello.o h1 OK hello.adb
./instr-child.o instr.child MOK instr-child.adb
./instr.o instr OK instr.adb
./tef.o tef DIF tef.adb
./text_io_example.o text_io_example OK text_io_example.adb
./tgef.o tgef DIF tgef.adb
The first line can be interpreted as follows: the main unit which is contained in object file demo1.o is demo1, whose main source is in demo1.adb. Furthermore, the version of the source used for the compilation of demo1 has been modified (DIF). Each source file has a status qualifier which can be:
OK (unchanged)MOK (slightly modified)DIF (modified)??? (file not found)HID (hidden, unchanged version not first on PATH)gnatlsgnatls recognizes the following switches:
PreelaborableNo_Elab_CodePureElaborate_BodyRemote_TypesShared_PassivePredefinedRemote_Call_Interfacegnatls UsageExample of using the verbose switch. Note how the source and object paths are affected by the -I switch.
$ gnatls -v -I.. demo1.o
GNATLS 5.03w (20041123-34)
Copyright 1997-2004 Free Software Foundation, Inc.
Source Search Path:
<Current_Directory>
../
/home/comar/local/adainclude/
Object Search Path:
<Current_Directory>
../
/home/comar/local/lib/gcc-lib/x86-linux/3.4.3/adalib/
Project Search Path:
<Current_Directory>
/home/comar/local/lib/gnat/
./demo1.o
Unit =>
Name => demo1
Kind => subprogram body
Flags => No_Elab_Code
Source => demo1.adb modified
The following is an example of use of the dependency list. Note the use of the -s switch which gives a straight list of source files. This can be useful for building specialized scripts.
$ gnatls -d demo2.o
./demo2.o demo2 OK demo2.adb
OK gen_list.ads
OK gen_list.adb
OK instr.ads
OK instr-child.ads
$ gnatls -d -s -a demo1.o
demo1.adb
/home/comar/local/adainclude/ada.ads
/home/comar/local/adainclude/a-finali.ads
/home/comar/local/adainclude/a-filico.ads
/home/comar/local/adainclude/a-stream.ads
/home/comar/local/adainclude/a-tags.ads
gen_list.ads
gen_list.adb
/home/comar/local/adainclude/gnat.ads
/home/comar/local/adainclude/g-io.ads
instr.ads
/home/comar/local/adainclude/system.ads
/home/comar/local/adainclude/s-exctab.ads
/home/comar/local/adainclude/s-finimp.ads
/home/comar/local/adainclude/s-finroo.ads
/home/comar/local/adainclude/s-secsta.ads
/home/comar/local/adainclude/s-stalib.ads
/home/comar/local/adainclude/s-stoele.ads
/home/comar/local/adainclude/s-stratt.ads
/home/comar/local/adainclude/s-tasoli.ads
/home/comar/local/adainclude/s-unstyp.ads
/home/comar/local/adainclude/unchconv.ads
gnatclean
gnatclean is a tool that allows the deletion of files produced by the
compiler, binder and linker, including ALI files, object files, tree files,
expanded source files, library files, interface copy source files, binder
generated files and executable files.
gnatcleanThe gnatclean command has the form:
$ gnatclean switches names
names is a list of source file names. Suffixes .ads and
adb may be omitted. If a project file is specified using switch
-P, then names may be completely omitted.
In normal mode, gnatclean delete the files produced by the compiler and,
if switch -c is not specified, by the binder and
the linker. In informative-only mode, specified by switch
-n, the list of files that would have been deleted in
normal mode is listed, but no file is actually deleted.
gnatcleangnatclean recognizes the following switches:
gnatclean.
external(name) when parsing the project file.
See Switches Related to Project Files.
gnatclean was invoked.
This chapter describes how to build and use libraries with GNAT, and also shows how to recompile the GNAT run-time library. You should be familiar with the Project Manager facility (see GNAT Project Manager) before reading this chapter.
A library is, conceptually, a collection of objects which does not have its own main thread of execution, but rather provides certain services to the applications that use it. A library can be either statically linked with the application, in which case its code is directly included in the application, or, on platforms that support it, be dynamically linked, in which case its code is shared by all applications making use of this library.
GNAT supports both types of libraries. In the static case, the compiled code can be provided in different ways. The simplest approach is to provide directly the set of objects resulting from compilation of the library source files. Alternatively, you can group the objects into an archive using whatever commands are provided by the operating system. For the latter case, the objects are grouped into a shared library.
In the GNAT environment, a library has three types of components:
A GNAT library may expose all its source files, which is useful for documentation purposes. Alternatively, it may expose only the units needed by an external user to make use of the library. That is to say, the specs reflecting the library services along with all the units needed to compile those specs, which can include generic bodies or any body implementing an inlined routine. In the case of stand-alone libraries those exposed units are called interface units (see Stand-alone Ada Libraries).
All compilation units comprising an application, including those in a library, need to be elaborated in an order partially defined by Ada's semantics. GNAT computes the elaboration order from the ALI files and this is why they constitute a mandatory part of GNAT libraries. Except in the case of stand-alone libraries, where a specific library elaboration routine is produced independently of the application(s) using the library.
The easiest way to build a library is to use the Project Manager, which supports a special type of project called a Library Project (see Library Projects).
A project is considered a library project, when two project-level attributes
are defined in it: Library_Name and Library_Dir. In order to
control different aspects of library configuration, additional optional
project-level attributes can be specified:
Library_KindLibrary_VersionLibrary_OptionsLibrary_GCCThe GNAT Project Manager takes full care of the library maintenance task, including recompilation of the source files for which objects do not exist or are not up to date, assembly of the library archive, and installation of the library (i.e., copying associated source, object and ALI files to the specified location).
Here is a simple library project file:
project My_Lib is
for Source_Dirs use ("src1", "src2");
for Object_Dir use "obj";
for Library_Name use "mylib";
for Library_Dir use "lib";
for Library_Kind use "dynamic";
end My_lib;
and the compilation command to build and install the library:
$ gnatmake -Pmy_lib
It is not entirely trivial to perform manually all the steps required to produce a library. We recommend that you use the GNAT Project Manager for this task. In special cases where this is not desired, the necessary steps are discussed below.
There are various possibilities for compiling the units that make up the library: for example with a Makefile (see Using the GNU make Utility) or with a conventional script. For simple libraries, it is also possible to create a dummy main program which depends upon all the packages that comprise the interface of the library. This dummy main program can then be given to gnatmake, which will ensure that all necessary objects are built.
After this task is accomplished, you should follow the standard procedure of the underlying operating system to produce the static or shared library.
Here is an example of such a dummy program:
with My_Lib.Service1;
with My_Lib.Service2;
with My_Lib.Service3;
procedure My_Lib_Dummy is
begin
null;
end;
Here are the generic commands that will build an archive or a shared library.
# compiling the library
$ gnatmake -c my_lib_dummy.adb
# we don't need the dummy object itself
$ rm my_lib_dummy.o my_lib_dummy.ali
# create an archive with the remaining objects
$ ar rc libmy_lib.a *.o
# some systems may require "ranlib" to be run as well
# or create a shared library
$ gcc -shared -o libmy_lib.so *.o
# some systems may require the code to have been compiled with -fPIC
# remove the object files that are now in the library
$ rm *.o
# Make the ALI files read-only so that gnatmake will not try to
# regenerate the objects that are in the library
$ chmod -w *.ali
Please note that the library must have a name of the form libxxx.a or libxxx.so (or libxxx.dll on Windows) in order to be accessed by the directive -lxxx at link time.
If you use project files, library installation is part of the library build
process. Thus no further action is needed in order to make use of the
libraries that are built as part of the general application build. A usable
version of the library is installed in the directory specified by the
Library_Dir attribute of the library project file.
You may want to install a library in a context different from where the library
is built. This situation arises with third party suppliers, who may want
to distribute a library in binary form where the user is not expected to be
able to recompile the library. The simplest option in this case is to provide
a project file slightly different from the one used to build the library, by
using the externally_built attribute. For instance, the project
file used to build the library in the previous section can be changed into the
following one when the library is installed:
project My_Lib is
for Source_Dirs use ("src1", "src2");
for Library_Name use "mylib";
for Library_Dir use "lib";
for Library_Kind use "dynamic";
for Externally_Built use "true";
end My_lib;
This project file assumes that the directories src1,
src2, and lib exist in
the directory containing the project file. The externally_built
attribute makes it clear to the GNAT builder that it should not attempt to
recompile any of the units from this library. It allows the library provider to
restrict the source set to the minimum necessary for clients to make use of the
library as described in the first section of this chapter. It is the
responsibility of the library provider to install the necessary sources, ALI
files and libraries in the directories mentioned in the project file. For
convenience, the user's library project file should be installed in a location
that will be searched automatically by the GNAT
builder. These are the directories referenced in the ADA_PROJECT_PATH
environment variable (see Importing Projects), and also the default GNAT
library location that can be queried with gnatls -v and is usually of
the form $gnat_install_root/lib/gnat.
When project files are not an option, it is also possible, but not recommended, to install the library so that the sources needed to use the library are on the Ada source path and the ALI files & libraries be on the Ada Object path (see Search Paths and the Run-Time Library (RTL). Alternatively, the system administrator can place general-purpose libraries in the default compiler paths, by specifying the libraries' location in the configuration files ada_source_path and ada_object_path. These configuration files must be located in the GNAT installation tree at the same place as the gcc spec file. The location of the gcc spec file can be determined as follows:
$ gcc -v
The configuration files mentioned above have a simple format: each line must contain one unique directory name. Those names are added to the corresponding path in their order of appearance in the file. The names can be either absolute or relative; in the latter case, they are relative to where theses files are located.
The files ada_source_path and ada_object_path might not be present in a GNAT installation, in which case, GNAT will look for its run-time library in the directories adainclude (for the sources) and adalib (for the objects and ALI files). When the files exist, the compiler does not look in adainclude and adalib, and thus the ada_source_path file must contain the location for the GNAT run-time sources (which can simply be adainclude). In the same way, the ada_object_path file must contain the location for the GNAT run-time objects (which can simply be adalib).
You can also specify a new default path to the run-time library at compilation time with the switch --RTS=rts-path. You can thus choose / change the run-time library you want your program to be compiled with. This switch is recognized by gcc, gnatmake, gnatbind, gnatls, gnatfind and gnatxref.
It is possible to install a library before or after the standard GNAT library, by reordering the lines in the configuration files. In general, a library must be installed before the GNAT library if it redefines any part of it.
Once again, the project facility greatly simplifies the use of
libraries. In this context, using a library is just a matter of adding a
with clause in the user project. For instance, to make use of the
library My_Lib shown in examples in earlier sections, you can
write:
with "my_lib";
project My_Proj is
...
end My_Proj;
Even if you have a third-party, non-Ada library, you can still use GNAT's
Project Manager facility to provide a wrapper for it. For example, the
following project, when withed by your main project, will link with the
third-party library liba.a:
project Liba is
for Externally_Built use "true";
for Source_Files use ();
for Library_Dir use "lib";
for Library_Name use "a";
for Library_Kind use "static";
end Liba;
This is an alternative to the use of pragma Linker_Options. It is
especially interesting in the context of systems with several interdependent
static libraries where finding a proper linker order is not easy and best be
left to the tools having visibility over project dependence information.
In order to use an Ada library manually, you need to make sure that this library is on both your source and object path (see Search Paths and the Run-Time Library (RTL) and Search Paths for gnatbind). Furthermore, when the objects are grouped in an archive or a shared library, you need to specify the desired library at link time.
For example, you can use the library mylib installed in /dir/my_lib_src and /dir/my_lib_obj with the following commands:
$ gnatmake -aI/dir/my_lib_src -aO/dir/my_lib_obj my_appl \
-largs -lmy_lib
This can be expressed more simply:
$ gnatmake my_appl
when the following conditions are met:
Linker_Options has been added to one of the sources.
For example:
pragma Linker_Options ("-lmy_lib");
A Stand-alone Library (abbreviated “SAL”) is a library that contains the necessary code to elaborate the Ada units that are included in the library. In contrast with an ordinary library, which consists of all sources, objects and ALI files of the library, a SAL may specify a restricted subset of compilation units to serve as a library interface. In this case, the fully self-sufficient set of files will normally consist of an objects archive, the sources of interface units' specs, and the ALI files of interface units. If an interface spec contains a generic unit or an inlined subprogram, the body's source must also be provided; if the units that must be provided in the source form depend on other units, the source and ALI files of those must also be provided.
The main purpose of a SAL is to minimize the recompilation overhead of client
applications when a new version of the library is installed. Specifically,
if the interface sources have not changed, client applications do not need to
be recompiled. If, furthermore, a SAL is provided in the shared form and its
version, controlled by Library_Version attribute, is not changed,
then the clients do not need to be relinked.
SALs also allow the library providers to minimize the amount of library source text exposed to the clients. Such “information hiding” might be useful or necessary for various reasons.
Stand-alone libraries are also well suited to be used in an executable whose main routine is not written in Ada.
GNAT's Project facility provides a simple way of building and installing
stand-alone libraries; see Stand-alone Library Projects.
To be a Stand-alone Library Project, in addition to the two attributes
that make a project a Library Project (Library_Name and
Library_Dir; see Library Projects), the attribute
Library_Interface must be defined. For example:
for Library_Dir use "lib_dir";
for Library_Name use "dummy";
for Library_Interface use ("int1", "int1.child");
Attribute Library_Interface has a non-empty string list value,
each string in the list designating a unit contained in an immediate source
of the project file.
When a Stand-alone Library is built, first the binder is invoked to build
a package whose name depends on the library name
(b~dummy.ads/b in the example above).
This binder-generated package includes initialization and
finalization procedures whose
names depend on the library name (dummyinit and dummyfinal
in the example
above). The object corresponding to this package is included in the library.
You must ensure timely (e.g., prior to any use of interfaces in the SAL)
calling of these procedures if a static SAL is built, or if a shared SAL
is built
with the project-level attribute Library_Auto_Init set to
"false".
For a Stand-Alone Library, only the ALI files of the Interface Units
(those that are listed in attribute Library_Interface) are copied to
the Library Directory. As a consequence, only the Interface Units may be
imported from Ada units outside of the library. If other units are imported,
the binding phase will fail.
The attribute Library_Src_Dir may be specified for a
Stand-Alone Library. Library_Src_Dir is a simple attribute that has a
single string value. Its value must be the path (absolute or relative to the
project directory) of an existing directory. This directory cannot be the
object directory or one of the source directories, but it can be the same as
the library directory. The sources of the Interface
Units of the library that are needed by an Ada client of the library will be
copied to the designated directory, called the Interface Copy directory.
These sources include the specs of the Interface Units, but they may also
include bodies and subunits, when pragmas Inline or Inline_Always
are used, or when there is a generic unit in the spec. Before the sources
are copied to the Interface Copy directory, an attempt is made to delete all
files in the Interface Copy directory.
Building stand-alone libraries by hand is somewhat tedious, but for those occasions when it is necessary here are the steps that you need to perform:
init
and final procedures. For example:
gnatbind -n int1.ali int2.ali -Lsal1
gcc -c b~int2.adb
init (and possibly
final) procedures for automatic initialization (and finalization).
The built library should be placed in a directory different from
the object directory.
ALI files of the interface to the library directory,
add in this copy an indication that it is an interface to a SAL
(i.e., add a word SL on the line in the ALI file that starts
with letter “P”) and make the modified copy of the ALI file
read-only.
Using SALs is not different from using other libraries (see Using a library).
It is easy to adapt the SAL build procedure discussed above for use of a SAL in a non-Ada context.
The only extra step required is to ensure that library interface subprograms
are compatible with the main program, by means of pragma Export
or pragma Convention.
Here is an example of simple library interface for use with C main program:
package Interface is
procedure Do_Something;
pragma Export (C, Do_Something, "do_something");
procedure Do_Something_Else;
pragma Export (C, Do_Something_Else, "do_something_else");
end Interface;
On the foreign language side, you must provide a “foreign” view of the library interface; remember that it should contain elaboration routines in addition to interface subprograms.
The example below shows the content of mylib_interface.h (note
that there is no rule for the naming of this file, any name can be used)
/* the library elaboration procedure */
extern void mylibinit (void);
/* the library finalization procedure */
extern void mylibfinal (void);
/* the interface exported by the library */
extern void do_something (void);
extern void do_something_else (void);
Libraries built as explained above can be used from any program, provided
that the elaboration procedures (named mylibinit in the previous
example) are called before the library services are used. Any number of
libraries can be used simultaneously, as long as the elaboration
procedure of each library is called.
Below is an example of a C program that uses the mylib library.
#include "mylib_interface.h"
int
main (void)
{
/* First, elaborate the library before using it */
mylibinit ();
/* Main program, using the library exported entities */
do_something ();
do_something_else ();
/* Library finalization at the end of the program */
mylibfinal ();
return 0;
}
Note that invoking any library finalization procedure generated by
gnatbind shuts down the Ada run-time environment.
Consequently, the
finalization of all Ada libraries must be performed at the end of the program.
No call to these libraries or to the Ada run-time library should be made
after the finalization phase.
The pragmas listed below should be used with caution inside libraries, as they can create incompatibilities with other Ada libraries:
Locking_Policy
Queuing_Policy
Task_Dispatching_Policy
Unreserve_All_Interrupts
When using a library that contains such pragmas, the user must make sure
that all libraries use the same pragmas with the same values. Otherwise,
Program_Error will
be raised during the elaboration of the conflicting
libraries. The usage of these pragmas and its consequences for the user
should therefore be well documented.
Similarly, the traceback in the exception occurrence mechanism should be enabled or disabled in a consistent manner across all libraries. Otherwise, Program_Error will be raised during the elaboration of the conflicting libraries.
If the Version or Body_Version
attributes are used inside a library, then you need to
perform a gnatbind step that specifies all ALI files in all
libraries, so that version identifiers can be properly computed.
In practice these attributes are rarely used, so this is unlikely
to be a consideration.
It may be useful to recompile the GNAT library in various contexts, the
most important one being the use of partition-wide configuration pragmas
such as Normalize_Scalars. A special Makefile called
Makefile.adalib is provided to that effect and can be found in
the directory containing the GNAT library. The location of this
directory depends on the way the GNAT environment has been installed and can
be determined by means of the command:
$ gnatls -v
The last entry in the object search path usually contains the gnat library. This Makefile contains its own documentation and in particular the set of instructions needed to rebuild a new library and to use it.
make UtilityThis chapter offers some examples of makefiles that solve specific problems. It does not explain how to write a makefile (see GNU make), nor does it try to replace the gnatmake utility (see The GNAT Make Program gnatmake).
All the examples in this section are specific to the GNU version of
make. Although make is a standard utility, and the basic language
is the same, these examples use some advanced features found only in
GNU make.
Complex project organizations can be handled in a very powerful way by using GNU make combined with gnatmake. For instance, here is a Makefile which allows you to build each subsystem of a big project into a separate shared library. Such a makefile allows you to significantly reduce the link time of very big applications while maintaining full coherence at each step of the build process.
The list of dependencies are handled automatically by gnatmake. The Makefile is simply used to call gnatmake in each of the appropriate directories.
Note that you should also read the example on how to automatically create the list of directories (see Automatically Creating a List of Directories) which might help you in case your project has a lot of subdirectories.
## This Makefile is intended to be used with the following directory
## configuration:
## - The sources are split into a series of csc (computer software components)
## Each of these csc is put in its own directory.
## Their name are referenced by the directory names.
## They will be compiled into shared library (although this would also work
## with static libraries
## - The main program (and possibly other packages that do not belong to any
## csc is put in the top level directory (where the Makefile is).
## toplevel_dir __ first_csc (sources) __ lib (will contain the library)
## \_ second_csc (sources) __ lib (will contain the library)
## \_ ...
## Although this Makefile is build for shared library, it is easy to modify
## to build partial link objects instead (modify the lines with -shared and
## gnatlink below)
##
## With this makefile, you can change any file in the system or add any new
## file, and everything will be recompiled correctly (only the relevant shared
## objects will be recompiled, and the main program will be re-linked).
# The list of computer software component for your project. This might be
# generated automatically.
CSC_LIST=aa bb cc
# Name of the main program (no extension)
MAIN=main
# If we need to build objects with -fPIC, uncomment the following line
#NEED_FPIC=-fPIC
# The following variable should give the directory containing libgnat.so
# You can get this directory through 'gnatls -v'. This is usually the last
# directory in the Object_Path.
GLIB=...
# The directories for the libraries
# (This macro expands the list of CSC to the list of shared libraries, you
# could simply use the expanded form:
# LIB_DIR=aa/lib/libaa.so bb/lib/libbb.so cc/lib/libcc.so
LIB_DIR=${foreach dir,${CSC_LIST},${dir}/lib/lib${dir}.so}
${MAIN}: objects ${LIB_DIR}
gnatbind ${MAIN} ${CSC_LIST:%=-aO%/lib} -shared
gnatlink ${MAIN} ${CSC_LIST:%=-l%}
objects::
# recompile the sources
gnatmake -c -i ${MAIN}.adb ${NEED_FPIC} ${CSC_LIST:%=-I%}
# Note: In a future version of GNAT, the following commands will be simplified
# by a new tool, gnatmlib
${LIB_DIR}:
mkdir -p ${dir $@ }
cd ${dir $@ } && gcc -shared -o ${notdir $@ } ../*.o -L${GLIB} -lgnat
cd ${dir $@ } && cp -f ../*.ali .
# The dependencies for the modules
# Note that we have to force the expansion of *.o, since in some cases
# make won't be able to do it itself.
aa/lib/libaa.so: ${wildcard aa/*.o}
bb/lib/libbb.so: ${wildcard bb/*.o}
cc/lib/libcc.so: ${wildcard cc/*.o}
# Make sure all of the shared libraries are in the path before starting the
# program
run::
LD_LIBRARY_PATH=`pwd`/aa/lib:`pwd`/bb/lib:`pwd`/cc/lib ./${MAIN}
clean::
${RM} -rf ${CSC_LIST:%=%/lib}
${RM} ${CSC_LIST:%=%/*.ali}
${RM} ${CSC_LIST:%=%/*.o}
${RM} *.o *.ali ${MAIN}
In most makefiles, you will have to specify a list of directories, and store it in a variable. For small projects, it is often easier to specify each of them by hand, since you then have full control over what is the proper order for these directories, which ones should be included.
However, in larger projects, which might involve hundreds of subdirectories, it might be more convenient to generate this list automatically.
The example below presents two methods. The first one, although less general, gives you more control over the list. It involves wildcard characters, that are automatically expanded by make. Its shortcoming is that you need to explicitly specify some of the organization of your project, such as for instance the directory tree depth, whether some directories are found in a separate tree, ...
The second method is the most general one. It requires an external program, called find, which is standard on all Unix systems. All the directories found under a given root directory will be added to the list.
# The examples below are based on the following directory hierarchy:
# All the directories can contain any number of files
# ROOT_DIRECTORY -> a -> aa -> aaa
# -> ab
# -> ac
# -> b -> ba -> baa
# -> bb
# -> bc
# This Makefile creates a variable called DIRS, that can be reused any time
# you need this list (see the other examples in this section)
# The root of your project's directory hierarchy
ROOT_DIRECTORY=.
####
# First method: specify explicitly the list of directories
# This allows you to specify any subset of all the directories you need.
####
DIRS := a/aa/ a/ab/ b/ba/
####
# Second method: use wildcards
# Note that the argument(s) to wildcard below should end with a '/'.
# Since wildcards also return file names, we have to filter them out
# to avoid duplicate directory names.
# We thus use make's dir and sort functions.
# It sets DIRs to the following value (note that the directories aaa and baa
# are not given, unless you change the arguments to wildcard).
# DIRS= ./a/a/ ./b/ ./a/aa/ ./a/ab/ ./a/ac/ ./b/ba/ ./b/bb/ ./b/bc/
####
DIRS := ${sort ${dir ${wildcard ${ROOT_DIRECTORY}/*/
${ROOT_DIRECTORY}/*/*/}}}
####
# Third method: use an external program
# This command is much faster if run on local disks, avoiding NFS slowdowns.
# This is the most complete command: it sets DIRs to the following value:
# DIRS= ./a ./a/aa ./a/aa/aaa ./a/ab ./a/ac ./b ./b/ba ./b/ba/baa ./b/bb ./b/bc
####
DIRS := ${shell find ${ROOT_DIRECTORY} -type d -print}
Once you have created the list of directories as explained in the previous section (see Automatically Creating a List of Directories), you can easily generate the command line arguments to pass to gnatmake.
For the sake of completeness, this example assumes that the source path is not the same as the object path, and that you have two separate lists of directories.
# see "Automatically creating a list of directories" to create
# these variables
SOURCE_DIRS=
OBJECT_DIRS=
GNATMAKE_SWITCHES := ${patsubst %,-aI%,${SOURCE_DIRS}}
GNATMAKE_SWITCHES += ${patsubst %,-aO%,${OBJECT_DIRS}}
all:
gnatmake ${GNATMAKE_SWITCHES} main_unit
One problem that might be encountered on big projects is that many operating systems limit the length of the command line. It is thus hard to give gnatmake the list of source and object directories.
This example shows how you can set up environment variables, which will make gnatmake behave exactly as if the directories had been specified on the command line, but have a much higher length limit (or even none on most systems).
It assumes that you have created a list of directories in your Makefile, using one of the methods presented in Automatically Creating a List of Directories. For the sake of completeness, we assume that the object path (where the ALI files are found) is different from the sources patch.
Note a small trick in the Makefile below: for efficiency reasons, we
create two temporary variables (SOURCE_LIST and OBJECT_LIST), that are
expanded immediately by make. This way we overcome the standard
make behavior which is to expand the variables only when they are
actually used.
On Windows, if you are using the standard Windows command shell, you must replace colons with semicolons in the assignments to these variables.
# In this example, we create both ADA_INCLUDE_PATH and ADA_OBJECT_PATH.
# This is the same thing as putting the -I arguments on the command line.
# (the equivalent of using -aI on the command line would be to define
# only ADA_INCLUDE_PATH, the equivalent of -aO is ADA_OBJECT_PATH).
# You can of course have different values for these variables.
#
# Note also that we need to keep the previous values of these variables, since
# they might have been set before running 'make' to specify where the GNAT
# library is installed.
# see "Automatically creating a list of directories" to create these
# variables
SOURCE_DIRS=
OBJECT_DIRS=
empty:=
space:=${empty} ${empty}
SOURCE_LIST := ${subst ${space},:,${SOURCE_DIRS}}
OBJECT_LIST := ${subst ${space},:,${OBJECT_DIRS}}
ADA_INCLUDE_PATH += ${SOURCE_LIST}
ADA_OBJECT_PATH += ${OBJECT_LIST}
export ADA_INCLUDE_PATH
export ADA_OBJECT_PATH
all:
gnatmake main_unit
This chapter describes some useful memory pools provided in the GNAT library and in particular the GNAT Debug Pool facility, which can be used to detect incorrect uses of access values (including “dangling references”). It also describes the gnatmem tool, which can be used to track down “memory leaks”.
The System.Pool_Global package offers the Unbounded_No_Reclaim_Pool
storage pool. Allocations use the standard system call malloc while
deallocations use the standard system call free. No reclamation is
performed when the pool goes out of scope. For performance reasons, the
standard default Ada allocators/deallocators do not use any explicit storage
pools but if they did, they could use this storage pool without any change in
behavior. That is why this storage pool is used when the user
manages to make the default implicit allocator explicit as in this example:
type T1 is access Something;
-- no Storage pool is defined for T2
type T2 is access Something_Else;
for T2'Storage_Pool use T1'Storage_Pool;
-- the above is equivalent to
for T2'Storage_Pool use System.Pool_Global.Global_Pool_Object;
The System.Pool_Local package offers the Unbounded_Reclaim_Pool storage
pool. The allocation strategy is similar to Pool_Local's
except that the all
storage allocated with this pool is reclaimed when the pool object goes out of
scope. This pool provides a explicit mechanism similar to the implicit one
provided by several Ada 83 compilers for allocations performed through a local
access type and whose purpose was to reclaim memory when exiting the
scope of a given local access. As an example, the following program does not
leak memory even though it does not perform explicit deallocation:
with System.Pool_Local;
procedure Pooloc1 is
procedure Internal is
type A is access Integer;
X : System.Pool_Local.Unbounded_Reclaim_Pool;
for A'Storage_Pool use X;
v : A;
begin
for I in 1 .. 50 loop
v := new Integer;
end loop;
end Internal;
begin
for I in 1 .. 100 loop
Internal;
end loop;
end Pooloc1;
The System.Pool_Size package implements the Stack_Bounded_Pool used when
Storage_Size is specified for an access type.
The whole storage for the pool is
allocated at once, usually on the stack at the point where the access type is
elaborated. It is automatically reclaimed when exiting the scope where the
access type is defined. This package is not intended to be used directly by the
user and it is implicitly used for each such declaration:
type T1 is access Something;
for T1'Storage_Size use 10_000;
The use of unchecked deallocation and unchecked conversion can easily
lead to incorrect memory references. The problems generated by such
references are usually difficult to tackle because the symptoms can be
very remote from the origin of the problem. In such cases, it is
very helpful to detect the problem as early as possible. This is the
purpose of the Storage Pool provided by GNAT.Debug_Pools.
In order to use the GNAT specific debugging pool, the user must associate a debug pool object with each of the access types that may be related to suspected memory problems. See Ada Reference Manual 13.11.
type Ptr is access Some_Type;
Pool : GNAT.Debug_Pools.Debug_Pool;
for Ptr'Storage_Pool use Pool;
GNAT.Debug_Pools is derived from a GNAT-specific kind of
pool: the Checked_Pool. Such pools, like standard Ada storage pools,
allow the user to redefine allocation and deallocation strategies. They
also provide a checkpoint for each dereference, through the use of
the primitive operation Dereference which is implicitly called at
each dereference of an access value.
Once an access type has been associated with a debug pool, operations on values of the type may raise four distinct exceptions, which correspond to four potential kinds of memory corruption:
GNAT.Debug_Pools.Accessing_Not_Allocated_Storage
GNAT.Debug_Pools.Accessing_Deallocated_Storage
GNAT.Debug_Pools.Freeing_Not_Allocated_Storage
GNAT.Debug_Pools.Freeing_Deallocated_Storage
For types associated with a Debug_Pool, dynamic allocation is performed using
the standard GNAT allocation routine. References to all allocated chunks of
memory are kept in an internal dictionary. Several deallocation strategies are
provided, whereupon the user can choose to release the memory to the system,
keep it allocated for further invalid access checks, or fill it with an easily
recognizable pattern for debug sessions. The memory pattern is the old IBM
hexadecimal convention: 16#DEADBEEF#.
See the documentation in the file g-debpoo.ads for more information on the various strategies.
Upon each dereference, a check is made that the access value denotes a
properly allocated memory location. Here is a complete example of use of
Debug_Pools, that includes typical instances of memory corruption:
with Gnat.Io; use Gnat.Io;
with Unchecked_Deallocation;
with Unchecked_Conversion;
with GNAT.Debug_Pools;
with System.Storage_Elements;
with Ada.Exceptions; use Ada.Exceptions;
procedure Debug_Pool_Test is
type T is access Integer;
type U is access all T;
P : GNAT.Debug_Pools.Debug_Pool;
for T'Storage_Pool use P;
procedure Free is new Unchecked_Deallocation (Integer, T);
function UC is new Unchecked_Conversion (U, T);
A, B : aliased T;
procedure Info is new GNAT.Debug_Pools.Print_Info(Put_Line);
begin
Info (P);
A := new Integer;
B := new Integer;
B := A;
Info (P);
Free (A);
begin
Put_Line (Integer'Image(B.all));
exception
when E : others => Put_Line ("raised: " & Exception_Name (E));
end;
begin
Free (B);
exception
when E : others => Put_Line ("raised: " & Exception_Name (E));
end;
B := UC(A'Access);
begin
Put_Line (Integer'Image(B.all));
exception
when E : others => Put_Line ("raised: " & Exception_Name (E));
end;
begin
Free (B);
exception
when E : others => Put_Line ("raised: " & Exception_Name (E));
end;
Info (P);
end Debug_Pool_Test;
The debug pool mechanism provides the following precise diagnostics on the execution of this erroneous program:
Debug Pool info:
Total allocated bytes : 0
Total deallocated bytes : 0
Current Water Mark: 0
High Water Mark: 0
Debug Pool info:
Total allocated bytes : 8
Total deallocated bytes : 0
Current Water Mark: 8
High Water Mark: 8
raised: GNAT.DEBUG_POOLS.ACCESSING_DEALLOCATED_STORAGE
raised: GNAT.DEBUG_POOLS.FREEING_DEALLOCATED_STORAGE
raised: GNAT.DEBUG_POOLS.ACCESSING_NOT_ALLOCATED_STORAGE
raised: GNAT.DEBUG_POOLS.FREEING_NOT_ALLOCATED_STORAGE
Debug Pool info:
Total allocated bytes : 8
Total deallocated bytes : 4
Current Water Mark: 4
High Water Mark: 8
The gnatmem utility monitors dynamic allocation and
deallocation activity in a program, and displays information about
incorrect deallocations and possible sources of memory leaks.
It provides three type of information:
gnatmemgnatmem makes use of the output created by the special version of
allocation and deallocation routines that record call information. This
allows to obtain accurate dynamic memory usage history at a minimal cost to
the execution speed. Note however, that gnatmem is not supported on
all platforms (currently, it is supported on AIX, HP-UX, GNU/Linux,
Solaris and Windows NT/2000/XP (x86).
The gnatmem command has the form
$ gnatmem [switches] user_program
The program must have been linked with the instrumented version of the allocation and deallocation routines. This is done by linking with the libgmem.a library. For correct symbolic backtrace information, the user program should be compiled with debugging options (see Switches for gcc). For example to build my_program:
$ gnatmake -g my_program -largs -lgmem
As library libgmem.a contains an alternate body for package
System.Memory, s-memory.adb should not be compiled and linked
when an executable is linked with library libgmem.a. It is then not
recommended to use gnatmake with switch -a.
When my_program is executed, the file gmem.out is produced.
This file contains information about all allocations and deallocations
performed by the program. It is produced by the instrumented allocations and
deallocations routines and will be used by gnatmem.
In order to produce symbolic backtrace information for allocations and deallocations performed by the GNAT run-time library, you need to use a version of that library that has been compiled with the -g switch (see Rebuilding the GNAT Run-Time Library).
Gnatmem must be supplied with the gmem.out file and the executable to
examine. If the location of gmem.out file was not explicitly supplied by
-i switch, gnatmem will assume that this file can be found in the
current directory. For example, after you have executed my_program,
gmem.out can be analyzed by gnatmem using the command:
$ gnatmem my_program
This will produce the output with the following format:
*************** debut cc
$ gnatmem my_program
Global information
------------------
Total number of allocations : 45
Total number of deallocations : 6
Final Water Mark (non freed mem) : 11.29 Kilobytes
High Water Mark : 11.40 Kilobytes
.
.
.
Allocation Root # 2
-------------------
Number of non freed allocations : 11
Final Water Mark (non freed mem) : 1.16 Kilobytes
High Water Mark : 1.27 Kilobytes
Backtrace :
my_program.adb:23 my_program.alloc
.
.
.
The first block of output gives general information. In this case, the Ada construct “new” was executed 45 times, and only 6 calls to an Unchecked_Deallocation routine occurred.
Subsequent paragraphs display information on all allocation roots. An allocation root is a specific point in the execution of the program that generates some dynamic allocation, such as a “new” construct. This root is represented by an execution backtrace (or subprogram call stack). By default the backtrace depth for allocations roots is 1, so that a root corresponds exactly to a source location. The backtrace can be made deeper, to make the root more specific.
gnatmemgnatmem recognizes the following switches:
gnatmem processing starting from file, rather than
gmem.out in the current directory.
gnatmem to mask the allocation roots that have less
than n leaks. The default value is 1. Specifying the value of 0 will allow to
examine even the roots that didn't result in leaks.
gnatmem to sort the allocation roots according to the
specified order of sort criteria, each identified by a single letter. The
currently supported criteria are n, h, w standing respectively for
number of unfreed allocations, high watermark, and final watermark
corresponding to a specific root. The default order is nwh.
gnatmem UsageThe following example shows the use of gnatmem
on a simple memory-leaking program.
Suppose that we have the following Ada program:
| with Unchecked_Deallocation; procedure Test_Gm is type T is array (1..1000) of Integer; type Ptr is access T; procedure Free is new Unchecked_Deallocation (T, Ptr); A : Ptr; procedure My_Alloc is begin A := new T; end My_Alloc; procedure My_DeAlloc is B : Ptr := A; begin Free (B); end My_DeAlloc; begin My_Alloc; for I in 1 .. 5 loop for J in I .. 5 loop My_Alloc; end loop; My_Dealloc; end loop; end; |
The program needs to be compiled with debugging option and linked with
gmem library:
$ gnatmake -g test_gm -largs -lgmem
Then we execute the program as usual:
$ test_gm
Then gnatmem is invoked simply with
$ gnatmem test_gm
which produces the following output (result may vary on different platforms):
Global information
------------------
Total number of allocations : 18
Total number of deallocations : 5
Final Water Mark (non freed mem) : 53.00 Kilobytes
High Water Mark : 56.90 Kilobytes
Allocation Root # 1
-------------------
Number of non freed allocations : 11
Final Water Mark (non freed mem) : 42.97 Kilobytes
High Water Mark : 46.88 Kilobytes
Backtrace :
test_gm.adb:11 test_gm.my_alloc
Allocation Root # 2
-------------------
Number of non freed allocations : 1
Final Water Mark (non freed mem) : 10.02 Kilobytes
High Water Mark : 10.02 Kilobytes
Backtrace :
s-secsta.adb:81 system.secondary_stack.ss_init
Allocation Root # 3
-------------------
Number of non freed allocations : 1
Final Water Mark (non freed mem) : 12 Bytes
High Water Mark : 12 Bytes
Backtrace :
s-secsta.adb:181 system.secondary_stack.ss_init
Note that the GNAT run time contains itself a certain number of allocations that have no corresponding deallocation, as shown here for root #2 and root #3. This is a normal behavior when the number of non-freed allocations is one, it allocates dynamic data structures that the run time needs for the complete lifetime of the program. Note also that there is only one allocation root in the user program with a single line back trace: test_gm.adb:11 test_gm.my_alloc, whereas a careful analysis of the program shows that 'My_Alloc' is called at 2 different points in the source (line 21 and line 24). If those two allocation roots need to be distinguished, the backtrace depth parameter can be used:
$ gnatmem 3 test_gm
which will give the following output:
Global information
------------------
Total number of allocations : 18
Total number of deallocations : 5
Final Water Mark (non freed mem) : 53.00 Kilobytes
High Water Mark : 56.90 Kilobytes
Allocation Root # 1
-------------------
Number of non freed allocations : 10
Final Water Mark (non freed mem) : 39.06 Kilobytes
High Water Mark : 42.97 Kilobytes
Backtrace :
test_gm.adb:11 test_gm.my_alloc
test_gm.adb:24 test_gm
b_test_gm.c:52 main
Allocation Root # 2
-------------------
Number of non freed allocations : 1
Final Water Mark (non freed mem) : 10.02 Kilobytes
High Water Mark : 10.02 Kilobytes
Backtrace :
s-secsta.adb:81 system.secondary_stack.ss_init
s-secsta.adb:283 <system__secondary_stack___elabb>
b_test_gm.c:33 adainit
Allocation Root # 3
-------------------
Number of non freed allocations : 1
Final Water Mark (non freed mem) : 3.91 Kilobytes
High Water Mark : 3.91 Kilobytes
Backtrace :
test_gm.adb:11 test_gm.my_alloc
test_gm.adb:21 test_gm
b_test_gm.c:52 main
Allocation Root # 4
-------------------
Number of non freed allocations : 1
Final Water Mark (non freed mem) : 12 Bytes
High Water Mark : 12 Bytes
Backtrace :
s-secsta.adb:181 system.secondary_stack.ss_init
s-secsta.adb:283 <system__secondary_stack___elabb>
b_test_gm.c:33 adainit
The allocation root #1 of the first example has been split in 2 roots #1 and #3 thanks to the more precise associated backtrace.
This chapter describes some useful tools associated with stack checking and analysis. In particular, it deals with dynamic and static stack usage measurements.
For most operating systems, gcc does not perform stack overflow checking by default. This means that if the main environment task or some other task exceeds the available stack space, then unpredictable behavior will occur. Most native systems offer some level of protection by adding a guard page at the end of each task stack. This mechanism is usually not enough for dealing properly with stack overflow situations because a large local variable could “jump” above the guard page. Furthermore, when the guard page is hit, there may not be any space left on the stack for executing the exception propagation code. Enabling stack checking avoids such situations.
To activate stack checking, compile all units with the gcc option -fstack-check. For example:
gcc -c -fstack-check package1.adb
Units compiled with this option will generate extra instructions to check
that any use of the stack (for procedure calls or for declaring local
variables in declare blocks) does not exceed the available stack space.
If the space is exceeded, then a Storage_Error exception is raised.
For declared tasks, the stack size is controlled by the size
given in an applicable Storage_Size pragma or by the value specified
at bind time with -d (see Switches for gnatbind) or is set to
the default size as defined in the GNAT runtime otherwise.
For the environment task, the stack size depends on system defaults and is unknown to the compiler. Stack checking may still work correctly if a fixed size stack is allocated, but this cannot be guaranteed. To ensure that a clean exception is signalled for stack overflow, set the environment variable GNAT_STACK_LIMIT to indicate the maximum stack area that can be used, as in:
SET GNAT_STACK_LIMIT 1600
The limit is given in kilobytes, so the above declaration would set the stack limit of the environment task to 1.6 megabytes. Note that the only purpose of this usage is to limit the amount of stack used by the environment task. If it is necessary to increase the amount of stack for the environment task, then this is an operating systems issue, and must be addressed with the appropriate operating systems commands.
A unit compiled with -fstack-usage will generate an extra file that specifies the maximum amount of stack used, on a per-function basis. The file has the same basename as the target object file with a .su extension. Each line of this file is made up of three fields:
static, dynamic, bounded.
The second field corresponds to the size of the known part of the function frame.
The qualifier static means that the function frame size
is purely static.
It usually means that all local variables have a static size.
In this case, the second field is a reliable measure of the function stack
utilization.
The qualifier dynamic means that the function frame size is not static.
It happens mainly when some local variables have a dynamic size. When this
qualifier appears alone, the second field is not a reliable measure
of the function stack analysis. When it is qualified with bounded, it
means that the second field is a reliable maximum of the function stack
utilization.
It is possible to measure the maximum amount of stack used by a task, by adding a switch to gnatbind, as:
$ gnatbind -u0 file
With this option, at each task termination, its stack usage is output on stderr. It is not always convenient to output the stack usage when the program is still running. Hence, it is possible to delay this output until program termination. for a given number of tasks specified as the argument of the -u option. For instance:
$ gnatbind -u100 file
will buffer the stack usage information of the first 100 tasks to terminate and output this info at program termination. Results are displayed in four columns:
Index | Task Name | Stack Size | Actual Use [min - max]
where:
The environment task stack, e.g., the stack that contains the main unit, is only processed when the environment variable GNAT_STACK_LIMIT is set.
The gnatcheck tool is an ASIS-based utility that checks properties of Ada source files according to a given set of semantic rules. In order to check compliance with a given rule, gnatcheck has to semantically analyze the Ada sources. Therefore, checks can only be performed on legal Ada units. Moreover, when a unit depends semantically upon units located outside the current directory, the source search path has to be provided when calling gnatcheck, either through a specified project file or through gnatcheck switches as described below.
A number of rules are predefined in gnatcheck and are described later in this chapter. You can also add new rules, by modifying the gnatcheck code and rebuilding the tool. In order to add a simple rule making some local checks, a small amount of straightforward ASIS-based programming is usually needed.
Project support for gnatcheck is provided by the GNAT driver (see The GNAT Driver and Project Files).
Invoking gnatcheck on the command line has the form:
$ gnatcheck [switches] {filename} [-files={arg_list_filename}] [-cargs gcc_switches] [-rules rule_options]
where
Either a filename or an arg_list_filename must be supplied.
The gnatcheck tool outputs on stdout all messages concerning rule violations. It also creates, in the current directory, a text file named gnatcheck.out that contains the complete report of the last gnatcheck run. This report contains:
The following switches control the general gnatcheck behavior
Note that if any of the options -s1, -s2 or -s3 is specified, then the gnatcheck report file will only contain sections explicitly denoted by these options.
The following options control the processing performed by gnatcheck.
The default behavior is that all the rule checks are disabled.
A rule file is a text file containing a set of rule options. The file may contain empty lines and Ada-style comments (comment lines and end-of-line comments). The rule file has free format; that is, you do not have to start a new rule option on a new line.
A rule file may contain other -from=rule_option_filename options, each such option being replaced with the content of the corresponding rule file during the rule files processing. In case a cycle is detected (that is, rule_file_1 reads rule options from rule_file_2, and rule_file_2 reads (directly or indirectly) rule options from rule_file_1), the processing of rule files is interrupted and a part of their content is ignored.
The gnatcheck tool can include in the generated diagnostic messages and in the report file the results of the checks performed by the compiler. Though disabled by default, this effect may be obtained by using +R with the following rule identifiers and parameters:
Restrictions or Restriction_Warnings are given),
use the rule named
Restrictions with the same parameters as pragma
Restrictions or Restriction_Warnings.
Style_Checks. A parameter of this rule can be either All_Checks,
which enables all the standard style checks that corresponds to -gnatyy
GNAT style check option, or a string that has exactly the same
structure and semantics as the string_LITERAL parameter of GNAT pragma
Style_Checks (for further information about this pragma,
see Pragma Style_Checks).
Warnings with a parameter that is a valid
static_string_expression argument of GNAT pragma Warnings
(for further information about this pragma, see Pragma Warnings). Note, that in case of gnatcheck
's' parameter, that corresponds to the GNAT -gnatws option, disables
all the specific warnings, but not suppresses the warning mode,
and 'e' parameter, corresponding to -gnatwe that means
"treat warnings as errors", does not have any effect.
To disable a specific restriction check, use -RStyle_Checks gnatcheck
option with the corresponding restriction name as a parameter. -R is
not available for Style_Checks and Warnings options, to disable
warnings and style checks, use the corresponding warning and style options.
In order to perform checks on all units of a given project, you can use the GNAT driver along with the -P option:
gnat check -Pproj -rules -from=my_rules
If the project proj depends upon other projects, you can perform
checks on the project closure using the -U option:
gnat check -Pproj -U -rules -from=my_rules
Finally, if not all the units are relevant to a particular main program in the project closure, you can perform checks for the set of units needed to create a given main program (unit closure) using the -U option followed by the name of the main unit:
gnat check -Pproj -U main -rules -from=my_rules
The following subsections document the rules implemented in gnatcheck. The subsection title is the same as the rule identifier, which may be used as a parameter of the +R or -R options.
Abstract_Type_DeclarationsFlag all declarations of abstract types. For an abstract private type, both the private and full type declarations are flagged.
This rule has no parameters.
Anonymous_ArraysFlag all anonymous array type definitions (by Ada semantics these can only occur in object declarations).
This rule has no parameters.
Anonymous_SubtypesFlag all uses of anonymous subtypes. A use of an anonymous subtype is any instance of a subtype indication with a constraint, other than one that occurs immediately within a subtype declaration. Any use of a range other than as a constraint used immediately within a subtype declaration is considered as an anonymous subtype.
An effect of this rule is that for loops such as the following are
flagged (since 1..N is formally a “range”):
for I in 1 .. N loop
...
end loop;
Declaring an explicit subtype solves the problem:
subtype S is Integer range 1..N;
...
for I in S loop
...
end loop;
This rule has no parameters.
BlocksThis rule has no parameters.
Boolean_Relational_OperatorsFlag each call to a predefined relational operator (“<”, “>”, “<=”, “>=”, “=” and “/=”) for the predefined Boolean type. (This rule is useful in enforcing the SPARK language restrictions.)
Calls to predefined relational operators of any type derived from
Standard.Boolean are not detected. Calls to user-defined functions
with these designators, and uses of operators that are renamings
of the predefined relational operators for Standard.Boolean,
are likewise not detected.
This rule has no parameters.
Controlled_Type_Declarations
Flag all declarations of controlled types. A declaration of a private type
is flagged if its full declaration declares a controlled type. A declaration
of a derived type is flagged if its ancestor type is controlled. Subtype
declarations are not checked. A declaration of a type that itself is not a
descendant of a type declared in Ada.Finalization but has a controlled
component is not checked.
This rule has no parameters.
Declarations_In_Blocks
Flag all block statements containing local declarations. A declare
block with an empty declarative_part or with a declarative part
containing only pragmas and/or use clauses is not flagged.
This rule has no parameters.
Default_ParametersFlag all default expressions for subprogram parameters. Parameter declarations of formal and generic subprograms are also checked.
This rule has no parameters.
Discriminated_RecordsFlag all declarations of record types with discriminants. Only the declarations of record and record extension types are checked. Incomplete, formal, private, derived and private extension type declarations are not checked. Task and protected type declarations also are not checked.
This rule has no parameters.
Enumeration_Ranges_In_CASE_Statements
Flag each use of a range of enumeration literals as a choice in a
case statement.
All forms for specifying a range (explicit ranges
such as A .. B, subtype marks and 'Range attributes) are flagged.
An enumeration range is
flagged even if contains exactly one enumeration value or no values at all. A
type derived from an enumeration type is considered as an enumeration type.
This rule helps prevent maintenance problems arising from adding an
enumeration value to a type and having it implicitly handled by an existing
case statement with an enumeration range that includes the new literal.
This rule has no parameters.
Exceptions_As_Control_Flow
Flag each place where an exception is explicitly raised and handled in the
same subprogram body. A raise statement in an exception handler,
package body, task body or entry body is not flagged.
The rule has no parameters.
EXIT_Statements_With_No_Loop_Name
Flag each exit statement that does not specify the name of the loop
being exited.
The rule has no parameters.
Expanded_Loop_Exit_Names
Flag all expanded loop names in exit statements.
This rule has no parameters.
Explicit_Full_Discrete_Ranges
Flag each discrete range that has the form A'First .. A'Last.
This rule has no parameters.
Float_Equality_Checks
Flag all calls to the predefined equality operations for floating-point types.
Both “=” and “/=” operations are checked.
User-defined equality operations are not flagged, nor are “=”
and “/=” operations for fixed-point types.
This rule has no parameters.
Forbidden_PragmasFlag each use of the specified pragmas. The pragmas to be detected are named in the rule's parameters.
This rule has the following parameters:
GNATALLParameters are not case sensitive. If Pragma_Name does not have the syntax of an Ada identifier and therefore can not be considered as a pragma name, a diagnostic message is generated and the corresponding parameter is ignored.
When more then one parameter is given in the same rule option, the parameters must be separated by a comma.
If more then one option for this rule is specified for the gnatcheck call, a new option overrides the previous one(s).
The +R option with no parameters turns the rule ON with the set of pragmas to be detected defined by the previous rule options. (By default this set is empty, so if the only option specified for the rule is +RForbidden_Pragmas (with no parameter), then the rule is enabled, but it does not detect anything). The -R option with no parameter turns the rule OFF, but it does not affect the set of pragmas to be detected.
Function_Style_Procedures
Flag each procedure that can be rewritten as a function. A procedure can be
converted into a function if it has exactly one parameter of mode out
and no parameters of mode in out. Procedure declarations,
formal procedure declarations, and generic procedure declarations are always
checked. Procedure
bodies and body stubs are flagged only if they do not have corresponding
separate declarations. Procedure renamings and procedure instantiations are
not flagged.
If a procedure can be rewritten as a function, but its out parameter is
of a limited type, it is not flagged.
Protected procedures are not flagged. Null procedures also are not flagged.
This rule has no parameters.
Generics_In_SubprogramsFlag each declaration of a generic unit in a subprogram. Generic declarations in the bodies of generic subprograms are also flagged. A generic unit nested in another generic unit is not flagged. If a generic unit is declared in a local package that is declared in a subprogram body, the generic unit is flagged.
This rule has no parameters.
GOTO_Statements
Flag each occurrence of a goto statement.
This rule has no parameters.
Implicit_IN_Mode_Parameters
Flag each occurrence of a formal parameter with an implicit in mode.
Note that access parameters, although they technically behave
like in parameters, are not flagged.
This rule has no parameters.
Implicit_SMALL_For_Fixed_Point_Types
Flag each fixed point type declaration that lacks an explicit
representation clause to define its 'Small value.
Since 'Small can be defined only for ordinary fixed point types,
decimal fixed point type declarations are not checked.
This rule has no parameters.
Improperly_Located_InstantiationsFlag all generic instantiations in library-level package specs (including library generic packages) and in all subprogram bodies.
Instantiations in task and entry bodies are not flagged. Instantiations in the bodies of protected subprograms are flagged.
This rule has no parameters.
Improper_Returns
Flag each explicit return statement in procedures, and
multiple return statements in functions.
Diagnostic messages are generated for all return statements
in a procedure (thus each procedure must be written so that it
returns implicitly at the end of its statement part),
and for all return statements in a function after the first one.
This rule supports the stylistic convention that each subprogram
should have no more than one point of normal return.
This rule has no parameters.
Library_Level_SubprogramsFlag all library-level subprograms (including generic subprogram instantiations).
This rule has no parameters.
Local_PackagesFlag all local packages declared in package and generic package specs. Local packages in bodies are not flagged.
This rule has no parameters.
MetricsThere is a set of checks based on computing a metric value and comparing the result with the specified upper (or lower, depending on a specific metric) value specified for a given metric. A construct is flagged if a given metric is applicable (can be computed) for it and the computed value is greater then (lover then) the specified upper (lower) bound.
The name of any metric-based rule consists of the prefix Metrics_
followed by the name of the corresponding metric (see the table below).
For +R option, each metric-based rule has a numeric parameter
specifying the bound (integer or real, depending on a metric), -R
option for metric rules does not have a parameter.
The following table shows the metric names for that the corresponding metrics-based checks are supported by gnatcheck, including the constraint that must be satisfied by the bound that is specified for the check and what bound - upper (U) or lower (L) - should be specified.
| Check Name | Description | Bounds Value
|
Essential_Complexity | Essential complexity | Positive integer (U)
|
Cyclomatic_Complexity | Cyclomatic complexity | Positive integer (U)
|
LSLOC | Logical Source Lines of Code | Positive integer (U)
|
The meaning and the computed values for all these metrics are exactly the same as for the corresponding metrics in gnatmetric.
Example: the rule
+RMetrics_Cyclomatic_Complexity : 7
means that all bodies with cyclomatic complexity exceeding 7 will be flagged.
To turn OFF the check for cyclomatic complexity metric, use the following option:
-RMetrics_Cyclomatic_Complexity
Misnamed_IdentifiersFlag the declaration of each identifier that does not have a suffix corresponding to the kind of entity being declared. The following declarations are checked:
This rule may have parameters. When used without parameters, the rule enforces the following checks:
_T, unless the type is an access type,
in which case the suffix must be _A
_C
_R
For a private or incomplete type declaration the following checks are made for the defining name suffix:
For a deferred constant, the defining name in the corresponding full constant declaration is not checked.
Defining names of formal types are not checked.
The rule may have the following parameters:
DefaultType_Suffix=stringAccess_Suffix=stringType_Suffix parameter.
Constant_Suffix=stringRenaming_Suffix=stringAll_SuffixesType_SuffixAccess_Suffix is
set).
Access_SuffixType_Suffix is set, access type names are
checked as ordinary type names.
Constant_SuffixRenaming_SuffixIf more than one parameter is used, parameters must be separated by commas.
If more than one option is specified for the gnatcheck invocation, a new option overrides the previous one(s).
The +RMisnamed_Identifiers option (with no parameter) enables checks for all the name suffixes specified by previous options used for this rule.
The -RMisnamed_Identifiers option (with no parameter) disables all the checks but keeps all the suffixes specified by previous options used for this rule.
The string value must be a valid suffix for an Ada identifier (after trimming all the leading and trailing space characters, if any). Parameters are not case sensitive, except the string part.
If any error is detected in a rule parameter, the parameter is ignored. In such a case the options that are set for the rule are not specified.
Multiple_Entries_In_Protected_DefinitionsFlag each protected definition (i.e., each protected object/type declaration) that defines more than one entry. Diagnostic messages are generated for all the entry declarations except the first one. An entry family is counted as one entry. Entries from the private part of the protected definition are also checked.
This rule has no parameters.
Name_ClashesCheck that certain names are not used as defining identifiers. To activate this rule, you need to supply a reference to the dictionary file(s) as a rule parameter(s) (more then one dictionary file can be specified). If no dictionary file is set, this rule will not cause anything to be flagged. Only defining occurrences, not references, are checked. The check is not case-sensitive.
This rule is enabled by default, but without setting any corresponding dictionary file(s); thus the default effect is to do no checks.
A dictionary file is a plain text file. The maximum line length for this file is 1024 characters. If the line is longer then this limit, extra characters are ignored.
Each line can be either an empty line, a comment line, or a line containing
a list of identifiers separated by space or HT characters.
A comment is an Ada-style comment (from -- to end-of-line).
Identifiers must follow the Ada syntax for identifiers.
A line containing one or more identifiers may end with a comment.
Non_Qualified_AggregatesFlag each non-qualified aggregate. A non-qualified aggregate is an aggregate that is not the expression of a qualified expression. A string literal is not considered an aggregate, but an array aggregate of a string type is considered as a normal aggregate. Aggregates of anonymous array types are not flagged.
This rule has no parameters.
Non_Short_Circuit_Operators
Flag all calls to predefined and and or operators for
any boolean type. Calls to
user-defined and and or and to operators defined by renaming
declarations are not flagged. Calls to predefined and and or
operators for modular types or boolean array types are not flagged.
This rule has no parameters.
Non_SPARK_AttributesThe SPARK language defines the following subset of Ada 95 attribute designators as those that can be used in SPARK programs. The use of any other attribute is flagged.
'Adjacent
'Aft
'Base
'Ceiling
'Component_Size
'Compose
'Copy_Sign
'Delta
'Denorm
'Digits
'Exponent
'First
'Floor
'Fore
'Fraction
'Last
'Leading_Part
'Length
'Machine
'Machine_Emax
'Machine_Emin
'Machine_Mantissa
'Machine_Overflows
'Machine_Radix
'Machine_Rounds
'Max
'Min
'Model
'Model_Emin
'Model_Epsilon
'Model_Mantissa
'Model_Small
'Modulus
'Pos
'Pred
'Range
'Remainder
'Rounding
'Safe_First
'Safe_Last
'Scaling
'Signed_Zeros
'Size
'Small
'Succ
'Truncation
'Unbiased_Rounding
'Val
'Valid
This rule has no parameters.
Non_Tagged_Derived_TypesFlag all derived type declarations that do not have a record extension part.
This rule has no parameters.
Non_Visible_ExceptionsFlag constructs leading to the possibility of propagating an exception out of the scope in which the exception is declared. Two cases are detected:
others choice.
raise statement in an exception handler of a subprogram body,
task body or block statement is flagged if it (re)raises a locally
declared exception. This may occur under the following circumstances:
raise;)
and the enclosing handler contains a locally declared exception in its
exception choices.
Renamings of local exceptions are not flagged.
This rule has no parameters.
Numeric_LiteralsFlag each use of a numeric literal in an index expression, and in any circumstance except for the following:
This rule may have the following parameters for the +R option:
ALLIf no parameters are set, the maximum unflagged value is 1.
The last specified check limit (or the fact that there is no limit at all) is used when multiple +R options appear.
The -R option for this rule has no parameters. It disables the rule but retains the last specified maximum unflagged value. If the +R option subsequently appears, this value is used as the threshold for the check.
OTHERS_In_Aggregates
Flag each use of an others choice in extension aggregates.
In record and array aggregates, an others choice is flagged unless
it is used to refer to all components, or to all but one component.
If, in case of a named array aggregate, there are two associations, one
with an others choice and another with a discrete range, the
others choice is flagged even if the discrete range specifies
exactly one component; for example, (1..1 => 0, others => 1).
This rule has no parameters.
OTHERS_In_CASE_Statements
Flag any use of an others choice in a case statement.
This rule has no parameters.
OTHERS_In_Exception_Handlers
Flag any use of an others choice in an exception handler.
This rule has no parameters.
Outer_Loop_Exits
Flag each exit statement containing a loop name that is not the name
of the immediately enclosing loop statement.
This rule has no parameters.
Overloaded_OperatorsFlag each function declaration that overloads an operator symbol. A function body is checked only if the body does not have a separate spec. Formal functions are also checked. For a renaming declaration, only renaming-as-declaration is checked
This rule has no parameters.
Overly_Nested_Control_StructuresFlag each control structure whose nesting level exceeds the value provided in the rule parameter.
The control structures checked are the following:
if statement
case statement
loop statement
The rule has the following parameter for the +R option:
If the parameter for the +R option is not specified or if it is not a positive integer, +R option is ignored.
If more then one option is specified for the gnatcheck call, the later option and new parameter override the previous one(s).
Parameters_Out_Of_OrderFlag each subprogram and entry declaration whose formal parameters are not ordered according to the following scheme:
in and access parameters first,
then in out parameters,
and then out parameters;
in mode, parameters with default initialization expressions
occur last
Only the first violation of the described order is flagged.
The following constructs are checked:
Subprogram renamings are not checked.
This rule has no parameters.
Positional_Actuals_For_Defaulted_Generic_ParametersFlag each generic actual parameter corresponding to a generic formal parameter with a default initialization, if positional notation is used.
This rule has no parameters.
Positional_Actuals_For_Defaulted_ParametersFlag each actual parameter to a subprogram or entry call where the corresponding formal parameter has a default expression, if positional notation is used.
This rule has no parameters.
Positional_ComponentsFlag each array, record and extension aggregate that includes positional notation.
This rule has no parameters.
Positional_Generic_ParametersFlag each instantiation using positional parameter notation.
This rule has no parameters.
Positional_ParametersFlag each subprogram or entry call using positional parameter notation, except for the following:
This rule has no parameters.
Predefined_Numeric_Types
Flag each explicit use of the name of any numeric type or subtype defined
in package Standard.
The rationale for this rule is to detect when the
program may depend on platform-specific characteristics of the implementation
of the predefined numeric types. Note that this rule is over-pessimistic;
for example, a program that uses String indexing
likely needs a variable of type Integer.
Another example is the flagging of predefined numeric types with explicit
constraints:
subtype My_Integer is Integer range Left .. Right;
Vy_Var : My_Integer;
This rule detects only numeric types and subtypes defined in
Standard. The use of numeric types and subtypes defined in other
predefined packages (such as System.Any_Priority or
Ada.Text_IO.Count) is not flagged
This rule has no parameters.
Raising_External_Exceptions
Flag any raise statement, in a program unit declared in a library
package or in a generic library package, for an exception that is
neither a predefined exception nor an exception that is also declared (or
renamed) in the visible part of the package.
This rule has no parameters.
Raising_Predefined_Exceptions
Flag each raise statement that raises a predefined exception
(i.e., one of the exceptions Constraint_Error, Numeric_Error,
Program_Error, Storage_Error, or Tasking_Error).
This rule has no parameters.
Separate_Numeric_Error_Handlers
Flags each exception handler that contains a choice for
the predefined Constraint_Error exception, but does not contain
the choice for the predefined Numeric_Error exception, or
that contains the choice for Numeric_Error, but does not contain the
choice for Constraint_Error.
This rule has no parameters.
SlicesFlag all uses of array slicing
This rule has no parameters.
Unassigned_OUT_Parameters
Flags procedures' out parameters that are not assigned, and
identifies the contexts in which the assignments are missing.
An out parameter is flagged in the statements in the procedure
body's handled sequence of statements (before the procedure body's
exception part, if any) if this sequence of statements contains
no assignments to the parameter.
An out parameter is flagged in an exception handler in the exception
part of the procedure body's handled sequence of statements if the handler
contains no assignment to the parameter.
Bodies of generic procedures are also considered.
The following are treated as assignments to an out parameter:
out or
in out parameter.
This rule does not have any parameters.
Uncommented_BEGIN_In_Package_Bodies
Flags each package body with declarations and a statement part that does not
include a trailing comment on the line containing the begin keyword;
this trailing comment needs to specify the package name and nothing else.
The begin is not flagged if the package body does not
contain any declarations.
If the begin keyword is placed on the
same line as the last declaration or the first statement, it is flagged
independently of whether the line contains a trailing comment. The
diagnostic message is attached to the line containing the first statement.
This rule has no parameters.
Unconstrained_Array_ReturnsFlag each function returning an unconstrained array. Function declarations, function bodies (and body stubs) having no separate specifications, and generic function instantiations are checked. Generic function declarations, function calls and function renamings are not checked.
This rule has no parameters.
Universal_Ranges
Flag discrete ranges that are a part of an index constraint, constrained
array definition, or for-loop parameter specification, and whose bounds
are both of type universal_integer. Ranges that have at least one
bound of a specific type (such as 1 .. N, where N is a variable
or an expression of non-universal type) are not flagged.
This rule has no parameters.
Unnamed_Blocks_And_LoopsFlag each unnamed block statement and loop statement.
The rule has no parameters.
USE_PACKAGE_Clauses
Flag all use clauses for packages; use type clauses are
not flagged.
This rule has no parameters.
Volatile_Objects_Without_Address_ClausesFlag each volatile object that does not have an address clause.
The following check is made: if the pragma Volatile is applied to a
data object or to its type, then an address clause must
be supplied for this object.
This rule does not check the components of data objects,
array components that are volatile as a result of the pragma
Volatile_Components, or objects that are volatile because
they are atomic as a result of pragmas Atomic or
Atomic_Components.
Only variable declarations, and not constant declarations, are checked.
This rule has no parameters.
gnatstub creates body stubs, that is, empty but compilable bodies for library unit declarations.
Note: to invoke gnatstub with a project file, use the gnat
driver (see The GNAT Driver and Project Files).
To create a body stub, gnatstub has to compile the library unit declaration. Therefore, bodies can be created only for legal library units. Moreover, if a library unit depends semantically upon units located outside the current directory, you have to provide the source search path when calling gnatstub, see the description of gnatstub switches below.
gnatstub has the command-line interface of the form
$ gnatstub [switches] filename [directory]
where
This chapter discusses some other utility programs available in the Ada environment.
The object files generated by GNAT are in standard system format and in particular the debugging information uses this format. This means programs generated by GNAT can be used with existing utilities that depend on these formats.
In general, any utility program that works with C will also often work with
Ada programs generated by GNAT. This includes software utilities such as
gprof (a profiling program), gdb (the FSF debugger), and utilities such
as Purify.
In order to interpret the output from GNAT, when using tools that are originally intended for use with other languages, it is useful to understand the conventions used to generate link names from the Ada entity names.
All link names are in all lowercase letters. With the exception of library procedure names, the mechanism used is simply to use the full expanded Ada name with dots replaced by double underscores. For example, suppose we have the following package spec:
| package QRS is MN : Integer; end QRS; |
The variable MN has a full expanded Ada name of QRS.MN, so
the corresponding link name is qrs__mn.
Of course if a pragma Export is used this may be overridden:
| package Exports is Var1 : Integer; pragma Export (Var1, C, External_Name => "var1_name"); Var2 : Integer; pragma Export (Var2, C, Link_Name => "var2_link_name"); end Exports; |
In this case, the link name for Var1 is whatever link name the C compiler would assign for the C function var1_name. This typically would be either var1_name or _var1_name, depending on operating system conventions, but other possibilities exist. The link name for Var2 is var2_link_name, and this is not operating system dependent.
One exception occurs for library level procedures. A potential ambiguity
arises between the required name _main for the C main program,
and the name we would otherwise assign to an Ada library level procedure
called Main (which might well not be the main program).
To avoid this ambiguity, we attach the prefix _ada_ to such
names. So if we have a library level procedure such as
| procedure Hello (S : String); |
the external name of this procedure will be _ada_hello.
gnathtmlThis Perl script allows Ada source files to be browsed using
standard Web browsers. For installation procedure, see the section
See Installing gnathtml.
Ada reserved keywords are highlighted in a bold font and Ada comments in a blue font. Unless your program was compiled with the gcc -gnatx switch to suppress the generation of cross-referencing information, user defined variables and types will appear in a different color; you will be able to click on any identifier and go to its declaration.
The command line is as follow:
$ perl gnathtml.pl [switches] ada-files
You can pass it as many Ada files as you want. gnathtml will generate
an html file for every ada file, and a global file called index.htm.
This file is an index of every identifier defined in the files.
The available switches are the following ones:
with clauses, the latter files will also be converted to html.
Only the files in the user project will be converted to html, not the files
in the run-time library itself.
gnathtml will number the html files every number line.
Using this switch, you can tell gnathtml to use these files.
This allows you to get an html version of your application, even if it
is spread over multiple directories.
gnathtmlPerl needs to be installed on your machine to run this script.
Perl is freely available for almost every architecture and
Operating System via the Internet.
On Unix systems, you may want to modify the first line of the script
gnathtml, to explicitly tell the Operating system where Perl
is. The syntax of this line is:
#!full_path_name_to_perl
Alternatively, you may run the script using the following command line:
$ perl gnathtml.pl [switches] files
This chapter describes how to use gcov - coverage testing tool - and
gprof - profiler tool - on your Ada programs.
gcov is a test coverage program: it analyzes the execution of a given
program on selected tests, to help you determine the portions of the program
that are still untested.
gcov is part of the GCC suite, and is described in detail in the GCC
User's Guide. You can refer to this documentation for a more complete
description.
This chapter provides a quick startup guide, and details some Gnat-specific features.
In order to perform coverage analysis of a program using gcov, 3
steps are needed:
gcov tool to generate the result.
The code instrumentation needed by gcov is created at the object level:
The source code is not modified in any way, because the instrumentation code is
inserted by gcc during the compilation process. To compile your code with code
coverage activated, you need to recompile your whole project using the
switches
-fprofile-arcs and -ftest-coverage, and link it using
-fprofile-arcs.
$ gnatmake -P my_project.gpr -f -cargs -fprofile-arcs -ftest-coverage \
-largs -fprofile-arcs
This compilation process will create .gcno files together with the usual object files.
Once the program is compiled with coverage instrumentation, you can run it as many times as needed - on portions of a test suite for example. The first execution will produce .gcda files at the same location as the .gcno files. The following executions will update those files, so that a cumulative result of the covered portions of the program is generated.
Finally, you need to call the gcov tool. The different options of
gcov are available in the GCC User's Guide, section 'Invoking gcov'.
This will create annotated source files with a .gcov extension: my_main.adb file will be analysed in my_main.adb.gcov.
Because Ada semantics, portions of the source code may be shared among
several object files. This is the case for example when generics are
involved, when inlining is active or when declarations generate initialisation
calls. In order to take
into account this shared code, you need to call gcov on all
source files of the tested program at once.
The list of source files might exceed the system's maximum command line
length. In order to bypass this limitation, a new mechanism has been
implemented in gcov: you can now list all your project's files into a
text file, and provide this file to gcov as a parameter, preceded by a @
(e.g. ‘gcov @mysrclist.txt’).
Note that on AIX compiling a static library with -fprofile-arcs is
not supported as there can be unresolved symbols during the final link.
This section is not meant to be an exhaustive documentation of gprof.
Full documentation for it can be found in the GNU Profiler User's Guide
documentation that is part of this GNAT distribution.
Profiling a program helps determine the parts of a program that are executed most often, and are therefore the most time-consuming.
gprof is the standard GNU profiling tool; it has been enhanced to
better handle Ada programs and multitasking.
It is currently supported on the following platforms
In order to profile a program using gprof, 3 steps are needed:
gprof tool.
The following sections detail the different steps, and indicate how to interpret the results:
In order to profile a program the first step is to tell the compiler
to generate the necessary profiling information. The compiler switch to be used
is -pg, which must be added to other compilation switches. This
switch needs to be specified both during compilation and link stages, and can
be specified once when using gnatmake:
gnatmake -f -pg -P my_project
Note that only the objects that were compiled with the ‘-pg’ switch will be profiled; if you need to profile your whole project, use the ‘-f’ gnatmake switch to force full recompilation.
Once the program has been compiled for profiling, you can run it as usual.
The only constraint imposed by profiling is that the program must terminate normally. An interrupted program (via a Ctrl-C, kill, etc.) will not be properly analyzed.
Once the program completes execution, a data file called gmon.out is generated in the directory where the program was launched from. If this file already exists, it will be overwritten.
The gprof tool is called as follow:
gprof my_prog gmon.out
or simpler:
gprof my_prog
The complete form of the gprof command line is the following:
gprof [switches] [executable [data-file]]
gprof supports numerous switch. The order of these
switch does not matter. The full list of options can be found in
the GNU Profiler User's Guide documentation that comes with this documentation.
The following is the subset of those switches that is most relevant:
--no-demangle option may be used to turn off demangling. Different
compilers have different mangling styles. The optional demangling style
argument can be used to choose an appropriate demangling style for your
compiler, in particular Ada symbols generated by GNAT can be demangled using
--demangle=gnat.
gprof not to print
information about the function function_name (and its
children...) in the call graph. The function will still be listed
as a child of any functions that call it, but its index number will be
shown as ‘[not printed]’. More than one ‘-e’ option may be
given; only one function_name may be indicated with each ‘-e’
option.
-E function option works like the -e option, but
execution time spent in the function (and children who were not called from
anywhere else), will not be used to compute the percentages-of-time for
the call graph. More than one ‘-E’ option may be given; only one
function_name may be indicated with each ‘-E’ option.
gprof to limit the
call graph to the function function_name and its children (and
their children...). More than one ‘-f’ option may be given;
only one function_name may be indicated with each ‘-f’
option.
-f option, but
only time spent in the function and its children (and their
children...) will be used to determine total-time and
percentages-of-time for the call graph. More than one ‘-F’ option
may be given; only one function_name may be indicated with each
‘-F’ option. The ‘-F’ option overrides the ‘-E’ option.
The results of the profiling analysis are represented by two arrays: the 'flat profile' and the 'call graph'. Full documentation of those outputs can be found in the GNU Profiler User's Guide.
The flat profile shows the time spent in each function of the program, and how many time it has been called. This allows you to locate easily the most time-consuming functions.
The call graph shows, for each subprogram, the subprograms that call it, and the subprograms that it calls. It also provides an estimate of the time spent in each of those callers/called subprograms.
This chapter discusses how to debug Ada programs.
An incorrect Ada program may be handled in three ways by the GNAT compiler:
GDB is a general purpose, platform-independent debugger that
can be used to debug mixed-language programs compiled with gcc,
and in particular is capable of debugging Ada programs compiled with
GNAT. The latest versions of GDB are Ada-aware and can handle
complex Ada data structures.
See Debugging with GDB,
for full details on the usage of GDB, including a section on
its usage on programs. This manual should be consulted for full
details. The section that follows is a brief introduction to the
philosophy and use of GDB.
When GNAT programs are compiled, the compiler optionally writes debugging information into the generated object file, including information on line numbers, and on declared types and variables. This information is separate from the generated code. It makes the object files considerably larger, but it does not add to the size of the actual executable that will be loaded into memory, and has no impact on run-time performance. The generation of debug information is triggered by the use of the -g switch in the gcc or gnatmake command used to carry out the compilations. It is important to emphasize that the use of these options does not change the generated code.
The debugging information is written in standard system formats that
are used by many tools, including debuggers and profilers. The format
of the information is typically designed to describe C types and
semantics, but GNAT implements a translation scheme which allows full
details about Ada types and variables to be encoded into these
standard C formats. Details of this encoding scheme may be found in
the file exp_dbug.ads in the GNAT source distribution. However, the
details of this encoding are, in general, of no interest to a user,
since GDB automatically performs the necessary decoding.
When a program is bound and linked, the debugging information is collected from the object files, and stored in the executable image of the program. Again, this process significantly increases the size of the generated executable file, but it does not increase the size of the executable program itself. Furthermore, if this program is run in the normal manner, it runs exactly as if the debug information were not present, and takes no more actual memory.
However, if the program is run under control of GDB, the
debugger is activated. The image of the program is loaded, at which
point it is ready to run. If a run command is given, then the program
will run exactly as it would have if GDB were not present. This
is a crucial part of the GDB design philosophy. GDB is
entirely non-intrusive until a breakpoint is encountered. If no
breakpoint is ever hit, the program will run exactly as it would if no
debugger were present. When a breakpoint is hit, GDB accesses
the debugging information and can respond to user commands to inspect
variables, and more generally to report on the state of execution.
This section describes how to initiate the debugger.
The debugger can be launched from a GPS menu or
directly from the command line. The description below covers the latter use.
All the commands shown can be used in the GPS debug console window,
but there are usually more GUI-based ways to achieve the same effect.
The command to run GDB is
$ gdb program
where program is the name of the executable file. This
activates the debugger and results in a prompt for debugger commands.
The simplest command is simply run, which causes the program to run
exactly as if the debugger were not present. The following section
describes some of the additional commands that can be given to GDB.
GDB contains a large repertoire of commands. See Debugging with GDB,
for extensive documentation on the use
of these commands, together with examples of their use. Furthermore,
the command help invoked from within GDB activates a simple help
facility which summarizes the available commands and their options.
In this section we summarize a few of the most commonly
used commands to give an idea of what GDB is about. You should create
a simple program with debugging information and experiment with the use of
these GDB commands on the program as you read through the
following section.
set args argumentsset args
command is not needed if the program does not require arguments.
runrun command causes execution of the program to start from
the beginning. If the program is already running, that is to say if
you are currently positioned at a breakpoint, then a prompt will ask
for confirmation that you want to abandon the current execution and
restart.
breakpoint locationGDB will await further
commands. location is
either a line number within a file, given in the format file:linenumber,
or it is the name of a subprogram. If you request that a breakpoint be set on
a subprogram that is overloaded, a prompt will ask you to specify on which of
those subprograms you want to breakpoint. You can also
specify that all of them should be breakpointed. If the program is run
and execution encounters the breakpoint, then the program
stops and GDB signals that the breakpoint was encountered by
printing the line of code before which the program is halted.
breakpoint exception nameprint expressionGDB, so the expression
can contain function calls, variables, operators, and attribute references.
continuestepnextlistbacktraceupGDB can display the values of variables local
to the current frame. The command up can be used to
examine the contents of other active frames, by moving the focus up
the stack, that is to say from callee to caller, one frame at a time.
downGDB down from the frame currently being
examined to the frame of its callee (the reverse of the previous command),
frame nThe above list is a very short introduction to the commands that
GDB provides. Important additional capabilities, including conditional
breakpoints, the ability to execute command sequences on a breakpoint,
the ability to debug at the machine instruction level and many other
features are described in detail in Debugging with GDB. Note that most commands can be abbreviated
(for example, c for continue, bt for backtrace).
GDB supports a fairly large subset of Ada expression syntax, with some
extensions. The philosophy behind the design of this subset is
GDB should provide basic literals and access to operations for
arithmetic, dereferencing, field selection, indexing, and subprogram calls,
leaving more sophisticated computations to subprograms written into the
program (which therefore may be called from GDB).
GDB user.
GDB user.
Thus, for brevity, the debugger acts as if there were
implicit with and use clauses in effect for all user-written
packages, thus making it unnecessary to fully qualify most names with
their packages, regardless of context. Where this causes ambiguity,
GDB asks the user's intent.
For details on the supported Ada syntax, see Debugging with GDB.
An important capability of GDB is the ability to call user-defined
subprograms while debugging. This is achieved simply by entering
a subprogram call statement in the form:
call subprogram-name (parameters)
The keyword call can be omitted in the normal case where the
subprogram-name does not coincide with any of the predefined
GDB commands.
The effect is to invoke the given subprogram, passing it the
list of parameters that is supplied. The parameters can be expressions and
can include variables from the program being debugged. The
subprogram must be defined
at the library level within your program, and GDB will call the
subprogram within the environment of your program execution (which
means that the subprogram is free to access or even modify variables
within your program).
The most important use of this facility is in allowing the inclusion of
debugging routines that are tailored to particular data structures
in your program. Such debugging routines can be written to provide a suitably
high-level description of an abstract type, rather than a low-level dump
of its physical layout. After all, the standard
GDB print command only knows the physical layout of your
types, not their abstract meaning. Debugging routines can provide information
at the desired semantic level and are thus enormously useful.
For example, when debugging GNAT itself, it is crucial to have access to
the contents of the tree nodes used to represent the program internally.
But tree nodes are represented simply by an integer value (which in turn
is an index into a table of nodes).
Using the print command on a tree node would simply print this integer
value, which is not very useful. But the PN routine (defined in file
treepr.adb in the GNAT sources) takes a tree node as input, and displays
a useful high level representation of the tree node, which includes the
syntactic category of the node, its position in the source, the integers
that denote descendant nodes and parent node, as well as varied
semantic information. To study this example in more detail, you might want to
look at the body of the PN procedure in the stated file.
When you use the next command in a function, the current source
location will advance to the next statement as usual. A special case
arises in the case of a return statement.
Part of the code for a return statement is the “epilog” of the function. This is the code that returns to the caller. There is only one copy of this epilog code, and it is typically associated with the last return statement in the function if there is more than one return. In some implementations, this epilog is associated with the first statement of the function.
The result is that if you use the next command from a return
statement that is not the last return statement of the function you
may see a strange apparent jump to the last return statement or to
the start of the function. You should simply ignore this odd jump.
The value returned is always that from the first return statement
that was stepped through.
You can set breakpoints that trip when your program raises selected exceptions.
break exceptionbreak exception namebreak exception unhandledinfo exceptionsinfo exceptions regexpinfo exceptions command permits the user to examine all defined
exceptions within Ada programs. With a regular expression, regexp, as
argument, prints out only those exceptions whose name matches regexp.
GDB allows the following task-related commands:
info tasks (gdb) info tasks
ID TID P-ID Thread Pri State Name
1 8088000 0 807e000 15 Child Activation Wait main_task
2 80a4000 1 80ae000 15 Accept/Select Wait b
3 809a800 1 80a4800 15 Child Activation Wait a
* 4 80ae800 3 80b8000 15 Running c
In this listing, the asterisk before the first task indicates it to be the
currently running task. The first column lists the task ID that is used
to refer to tasks in the following commands.
break linespec task taskidbreak linespec task taskid if ...break ... thread ....
linespec specifies source lines.
Use the qualifier ‘task taskid’ with a breakpoint command
to specify that you only want GDB to stop the program when a
particular Ada task reaches this breakpoint. taskid is one of the
numeric task identifiers assigned by GDB, shown in the first
column of the ‘info tasks’ display.
If you do not specify ‘task taskid’ when you set a breakpoint, the breakpoint applies to all tasks of your program.
You can use the task qualifier on conditional breakpoints as
well; in this case, place ‘task taskid’ before the
breakpoint condition (before the if).
task tasknoFor more detailed information on the tasking support, see Debugging with GDB.
GNAT always uses code expansion for generic instantiation. This means that each time an instantiation occurs, a complete copy of the original code is made, with appropriate substitutions of formals by actuals.
It is not possible to refer to the original generic entities in
GDB, but it is always possible to debug a particular instance of
a generic, by using the appropriate expanded names. For example, if we have
| procedure g is generic package k is procedure kp (v1 : in out integer); end k; package body k is procedure kp (v1 : in out integer) is begin v1 := v1 + 1; end kp; end k; package k1 is new k; package k2 is new k; var : integer := 1; begin k1.kp (var); k2.kp (var); k1.kp (var); k2.kp (var); end; |
Then to break on a call to procedure kp in the k2 instance, simply use the command:
(gdb) break g.k2.kp
When the breakpoint occurs, you can step through the code of the instance in the normal manner and examine the values of local variables, as for other units.
When presented with programs that contain serious errors in syntax or semantics, GNAT may on rare occasions experience problems in operation, such as aborting with a segmentation fault or illegal memory access, raising an internal exception, terminating abnormally, or failing to terminate at all. In such cases, you can activate various features of GNAT that can help you pinpoint the construct in your program that is the likely source of the problem.
The following strategies are presented in increasing order of difficulty, corresponding to your experience in using GNAT and your familiarity with compiler internals.
The -gnatdO switch causes errors to be displayed as soon as they are encountered, rather than after compilation is terminated. If GNAT terminates prematurely or goes into an infinite loop, the last error message displayed may help to pinpoint the culprit.
gdb directly on the gnat1 executable. gnat1 is the
front-end of GNAT, and can be run independently (normally it is just
called from gcc). You can use gdb on gnat1 as you
would on a C program (but see The GNAT Debugger GDB for caveats). The
where command is the first line of attack; the variable
lineno (seen by print lineno), used by the second phase of
gnat1 and by the gcc backend, indicates the source line at
which the execution stopped, and input_file name indicates the name of
the source file.
In order to examine the workings of the GNAT system, the following brief description of its organization may be helpful:
Ada, as
defined in Annex A.
Interfaces, as
defined in Annex B.
System. This includes
both language-defined children and GNAT run-time routines.
GNAT. These are useful
general-purpose packages, fully documented in their specs. All
the other .c files are modifications of common gcc files.
Most compilers have internal debugging switches and modes. GNAT does also, except GNAT internal debugging switches and modes are not secret. A summary and full description of all the compiler and binder debug flags are in the file debug.adb. You must obtain the sources of the compiler to see the full detailed effects of these flags.
The switches that print the source of the program (reconstructed from the internal tree) are of general interest for user programs, as are the options to print the full internal tree, and the entity table (the symbol table information). The reconstructed source provides a readable version of the program after the front-end has completed analysis and expansion, and is useful when studying the performance of specific constructs. For example, constraint checks are indicated, complex aggregates are replaced with loops and assignments, and tasking primitives are replaced with run-time calls.
Traceback is a mechanism to display the sequence of subprogram calls that leads to a specified execution point in a program. Often (but not always) the execution point is an instruction at which an exception has been raised. This mechanism is also known as stack unwinding because it obtains its information by scanning the run-time stack and recovering the activation records of all active subprograms. Stack unwinding is one of the most important tools for program debugging.
The first entry stored in traceback corresponds to the deepest calling level, that is to say the subprogram currently executing the instruction from which we want to obtain the traceback.
Note that there is no runtime performance penalty when stack traceback is enabled, and no exception is raised during program execution.
Note: this feature is not supported on all platforms. See GNAT.Traceback spec in g-traceb.ads for a complete list of supported platforms.
A runtime non-symbolic traceback is a list of addresses of call instructions.
To enable this feature you must use the -E
gnatbind's option. With this option a stack traceback is stored as part
of exception information. You can retrieve this information using the
addr2line tool.
Here is a simple example:
| procedure STB is procedure P1 is begin raise Constraint_Error; end P1; procedure P2 is begin P1; end P2; begin P2; end STB; |
$ gnatmake stb -bargs -E
$ stb
Execution terminated by unhandled exception
Exception name: CONSTRAINT_ERROR
Message: stb.adb:5
Call stack traceback locations:
0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4
As we see the traceback lists a sequence of addresses for the unhandled
exception CONSTRAINT_ERROR raised in procedure P1. It is easy to
guess that this exception come from procedure P1. To translate these
addresses into the source lines where the calls appear, the
addr2line tool, described below, is invaluable. The use of this tool
requires the program to be compiled with debug information.
$ gnatmake -g stb -bargs -E
$ stb
Execution terminated by unhandled exception
Exception name: CONSTRAINT_ERROR
Message: stb.adb:5
Call stack traceback locations:
0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4
$ addr2line --exe=stb 0x401373 0x40138b 0x40139c 0x401335 0x4011c4
0x4011f1 0x77e892a4
00401373 at d:/stb/stb.adb:5
0040138B at d:/stb/stb.adb:10
0040139C at d:/stb/stb.adb:14
00401335 at d:/stb/b~stb.adb:104
004011C4 at /build/.../crt1.c:200
004011F1 at /build/.../crt1.c:222
77E892A4 in ?? at ??:0
The addr2line tool has several other useful options:
--functions--demangle=gnat $ addr2line --exe=stb --functions --demangle=gnat 0x401373 0x40138b
0x40139c 0x401335 0x4011c4 0x4011f1
00401373 in stb.p1 at d:/stb/stb.adb:5
0040138B in stb.p2 at d:/stb/stb.adb:10
0040139C in stb at d:/stb/stb.adb:14
00401335 in main at d:/stb/b~stb.adb:104
004011C4 in <__mingw_CRTStartup> at /build/.../crt1.c:200
004011F1 in <mainCRTStartup> at /build/.../crt1.c:222
From this traceback we can see that the exception was raised in stb.adb at line 5, which was reached from a procedure call in stb.adb at line 10, and so on. The b~std.adb is the binder file, which contains the call to the main program. See Running gnatbind. The remaining entries are assorted runtime routines, and the output will vary from platform to platform.
It is also possible to use GDB with these traceback addresses to debug
the program. For example, we can break at a given code location, as reported
in the stack traceback:
$ gdb -nw stb
Furthermore, this feature is not implemented inside Windows DLL. Only
the non-symbolic traceback is reported in this case.
(gdb) break *0x401373
Breakpoint 1 at 0x401373: file stb.adb, line 5.
It is important to note that the stack traceback addresses do not change when debug information is included. This is particularly useful because it makes it possible to release software without debug information (to minimize object size), get a field report that includes a stack traceback whenever an internal bug occurs, and then be able to retrieve the sequence of calls with the same program compiled with debug information.
Non-symbolic tracebacks are obtained by using the -E binder argument.
The stack traceback is attached to the exception information string, and can
be retrieved in an exception handler within the Ada program, by means of the
Ada facilities defined in Ada.Exceptions. Here is a simple example:
with Ada.Text_IO;
with Ada.Exceptions;
procedure STB is
use Ada;
use Ada.Exceptions;
procedure P1 is
K : Positive := 1;
begin
K := K - 1;
exception
when E : others =>
Text_IO.Put_Line (Exception_Information (E));
end P1;
procedure P2 is
begin
P1;
end P2;
begin
P2;
end STB;
This program will output:
$ stb
Exception name: CONSTRAINT_ERROR
Message: stb.adb:12
Call stack traceback locations:
0x4015e4 0x401633 0x401644 0x401461 0x4011c4 0x4011f1 0x77e892a4
It is also possible to retrieve a stack traceback from anywhere in a
program. For this you need to
use the GNAT.Traceback API. This package includes a procedure called
Call_Chain that computes a complete stack traceback, as well as useful
display procedures described below. It is not necessary to use the
-E gnatbind option in this case, because the stack traceback mechanism
is invoked explicitly.
In the following example we compute a traceback at a specific location in
the program, and we display it using GNAT.Debug_Utilities.Image to
convert addresses to strings:
with Ada.Text_IO;
with GNAT.Traceback;
with GNAT.Debug_Utilities;
procedure STB is
use Ada;
use GNAT;
use GNAT.Traceback;
procedure P1 is
TB : Tracebacks_Array (1 .. 10);
-- We are asking for a maximum of 10 stack frames.
Len : Natural;
-- Len will receive the actual number of stack frames returned.
begin
Call_Chain (TB, Len);
Text_IO.Put ("In STB.P1 : ");
for K in 1 .. Len loop
Text_IO.Put (Debug_Utilities.Image (TB (K)));
Text_IO.Put (' ');
end loop;
Text_IO.New_Line;
end P1;
procedure P2 is
begin
P1;
end P2;
begin
P2;
end STB;
$ gnatmake -g stb
$ stb
In STB.P1 : 16#0040_F1E4# 16#0040_14F2# 16#0040_170B# 16#0040_171C#
16#0040_1461# 16#0040_11C4# 16#0040_11F1# 16#77E8_92A4#
You can then get further information by invoking the addr2line
tool as described earlier (note that the hexadecimal addresses
need to be specified in C format, with a leading “0x”).
A symbolic traceback is a stack traceback in which procedure names are associated with each code location.
Note that this feature is not supported on all platforms. See GNAT.Traceback.Symbolic spec in g-trasym.ads for a complete list of currently supported platforms.
Note that the symbolic traceback requires that the program be compiled with debug information. If it is not compiled with debug information only the non-symbolic information will be valid.
with Ada.Text_IO;
with GNAT.Traceback.Symbolic;
procedure STB is
procedure P1 is
begin
raise Constraint_Error;
end P1;
procedure P2 is
begin
P1;
end P2;
procedure P3 is
begin
P2;
end P3;
begin
P3;
exception
when E : others =>
Ada.Text_IO.Put_Line (GNAT.Traceback.Symbolic.Symbolic_Traceback (E));
end STB;
$ gnatmake -g .\stb -bargs -E -largs -lgnat -laddr2line -lintl
$ stb
0040149F in stb.p1 at stb.adb:8
004014B7 in stb.p2 at stb.adb:13
004014CF in stb.p3 at stb.adb:18
004015DD in ada.stb at stb.adb:22
00401461 in main at b~stb.adb:168
004011C4 in __mingw_CRTStartup at crt1.c:200
004011F1 in mainCRTStartup at crt1.c:222
77E892A4 in ?? at ??:0
In the above example the “.\” syntax in the gnatmake command is currently required by addr2line for files that are in the current working directory. Moreover, the exact sequence of linker options may vary from platform to platform. The above -largs section is for Windows platforms. By contrast, under Unix there is no need for the -largs section. Differences across platforms are due to details of linker implementation.
It is possible to get a symbolic stack traceback
from anywhere in a program, just as for non-symbolic tracebacks.
The first step is to obtain a non-symbolic
traceback, and then call Symbolic_Traceback to compute the symbolic
information. Here is an example:
with Ada.Text_IO;
with GNAT.Traceback;
with GNAT.Traceback.Symbolic;
procedure STB is
use Ada;
use GNAT.Traceback;
use GNAT.Traceback.Symbolic;
procedure P1 is
TB : Tracebacks_Array (1 .. 10);
-- We are asking for a maximum of 10 stack frames.
Len : Natural;
-- Len will receive the actual number of stack frames returned.
begin
Call_Chain (TB, Len);
Text_IO.Put_Line (Symbolic_Traceback (TB (1 .. Len)));
end P1;
procedure P2 is
begin
P1;
end P2;
begin
P2;
end STB;
The GNAT run-time implementation may vary with respect to both the underlying threads library and the exception handling scheme. For threads support, one or more of the following are supplied:
For exception handling, either or both of two models are supplied:
This appendix summarizes which combinations of threads and exception support are supplied on various GNAT platforms. It then shows how to select a particular library either permanently or temporarily, explains the properties of (and tradeoffs among) the various threads libraries, and provides some additional information about several specific platforms.
| alpha-openvms
| |
| rts-native (default)
| |
| Tasking | native VMS threads
|
| Exceptions | ZCX
|
| alpha-tru64
| |
| rts-native (default)
| |
| Tasking | native TRU64 threads
|
| Exceptions | ZCX
|
| rts-sjlj
| |
| Tasking | native TRU64 threads
|
| Exceptions | SJLJ
|
| ia64-hp_linux
| |
| rts-native (default)
| |
| Tasking | pthread library
|
| Exceptions | ZCX
|
| ia64-hpux
| |
| rts-native (default)
| |
| Tasking | native HP-UX threads
|
| Exceptions | SJLJ
|
| ia64-openvms
| |
| rts-native (default)
| |
| Tasking | native VMS threads
|
| Exceptions | ZCX
|
| ia64-sgi_linux
| |
| rts-native (default)
| |
| Tasking | pthread library
|
| Exceptions | ZCX
|
| mips-irix
| |
| rts-native (default)
| |
| Tasking | native IRIX threads
|
| Exceptions | ZCX
|
| pa-hpux
| |
| rts-native (default)
| |
| Tasking | native HP-UX threads
|
| Exceptions | ZCX
|
| rts-sjlj
| |
| Tasking | native HP-UX threads
|
| Exceptions | SJLJ
|
| ppc-aix
| |
| rts-native (default)
| |
| Tasking | native AIX threads
|
| Exceptions | SJLJ
|
| ppc-darwin
| |
| rts-native (default)
| |
| Tasking | native MacOS threads
|
| Exceptions | ZCX
|
| sparc-solaris |
|
| rts-native (default)
| |
| Tasking | native Solaris threads library
|
| Exceptions | ZCX
|
| rts-pthread
| |
| Tasking | pthread library
|
| Exceptions | ZCX
|
| rts-sjlj
| |
| Tasking | native Solaris threads library
|
| Exceptions | SJLJ
|
| sparc64-solaris |
|
| rts-native (default)
| |
| Tasking | native Solaris threads library
|
| Exceptions | ZCX
|
| x86-linux
| |
| rts-native (default)
| |
| Tasking | pthread library
|
| Exceptions | ZCX
|
| rts-sjlj
| |
| Tasking | pthread library
|
| Exceptions | SJLJ
|
| x86-lynx
| |
| rts-native (default)
| |
| Tasking | native LynxOS threads
|
| Exceptions | SJLJ
|
| x86-solaris
| |
| rts-native (default)
| |
| Tasking | native Solaris threads
|
| Exceptions | SJLJ
|
| x86-windows
| |
| rts-native (default)
| |
| Tasking | native Win32 threads
|
| Exceptions | ZCX
|
| rts-sjlj (default)
| |
| Tasking | native Win32 threads
|
| Exceptions | SJLJ
|
| x86-windows-rtx
| |
| rts-rtx-rtss (default)
| |
| Tasking | RTX real-time subsystem RTSS threads (kernel mode)
|
| Exceptions | SJLJ
|
| rts-rtx-w32
| |
| Tasking | RTX Win32 threads (user mode)
|
| Exceptions | ZCX
|
| x86_64-linux
| |
| rts-native (default)
| |
| Tasking | pthread library
|
| Exceptions | ZCX
|
| rts-sjlj
| |
| Tasking | pthread library
|
| Exceptions | SJLJ
|
The adainclude subdirectory containing the sources of the GNAT run-time library, and the adalib subdirectory containing the ALI files and the static and/or shared GNAT library, are located in the gcc target-dependent area:
target=$prefix/lib/gcc/gcc-dumpmachine/gcc-dumpversion/
As indicated above, on some platforms several run-time libraries are supplied. These libraries are installed in the target dependent area and contain a complete source and binary subdirectory. The detailed description below explains the differences between the different libraries in terms of their thread support.
The default run-time library (when GNAT is installed) is rts-native. This default run time is selected by the means of soft links. For example on x86-linux:
$(target-dir)
|
+--- adainclude----------+
| |
+--- adalib-----------+ |
| | |
+--- rts-native | |
| | | |
| +--- adainclude <---+
| | |
| +--- adalib <----+
|
+--- rts-sjlj
|
+--- adainclude
|
+--- adalib
If the rts-sjlj library is to be selected on a permanent basis, these soft links can be modified with the following commands:
$ cd $target
$ rm -f adainclude adalib
$ ln -s rts-sjlj/adainclude adainclude
$ ln -s rts-sjlj/adalib adalib
Alternatively, you can specify rts-sjlj/adainclude in the file $target/ada_source_path and rts-sjlj/adalib in $target/ada_object_path.
Selecting another run-time library temporarily can be achieved by using the --RTS switch, e.g., --RTS=sjlj
When using a POSIX threads implementation, you have a choice of several
scheduling policies: SCHED_FIFO,
SCHED_RR
and SCHED_OTHER.
Typically, the default is SCHED_OTHER, while using SCHED_FIFO
or SCHED_RR requires special (e.g., root) privileges.
By default, GNAT uses the SCHED_OTHER policy. To specify
SCHED_FIFO,
you can use one of the following:
pragma Time_Slice (0.0)
pragma Task_Dispatching_Policy (FIFO_Within_Priorities)
To specify SCHED_RR,
you should use pragma Time_Slice with a
value greater than 0.0, or else use the corresponding -T
binder option.
This section addresses some topics related to the various threads libraries on Sparc Solaris.
GNAT under Solaris/Sparc 32 bits comes with an alternate tasking run-time
library based on POSIX threads — rts-pthread.
This run-time library has the advantage of being mostly shared across all
POSIX-compliant thread implementations, and it also provides under
Solaris 8 the PTHREAD_PRIO_INHERIT
and PTHREAD_PRIO_PROTECT
semantics that can be selected using the predefined pragma
Locking_Policy
with respectively
Inheritance_Locking and Ceiling_Locking as the policy.
As explained above, the native run-time library is based on the Solaris thread
library (libthread) and is the default library.
When the Solaris threads library is used (this is the default), programs compiled with GNAT can automatically take advantage of and can thus execute on multiple processors. The user can alternatively specify a processor on which the program should run to emulate a single-processor system. The multiprocessor / uniprocessor choice is made by setting the environment variable GNAT_PROCESSOR to one of the following:
-2GNAT_PROCESSOR
unset
-10 .. Last_ProcLast_Proc is equal to _SC_NPROCESSORS_CONF - 1
(where _SC_NPROCESSORS_CONF is a system variable).
On GNU/Linux without NPTL support (usually system with GNU C Library
older than 2.3), the signal model is not POSIX compliant, which means
that to send a signal to the process, you need to send the signal to all
threads, e.g. by using killpg().
On AIX, the resolver library initializes some internal structure on
the first call to get*by* functions, which are used to implement
GNAT.Sockets.Get_Host_By_Name and
GNAT.Sockets.Get_Host_By_Address.
If such initialization occurs within an Ada task, and the stack size for
the task is the default size, a stack overflow may occur.
To avoid this overflow, the user should either ensure that the first call
to GNAT.Sockets.Get_Host_By_Name or
GNAT.Sockets.Get_Host_By_Addrss
occurs in the environment task, or use pragma Storage_Size to
specify a sufficiently large size for the stack of the task that contains
this call.
The GCC support libraries coming with the Irix compiler have moved to their canonical place with respect to the general Irix ABI related conventions. Running applications built with the default shared GNAT run-time now requires the LD_LIBRARY_PATH environment variable to include this location. A possible way to achieve this is to issue the following command line on a bash prompt:
$ LD_LIBRARY_PATH=$LD_LIBRARY_PATH:`dirname \`gcc --print-file-name=libgcc_s.so\``
The Real-time Extension (RTX) to Windows is based on the Windows Win32 API. Applications can be built to work in two different modes:
This Appendix displays the source code for gnatbind's output file generated for a simple “Hello World” program. Comments have been added for clarification purposes.
-- The package is called Ada_Main unless this name is actually used
-- as a unit name in the partition, in which case some other unique
-- name is used.
with System;
package ada_main is
Elab_Final_Code : Integer;
pragma Import (C, Elab_Final_Code, "__gnat_inside_elab_final_code");
-- The main program saves the parameters (argument count,
-- argument values, environment pointer) in global variables
-- for later access by other units including
-- Ada.Command_Line.
gnat_argc : Integer;
gnat_argv : System.Address;
gnat_envp : System.Address;
-- The actual variables are stored in a library routine. This
-- is useful for some shared library situations, where there
-- are problems if variables are not in the library.
pragma Import (C, gnat_argc);
pragma Import (C, gnat_argv);
pragma Import (C, gnat_envp);
-- The exit status is similarly an external location
gnat_exit_status : Integer;
pragma Import (C, gnat_exit_status);
GNAT_Version : constant String :=
"GNAT Version: 6.0.0w (20061115)";
pragma Export (C, GNAT_Version, "__gnat_version");
-- This is the generated adafinal routine that performs
-- finalization at the end of execution. In the case where
-- Ada is the main program, this main program makes a call
-- to adafinal at program termination.
procedure adafinal;
pragma Export (C, adafinal, "adafinal");
-- This is the generated adainit routine that performs
-- initialization at the start of execution. In the case
-- where Ada is the main program, this main program makes
-- a call to adainit at program startup.
procedure adainit;
pragma Export (C, adainit, "adainit");
-- This routine is called at the start of execution. It is
-- a dummy routine that is used by the debugger to breakpoint
-- at the start of execution.
procedure Break_Start;
pragma Import (C, Break_Start, "__gnat_break_start");
-- This is the actual generated main program (it would be
-- suppressed if the no main program switch were used). As
-- required by standard system conventions, this program has
-- the external name main.
function main
(argc : Integer;
argv : System.Address;
envp : System.Address)
return Integer;
pragma Export (C, main, "main");
-- The following set of constants give the version
-- identification values for every unit in the bound
-- partition. This identification is computed from all
-- dependent semantic units, and corresponds to the
-- string that would be returned by use of the
-- Body_Version or Version attributes.
type Version_32 is mod 2 ** 32;
u00001 : constant Version_32 := 16#7880BEB3#;
u00002 : constant Version_32 := 16#0D24CBD0#;
u00003 : constant Version_32 := 16#3283DBEB#;
u00004 : constant Version_32 := 16#2359F9ED#;
u00005 : constant Version_32 := 16#664FB847#;
u00006 : constant Version_32 := 16#68E803DF#;
u00007 : constant Version_32 := 16#5572E604#;
u00008 : constant Version_32 := 16#46B173D8#;
u00009 : constant Version_32 := 16#156A40CF#;
u00010 : constant Version_32 := 16#033DABE0#;
u00011 : constant Version_32 := 16#6AB38FEA#;
u00012 : constant Version_32 := 16#22B6217D#;
u00013 : constant Version_32 := 16#68A22947#;
u00014 : constant Version_32 := 16#18CC4A56#;
u00015 : constant Version_32 := 16#08258E1B#;
u00016 : constant Version_32 := 16#367D5222#;
u00017 : constant Version_32 := 16#20C9ECA4#;
u00018 : constant Version_32 := 16#50D32CB6#;
u00019 : constant Version_32 := 16#39A8BB77#;
u00020 : constant Version_32 := 16#5CF8FA2B#;
u00021 : constant Version_32 := 16#2F1EB794#;
u00022 : constant Version_32 := 16#31AB6444#;
u00023 : constant Version_32 := 16#1574B6E9#;
u00024 : constant Version_32 := 16#5109C189#;
u00025 : constant Version_32 := 16#56D770CD#;
u00026 : constant Version_32 := 16#02F9DE3D#;
u00027 : constant Version_32 := 16#08AB6B2C#;
u00028 : constant Version_32 := 16#3FA37670#;
u00029 : constant Version_32 := 16#476457A0#;
u00030 : constant Version_32 := 16#731E1B6E#;
u00031 : constant Version_32 := 16#23C2E789#;
u00032 : constant Version_32 := 16#0F1BD6A1#;
u00033 : constant Version_32 := 16#7C25DE96#;
u00034 : constant Version_32 := 16#39ADFFA2#;
u00035 : constant Version_32 := 16#571DE3E7#;
u00036 : constant Version_32 := 16#5EB646AB#;
u00037 : constant Version_32 := 16#4249379B#;
u00038 : constant Version_32 := 16#0357E00A#;
u00039 : constant Version_32 := 16#3784FB72#;
u00040 : constant Version_32 := 16#2E723019#;
u00041 : constant Version_32 := 16#623358EA#;
u00042 : constant Version_32 := 16#107F9465#;
u00043 : constant Version_32 := 16#6843F68A#;
u00044 : constant Version_32 := 16#63305874#;
u00045 : constant Version_32 := 16#31E56CE1#;
u00046 : constant Version_32 := 16#02917970#;
u00047 : constant Version_32 := 16#6CCBA70E#;
u00048 : constant Version_32 := 16#41CD4204#;
u00049 : constant Version_32 := 16#572E3F58#;
u00050 : constant Version_32 := 16#20729FF5#;
u00051 : constant Version_32 := 16#1D4F93E8#;
u00052 : constant Version_32 := 16#30B2EC3D#;
u00053 : constant Version_32 := 16#34054F96#;
u00054 : constant Version_32 := 16#5A199860#;
u00055 : constant Version_32 := 16#0E7F912B#;
u00056 : constant Version_32 := 16#5760634A#;
u00057 : constant Version_32 := 16#5D851835#;
-- The following Export pragmas export the version numbers
-- with symbolic names ending in B (for body) or S
-- (for spec) so that they can be located in a link. The
-- information provided here is sufficient to track down
-- the exact versions of units used in a given build.
pragma Export (C, u00001, "helloB");
pragma Export (C, u00002, "system__standard_libraryB");
pragma Export (C, u00003, "system__standard_libraryS");
pragma Export (C, u00004, "adaS");
pragma Export (C, u00005, "ada__text_ioB");
pragma Export (C, u00006, "ada__text_ioS");
pragma Export (C, u00007, "ada__exceptionsB");
pragma Export (C, u00008, "ada__exceptionsS");
pragma Export (C, u00009, "gnatS");
pragma Export (C, u00010, "gnat__heap_sort_aB");
pragma Export (C, u00011, "gnat__heap_sort_aS");
pragma Export (C, u00012, "systemS");
pragma Export (C, u00013, "system__exception_tableB");
pragma Export (C, u00014, "system__exception_tableS");
pragma Export (C, u00015, "gnat__htableB");
pragma Export (C, u00016, "gnat__htableS");
pragma Export (C, u00017, "system__exceptionsS");
pragma Export (C, u00018, "system__machine_state_operationsB");
pragma Export (C, u00019, "system__machine_state_operationsS");
pragma Export (C, u00020, "system__machine_codeS");
pragma Export (C, u00021, "system__storage_elementsB");
pragma Export (C, u00022, "system__storage_elementsS");
pragma Export (C, u00023, "system__secondary_stackB");
pragma Export (C, u00024, "system__secondary_stackS");
pragma Export (C, u00025, "system__parametersB");
pragma Export (C, u00026, "system__parametersS");
pragma Export (C, u00027, "system__soft_linksB");
pragma Export (C, u00028, "system__soft_linksS");
pragma Export (C, u00029, "system__stack_checkingB");
pragma Export (C, u00030, "system__stack_checkingS");
pragma Export (C, u00031, "system__tracebackB");
pragma Export (C, u00032, "system__tracebackS");
pragma Export (C, u00033, "ada__streamsS");
pragma Export (C, u00034, "ada__tagsB");
pragma Export (C, u00035, "ada__tagsS");
pragma Export (C, u00036, "system__string_opsB");
pragma Export (C, u00037, "system__string_opsS");
pragma Export (C, u00038, "interfacesS");
pragma Export (C, u00039, "interfaces__c_streamsB");
pragma Export (C, u00040, "interfaces__c_streamsS");
pragma Export (C, u00041, "system__file_ioB");
pragma Export (C, u00042, "system__file_ioS");
pragma Export (C, u00043, "ada__finalizationB");
pragma Export (C, u00044, "ada__finalizationS");
pragma Export (C, u00045, "system__finalization_rootB");
pragma Export (C, u00046, "system__finalization_rootS");
pragma Export (C, u00047, "system__finalization_implementationB");
pragma Export (C, u00048, "system__finalization_implementationS");
pragma Export (C, u00049, "system__string_ops_concat_3B");
pragma Export (C, u00050, "system__string_ops_concat_3S");
pragma Export (C, u00051, "system__stream_attributesB");
pragma Export (C, u00052, "system__stream_attributesS");
pragma Export (C, u00053, "ada__io_exceptionsS");
pragma Export (C, u00054, "system__unsigned_typesS");
pragma Export (C, u00055, "system__file_control_blockS");
pragma Export (C, u00056, "ada__finalization__list_controllerB");
pragma Export (C, u00057, "ada__finalization__list_controllerS");
-- BEGIN ELABORATION ORDER
-- ada (spec)
-- gnat (spec)
-- gnat.heap_sort_a (spec)
-- gnat.heap_sort_a (body)
-- gnat.htable (spec)
-- gnat.htable (body)
-- interfaces (spec)
-- system (spec)
-- system.machine_code (spec)
-- system.parameters (spec)
-- system.parameters (body)
-- interfaces.c_streams (spec)
-- interfaces.c_streams (body)
-- system.standard_library (spec)
-- ada.exceptions (spec)
-- system.exception_table (spec)
-- system.exception_table (body)
-- ada.io_exceptions (spec)
-- system.exceptions (spec)
-- system.storage_elements (spec)
-- system.storage_elements (body)
-- system.machine_state_operations (spec)
-- system.machine_state_operations (body)
-- system.secondary_stack (spec)
-- system.stack_checking (spec)
-- system.soft_links (spec)
-- system.soft_links (body)
-- system.stack_checking (body)
-- system.secondary_stack (body)
-- system.standard_library (body)
-- system.string_ops (spec)
-- system.string_ops (body)
-- ada.tags (spec)
-- ada.tags (body)
-- ada.streams (spec)
-- system.finalization_root (spec)
-- system.finalization_root (body)
-- system.string_ops_concat_3 (spec)
-- system.string_ops_concat_3 (body)
-- system.traceback (spec)
-- system.traceback (body)
-- ada.exceptions (body)
-- system.unsigned_types (spec)
-- system.stream_attributes (spec)
-- system.stream_attributes (body)
-- system.finalization_implementation (spec)
-- system.finalization_implementation (body)
-- ada.finalization (spec)
-- ada.finalization (body)
-- ada.finalization.list_controller (spec)
-- ada.finalization.list_controller (body)
-- system.file_control_block (spec)
-- system.file_io (spec)
-- system.file_io (body)
-- ada.text_io (spec)
-- ada.text_io (body)
-- hello (body)
-- END ELABORATION ORDER
end ada_main;
-- The following source file name pragmas allow the generated file
-- names to be unique for different main programs. They are needed
-- since the package name will always be Ada_Main.
pragma Source_File_Name (ada_main, Spec_File_Name => "b~hello.ads");
pragma Source_File_Name (ada_main, Body_File_Name => "b~hello.adb");
-- Generated package body for Ada_Main starts here
package body ada_main is
-- The actual finalization is performed by calling the
-- library routine in System.Standard_Library.Adafinal
procedure Do_Finalize;
pragma Import (C, Do_Finalize, "system__standard_library__adafinal");
-------------
-- adainit --
-------------
procedure adainit is
-- These booleans are set to True once the associated unit has
-- been elaborated. It is also used to avoid elaborating the
-- same unit twice.
E040 : Boolean;
pragma Import (Ada, E040, "interfaces__c_streams_E");
E008 : Boolean;
pragma Import (Ada, E008, "ada__exceptions_E");
E014 : Boolean;
pragma Import (Ada, E014, "system__exception_table_E");
E053 : Boolean;
pragma Import (Ada, E053, "ada__io_exceptions_E");
E017 : Boolean;
pragma Import (Ada, E017, "system__exceptions_E");
E024 : Boolean;
pragma Import (Ada, E024, "system__secondary_stack_E");
E030 : Boolean;
pragma Import (Ada, E030, "system__stack_checking_E");
E028 : Boolean;
pragma Import (Ada, E028, "system__soft_links_E");
E035 : Boolean;
pragma Import (Ada, E035, "ada__tags_E");
E033 : Boolean;
pragma Import (Ada, E033, "ada__streams_E");
E046 : Boolean;
pragma Import (Ada, E046, "system__finalization_root_E");
E048 : Boolean;
pragma Import (Ada, E048, "system__finalization_implementation_E");
E044 : Boolean;
pragma Import (Ada, E044, "ada__finalization_E");
E057 : Boolean;
pragma Import (Ada, E057, "ada__finalization__list_controller_E");
E055 : Boolean;
pragma Import (Ada, E055, "system__file_control_block_E");
E042 : Boolean;
pragma Import (Ada, E042, "system__file_io_E");
E006 : Boolean;
pragma Import (Ada, E006, "ada__text_io_E");
-- Set_Globals is a library routine that stores away the
-- value of the indicated set of global values in global
-- variables within the library.
procedure Set_Globals
(Main_Priority : Integer;
Time_Slice_Value : Integer;
WC_Encoding : Character;
Locking_Policy : Character;
Queuing_Policy : Character;
Task_Dispatching_Policy : Character;
Adafinal : System.Address;
Unreserve_All_Interrupts : Integer;
Exception_Tracebacks : Integer);
pragma Import (C, Set_Globals, "__gnat_set_globals");
-- SDP_Table_Build is a library routine used to build the
-- exception tables. See unit Ada.Exceptions in files
-- a-except.ads/adb for full details of how zero cost
-- exception handling works. This procedure, the call to
-- it, and the two following tables are all omitted if the
-- build is in longjmp/setjmp exception mode.
procedure SDP_Table_Build
(SDP_Addresses : System.Address;
SDP_Count : Natural;
Elab_Addresses : System.Address;
Elab_Addr_Count : Natural);
pragma Import (C, SDP_Table_Build, "__gnat_SDP_Table_Build");
-- Table of Unit_Exception_Table addresses. Used for zero
-- cost exception handling to build the top level table.
ST : aliased constant array (1 .. 23) of System.Address := (
Hello'UET_Address,
Ada.Text_Io'UET_Address,
Ada.Exceptions'UET_Address,
Gnat.Heap_Sort_A'UET_Address,
System.Exception_Table'UET_Address,
System.Machine_State_Operations'UET_Address,
System.Secondary_Stack'UET_Address,
System.Parameters'UET_Address,
System.Soft_Links'UET_Address,
System.Stack_Checking'UET_Address,
System.Traceback'UET_Address,
Ada.Streams'UET_Address,
Ada.Tags'UET_Address,
System.String_Ops'UET_Address,
Interfaces.C_Streams'UET_Address,
System.File_Io'UET_Address,
Ada.Finalization'UET_Address,
System.Finalization_Root'UET_Address,
System.Finalization_Implementation'UET_Address,
System.String_Ops_Concat_3'UET_Address,
System.Stream_Attributes'UET_Address,
System.File_Control_Block'UET_Address,
Ada.Finalization.List_Controller'UET_Address);
-- Table of addresses of elaboration routines. Used for
-- zero cost exception handling to make sure these
-- addresses are included in the top level procedure
-- address table.
EA : aliased constant array (1 .. 23) of System.Address := (
adainit'Code_Address,
Do_Finalize'Code_Address,
Ada.Exceptions'Elab_Spec'Address,
System.Exceptions'Elab_Spec'Address,
Interfaces.C_Streams'Elab_Spec'Address,
System.Exception_Table'Elab_Body'Address,
Ada.Io_Exceptions'Elab_Spec'Address,
System.Stack_Checking'Elab_Spec'Address,
System.Soft_Links'Elab_Body'Address,
System.Secondary_Stack'Elab_Body'Address,
Ada.Tags'Elab_Spec'Address,
Ada.Tags'Elab_Body'Address,
Ada.Streams'Elab_Spec'Address,
System.Finalization_Root'Elab_Spec'Address,
Ada.Exceptions'Elab_Body'Address,
System.Finalization_Implementation'Elab_Spec'Address,
System.Finalization_Implementation'Elab_Body'Address,
Ada.Finalization'Elab_Spec'Address,
Ada.Finalization.List_Controller'Elab_Spec'Address,
System.File_Control_Block'Elab_Spec'Address,
System.File_Io'Elab_Body'Address,
Ada.Text_Io'Elab_Spec'Address,
Ada.Text_Io'Elab_Body'Address);
-- Start of processing for adainit
begin
-- Call SDP_Table_Build to build the top level procedure
-- table for zero cost exception handling (omitted in
-- longjmp/setjmp mode).
SDP_Table_Build (ST'Address, 23, EA'Address, 23);
-- Call Set_Globals to record various information for
-- this partition. The values are derived by the binder
-- from information stored in the ali files by the compiler.
Set_Globals
(Main_Priority => -1,
-- Priority of main program, -1 if no pragma Priority used
Time_Slice_Value => -1,
-- Time slice from Time_Slice pragma, -1 if none used
WC_Encoding => 'b',
-- Wide_Character encoding used, default is brackets
Locking_Policy => ' ',
-- Locking_Policy used, default of space means not
-- specified, otherwise it is the first character of
-- the policy name.
Queuing_Policy => ' ',
-- Queuing_Policy used, default of space means not
-- specified, otherwise it is the first character of
-- the policy name.
Task_Dispatching_Policy => ' ',
-- Task_Dispatching_Policy used, default of space means
-- not specified, otherwise first character of the
-- policy name.
Adafinal => System.Null_Address,
-- Address of Adafinal routine, not used anymore
Unreserve_All_Interrupts => 0,
-- Set true if pragma Unreserve_All_Interrupts was used
Exception_Tracebacks => 0);
-- Indicates if exception tracebacks are enabled
Elab_Final_Code := 1;
-- Now we have the elaboration calls for all units in the partition.
-- The Elab_Spec and Elab_Body attributes generate references to the
-- implicit elaboration procedures generated by the compiler for
-- each unit that requires elaboration.
if not E040 then
Interfaces.C_Streams'Elab_Spec;
end if;
E040 := True;
if not E008 then
Ada.Exceptions'Elab_Spec;
end if;
if not E014 then
System.Exception_Table'Elab_Body;
E014 := True;
end if;
if not E053 then
Ada.Io_Exceptions'Elab_Spec;
E053 := True;
end if;
if not E017 then
System.Exceptions'Elab_Spec;
E017 := True;
end if;
if not E030 then
System.Stack_Checking'Elab_Spec;
end if;
if not E028 then
System.Soft_Links'Elab_Body;
E028 := True;
end if;
E030 := True;
if not E024 then
System.Secondary_Stack'Elab_Body;
E024 := True;
end if;
if not E035 then
Ada.Tags'Elab_Spec;
end if;
if not E035 then
Ada.Tags'Elab_Body;
E035 := True;
end if;
if not E033 then
Ada.Streams'Elab_Spec;
E033 := True;
end if;
if not E046 then
System.Finalization_Root'Elab_Spec;
end if;
E046 := True;
if not E008 then
Ada.Exceptions'Elab_Body;
E008 := True;
end if;
if not E048 then
System.Finalization_Implementation'Elab_Spec;
end if;
if not E048 then
System.Finalization_Implementation'Elab_Body;
E048 := True;
end if;
if not E044 then
Ada.Finalization'Elab_Spec;
end if;
E044 := True;
if not E057 then
Ada.Finalization.List_Controller'Elab_Spec;
end if;
E057 := True;
if not E055 then
System.File_Control_Block'Elab_Spec;
E055 := True;
end if;
if not E042 then
System.File_Io'Elab_Body;
E042 := True;
end if;
if not E006 then
Ada.Text_Io'Elab_Spec;
end if;
if not E006 then
Ada.Text_Io'Elab_Body;
E006 := True;
end if;
Elab_Final_Code := 0;
end adainit;
--------------
-- adafinal --
--------------
procedure adafinal is
begin
Do_Finalize;
end adafinal;
----------
-- main --
----------
-- main is actually a function, as in the ANSI C standard,
-- defined to return the exit status. The three parameters
-- are the argument count, argument values and environment
-- pointer.
function main
(argc : Integer;
argv : System.Address;
envp : System.Address)
return Integer
is
-- The initialize routine performs low level system
-- initialization using a standard library routine which
-- sets up signal handling and performs any other
-- required setup. The routine can be found in file
-- a-init.c.
procedure initialize;
pragma Import (C, initialize, "__gnat_initialize");
-- The finalize routine performs low level system
-- finalization using a standard library routine. The
-- routine is found in file a-final.c and in the standard
-- distribution is a dummy routine that does nothing, so
-- really this is a hook for special user finalization.
procedure finalize;
pragma Import (C, finalize, "__gnat_finalize");
-- We get to the main program of the partition by using
-- pragma Import because if we try to with the unit and
-- call it Ada style, then not only do we waste time
-- recompiling it, but also, we don't really know the right
-- switches (e.g. identifier character set) to be used
-- to compile it.
procedure Ada_Main_Program;
pragma Import (Ada, Ada_Main_Program, "_ada_hello");
-- Start of processing for main
begin
-- Save global variables
gnat_argc := argc;
gnat_argv := argv;
gnat_envp := envp;
-- Call low level system initialization
Initialize;
-- Call our generated Ada initialization routine
adainit;
-- This is the point at which we want the debugger to get
-- control
Break_Start;
-- Now we call the main program of the partition
Ada_Main_Program;
-- Perform Ada finalization
adafinal;
-- Perform low level system finalization
Finalize;
-- Return the proper exit status
return (gnat_exit_status);
end;
-- This section is entirely comments, so it has no effect on the
-- compilation of the Ada_Main package. It provides the list of
-- object files and linker options, as well as some standard
-- libraries needed for the link. The gnatlink utility parses
-- this b~hello.adb file to read these comment lines to generate
-- the appropriate command line arguments for the call to the
-- system linker. The BEGIN/END lines are used for sentinels for
-- this parsing operation.
-- The exact file names will of course depend on the environment,
-- host/target and location of files on the host system.
-- BEGIN Object file/option list
-- ./hello.o
-- -L./
-- -L/usr/local/gnat/lib/gcc-lib/i686-pc-linux-gnu/2.8.1/adalib/
-- /usr/local/gnat/lib/gcc-lib/i686-pc-linux-gnu/2.8.1/adalib/libgnat.a
-- END Object file/option list
end ada_main;
The Ada code in the above example is exactly what is generated by the
binder. We have added comments to more clearly indicate the function
of each part of the generated Ada_Main package.
The code is standard Ada in all respects, and can be processed by any
tools that handle Ada. In particular, it is possible to use the debugger
in Ada mode to debug the generated Ada_Main package. For example,
suppose that for reasons that you do not understand, your program is crashing
during elaboration of the body of Ada.Text_IO. To locate this bug,
you can place a breakpoint on the call:
Ada.Text_Io'Elab_Body;
and trace the elaboration routine for this package to find out where the problem might be (more usually of course you would be debugging elaboration code in your own application).
This chapter describes the handling of elaboration code in Ada and in GNAT, and discusses how the order of elaboration of program units can be controlled in GNAT, either automatically or with explicit programming features.
Ada provides rather general mechanisms for executing code at elaboration time, that is to say before the main program starts executing. Such code arises in three contexts:
| Sqrt_Half : Float := Sqrt (0.5); |
BEGIN-END section at the outer level of a package body is
executed as part of the package body elaboration code.
Subprogram calls are possible in any of these contexts, which means that any arbitrary part of the program may be executed as part of the elaboration code. It is even possible to write a program which does all its work at elaboration time, with a null main program, although stylistically this would usually be considered an inappropriate way to structure a program.
An important concern arises in the context of elaboration code:
we have to be sure that it is executed in an appropriate order. What we
have is a series of elaboration code sections, potentially one section
for each unit in the program. It is important that these execute
in the correct order. Correctness here means that, taking the above
example of the declaration of Sqrt_Half,
if some other piece of
elaboration code references Sqrt_Half,
then it must run after the
section of elaboration code that contains the declaration of
Sqrt_Half.
There would never be any order of elaboration problem if we made a rule
that whenever you with a unit, you must elaborate both the spec and body
of that unit before elaborating the unit doing the with'ing:
| with Unit_1; package Unit_2 is ... |
would require that both the body and spec of Unit_1 be elaborated
before the spec of Unit_2. However, a rule like that would be far too
restrictive. In particular, it would make it impossible to have routines
in separate packages that were mutually recursive.
You might think that a clever enough compiler could look at the actual elaboration code and determine an appropriate correct order of elaboration, but in the general case, this is not possible. Consider the following example.
In the body of Unit_1, we have a procedure Func_1
that references
the variable Sqrt_1, which is declared in the elaboration code
of the body of Unit_1:
| Sqrt_1 : Float := Sqrt (0.1); |
The elaboration code of the body of Unit_1 also contains:
| if expression_1 = 1 then Q := Unit_2.Func_2; end if; |
Unit_2 is exactly parallel,
it has a procedure Func_2 that references
the variable Sqrt_2, which is declared in the elaboration code of
the body Unit_2:
| Sqrt_2 : Float := Sqrt (0.1); |
The elaboration code of the body of Unit_2 also contains:
| if expression_2 = 2 then Q := Unit_1.Func_1; end if; |
Now the question is, which of the following orders of elaboration is acceptable:
Spec of Unit_1
Spec of Unit_2
Body of Unit_1
Body of Unit_2
or
Spec of Unit_2
Spec of Unit_1
Body of Unit_2
Body of Unit_1
If you carefully analyze the flow here, you will see that you cannot tell
at compile time the answer to this question.
If expression_1 is not equal to 1,
and expression_2 is not equal to 2,
then either order is acceptable, because neither of the function calls is
executed. If both tests evaluate to true, then neither order is acceptable
and in fact there is no correct order.
If one of the two expressions is true, and the other is false, then one
of the above orders is correct, and the other is incorrect. For example,
if expression_1 /= 1 and expression_2 = 2,
then the call to Func_1
will occur, but not the call to Func_2.
This means that it is essential
to elaborate the body of Unit_1 before
the body of Unit_2, so the first
order of elaboration is correct and the second is wrong.
By making expression_1 and expression_2
depend on input data, or perhaps
the time of day, we can make it impossible for the compiler or binder
to figure out which of these expressions will be true, and hence it
is impossible to guarantee a safe order of elaboration at run time.
In some languages that involve the same kind of elaboration problems, e.g. Java and C++, the programmer is expected to worry about these ordering problems himself, and it is common to write a program in which an incorrect elaboration order gives surprising results, because it references variables before they are initialized. Ada is designed to be a safe language, and a programmer-beware approach is clearly not sufficient. Consequently, the language provides three lines of defense:
with a unit, then its spec is always
elaborated before the unit doing the with. Similarly, a parent
spec is always elaborated before the child spec, and finally
a spec is always elaborated before its corresponding body.
Program_Error) is raised.
Let's look at these facilities in more detail. First, the rules for dynamic checking. One possible rule would be simply to say that the exception is raised if you access a variable which has not yet been elaborated. The trouble with this approach is that it could require expensive checks on every variable reference. Instead Ada has two rules which are a little more restrictive, but easier to check, and easier to state:
Program_Error is raised.
Program_Error is raised.
The idea is that if the body has been elaborated, then any variables it references must have been elaborated; by checking for the body being elaborated we guarantee that none of its references causes any trouble. As we noted above, this is a little too restrictive, because a subprogram that has no non-local references in its body may in fact be safe to call. However, it really would be unsafe to rely on this, because it would mean that the caller was aware of details of the implementation in the body. This goes against the basic tenets of Ada.
A plausible implementation can be described as follows.
A Boolean variable is associated with each subprogram
and each generic unit. This variable is initialized to False, and is set to
True at the point body is elaborated. Every call or instantiation checks the
variable, and raises Program_Error if the variable is False.
Note that one might think that it would be good enough to have one Boolean
variable for each package, but that would not deal with cases of trying
to call a body in the same package as the call
that has not been elaborated yet.
Of course a compiler may be able to do enough analysis to optimize away
some of the Boolean variables as unnecessary, and GNAT indeed
does such optimizations, but still the easiest conceptual model is to
think of there being one variable per subprogram.
In the previous section we discussed the rules in Ada which ensure
that Program_Error is raised if an incorrect elaboration order is
chosen. This prevents erroneous executions, but we need mechanisms to
specify a correct execution and avoid the exception altogether.
To achieve this, Ada provides a number of features for controlling
the order of elaboration. We discuss these features in this section.
First, there are several ways of indicating to the compiler that a given unit has no elaboration problems:
| package Definitions is generic type m is new integer; package Subp is type a is array (1 .. 10) of m; type b is array (1 .. 20) of m; end Subp; end Definitions; |
A package that with's Definitions may safely instantiate
Definitions.Subp because the compiler can determine that there
definitely is no package body to worry about in this case
A has such a pragma,
and unit B does
a with of unit A. Recall that the standard rules require
the spec of unit A
to be elaborated before the with'ing unit; given the pragma in
A, we also know that the body of A
will be elaborated before B, so
that calls to A are safe and do not need a check.
Note that,
unlike pragma Pure and pragma Preelaborate,
the use of
Elaborate_Body does not guarantee that the program is
free of elaboration problems, because it may not be possible
to satisfy the requested elaboration order.
Let's go back to the example with Unit_1 and Unit_2.
If a programmer
marks Unit_1 as Elaborate_Body,
and not Unit_2, then the order of
elaboration will be:
Spec of Unit_2
Spec of Unit_1
Body of Unit_1
Body of Unit_2
Now that means that the call to Func_1 in Unit_2
need not be checked,
it must be safe. But the call to Func_2 in
Unit_1 may still fail if
Expression_1 is equal to 1,
and the programmer must still take
responsibility for this not being the case.
If all units carry a pragma Elaborate_Body, then all problems are
eliminated, except for calls entirely within a body, which are
in any case fully under programmer control. However, using the pragma
everywhere is not always possible.
In particular, for our Unit_1/Unit_2 example, if
we marked both of them as having pragma Elaborate_Body, then
clearly there would be no possible elaboration order.
The above pragmas allow a server to guarantee safe use by clients, and
clearly this is the preferable approach. Consequently a good rule
is to mark units as Pure or Preelaborate if possible,
and if this is not possible,
mark them as Elaborate_Body if possible.
As we have seen, there are situations where neither of these
three pragmas can be used.
So we also provide methods for clients to control the
order of elaboration of the servers on which they depend:
with clause,
and it requires that the body of the named unit be elaborated before
the unit in which the pragma occurs. The idea is to use this pragma
if the current unit calls at elaboration time, directly or indirectly,
some subprogram in the named unit.
Unit Awith's unit B and calls B.Func in elab code Unit Bwith's unit C, and B.Func calls C.Func
Now if we put a pragma Elaborate (B)
in unit A, this ensures that the
body of B is elaborated before the call, but not the
body of C, so
the call to C.Func could still cause Program_Error to
be raised.
The effect of a pragma Elaborate_All is stronger, it requires
not only that the body of the named unit be elaborated before the
unit doing the with, but also the bodies of all units that the
named unit uses, following with links transitively. For example,
if we put a pragma Elaborate_All (B) in unit A,
then it requires
not only that the body of B be elaborated before A,
but also the
body of C, because B with's C.
We are now in a position to give a usage rule in Ada for avoiding elaboration problems, at least if dynamic dispatching and access to subprogram values are not used. We will handle these cases separately later.
The rule is simple. If a unit has elaboration code that can directly or
indirectly make a call to a subprogram in a with'ed unit, or instantiate
a generic package in a with'ed unit,
then if the with'ed unit does not have
pragma Pure or Preelaborate, then the client should have
a pragma Elaborate_All
for the with'ed unit. By following this rule a client is
assured that calls can be made without risk of an exception.
For generic subprogram instantiations, the rule can be relaxed to
require only a pragma Elaborate since elaborating the body
of a subprogram cannot cause any transitive elaboration (we are
not calling the subprogram in this case, just elaborating its
declaration).
If this rule is not followed, then a program may be in one of four states:
Elaborate, Elaborate_All,
or Elaborate_Body pragmas. In
this case, an Ada compiler must diagnose the situation at bind
time, and refuse to build an executable program.
Program_Error will be raised
when the program is run.
Note that one additional advantage of following our rules on the use
of Elaborate and Elaborate_All
is that the program continues to stay in the ideal (all orders OK) state
even if maintenance
changes some bodies of some units. Conversely, if a program that does
not follow this rule happens to be safe at some point, this state of affairs
may deteriorate silently as a result of maintenance changes.
You may have noticed that the above discussion did not mention
the use of Elaborate_Body. This was a deliberate omission. If you
with an Elaborate_Body unit, it still may be the case that
code in the body makes calls to some other unit, so it is still necessary
to use Elaborate_All on such units.
In the case of internal calls, i.e., calls within a single package, the programmer has full control over the order of elaboration, and it is up to the programmer to elaborate declarations in an appropriate order. For example writing:
| function One return Float; Q : Float := One; function One return Float is begin return 1.0; end One; |
will obviously raise Program_Error at run time, because function
One will be called before its body is elaborated. In this case GNAT will
generate a warning that the call will raise Program_Error:
| 1. procedure y is 2. function One return Float; 3. 4. Q : Float := One; | >>> warning: cannot call "One" before body is elaborated >>> warning: Program_Error will be raised at run time 5. 6. function One return Float is 7. begin 8. return 1.0; 9. end One; 10. 11. begin 12. null; 13. end; |
Note that in this particular case, it is likely that the call is safe, because
the function One does not access any global variables.
Nevertheless in Ada, we do not want the validity of the check to depend on
the contents of the body (think about the separate compilation case), so this
is still wrong, as we discussed in the previous sections.
The error is easily corrected by rearranging the declarations so that the
body of One appears before the declaration containing the call
(note that in Ada 95 and Ada 2005,
declarations can appear in any order, so there is no restriction that
would prevent this reordering, and if we write:
| function One return Float; function One return Float is begin return 1.0; end One; Q : Float := One; |
then all is well, no warning is generated, and no
Program_Error exception
will be raised.
Things are more complicated when a chain of subprograms is executed:
| function A return Integer; function B return Integer; function C return Integer; function B return Integer is begin return A; end; function C return Integer is begin return B; end; X : Integer := C; function A return Integer is begin return 1; end; |
Now the call to C
at elaboration time in the declaration of X is correct, because
the body of C is already elaborated,
and the call to B within the body of
C is correct, but the call
to A within the body of B is incorrect, because the body
of A has not been elaborated, so Program_Error
will be raised on the call to A.
In this case GNAT will generate a
warning that Program_Error may be
raised at the point of the call. Let's look at the warning:
| 1. procedure x is 2. function A return Integer; 3. function B return Integer; 4. function C return Integer; 5. 6. function B return Integer is begin return A; end; | >>> warning: call to "A" before body is elaborated may raise Program_Error >>> warning: "B" called at line 7 >>> warning: "C" called at line 9 7. function C return Integer is begin return B; end; 8. 9. X : Integer := C; 10. 11. function A return Integer is begin return 1; end; 12. 13. begin 14. null; 15. end; |
Note that the message here says “may raise”, instead of the direct case,
where the message says “will be raised”. That's because whether
A is
actually called depends in general on run-time flow of control.
For example, if the body of B said
| function B return Integer is begin if some-condition-depending-on-input-data then return A; else return 1; end if; end B; |
then we could not know until run time whether the incorrect call to A would
actually occur, so Program_Error might
or might not be raised. It is possible for a compiler to
do a better job of analyzing bodies, to
determine whether or not Program_Error
might be raised, but it certainly
couldn't do a perfect job (that would require solving the halting problem
and is provably impossible), and because this is a warning anyway, it does
not seem worth the effort to do the analysis. Cases in which it
would be relevant are rare.
In practice, warnings of either of the forms given above will usually correspond to real errors, and should be examined carefully and eliminated. In the rare case where a warning is bogus, it can be suppressed by any of the following methods:
Elaboration_Check for the called subprogram
Warnings_Off to turn warnings off for the call
For the internal elaboration check case,
GNAT by default generates the
necessary run-time checks to ensure
that Program_Error is raised if any
call fails an elaboration check. Of course this can only happen if a
warning has been issued as described above. The use of pragma
Suppress (Elaboration_Check) may (but is not guaranteed to) suppress
some of these checks, meaning that it may be possible (but is not
guaranteed) for a program to be able to call a subprogram whose body
is not yet elaborated, without raising a Program_Error exception.
The previous section discussed the case in which the execution of a particular thread of elaboration code occurred entirely within a single unit. This is the easy case to handle, because a programmer has direct and total control over the order of elaboration, and furthermore, checks need only be generated in cases which are rare and which the compiler can easily detect. The situation is more complex when separate compilation is taken into account. Consider the following:
|
package Math is function Sqrt (Arg : Float) return Float; end Math; package body Math is function Sqrt (Arg : Float) return Float is begin ... end Sqrt; end Math; with Math; package Stuff is X : Float := Math.Sqrt (0.5); end Stuff; with Stuff; procedure Main is begin ... end Main; |
where Main is the main program. When this program is executed, the
elaboration code must first be executed, and one of the jobs of the
binder is to determine the order in which the units of a program are
to be elaborated. In this case we have four units: the spec and body
of Math,
the spec of Stuff and the body of Main).
In what order should the four separate sections of elaboration code
be executed?
There are some restrictions in the order of elaboration that the binder
can choose. In particular, if unit U has a with
for a package X, then you
are assured that the spec of X
is elaborated before U , but you are
not assured that the body of X
is elaborated before U.
This means that in the above case, the binder is allowed to choose the
order:
spec of Math
spec of Stuff
body of Math
body of Main
but that's not good, because now the call to Math.Sqrt
that happens during
the elaboration of the Stuff
spec happens before the body of Math.Sqrt is
elaborated, and hence causes Program_Error exception to be raised.
At first glance, one might say that the binder is misbehaving, because
obviously you want to elaborate the body of something you with
first, but
that is not a general rule that can be followed in all cases. Consider
| package X is ... package Y is ... with X; package body Y is ... with Y; package body X is ... |
This is a common arrangement, and, apart from the order of elaboration
problems that might arise in connection with elaboration code, this works fine.
A rule that says that you must first elaborate the body of anything you
with cannot work in this case:
the body of X with's Y,
which means you would have to
elaborate the body of Y first, but that with's X,
which means
you have to elaborate the body of X first, but ... and we have a
loop that cannot be broken.
It is true that the binder can in many cases guess an order of elaboration
that is unlikely to cause a Program_Error
exception to be raised, and it tries to do so (in the
above example of Math/Stuff/Spec, the GNAT binder will
by default
elaborate the body of Math right after its spec, so all will be well).
However, a program that blindly relies on the binder to be helpful can get into trouble, as we discussed in the previous sections, so GNAT provides a number of facilities for assisting the programmer in developing programs that are robust with respect to elaboration order.
The default behavior in GNAT ensures elaboration safety. In its default mode GNAT implements the rule we previously described as the right approach. Let's restate it:
with'ed unit, or instantiate a generic
package in a with'ed unit, then if the with'ed unit
does not have pragma Pure or
Preelaborate, then the client should have an
Elaborate_All pragma for the with'ed unit.
In the case of instantiating a generic subprogram, it is always
sufficient to have only an Elaborate pragma for the
with'ed unit.
By following this rule a client is assured that calls and instantiations can be made without risk of an exception.
In this mode GNAT traces all calls that are potentially made from
elaboration code, and puts in any missing implicit Elaborate
and Elaborate_All pragmas.
The advantage of this approach is that no elaboration problems
are possible if the binder can find an elaboration order that is
consistent with these implicit Elaborate and
Elaborate_All pragmas. The
disadvantage of this approach is that no such order may exist.
If the binder does not generate any diagnostics, then it means that it has
found an elaboration order that is guaranteed to be safe. However, the binder
may still be relying on implicitly generated Elaborate and
Elaborate_All pragmas so portability to other compilers than GNAT is not
guaranteed.
If it is important to guarantee portability, then the compilations should
use the
-gnatwl
(warn on elaboration problems) switch. This will cause warning messages
to be generated indicating the missing Elaborate and
Elaborate_All pragmas.
Consider the following source program:
| with k; package j is m : integer := k.r; end; |
where it is clear that there
should be a pragma Elaborate_All
for unit k. An implicit pragma will be generated, and it is
likely that the binder will be able to honor it. However, if you want
to port this program to some other Ada compiler than GNAT.
it is safer to include the pragma explicitly in the source. If this
unit is compiled with the
-gnatwl
switch, then the compiler outputs a warning:
| 1. with k; 2. package j is 3. m : integer := k.r; | >>> warning: call to "r" may raise Program_Error >>> warning: missing pragma Elaborate_All for "k" 4. end; |
and these warnings can be used as a guide for supplying manually
the missing pragmas. It is usually a bad idea to use this warning
option during development. That's because it will warn you when
you need to put in a pragma, but cannot warn you when it is time
to take it out. So the use of pragma Elaborate_All may lead to
unnecessary dependencies and even false circularities.
This default mode is more restrictive than the Ada Reference Manual, and it is possible to construct programs which will compile using the dynamic model described there, but will run into a circularity using the safer static model we have described.
Of course any Ada compiler must be able to operate in a mode consistent with the requirements of the Ada Reference Manual, and in particular must have the capability of implementing the standard dynamic model of elaboration with run-time checks.
In GNAT, this standard mode can be achieved either by the use of the -gnatE switch on the compiler (gcc or gnatmake) command, or by the use of the configuration pragma:
pragma Elaboration_Checks (RM);
Either approach will cause the unit affected to be compiled using the standard dynamic run-time elaboration checks described in the Ada Reference Manual. The static model is generally preferable, since it is clearly safer to rely on compile and link time checks rather than run-time checks. However, in the case of legacy code, it may be difficult to meet the requirements of the static model. This issue is further discussed in What to Do If the Default Elaboration Behavior Fails.
Note that the static model provides a strict subset of the allowed behavior and programs of the Ada Reference Manual, so if you do adhere to the static model and no circularities exist, then you are assured that your program will work using the dynamic model, providing that you remove any pragma Elaborate statements from the source.
The use of pragma Elaborate
should generally be avoided in Ada 95 and Ada 2005 programs,
since there is no guarantee that transitive calls
will be properly handled. Indeed at one point, this pragma was placed
in Annex J (Obsolescent Features), on the grounds that it is never useful.
Now that's a bit restrictive. In practice, the case in which
pragma Elaborate is useful is when the caller knows that there
are no transitive calls, or that the called unit contains all necessary
transitive pragma Elaborate statements, and legacy code often
contains such uses.
Strictly speaking the static mode in GNAT should ignore such pragmas,
since there is no assurance at compile time that the necessary safety
conditions are met. In practice, this would cause GNAT to be incompatible
with correctly written Ada 83 code that had all necessary
pragma Elaborate statements in place. Consequently, we made the
decision that GNAT in its default mode will believe that if it encounters
a pragma Elaborate then the programmer knows what they are doing,
and it will trust that no elaboration errors can occur.
The result of this decision is two-fold. First to be safe using the
static mode, you should remove all pragma Elaborate statements.
Second, when fixing circularities in existing code, you can selectively
use pragma Elaborate statements to convince the static mode of
GNAT that it need not generate an implicit pragma Elaborate_All
statement.
When using the static mode with -gnatwl, any use of
pragma Elaborate will generate a warning about possible
problems.
In this section we examine special elaboration issues that arise for programs that declare library level tasks.
Generally the model of execution of an Ada program is that all units are elaborated, and then execution of the program starts. However, the declaration of library tasks definitely does not fit this model. The reason for this is that library tasks start as soon as they are declared (more precisely, as soon as the statement part of the enclosing package body is reached), that is to say before elaboration of the program is complete. This means that if such a task calls a subprogram, or an entry in another task, the callee may or may not be elaborated yet, and in the standard Reference Manual model of dynamic elaboration checks, you can even get timing dependent Program_Error exceptions, since there can be a race between the elaboration code and the task code.
The static model of elaboration in GNAT seeks to avoid all such dynamic behavior, by being conservative, and the conservative approach in this particular case is to assume that all the code in a task body is potentially executed at elaboration time if a task is declared at the library level.
This can definitely result in unexpected circularities. Consider the following example
package Decls is
task Lib_Task is
entry Start;
end Lib_Task;
type My_Int is new Integer;
function Ident (M : My_Int) return My_Int;
end Decls;
with Utils;
package body Decls is
task body Lib_Task is
begin
accept Start;
Utils.Put_Val (2);
end Lib_Task;
function Ident (M : My_Int) return My_Int is
begin
return M;
end Ident;
end Decls;
with Decls;
package Utils is
procedure Put_Val (Arg : Decls.My_Int);
end Utils;
with Text_IO;
package body Utils is
procedure Put_Val (Arg : Decls.My_Int) is
begin
Text_IO.Put_Line (Decls.My_Int'Image (Decls.Ident (Arg)));
end Put_Val;
end Utils;
with Decls;
procedure Main is
begin
Decls.Lib_Task.Start;
end;
If the above example is compiled in the default static elaboration
mode, then a circularity occurs. The circularity comes from the call
Utils.Put_Val in the task body of Decls.Lib_Task. Since
this call occurs in elaboration code, we need an implicit pragma
Elaborate_All for Utils. This means that not only must
the spec and body of Utils be elaborated before the body
of Decls, but also the spec and body of any unit that is
with'ed by the body of Utils must also be elaborated before
the body of Decls. This is the transitive implication of
pragma Elaborate_All and it makes sense, because in general
the body of Put_Val might have a call to something in a
with'ed unit.
In this case, the body of Utils (actually its spec) with's
Decls. Unfortunately this means that the body of Decls
must be elaborated before itself, in case there is a call from the
body of Utils.
Here is the exact chain of events we are worrying about:
Decls a call is made from within the body of a library
task to a subprogram in the package Utils. Since this call may
occur at elaboration time (given that the task is activated at elaboration
time), we have to assume the worst, i.e., that the
call does happen at elaboration time.
Util must be elaborated before
the body of Decls so that this call does not cause an access before
elaboration.
Util, specifically within the body of
Util.Put_Val there may be calls to any unit with'ed
by this package.
with'ed package is package Decls, so there
might be a call to a subprogram in Decls in Put_Val.
In fact there is such a call in this example, but we would have to
assume that there was such a call even if it were not there, since
we are not supposed to write the body of Decls knowing what
is in the body of Utils; certainly in the case of the
static elaboration model, the compiler does not know what is in
other bodies and must assume the worst.
Decls must also be
elaborated before we elaborate the unit containing the call, but
that unit is Decls! This means that the body of Decls
must be elaborated before itself, and that's a circularity.
Indeed, if you add an explicit pragma Elaborate_All for Utils in
the body of Decls you will get a true Ada Reference Manual
circularity that makes the program illegal.
In practice, we have found that problems with the static model of elaboration in existing code often arise from library tasks, so we must address this particular situation.
Note that if we compile and run the program above, using the dynamic model of elaboration (that is to say use the -gnatE switch), then it compiles, binds, links, and runs, printing the expected result of 2. Therefore in some sense the circularity here is only apparent, and we need to capture the properties of this program that distinguish it from other library-level tasks that have real elaboration problems.
We have four possible answers to this question:
If we use the -gnatE switch, then as noted above, the program works.
Why is this? If we examine the task body, it is apparent that the task cannot
proceed past the
accept statement until after elaboration has been completed, because
the corresponding entry call comes from the main program, not earlier.
This is why the dynamic model works here. But that's really giving
up on a precise analysis, and we prefer to take this approach only if we cannot
solve the
problem in any other manner. So let us examine two ways to reorganize
the program to avoid the potential elaboration problem.
Write separate packages, so that library tasks are isolated from other declarations as much as possible. Let us look at a variation on the above program.
package Decls1 is
task Lib_Task is
entry Start;
end Lib_Task;
end Decls1;
with Utils;
package body Decls1 is
task body Lib_Task is
begin
accept Start;
Utils.Put_Val (2);
end Lib_Task;
end Decls1;
package Decls2 is
type My_Int is new Integer;
function Ident (M : My_Int) return My_Int;
end Decls2;
with Utils;
package body Decls2 is
function Ident (M : My_Int) return My_Int is
begin
return M;
end Ident;
end Decls2;
with Decls2;
package Utils is
procedure Put_Val (Arg : Decls2.My_Int);
end Utils;
with Text_IO;
package body Utils is
procedure Put_Val (Arg : Decls2.My_Int) is
begin
Text_IO.Put_Line (Decls2.My_Int'Image (Decls2.Ident (Arg)));
end Put_Val;
end Utils;
with Decls1;
procedure Main is
begin
Decls1.Lib_Task.Start;
end;
All we have done is to split Decls into two packages, one
containing the library task, and one containing everything else. Now
there is no cycle, and the program compiles, binds, links and executes
using the default static model of elaboration.
A significant part of the problem arises because of the use of the single task declaration form. This means that the elaboration of the task type, and the elaboration of the task itself (i.e. the creation of the task) happen at the same time. A good rule of style in Ada is to always create explicit task types. By following the additional step of placing task objects in separate packages from the task type declaration, many elaboration problems are avoided. Here is another modified example of the example program:
package Decls is
task type Lib_Task_Type is
entry Start;
end Lib_Task_Type;
type My_Int is new Integer;
function Ident (M : My_Int) return My_Int;
end Decls;
with Utils;
package body Decls is
task body Lib_Task_Type is
begin
accept Start;
Utils.Put_Val (2);
end Lib_Task_Type;
function Ident (M : My_Int) return My_Int is
begin
return M;
end Ident;
end Decls;
with Decls;
package Utils is
procedure Put_Val (Arg : Decls.My_Int);
end Utils;
with Text_IO;
package body Utils is
procedure Put_Val (Arg : Decls.My_Int) is
begin
Text_IO.Put_Line (Decls.My_Int'Image (Decls.Ident (Arg)));
end Put_Val;
end Utils;
with Decls;
package Declst is
Lib_Task : Decls.Lib_Task_Type;
end Declst;
with Declst;
procedure Main is
begin
Declst.Lib_Task.Start;
end;
What we have done here is to replace the task declaration in
package Decls with a task type declaration. Then we
introduce a separate package Declst to contain the actual
task object. This separates the elaboration issues for
the task type
declaration, which causes no trouble, from the elaboration issues
of the task object, which is also unproblematic, since it is now independent
of the elaboration of Utils.
This separation of concerns also corresponds to
a generally sound engineering principle of separating declarations
from instances. This version of the program also compiles, binds, links,
and executes, generating the expected output.
Let us consider more carefully why our original sample program works
under the dynamic model of elaboration. The reason is that the code
in the task body blocks immediately on the accept
statement. Now of course there is nothing to prohibit elaboration
code from making entry calls (for example from another library level task),
so we cannot tell in isolation that
the task will not execute the accept statement during elaboration.
However, in practice it is very unusual to see elaboration code
make any entry calls, and the pattern of tasks starting
at elaboration time and then immediately blocking on accept or
select statements is very common. What this means is that
the compiler is being too pessimistic when it analyzes the
whole package body as though it might be executed at elaboration
time.
If we know that the elaboration code contains no entry calls, (a very safe assumption most of the time, that could almost be made the default behavior), then we can compile all units of the program under control of the following configuration pragma:
pragma Restrictions (No_Entry_Calls_In_Elaboration_Code);
This pragma can be placed in the gnat.adc file in the usual
manner. If we take our original unmodified program and compile it
in the presence of a gnat.adc containing the above pragma,
then once again, we can compile, bind, link, and execute, obtaining
the expected result. In the presence of this pragma, the compiler does
not trace calls in a task body, that appear after the first accept
or select statement, and therefore does not report a potential
circularity in the original program.
The compiler will check to the extent it can that the above restriction is not violated, but it is not always possible to do a complete check at compile time, so it is important to use this pragma only if the stated restriction is in fact met, that is to say no task receives an entry call before elaboration of all units is completed.
So far, we have assumed that the entire program is either compiled using the dynamic model or static model, ensuring consistency. It is possible to mix the two models, but rules have to be followed if this mixing is done to ensure that elaboration checks are not omitted.
The basic rule is that a unit compiled with the static model cannot
be with'ed by a unit compiled with the dynamic model. The
reason for this is that in the static model, a unit assumes that
its clients guarantee to use (the equivalent of) pragma
Elaborate_All so that no elaboration checks are required
in inner subprograms, and this assumption is violated if the
client is compiled with dynamic checks.
The precise rule is as follows. A unit that is compiled with dynamic
checks can only with a unit that meets at least one of the
following criteria:
with'ed unit is itself compiled with dynamic elaboration
checks (that is with the -gnatE switch.
with'ed unit is an internal GNAT implementation unit from
the System, Interfaces, Ada, or GNAT hierarchies.
with'ed unit has pragma Preelaborate or pragma Pure.
with'ing unit (that is the client) has an explicit pragma
Elaborate_All for the with'ed unit.
If this rule is violated, that is if a unit with dynamic elaboration
checks with's a unit that does not meet one of the above four
criteria, then the binder (gnatbind) will issue a warning
similar to that in the following example:
warning: "x.ads" has dynamic elaboration checks and with's
warning: "y.ads" which has static elaboration checks
These warnings indicate that the rule has been violated, and that as a result elaboration checks may be missed in the resulting executable file. This warning may be suppressed using the -ws binder switch in the usual manner.
One useful application of this mixing rule is in the case of a subsystem
which does not itself with units from the remainder of the
application. In this case, the entire subsystem can be compiled with
dynamic checks to resolve a circularity in the subsystem, while
allowing the main application that uses this subsystem to be compiled
using the more reliable default static model.
If the binder cannot find an acceptable order, it outputs detailed diagnostics. For example:
error: elaboration circularity detected
info: "proc (body)" must be elaborated before "pack (body)"
info: reason: Elaborate_All probably needed in unit "pack (body)"
info: recompile "pack (body)" with -gnatwl
info: for full details
info: "proc (body)"
info: is needed by its spec:
info: "proc (spec)"
info: which is withed by:
info: "pack (body)"
info: "pack (body)" must be elaborated before "proc (body)"
info: reason: pragma Elaborate in unit "proc (body)"
In this case we have a cycle that the binder cannot break. On the one
hand, there is an explicit pragma Elaborate in proc for
pack. This means that the body of pack must be elaborated
before the body of proc. On the other hand, there is elaboration
code in pack that calls a subprogram in proc. This means
that for maximum safety, there should really be a pragma
Elaborate_All in pack for proc which would require that
the body of proc be elaborated before the body of
pack. Clearly both requirements cannot be satisfied.
Faced with a circularity of this kind, you have three different options.
Elaborate or Elaborate_All pragmas. The behavior then is
exactly as specified in the Ada Reference Manual.
The binder will generate
an executable program that may or may not raise Program_Error, and then
it is the programmer's job to ensure that it does not raise an exception. Note
that it is important to compile all units with the switch, it cannot be used
selectively.
Suppress (Elaboration_Check) to suppress all such checks. For
example this pragma could be placed in the gnat.adc file.
Elaborate and Elaborate_All pragmas that lead to
elaboration circularities, it is possible to remove those warnings locally and
obtain a program that will bind. Clearly this can be unsafe, and it is the
responsibility of the programmer to make sure that the resulting program has no
elaboration anomalies. The pragma Suppress (Elaboration_Check) can be
used with different granularity to suppress warnings and break elaboration
circularities:
pragma Elaborate indicates correctly
that no elaboration checks are required on calls to the designated unit.
There may be cases in which the caller knows that no transitive calls
can occur, so that a pragma Elaborate will be sufficient in a
case where pragma Elaborate_All would cause a circularity.
These five cases are listed in order of decreasing safety, and therefore require increasing programmer care in their application. Consider the following program:
package Pack1 is
function F1 return Integer;
X1 : Integer;
end Pack1;
package Pack2 is
function F2 return Integer;
function Pure (x : integer) return integer;
-- pragma Suppress (Elaboration_Check, On => Pure); -- (3)
-- pragma Suppress (Elaboration_Check); -- (4)
end Pack2;
with Pack2;
package body Pack1 is
function F1 return Integer is
begin
return 100;
end F1;
Val : integer := Pack2.Pure (11); -- Elab. call (1)
begin
declare
-- pragma Suppress(Elaboration_Check, Pack2.F2); -- (1)
-- pragma Suppress(Elaboration_Check); -- (2)
begin
X1 := Pack2.F2 + 1; -- Elab. call (2)
end;
end Pack1;
with Pack1;
package body Pack2 is
function F2 return Integer is
begin
return Pack1.F1;
end F2;
function Pure (x : integer) return integer is
begin
return x ** 3 - 3 * x;
end;
end Pack2;
with Pack1, Ada.Text_IO;
procedure Proc3 is
begin
Ada.Text_IO.Put_Line(Pack1.X1'Img); -- 101
end Proc3;
In the absence of any pragmas, an attempt to bind this program produces the following diagnostics:
error: elaboration circularity detected
info: "pack1 (body)" must be elaborated before "pack1 (body)"
info: reason: Elaborate_All probably needed in unit "pack1 (body)"
info: recompile "pack1 (body)" with -gnatwl for full details
info: "pack1 (body)"
info: must be elaborated along with its spec:
info: "pack1 (spec)"
info: which is withed by:
info: "pack2 (body)"
info: which must be elaborated along with its spec:
info: "pack2 (spec)"
info: which is withed by:
info: "pack1 (body)"
The sources of the circularity are the two calls to Pack2.Pure and
Pack2.F2 in the body of Pack1. We can see that the call to
F2 is safe, even though F2 calls F1, because the call appears after the
elaboration of the body of F1. Therefore the pragma (1) is safe, and will
remove the warning on the call. It is also possible to use pragma (2)
because there are no other potentially unsafe calls in the block.
The call to Pure is safe because this function does not depend on the
state of Pack2. Therefore any call to this function is safe, and it
is correct to place pragma (3) in the corresponding package spec.
Finally, we could place pragma (4) in the spec of Pack2 to disable
warnings on all calls to functions declared therein. Note that this is not
necessarily safe, and requires more detailed examination of the subprogram
bodies involved. In particular, a call to F2 requires that F1
be already elaborated.
It is hard to generalize on which of these four approaches should be
taken. Obviously if it is possible to fix the program so that the default
treatment works, this is preferable, but this may not always be practical.
It is certainly simple enough to use
-gnatE
but the danger in this case is that, even if the GNAT binder
finds a correct elaboration order, it may not always do so,
and certainly a binder from another Ada compiler might not. A
combination of testing and analysis (for which the warnings generated
with the
-gnatwl
switch can be useful) must be used to ensure that the program is free
of errors. One switch that is useful in this testing is the
-p (pessimistic elaboration order)
switch for
gnatbind.
Normally the binder tries to find an order that has the best chance
of avoiding elaboration problems. However, if this switch is used, the binder
plays a devil's advocate role, and tries to choose the order that
has the best chance of failing. If your program works even with this
switch, then it has a better chance of being error free, but this is still
not a guarantee.
For an example of this approach in action, consider the C-tests (executable tests) from the ACVC suite. If these are compiled and run with the default treatment, then all but one of them succeed without generating any error diagnostics from the binder. However, there is one test that fails, and this is not surprising, because the whole point of this test is to ensure that the compiler can handle cases where it is impossible to determine a correct order statically, and it checks that an exception is indeed raised at run time.
This one test must be compiled and run using the -gnatE switch, and then it passes. Alternatively, the entire suite can be run using this switch. It is never wrong to run with the dynamic elaboration switch if your code is correct, and we assume that the C-tests are indeed correct (it is less efficient, but efficiency is not a factor in running the ACVC tests.)
Access-to-subprogram types (introduced in Ada 95) complicate the handling of elaboration. The trouble is that it becomes impossible to tell at compile time which procedure is being called. This means that it is not possible for the binder to analyze the elaboration requirements in this case.
If at the point at which the access value is created
(i.e., the evaluation of P'Access for a subprogram P),
the body of the subprogram is
known to have been elaborated, then the access value is safe, and its use
does not require a check. This may be achieved by appropriate arrangement
of the order of declarations if the subprogram is in the current unit,
or, if the subprogram is in another unit, by using pragma
Pure, Preelaborate, or Elaborate_Body
on the referenced unit.
If the referenced body is not known to have been elaborated at the point
the access value is created, then any use of the access value must do a
dynamic check, and this dynamic check will fail and raise a
Program_Error exception if the body has not been elaborated yet.
GNAT will generate the necessary checks, and in addition, if the
-gnatwl
switch is set, will generate warnings that such checks are required.
The use of dynamic dispatching for tagged types similarly generates
a requirement for dynamic checks, and premature calls to any primitive
operation of a tagged type before the body of the operation has been
elaborated, will result in the raising of Program_Error.
First, compile your program with the default options, using none of
the special elaboration control switches. If the binder successfully
binds your program, then you can be confident that, apart from issues
raised by the use of access-to-subprogram types and dynamic dispatching,
the program is free of elaboration errors. If it is important that the
program be portable, then use the
-gnatwl
switch to generate warnings about missing Elaborate or
Elaborate_All pragmas, and supply the missing pragmas.
If the program fails to bind using the default static elaboration
handling, then you can fix the program to eliminate the binder
message, or recompile the entire program with the
-gnatE switch to generate dynamic elaboration checks,
and, if you are sure there really are no elaboration problems,
use a global pragma Suppress (Elaboration_Check).
This section has been entirely concerned with the issue of finding a valid elaboration order, as defined by the Ada Reference Manual. In a case where several elaboration orders are valid, the task is to find one of the possible valid elaboration orders (and the static model in GNAT will ensure that this is achieved).
The purpose of the elaboration rules in the Ada Reference Manual is to make sure that no entity is accessed before it has been elaborated. For a subprogram, this means that the spec and body must have been elaborated before the subprogram is called. For an object, this means that the object must have been elaborated before its value is read or written. A violation of either of these two requirements is an access before elaboration order, and this section has been all about avoiding such errors.
In the case where more than one order of elaboration is possible, in the sense that access before elaboration errors are avoided, then any one of the orders is “correct” in the sense that it meets the requirements of the Ada Reference Manual, and no such error occurs.
However, it may be the case for a given program, that there are constraints on the order of elaboration that come not from consideration of avoiding elaboration errors, but rather from extra-lingual logic requirements. Consider this example:
with Init_Constants;
package Constants is
X : Integer := 0;
Y : Integer := 0;
end Constants;
package Init_Constants is
procedure P; -- require a body
end Init_Constants;
with Constants;
package body Init_Constants is
procedure P is begin null; end;
begin
Constants.X := 3;
Constants.Y := 4;
end Init_Constants;
with Constants;
package Calc is
Z : Integer := Constants.X + Constants.Y;
end Calc;
with Calc;
with Text_IO; use Text_IO;
procedure Main is
begin
Put_Line (Calc.Z'Img);
end Main;
In this example, there is more than one valid order of elaboration. For example both the following are correct orders:
Init_Constants spec
Constants spec
Calc spec
Init_Constants body
Main body
and
Init_Constants spec
Init_Constants body
Constants spec
Calc spec
Main body
There is no language rule to prefer one or the other, both are correct
from an order of elaboration point of view. But the programmatic effects
of the two orders are very different. In the first, the elaboration routine
of Calc initializes Z to zero, and then the main program
runs with this value of zero. But in the second order, the elaboration
routine of Calc runs after the body of Init_Constants has set
X and Y and thus Z is set to 7 before Main
runs.
One could perhaps by applying pretty clever non-artificial intelligence to the situation guess that it is more likely that the second order of elaboration is the one desired, but there is no formal linguistic reason to prefer one over the other. In fact in this particular case, GNAT will prefer the second order, because of the rule that bodies are elaborated as soon as possible, but it's just luck that this is what was wanted (if indeed the second order was preferred).
If the program cares about the order of elaboration routines in a case like this, it is important to specify the order required. In this particular case, that could have been achieved by adding to the spec of Calc:
pragma Elaborate_All (Constants);
which requires that the body (if any) and spec of Constants,
as well as the body and spec of any unit with'ed by
Constants be elaborated before Calc is elaborated.
Clearly no automatic method can always guess which alternative you require,
and if you are working with legacy code that had constraints of this kind
which were not properly specified by adding Elaborate or
Elaborate_All pragmas, then indeed it is possible that two different
compilers can choose different orders.
However, GNAT does attempt to diagnose the common situation where there are uninitialized variables in the visible part of a package spec, and the corresponding package body has an elaboration block that directly or indirectly initialized one or more of these variables. This is the situation in which a pragma Elaborate_Body is usually desirable, and GNAT will generate a warning that suggests this addition if it detects this situation.
The gnatbind
-p switch may be useful in smoking
out problems. This switch causes bodies to be elaborated as late as possible
instead of as early as possible. In the example above, it would have forced
the choice of the first elaboration order. If you get different results
when using this switch, and particularly if one set of results is right,
and one is wrong as far as you are concerned, it shows that you have some
missing Elaborate pragmas. For the example above, we have the
following output:
gnatmake -f -q main
main
7
gnatmake -f -q main -bargs -p
main
0
It is of course quite unlikely that both these results are correct, so
it is up to you in a case like this to investigate the source of the
difference, by looking at the two elaboration orders that are chosen,
and figuring out which is correct, and then adding the necessary
Elaborate or Elaborate_All pragmas to ensure the desired order.
It is often necessary to arrange for a single source program to serve multiple purposes, where it is compiled in different ways to achieve these different goals. Some examples of the need for this feature are
In C, or C++, the typical approach would be to use the preprocessor that is defined as part of the language. The Ada language does not contain such a feature. This is not an oversight, but rather a very deliberate design decision, based on the experience that overuse of the preprocessing features in C and C++ can result in programs that are extremely difficult to maintain. For example, if we have ten switches that can be on or off, this means that there are a thousand separate programs, any one of which might not even be syntactically correct, and even if syntactically correct, the resulting program might not work correctly. Testing all combinations can quickly become impossible.
Nevertheless, the need to tailor programs certainly exists, and in this Appendix we will discuss how this can be achieved using Ada in general, and GNAT in particular.
In the case where the difference is simply which code sequence is executed, the cleanest solution is to use Boolean constants to control which code is executed.
FP_Initialize_Required : constant Boolean := True;
...
if FP_Initialize_Required then
...
end if;
Not only will the code inside the if statement not be executed if
the constant Boolean is False, but it will also be completely
deleted from the program.
However, the code is only deleted after the if statement
has been checked for syntactic and semantic correctness.
(In contrast, with preprocessors the code is deleted before the
compiler ever gets to see it, so it is not checked until the switch
is turned on.)
Typically the Boolean constants will be in a separate package,
something like:
package Config is
FP_Initialize_Required : constant Boolean := True;
Reset_Available : constant Boolean := False;
...
end Config;
The Config package exists in multiple forms for the various targets,
with an appropriate script selecting the version of Config needed.
Then any other unit requiring conditional compilation can do a with
of Config to make the constants visible.
A common use of conditional code is to execute statements (for example dynamic checks, or output of intermediate results) under control of a debug switch, so that the debugging behavior can be turned on and off. This can be done using a Boolean constant to control whether the code is active:
if Debugging then
Put_Line ("got to the first stage!");
end if;
or
if Debugging and then Temperature > 999.0 then
raise Temperature_Crazy;
end if;
Since this is a common case, there are special features to deal with
this in a convenient manner. For the case of tests, Ada 2005 has added
a pragma Assert that can be used for such tests. This pragma is modeled
on the Assert pragma that has always been available in GNAT, so this
feature may be used with GNAT even if you are not using Ada 2005 features.
The use of pragma Assert is described in
Pragma Assert, but as an
example, the last test could be written:
pragma Assert (Temperature <= 999.0, "Temperature Crazy");
or simply
pragma Assert (Temperature <= 999.0);
In both cases, if assertions are active and the temperature is excessive,
the exception Assert_Failure will be raised, with the given string in
the first case or a string indicating the location of the pragma in the second
case used as the exception message.
You can turn assertions on and off by using the Assertion_Policy
pragma.
This is an Ada 2005 pragma which is implemented in all modes by
GNAT, but only in the latest versions of GNAT which include Ada 2005
capability. Alternatively, you can use the -gnata switch
to enable assertions from the command line (this is recognized by all versions
of GNAT).
For the example above with the Put_Line, the GNAT-specific pragma
Debug can be used:
pragma Debug (Put_Line ("got to the first stage!"));
If debug pragmas are enabled, the argument, which must be of the form of
a procedure call, is executed (in this case, Put_Line will be called).
Only one call can be present, but of course a special debugging procedure
containing any code you like can be included in the program and then
called in a pragma Debug argument as needed.
One advantage of pragma Debug over the if Debugging then
construct is that pragma Debug can appear in declarative contexts,
such as at the very beginning of a procedure, before local declarations have
been elaborated.
Debug pragmas are enabled using either the -gnata switch that also
controls assertions, or with a separate Debug_Policy pragma.
The latter pragma is new in the Ada 2005 versions of GNAT (but it can be used
in Ada 95 and Ada 83 programs as well), and is analogous to
pragma Assertion_Policy to control assertions.
Assertion_Policy and Debug_Policy are configuration pragmas,
and thus they can appear in gnat.adc if you are not using a
project file, or in the file designated to contain configuration pragmas
in a project file.
They then apply to all subsequent compilations. In practice the use of
the -gnata switch is often the most convenient method of controlling
the status of these pragmas.
Note that a pragma is not a statement, so in contexts where a statement
sequence is required, you can't just write a pragma on its own. You have
to add a null statement.
if ... then
... -- some statements
else
pragma Assert (Num_Cases < 10);
null;
end if;
In some cases, it may be necessary to conditionalize declarations to meet different requirements. For example we might want a bit string whose length is set to meet some hardware message requirement.
In some cases, it may be possible to do this using declare blocks controlled by conditional constants:
if Small_Machine then
declare
X : Bit_String (1 .. 10);
begin
...
end;
else
declare
X : Large_Bit_String (1 .. 1000);
begin
...
end;
end if;
Note that in this approach, both declarations are analyzed by the compiler so this can only be used where both declarations are legal, even though one of them will not be used.
Another approach is to define integer constants, e.g. Bits_Per_Word, or
Boolean constants, e.g. Little_Endian, and then write declarations
that are parameterized by these constants. For example
for Rec use
Field1 at 0 range Boolean'Pos (Little_Endian) * 10 .. Bits_Per_Word;
end record;
If Bits_Per_Word is set to 32, this generates either
for Rec use
Field1 at 0 range 0 .. 32;
end record;
for the big endian case, or
for Rec use record
Field1 at 0 range 10 .. 32;
end record;
for the little endian case. Since a powerful subset of Ada expression
notation is usable for creating static constants, clever use of this
feature can often solve quite difficult problems in conditionalizing
compilation (note incidentally that in Ada 95, the little endian
constant was introduced as System.Default_Bit_Order, so you do not
need to define this one yourself).
In some cases, none of the approaches described above are adequate. This can occur for example if the set of declarations required is radically different for two different configurations.
In this situation, the official Ada way of dealing with conditionalizing such code is to write separate units for the different cases. As long as this does not result in excessive duplication of code, this can be done without creating maintenance problems. The approach is to share common code as far as possible, and then isolate the code and declarations that are different. Subunits are often a convenient method for breaking out a piece of a unit that is to be conditionalized, with separate files for different versions of the subunit for different targets, where the build script selects the right one to give to the compiler. As an example, consider a situation where a new feature in Ada 2005 allows something to be done in a really nice way. But your code must be able to compile with an Ada 95 compiler. Conceptually you want to say:
if Ada_2005 then
... neat Ada 2005 code
else
... not quite as neat Ada 95 code
end if;
where Ada_2005 is a Boolean constant.
But this won't work when Ada_2005 is set to False,
since the then clause will be illegal for an Ada 95 compiler.
(Recall that although such unreachable code would eventually be deleted
by the compiler, it still needs to be legal. If it uses features
introduced in Ada 2005, it will be illegal in Ada 95.)
So instead we write
procedure Insert is separate;
Then we have two files for the subunit Insert, with the two sets of
code.
If the package containing this is called File_Queries, then we might
have two files
and the build script renames the appropriate file to
file_queries-insert.adb
and then carries out the compilation.
This can also be done with project files' naming schemes. For example:
For Body ("File_Queries.Insert") use "file_queries-insert-2005.ada";
Note also that with project files it is desirable to use a different extension than ads / adb for alternative versions. Otherwise a naming conflict may arise through another commonly used feature: to declare as part of the project a set of directories containing all the sources obeying the default naming scheme.
The use of alternative units is certainly feasible in all situations, and for example the Ada part of the GNAT run-time is conditionalized based on the target architecture using this approach. As a specific example, consider the implementation of the AST feature in VMS. There is one spec:
s-asthan.ads
which is the same for all architectures, and three bodies:
The dummy version s-asthan.adb simply raises exceptions noting that this operating system feature is not available, and the two remaining versions interface with the corresponding versions of VMS to provide VMS-compatible AST handling. The GNAT build script knows the architecture and operating system, and automatically selects the right version, renaming it if necessary to s-asthan.adb before the run-time build.
Another style for arranging alternative implementations is through Ada's
access-to-subprogram facility.
In case some functionality is to be conditionally included,
you can declare an access-to-procedure variable Ref that is initialized
to designate a “do nothing” procedure, and then invoke Ref.all
when appropriate.
In some library package, set Ref to Proc'Access for some
procedure Proc that performs the relevant processing.
The initialization only occurs if the library package is included in the
program.
The same idea can also be implemented using tagged types and dispatching
calls.
Although it is quite possible to conditionalize code without the use of C-style preprocessing, as described earlier in this section, it is nevertheless convenient in some cases to use the C approach. Moreover, older Ada compilers have often provided some preprocessing capability, so legacy code may depend on this approach, even though it is not standard.
To accommodate such use, GNAT provides a preprocessor (modeled to a large extent on the various preprocessors that have been used with legacy code on other compilers, to enable easier transition).
The preprocessor may be used in two separate modes. It can be used quite
separately from the compiler, to generate a separate output source file
that is then fed to the compiler as a separate step. This is the
gnatprep utility, whose use is fully described in
Preprocessing Using gnatprep.
The preprocessing language allows such constructs as
#if DEBUG or PRIORITY > 4 then
bunch of declarations
#else
completely different bunch of declarations
#end if;
The values of the symbols DEBUG and PRIORITY can be
defined either on the command line or in a separate file.
The other way of running the preprocessor is even closer to the C style and
often more convenient. In this approach the preprocessing is integrated into
the compilation process. The compiler is fed the preprocessor input which
includes #if lines etc, and then the compiler carries out the
preprocessing internally and processes the resulting output.
For more details on this approach, see Integrated Preprocessing.
If you need to write low-level software that interacts directly
with the hardware, Ada provides two ways to incorporate assembly
language code into your program. First, you can import and invoke
external routines written in assembly language, an Ada feature fully
supported by GNAT. However, for small sections of code it may be simpler
or more efficient to include assembly language statements directly
in your Ada source program, using the facilities of the implementation-defined
package System.Machine_Code, which incorporates the gcc
Inline Assembler. The Inline Assembler approach offers a number of advantages,
including the following:
This chapter presents a series of examples to show you how to use the Inline Assembler. Although it focuses on the Intel x86, the general approach applies also to other processors. It is assumed that you are familiar with Ada and with assembly language programming.
The assembler used by GNAT and gcc is based not on the Intel assembly language, but rather on a language that descends from the AT&T Unix assembler as (and which is often referred to as “AT&T syntax”). The following table summarizes the main features of as syntax and points out the differences from the Intel conventions. See the gcc as and gas (an as macro pre-processor) documentation for further information.
%eax
eax
$4
4
$loc
loc
loc
[loc]
(%eax)
[eax]
0xA0
A0h
movw to move
a 16-bit word
mov
rep
stosl
rep stosl
movw $4, %eax
mov eax, 4
The following example will generate a single assembly language statement,
nop, which does nothing. Despite its lack of run-time effect,
the example will be useful in illustrating the basics of
the Inline Assembler facility.
with System.Machine_Code; use System.Machine_Code;
procedure Nothing is
begin
Asm ("nop");
end Nothing;
Asm is a procedure declared in package System.Machine_Code;
here it takes one parameter, a template string that must be a static
expression and that will form the generated instruction.
Asm may be regarded as a compile-time procedure that parses
the template string and additional parameters (none here),
from which it generates a sequence of assembly language instructions.
The examples in this chapter will illustrate several of the forms
for invoking Asm; a complete specification of the syntax
is found in Machine Code Insertions.
Under the standard GNAT conventions, the Nothing procedure
should be in a file named nothing.adb.
You can build the executable in the usual way:
gnatmake nothing
However, the interesting aspect of this example is not its run-time behavior but rather the generated assembly code. To see this output, invoke the compiler as follows:
gcc -c -S -fomit-frame-pointer -gnatp nothing.adb
where the options are:
-c-S-fomit-frame-pointer-gnatpThis gives a human-readable assembler version of the code. The resulting
file will have the same name as the Ada source file, but with a .s
extension. In our example, the file nothing.s has the following
contents:
.file "nothing.adb"
gcc2_compiled.:
___gnu_compiled_ada:
.text
.align 4
.globl __ada_nothing
__ada_nothing:
#APP
nop
#NO_APP
jmp L1
.align 2,0x90
L1:
ret
The assembly code you included is clearly indicated by
the compiler, between the #APP and #NO_APP
delimiters. The character before the 'APP' and 'NOAPP'
can differ on different targets. For example, GNU/Linux uses '#APP' while
on NT you will see '/APP'.
If you make a mistake in your assembler code (such as using the wrong size modifier, or using a wrong operand for the instruction) GNAT will report this error in a temporary file, which will be deleted when the compilation is finished. Generating an assembler file will help in such cases, since you can assemble this file separately using the as assembler that comes with gcc.
Assembling the file using the command
as nothing.s
will give you error messages whose lines correspond to the assembler input file, so you can easily find and correct any mistakes you made. If there are no errors, as will generate an object file nothing.out.
The examples in this section, showing how to access the processor flags, illustrate how to specify the destination operands for assembly language statements.
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Get_Flags is
Flags : Unsigned_32;
use ASCII;
begin
Asm ("pushfl" & LF & HT & -- push flags on stack
"popl %%eax" & LF & HT & -- load eax with flags
"movl %%eax, %0", -- store flags in variable
Outputs => Unsigned_32'Asm_Output ("=g", Flags));
Put_Line ("Flags register:" & Flags'Img);
end Get_Flags;
In order to have a nicely aligned assembly listing, we have separated multiple assembler statements in the Asm template string with linefeed (ASCII.LF) and horizontal tab (ASCII.HT) characters. The resulting section of the assembly output file is:
#APP
pushfl
popl %eax
movl %eax, -40(%ebp)
#NO_APP
It would have been legal to write the Asm invocation as:
Asm ("pushfl popl %%eax movl %%eax, %0")
but in the generated assembler file, this would come out as:
#APP
pushfl popl %eax movl %eax, -40(%ebp)
#NO_APP
which is not so convenient for the human reader.
We use Ada comments at the end of each line to explain what the assembler instructions actually do. This is a useful convention.
When writing Inline Assembler instructions, you need to precede each register
and variable name with a percent sign. Since the assembler already requires
a percent sign at the beginning of a register name, you need two consecutive
percent signs for such names in the Asm template string, thus %%eax.
In the generated assembly code, one of the percent signs will be stripped off.
Names such as %0, %1, %2, etc., denote input or output
variables: operands you later define using Input or Output
parameters to Asm.
An output variable is illustrated in
the third statement in the Asm template string:
movl %%eax, %0
The intent is to store the contents of the eax register in a variable that can
be accessed in Ada. Simply writing movl %%eax, Flags would not
necessarily work, since the compiler might optimize by using a register
to hold Flags, and the expansion of the movl instruction would not be
aware of this optimization. The solution is not to store the result directly
but rather to advise the compiler to choose the correct operand form;
that is the purpose of the %0 output variable.
Information about the output variable is supplied in the Outputs
parameter to Asm:
Outputs => Unsigned_32'Asm_Output ("=g", Flags));
The output is defined by the Asm_Output attribute of the target type;
the general format is
Type'Asm_Output (constraint_string, variable_name)
The constraint string directs the compiler how to store/access the associated variable. In the example
Unsigned_32'Asm_Output ("=m", Flags);
the "m" (memory) constraint tells the compiler that the variable
Flags should be stored in a memory variable, thus preventing
the optimizer from keeping it in a register. In contrast,
Unsigned_32'Asm_Output ("=r", Flags);
uses the "r" (register) constraint, telling the compiler to
store the variable in a register.
If the constraint is preceded by the equal character (=), it tells the compiler that the variable will be used to store data into it.
In the Get_Flags example, we used the "g" (global) constraint,
allowing the optimizer to choose whatever it deems best.
There are a fairly large number of constraints, but the ones that are most useful (for the Intel x86 processor) are the following:
=gmIabcdSDrqThe full set of constraints is described in the gcc and as documentation; note that it is possible to combine certain constraints in one constraint string.
You specify the association of an output variable with an assembler operand
through the %n notation, where n is a non-negative
integer. Thus in
Asm ("pushfl" & LF & HT & -- push flags on stack
"popl %%eax" & LF & HT & -- load eax with flags
"movl %%eax, %0", -- store flags in variable
Outputs => Unsigned_32'Asm_Output ("=g", Flags));
%0 will be replaced in the expanded code by the appropriate operand,
whatever
the compiler decided for the Flags variable.
In general, you may have any number of output variables:
%0, %1, etc.
Outputs parameter as a parenthesized comma-separated list
of Asm_Output attributes
For example:
Asm ("movl %%eax, %0" & LF & HT &
"movl %%ebx, %1" & LF & HT &
"movl %%ecx, %2",
Outputs => (Unsigned_32'Asm_Output ("=g", Var_A), -- %0 = Var_A
Unsigned_32'Asm_Output ("=g", Var_B), -- %1 = Var_B
Unsigned_32'Asm_Output ("=g", Var_C))); -- %2 = Var_C
where Var_A, Var_B, and Var_C are variables
in the Ada program.
As a variation on the Get_Flags example, we can use the constraints
string to direct the compiler to store the eax register into the Flags
variable, instead of including the store instruction explicitly in the
Asm template string:
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Get_Flags_2 is
Flags : Unsigned_32;
use ASCII;
begin
Asm ("pushfl" & LF & HT & -- push flags on stack
"popl %%eax", -- save flags in eax
Outputs => Unsigned_32'Asm_Output ("=a", Flags));
Put_Line ("Flags register:" & Flags'Img);
end Get_Flags_2;
The "a" constraint tells the compiler that the Flags
variable will come from the eax register. Here is the resulting code:
#APP
pushfl
popl %eax
#NO_APP
movl %eax,-40(%ebp)
The compiler generated the store of eax into Flags after expanding the assembler code.
Actually, there was no need to pop the flags into the eax register; more simply, we could just pop the flags directly into the program variable:
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Get_Flags_3 is
Flags : Unsigned_32;
use ASCII;
begin
Asm ("pushfl" & LF & HT & -- push flags on stack
"pop %0", -- save flags in Flags
Outputs => Unsigned_32'Asm_Output ("=g", Flags));
Put_Line ("Flags register:" & Flags'Img);
end Get_Flags_3;
The example in this section illustrates how to specify the source operands for assembly language statements. The program simply increments its input value by 1:
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Increment is
function Incr (Value : Unsigned_32) return Unsigned_32 is
Result : Unsigned_32;
begin
Asm ("incl %0",
Inputs => Unsigned_32'Asm_Input ("a", Value),
Outputs => Unsigned_32'Asm_Output ("=a", Result));
return Result;
end Incr;
Value : Unsigned_32;
begin
Value := 5;
Put_Line ("Value before is" & Value'Img);
Value := Incr (Value);
Put_Line ("Value after is" & Value'Img);
end Increment;
The Outputs parameter to Asm specifies
that the result will be in the eax register and that it is to be stored
in the Result variable.
The Inputs parameter looks much like the Outputs parameter,
but with an Asm_Input attribute.
The "=" constraint, indicating an output value, is not present.
You can have multiple input variables, in the same way that you can have more than one output variable.
The parameter count (%0, %1) etc, now starts at the first input statement, and continues with the output statements. When both parameters use the same variable, the compiler will treat them as the same %n operand, which is the case here.
Just as the Outputs parameter causes the register to be stored into the
target variable after execution of the assembler statements, so does the
Inputs parameter cause its variable to be loaded into the register
before execution of the assembler statements.
Thus the effect of the Asm invocation is:
Value into eax
incl %eax instruction
Result variable
The resulting assembler file (with -O2 optimization) contains:
_increment__incr.1:
subl $4,%esp
movl 8(%esp),%eax
#APP
incl %eax
#NO_APP
movl %eax,%edx
movl %ecx,(%esp)
addl $4,%esp
ret
For a short subprogram such as the Incr function in the previous
section, the overhead of the call and return (creating / deleting the stack
frame) can be significant, compared to the amount of code in the subprogram
body. A solution is to apply Ada's Inline pragma to the subprogram,
which directs the compiler to expand invocations of the subprogram at the
point(s) of call, instead of setting up a stack frame for out-of-line calls.
Here is the resulting program:
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Increment_2 is
function Incr (Value : Unsigned_32) return Unsigned_32 is
Result : Unsigned_32;
begin
Asm ("incl %0",
Inputs => Unsigned_32'Asm_Input ("a", Value),
Outputs => Unsigned_32'Asm_Output ("=a", Result));
return Result;
end Incr;
pragma Inline (Increment);
Value : Unsigned_32;
begin
Value := 5;
Put_Line ("Value before is" & Value'Img);
Value := Increment (Value);
Put_Line ("Value after is" & Value'Img);
end Increment_2;
Compile the program with both optimization (-O2) and inlining (-gnatn) enabled.
The Incr function is still compiled as usual, but at the
point in Increment where our function used to be called:
pushl %edi
call _increment__incr.1
the code for the function body directly appears:
movl %esi,%eax
#APP
incl %eax
#NO_APP
movl %eax,%edx
thus saving the overhead of stack frame setup and an out-of-line call.
Asm FunctionalityThis section describes two important parameters to the Asm
procedure: Clobber, which identifies register usage;
and Volatile, which inhibits unwanted optimizations.
Clobber ParameterOne of the dangers of intermixing assembly language and a compiled language
such as Ada is that the compiler needs to be aware of which registers are
being used by the assembly code. In some cases, such as the earlier examples,
the constraint string is sufficient to indicate register usage (e.g.,
"a" for
the eax register). But more generally, the compiler needs an explicit
identification of the registers that are used by the Inline Assembly
statements.
Using a register that the compiler doesn't know about
could be a side effect of an instruction (like mull
storing its result in both eax and edx).
It can also arise from explicit register usage in your
assembly code; for example:
Asm ("movl %0, %%ebx" & LF & HT &
"movl %%ebx, %1",
Inputs => Unsigned_32'Asm_Input ("g", Var_In),
Outputs => Unsigned_32'Asm_Output ("=g", Var_Out));
where the compiler (since it does not analyze the Asm template string)
does not know you are using the ebx register.
In such cases you need to supply the Clobber parameter to Asm,
to identify the registers that will be used by your assembly code:
Asm ("movl %0, %%ebx" & LF & HT &
"movl %%ebx, %1",
Inputs => Unsigned_32'Asm_Input ("g", Var_In),
Outputs => Unsigned_32'Asm_Output ("=g", Var_Out),
Clobber => "ebx");
The Clobber parameter is a static string expression specifying the
register(s) you are using. Note that register names are not prefixed
by a percent sign. Also, if more than one register is used then their names
are separated by commas; e.g., "eax, ebx"
The Clobber parameter has several additional uses:
cc to indicate that flags might have changed
memory if you changed a memory location
Volatile Parameter
Compiler optimizations in the presence of Inline Assembler may sometimes have
unwanted effects. For example, when an Asm invocation with an input
variable is inside a loop, the compiler might move the loading of the input
variable outside the loop, regarding it as a one-time initialization.
If this effect is not desired, you can disable such optimizations by setting
the Volatile parameter to True; for example:
Asm ("movl %0, %%ebx" & LF & HT &
"movl %%ebx, %1",
Inputs => Unsigned_32'Asm_Input ("g", Var_In),
Outputs => Unsigned_32'Asm_Output ("=g", Var_Out),
Clobber => "ebx",
Volatile => True);
By default, Volatile is set to False unless there is no
Outputs parameter.
Although setting Volatile to True prevents unwanted
optimizations, it will also disable other optimizations that might be
important for efficiency. In general, you should set Volatile
to True only if the compiler's optimizations have created
problems.
This chapter describes the compatibility issues that may arise between GNAT and other Ada compilation systems (including those for Ada 83), and shows how GNAT can expedite porting applications developed in other Ada environments.
Ada 95 and Ada 2005 are highly upwards compatible with Ada 83. In particular, the design intention was that the difficulties associated with moving from Ada 83 to Ada 95 or Ada 2005 should be no greater than those that occur when moving from one Ada 83 system to another.
However, there are a number of points at which there are minor incompatibilities. The Ada 95 Annotated Reference Manual contains full details of these issues, and should be consulted for a complete treatment. In practice the following subsections treat the most likely issues to be encountered.
Some legal Ada 83 programs are illegal (i.e., they will fail to compile) in Ada 95 and thus also in Ada 2005:
Wide_Character as a new predefined character type, some uses of
character literals that were legal in Ada 83 are illegal in Ada 95.
For example:
for Char in 'A' .. 'Z' loop ... end loop;
The problem is that 'A' and 'Z' could be from either
Character or Wide_Character. The simplest correction
is to make the type explicit; e.g.:
for Char in Character range 'A' .. 'Z' loop ... end loop;
abstract, aliased, protected,
requeue, tagged, and until are reserved in Ada 95.
Existing Ada 83 code using any of these identifiers must be edited to
use some alternative name.
A particular case is that representation pragmas
cannot be applied to a subprogram body. If necessary, a separate subprogram
declaration must be introduced to which the pragma can be applied.
Requires_Body, which must then be given a dummy
procedure body in the package body, which then becomes required.
Another approach (assuming that this does not introduce elaboration
circularities) is to add an Elaborate_Body pragma to the package spec,
since one effect of this pragma is to require the presence of a package body.
Numeric_Error is now the same as Constraint_ErrorNumeric_Error is a renaming of
Constraint_Error.
This means that it is illegal to have separate exception handlers for
the two exceptions. The fix is simply to remove the handler for the
Numeric_Error case (since even in Ada 83, a compiler was free to raise
Constraint_Error in place of Numeric_Error in all cases).
String)
as the actual for a generic formal private type, but then the instantiation
would be illegal if there were any instances of declarations of variables
of this type in the generic body. In Ada 95, to avoid this clear violation
of the methodological principle known as the “contract model”,
the generic declaration explicitly indicates whether
or not such instantiations are permitted. If a generic formal parameter
has explicit unknown discriminants, indicated by using (<>) after the
type name, then it can be instantiated with indefinite types, but no
stand-alone variables can be declared of this type. Any attempt to declare
such a variable will result in an illegality at the time the generic is
declared. If the (<>) notation is not used, then it is illegal
to instantiate the generic with an indefinite type.
This is the potential incompatibility issue when porting Ada 83 code to Ada 95.
It will show up as a compile time error, and
the fix is usually simply to add the (<>) to the generic declaration.
The worst kind of incompatibility is one where a program that is legal in
Ada 83 is also legal in Ada 95 but can have an effect in Ada 95 that was not
possible in Ada 83. Fortunately this is extremely rare, but the one
situation that you should be alert to is the change in the predefined type
Character from 7-bit ASCII to 8-bit Latin-1.
CharacterStandard.Character is now the full 256 characters
of Latin-1, whereas in most Ada 83 implementations it was restricted
to 128 characters. Although some of the effects of
this change will be manifest in compile-time rejection of legal
Ada 83 programs it is possible for a working Ada 83 program to have
a different effect in Ada 95, one that was not permitted in Ada 83.
As an example, the expression
Character'Pos(Character'Last) returned 127 in Ada 83 and now
delivers 255 as its value.
In general, you should look at the logic of any
character-processing Ada 83 program and see whether it needs to be adapted
to work correctly with Latin-1. Note that the predefined Ada 95 API has a
character handling package that may be relevant if code needs to be adapted
to account for the additional Latin-1 elements.
The desirable fix is to
modify the program to accommodate the full character set, but in some cases
it may be convenient to define a subtype or derived type of Character that
covers only the restricted range.
pragma Interface and the floating point type attributes
(Emax, Mantissa, etc.), among other items.
Although Ada 2005 was designed to be upwards compatible with Ada 95, there are a number of incompatibilities. Several are enumerated below; for a complete description please see the Annotated Ada 2005 Reference Manual, or section 9.1.1 in Rationale for Ada 2005.
interface, overriding and synchronized are
reserved in Ada 2005.
A pre-Ada 2005 program that uses any of these as an identifier will be
illegal.
Ada.Exceptions, Ada.Real_Time, Ada.Strings,
Ada.Strings.Fixed, Ada.Strings.Bounded,
Ada.Strings.Unbounded, Ada.Strings.Wide_Fixed,
Ada.Strings.Wide_Bounded, Ada.Strings.Wide_Unbounded,
Ada.Tags, Ada.Text_IO, and Interfaces.C.
If an Ada 95 program does a with and use of any of these
packages, the new declarations may cause name clashes.
Standard.
Although the Ada language defines the semantics of each construct as precisely as practical, in some situations (for example for reasons of efficiency, or where the effect is heavily dependent on the host or target platform) the implementation is allowed some freedom. In porting Ada 83 code to GNAT, you need to be aware of whether / how the existing code exercised such implementation dependencies. Such characteristics fall into several categories, and GNAT offers specific support in assisting the transition from certain Ada 83 compilers.
Ada compilers are allowed to supplement the language-defined pragmas, and
these are a potential source of non-portability. All GNAT-defined pragmas
are described in Implementation Defined Pragmas, and these include several that are specifically
intended to correspond to other vendors' Ada 83 pragmas.
For migrating from VADS, the pragma Use_VADS_Size may be useful.
For compatibility with HP Ada 83, GNAT supplies the pragmas
Extend_System, Ident, Inline_Generic,
Interface_Name, Passive, Suppress_All,
and Volatile.
Other relevant pragmas include External and Link_With.
Some vendor-specific
Ada 83 pragmas (Share_Generic, Subtitle, and Title) are
recognized, thus
avoiding compiler rejection of units that contain such pragmas; they are not
relevant in a GNAT context and hence are not otherwise implemented.
Analogous to pragmas, the set of attributes may be extended by an
implementation. All GNAT-defined attributes are described in
Implementation Defined Attributes, and these include several that are specifically intended
to correspond to other vendors' Ada 83 attributes. For migrating from VADS,
the attribute VADS_Size may be useful. For compatibility with HP
Ada 83, GNAT supplies the attributes Bit, Machine_Size and
Type_Class.
Vendors may supply libraries to supplement the standard Ada API. If Ada 83 code uses vendor-specific libraries then there are several ways to manage this in Ada 95 or Ada 2005:
The implementation can choose any elaboration order consistent with the unit
dependency relationship. This freedom means that some orders can result in
Program_Error being raised due to an “Access Before Elaboration”: an attempt
to invoke a subprogram its body has been elaborated, or to instantiate a
generic before the generic body has been elaborated. By default GNAT
attempts to choose a safe order (one that will not encounter access before
elaboration problems) by implicitly inserting Elaborate or
Elaborate_All pragmas where
needed. However, this can lead to the creation of elaboration circularities
and a resulting rejection of the program by gnatbind. This issue is
thoroughly described in Elaboration Order Handling in GNAT.
In brief, there are several
ways to deal with this situation:
Elaborate_Body or
Elaborate pragmas, and then inhibit the generation of implicit
Elaborate_All
pragmas either globally (as an effect of the -gnatE switch) or locally
(by selectively suppressing elaboration checks via pragma
Suppress(Elaboration_Check) when it is safe to do so).
Low-level applications need to deal with machine addresses, data representations, interfacing with assembler code, and similar issues. If such an Ada 83 application is being ported to different target hardware (for example where the byte endianness has changed) then you will need to carefully examine the program logic; the porting effort will heavily depend on the robustness of the original design. Moreover, Ada 95 (and thus Ada 2005) are sometimes incompatible with typical Ada 83 compiler practices regarding implicit packing, the meaning of the Size attribute, and the size of access values. GNAT's approach to these issues is described in Representation Clauses.
If programs avoid the use of implementation dependent and implementation defined features, as documented in the Ada Reference Manual, there should be a high degree of portability between GNAT and other Ada systems. The following are specific items which have proved troublesome in moving Ada 95 programs from GNAT to other Ada 95 compilers, but do not affect porting code to GNAT. (As of January 2007, GNAT is the only compiler available for Ada 2005; the following issues may or may not arise for Ada 2005 programs when other compilers appear.)
The Ada 83 reference manual was quite vague in describing both the minimal required implementation of representation clauses, and also their precise effects. Ada 95 (and thus also Ada 2005) are much more explicit, but the minimal set of capabilities required is still quite limited.
GNAT implements the full required set of capabilities in Ada 95 and Ada 2005, but also goes much further, and in particular an effort has been made to be compatible with existing Ada 83 usage to the greatest extent possible.
A few cases exist in which Ada 83 compiler behavior is incompatible with the requirements in Ada 95 (and thus also Ada 2005). These are instances of intentional or accidental dependence on specific implementation dependent characteristics of these Ada 83 compilers. The following is a list of the cases most likely to arise in existing Ada 83 code.
Pack, or for more fine tuned control, provide
a Component_Size clause.
Natural will typically be 31 and not
32 (since no sign bit is required). Some Ada 83 compilers gave 31, and
some 32 in this situation. This problem will usually show up as a compile
time error, but not always. It is a good idea to check all uses of the
'Size attribute when porting Ada 83 code. The GNAT specific attribute
Object_Size can provide a useful way of duplicating the behavior of
some Ada 83 compiler systems.
To get around this problem, GNAT also permits the use of “thin pointers” for access types in this case (where the designated type is an unconstrained array type). These thin pointers are indeed the same size as a System.Address value. To specify a thin pointer, use a size clause for the type, for example:
type X is access all String;
for X'Size use Standard'Address_Size;
which will cause the type X to be represented using a single pointer. When using this representation, the bounds are right behind the array. This representation is slightly less efficient, and does not allow quite such flexibility in the use of foreign pointers or in using the Unrestricted_Access attribute to create pointers to non-aliased objects. But for any standard portable use of the access type it will work in a functionally correct manner and allow porting of existing code. Note that another way of forcing a thin pointer representation is to use a component size clause for the element size in an array, or a record representation clause for an access field in a record.
The VMS version of GNAT fully implements all the pragmas and attributes provided by HP Ada 83, as well as providing the standard HP Ada 83 libraries, including Starlet. In addition, data layouts and parameter passing conventions are highly compatible. This means that porting existing HP Ada 83 code to GNAT in VMS systems should be easier than most other porting efforts. The following are some of the most significant differences between GNAT and HP Ada 83.
TO_ADDRESS (INTEGER)
TO_ADDRESS (UNSIGNED_LONGWORD)
TO_ADDRESS (universal_integer)
The version of TO_ADDRESS taking a universal integer argument is in fact an extension to Ada 83 not strictly compatible with the reference manual. In GNAT, we are constrained to be exactly compatible with the standard, and this means we cannot provide this capability. In HP Ada 83, the point of this definition is to deal with a call like:
TO_ADDRESS (16#12777#);
Normally, according to the Ada 83 standard, one would expect this to be ambiguous, since it matches both the INTEGER and UNSIGNED_LONGWORD forms of TO_ADDRESS. However, in HP Ada 83, there is no ambiguity, since the definition using universal_integer takes precedence.
In GNAT, since the version with universal_integer cannot be supplied, it is not possible to be 100% compatible. Since there are many programs using numeric constants for the argument to TO_ADDRESS, the decision in GNAT was to change the name of the function in the UNSIGNED_LONGWORD case, so the declarations provided in the GNAT version of AUX_Dec are:
function To_Address (X : Integer) return Address;
pragma Pure_Function (To_Address);
function To_Address_Long (X : Unsigned_Longword)
return Address;
pragma Pure_Function (To_Address_Long);
This means that programs using TO_ADDRESS for UNSIGNED_LONGWORD must
change the name to TO_ADDRESS_LONG.
For full details on these and other less significant compatibility issues, see appendix E of the HP publication entitled HP Ada, Technical Overview and Comparison on HP Platforms.
For GNAT running on other than VMS systems, all the HP Ada 83 pragmas and attributes are recognized, although only a subset of them can sensibly be implemented. The description of pragmas in Implementation Defined Pragmas indicates whether or not they are applicable to non-VMS systems.
This chapter describes topics that are specific to the Microsoft Windows platforms (NT, 2000, and XP Professional).
One of the strengths of the GNAT technology is that its tool set
(gcc, gnatbind, gnatlink, gnatmake, the
gdb debugger, etc.) is used in the same way regardless of the
platform.
On Windows this tool set is complemented by a number of Microsoft-specific tools that have been provided to facilitate interoperability with Windows when this is required. With these tools:
CONSOLE or WINDOWS
subsystems.
Immediately below are listed all known general GNAT-for-Windows restrictions. Other restrictions about specific features like Windows Resources and DLLs are listed in separate sections below.
GetLastError and SetLastError
when tasking, protected records, or exceptions are used. In these
cases, in order to implement Ada semantics, the GNAT run-time system
calls certain Win32 routines that set the last error variable to 0 upon
success. It should be possible to use GetLastError and
SetLastError when tasking, protected record, and exception
features are not used, but it is not guaranteed to work.
Make sure the system on which GNAT is installed is accessible from the
current machine, i.e., the install location is shared over the network.
Shared resources are accessed on Windows by means of UNC paths, which
have the format \\server\sharename\path
In order to use such a network installation, simply add the UNC path of the bin directory of your GNAT installation in front of your PATH. For example, if GNAT is installed in \GNAT directory of a share location called c-drive on a machine LOKI, the following command will make it available:
path \\loki\c-drive\gnat\bin;%path%
Be aware that every compilation using the network installation results in the transfer of large amounts of data across the network and will likely cause serious performance penalty.
There are two main subsystems under Windows. The CONSOLE subsystem
(which is the default subsystem) will always create a console when
launching the application. This is not something desirable when the
application has a Windows GUI. To get rid of this console the
application must be using the WINDOWS subsystem. To do so
the -mwindows linker option must be specified.
$ gnatmake winprog -largs -mwindows
It is possible to control where temporary files gets created by setting the TMP environment variable. The file will be created:
This allows you to determine exactly where the temporary file will be created. This is particularly useful in networked environments where you may not have write access to some directories.
Developing pure Ada applications on Windows is no different than on other GNAT-supported platforms. However, when developing or porting an application that contains a mix of Ada and C/C++, the choice of your Windows C/C++ development environment conditions your overall interoperability strategy.
If you use gcc to compile the non-Ada part of your application, there are no Windows-specific restrictions that affect the overall interoperability with your Ada code. If you plan to use Microsoft tools (e.g. Microsoft Visual C/C++), you should be aware of the following limitations:
.tls section (Thread Local
Storage section) since the GNAT linker does not yet support this section.
msvcrt.dll. This is because the GNAT run time
uses the services of msvcrt.dll for its I/Os. Use of other I/O
libraries can cause a conflict with msvcrt.dll services. For
instance Visual C++ I/O stream routines conflict with those in
msvcrt.dll.
If you do want to use the Microsoft tools for your non-Ada code and hit one of the above limitations, you have two choices:
When a subprogram F (caller) calls a subprogram G
(callee), there are several ways to push G's parameters on the
stack and there are several possible scenarios to clean up the stack
upon G's return. A calling convention is an agreed upon software
protocol whereby the responsibilities between the caller (F) and
the callee (G) are clearly defined. Several calling conventions
are available for Windows:
C (Microsoft defined)
Stdcall (Microsoft defined)
Win32 (GNAT specific)
DLL (GNAT specific)
C Calling ConventionThis is the default calling convention used when interfacing to C/C++ routines compiled with either gcc or Microsoft Visual C++.
In the C calling convention subprogram parameters are pushed on the
stack by the caller from right to left. The caller itself is in charge of
cleaning up the stack after the call. In addition, the name of a routine
with C calling convention is mangled by adding a leading underscore.
The name to use on the Ada side when importing (or exporting) a routine
with C calling convention is the name of the routine. For
instance the C function:
int get_val (long);
should be imported from Ada as follows:
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int;
pragma Import (C, Get_Val, External_Name => "get_val");
Note that in this particular case the External_Name parameter could
have been omitted since, when missing, this parameter is taken to be the
name of the Ada entity in lower case. When the Link_Name parameter
is missing, as in the above example, this parameter is set to be the
External_Name with a leading underscore.
When importing a variable defined in C, you should always use the C
calling convention unless the object containing the variable is part of a
DLL (in which case you should use the Stdcall calling
convention, see Stdcall Calling Convention).
Stdcall Calling ConventionThis convention, which was the calling convention used for Pascal programs, is used by Microsoft for all the routines in the Win32 API for efficiency reasons. It must be used to import any routine for which this convention was specified.
In the Stdcall calling convention subprogram parameters are pushed
on the stack by the caller from right to left. The callee (and not the
caller) is in charge of cleaning the stack on routine exit. In addition,
the name of a routine with Stdcall calling convention is mangled by
adding a leading underscore (as for the C calling convention) and a
trailing @nn, where nn is the overall size (in
bytes) of the parameters passed to the routine.
The name to use on the Ada side when importing a C routine with a
Stdcall calling convention is the name of the C routine. The leading
underscore and trailing @nn are added automatically by
the compiler. For instance the Win32 function:
APIENTRY int get_val (long);
should be imported from Ada as follows:
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int;
pragma Import (Stdcall, Get_Val);
-- On the x86 a long is 4 bytes, so the Link_Name is "_get_val@4"
As for the C calling convention, when the External_Name
parameter is missing, it is taken to be the name of the Ada entity in lower
case. If instead of writing the above import pragma you write:
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int;
pragma Import (Stdcall, Get_Val, External_Name => "retrieve_val");
then the imported routine is _retrieve_val@4. However, if instead
of specifying the External_Name parameter you specify the
Link_Name as in the following example:
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int;
pragma Import (Stdcall, Get_Val, Link_Name => "retrieve_val");
then the imported routine is retrieve_val, that is, there is no
decoration at all. No leading underscore and no Stdcall suffix
@nn.
This is especially important as in some special cases a DLL's entry
point name lacks a trailing @nn while the exported
name generated for a call has it.
It is also possible to import variables defined in a DLL by using an import pragma for a variable. As an example, if a DLL contains a variable defined as:
int my_var;
then, to access this variable from Ada you should write:
My_Var : Interfaces.C.int;
pragma Import (Stdcall, My_Var);
Note that to ease building cross-platform bindings this convention
will be handled as a C calling convention on non-Windows platforms.
Win32 Calling ConventionThis convention, which is GNAT-specific is fully equivalent to the
Stdcall calling convention described above.
DLL Calling ConventionThis convention, which is GNAT-specific is fully equivalent to the
Stdcall calling convention described above.
A Dynamically Linked Library (DLL) is a library that can be shared by several applications running under Windows. A DLL can contain any number of routines and variables.
One advantage of DLLs is that you can change and enhance them without forcing all the applications that depend on them to be relinked or recompiled. However, you should be aware than all calls to DLL routines are slower since, as you will understand below, such calls are indirect.
To illustrate the remainder of this section, suppose that an application wants to use the services of a DLL API.dll. To use the services provided by API.dll you must statically link against the DLL or an import library which contains a jump table with an entry for each routine and variable exported by the DLL. In the Microsoft world this import library is called API.lib. When using GNAT this import library is called either libAPI.dll.a, libapi.dll.a, libAPI.a or libapi.a (names are case insensitive).
After you have linked your application with the DLL or the import library and you run your application, here is what happens:
DllMain or
DllMainCRTStartup are invoked. These routines typically contain
the initialization code needed for the well-being of the routines and
variables exported by the DLL.
There is an additional point which is worth mentioning. In the Windows world there are two kind of DLLs: relocatable and non-relocatable DLLs. Non-relocatable DLLs can only be loaded at a very specific address in the target application address space. If the addresses of two non-relocatable DLLs overlap and these happen to be used by the same application, a conflict will occur and the application will run incorrectly. Hence, when possible, it is always preferable to use and build relocatable DLLs. Both relocatable and non-relocatable DLLs are supported by GNAT. Note that the -s linker option (see GNU Linker User's Guide) removes the debugging symbols from the DLL but the DLL can still be relocated.
As a side note, an interesting difference between Microsoft DLLs and Unix shared libraries, is the fact that on most Unix systems all public routines are exported by default in a Unix shared library, while under Windows it is possible (but not required) to list exported routines in a definition file (see The Definition File).
To use the services of a DLL, say API.dll, in your Ada application you must have:
Once you have all the above, to compile an Ada application that uses the
services of API.dll and whose main subprogram is My_Ada_App,
you simply issue the command
$ gnatmake my_ada_app -largs -lAPI
The argument -largs -lAPI at the end of the gnatmake command tells the GNAT linker to look first for a library named API.lib (Microsoft-style name) and if not found for a libraries named libAPI.dll.a, API.dll.a or libAPI.a. (GNAT-style name). Note that if the Ada package spec for API.dll contains the following pragma
pragma Linker_Options ("-lAPI");
you do not have to add -largs -lAPI at the end of the gnatmake command.
If any one of the items above is missing you will have to create it yourself. The following sections explain how to do so using as an example a fictitious DLL called API.dll.
A DLL typically comes with a C/C++ header file which provides the definitions of the routines and variables exported by the DLL. The Ada equivalent of this header file is a package spec that contains definitions for the imported entities. If the DLL you intend to use does not come with an Ada spec you have to generate one such spec yourself. For example if the header file of API.dll is a file api.h containing the following two definitions:
| int some_var; int get (char *); |
then the equivalent Ada spec could be:
| with Interfaces.C.Strings; package API is use Interfaces; Some_Var : C.int; function Get (Str : C.Strings.Chars_Ptr) return C.int; private pragma Import (C, Get); pragma Import (DLL, Some_Var); end API; |
Note that a variable is
always imported with a Stdcall convention. A function
can have C or Stdcall convention.
(see Windows Calling Conventions).
If a Microsoft-style import library API.lib or a GNAT-style import library libAPI.dll.a or libAPI.a is available with API.dll you can skip this section. You can also skip this section if API.dll or libAPI.dll is built with GNU tools as in this case it is possible to link directly against the DLL. Otherwise read on.
As previously mentioned, and unlike Unix systems, the list of symbols
that are exported from a DLL must be provided explicitly in Windows.
The main goal of a definition file is precisely that: list the symbols
exported by a DLL. A definition file (usually a file with a .def
suffix) has the following structure:
| [LIBRARY name] [DESCRIPTION string] EXPORTS symbol1 symbol2 ... |
LIBRARY nameDESCRIPTION stringEXPORTSEXPORTS
section of API.def looks like:
| EXPORTS some_var get |
Note that you must specify the correct suffix (@nn)
(see Windows Calling Conventions) for a Stdcall
calling convention function in the exported symbols list.
There can actually be other sections in a definition file, but these sections are not relevant to the discussion at hand.
To create a static import library from API.dll with the GNAT tools you should proceed as follows:
dll2def tool as follows:
$ dll2def API.dll > API.def
dll2def is a very simple tool: it takes as input a DLL and prints
to standard output the list of entry points in the DLL. Note that if
some routines in the DLL have the Stdcall convention
(see Windows Calling Conventions) with stripped @nn
suffix then you'll have to edit api.def to add it, and specify
-k to gnatdll when creating the import library.
Here are some hints to find the right @nn suffix.
dumpbin tool (see the
corresponding Microsoft documentation for further details).
$ dumpbin /exports api.lib
libAPI.dll.a, using gnatdll
(see Using gnatdll) as follows:
$ gnatdll -e API.def -d API.dll
gnatdll takes as input a definition file API.def and the
name of the DLL containing the services listed in the definition file
API.dll. The name of the static import library generated is
computed from the name of the definition file as follows: if the
definition file name is xyz.def, the import library name will
be libxyz.a. Note that in the previous example option
-e could have been removed because the name of the definition
file (before the “.def” suffix) is the same as the name of the
DLL (see Using gnatdll for more information about gnatdll).
With GNAT you can either use a GNAT-style or Microsoft-style import library. A Microsoft import library is needed only if you plan to make an Ada DLL available to applications developed with Microsoft tools (see Mixed-Language Programming on Windows).
To create a Microsoft-style import library for API.dll you should proceed as follows:
dll2def tool as described above or the Microsoft dumpbin
tool (see the corresponding Microsoft documentation for further details).
lib utility:
$ lib -machine:IX86 -def:API.def -out:API.lib
If you use the above command the definition file API.def must contain a line giving the name of the DLL:
LIBRARY "API"
See the Microsoft documentation for further details about the usage of
lib.
This section explain how to build DLLs using the GNAT built-in DLL support. With the following procedure it is straight forward to build and use DLLs with GNAT.
The first step is to build all objects files that are to be included into the DLL. This is done by using the standard gnatmake tool.
To build the DLL you must use gcc's -shared option. It is quite simple to use this method:
$ gcc -shared -o api.dll obj1.o obj2.o ...
It is important to note that in this case all symbols found in the object files are automatically exported. It is possible to restrict the set of symbols to export by passing to gcc a definition file, see The Definition File. For example:
$ gcc -shared -o api.dll api.def obj1.o obj2.o ...
If you use a definition file you must export the elaboration procedures for every package that required one. Elaboration procedures are named using the package name followed by "_E".
For the DLL to be used by client programs the bodies must be hidden from it and the .ali set with read-only attribute. This is very important otherwise GNAT will recompile all packages and will not actually use the code in the DLL. For example:
$ mkdir apilib
$ copy *.ads *.ali api.dll apilib
$ attrib +R apilib\*.ali
At this point it is possible to use the DLL by directly linking against it. Note that you must use the GNAT shared runtime when using GNAT shared libraries. This is achieved by using -shared binder's option.
$ gnatmake main -Iapilib -bargs -shared -largs -Lapilib -lAPI
There is nothing specific to Windows in the build process. see Library Projects.
Due to a system limitation, it is not possible under Windows to create threads
when inside the DllMain routine which is used for auto-initialization
of shared libraries, so it is not possible to have library level tasks in SALs.
Note that it is preferred to use the built-in GNAT DLL support (see Building DLLs with GNAT) or GNAT Project files (see Building DLLs with GNAT Project files) to build DLLs.
This section explains how to build DLLs containing Ada code using
gnatdll. These DLLs will be referred to as Ada DLLs in the
remainder of this section.
The steps required to build an Ada DLL that is to be used by Ada as well as non-Ada applications are as follows:
C or
Stdcall calling convention to avoid any Ada name mangling for the
entities exported by the DLL (see Exporting Ada Entities). You can
skip this step if you plan to use the Ada DLL only from Ada applications.
adainit generated by gnatbind to perform the elaboration of
the Ada code in the DLL (see Ada DLLs and Elaboration). The initialization
routine exported by the Ada DLL must be invoked by the clients of the DLL
to initialize the DLL.
adafinal generated by gnatbind to perform the
finalization of the Ada code in the DLL (see Ada DLLs and Finalization).
The finalization routine exported by the Ada DLL must be invoked by the
clients of the DLL when the DLL services are no further needed.
gnatdll to produce the DLL and the import
library (see Using gnatdll).
Note that a relocatable DLL stripped using the strip
binutils tool will not be relocatable anymore. To build a DLL without
debug information pass -largs -s to gnatdll. This
restriction does not apply to a DLL built using a Library Project.
see Library Projects.
When using Ada DLLs from Ada applications there is a limitation users should be aware of. Because on Windows the GNAT run time is not in a DLL of its own, each Ada DLL includes a part of the GNAT run time. Specifically, each Ada DLL includes the services of the GNAT run time that are necessary to the Ada code inside the DLL. As a result, when an Ada program uses an Ada DLL there are two independent GNAT run times: one in the Ada DLL and one in the main program.
It is therefore not possible to exchange GNAT run-time objects between the
Ada DLL and the main Ada program. Example of GNAT run-time objects are file
handles (e.g. Text_IO.File_Type), tasks types, protected objects
types, etc.
It is completely safe to exchange plain elementary, array or record types, Windows object handles, etc.
Building a DLL is a way to encapsulate a set of services usable from any
application. As a result, the Ada entities exported by a DLL should be
exported with the C or Stdcall calling conventions to avoid
any Ada name mangling. As an example here is an Ada package
API, spec and body, exporting two procedures, a function, and a
variable:
| with Interfaces.C; use Interfaces; package API is Count : C.int := 0; function Factorial (Val : C.int) return C.int; procedure Initialize_API; procedure Finalize_API; -- Initialization & Finalization routines. More in the next section. private pragma Export (C, Initialize_API); pragma Export (C, Finalize_API); pragma Export (C, Count); pragma Export (C, Factorial); end API; |
| package body API is function Factorial (Val : C.int) return C.int is Fact : C.int := 1; begin Count := Count + 1; for K in 1 .. Val loop Fact := Fact * K; end loop; return Fact; end Factorial; procedure Initialize_API is procedure Adainit; pragma Import (C, Adainit); begin Adainit; end Initialize_API; procedure Finalize_API is procedure Adafinal; pragma Import (C, Adafinal); begin Adafinal; end Finalize_API; end API; |
If the Ada DLL you are building will only be used by Ada applications
you do not have to export Ada entities with a C or Stdcall
convention. As an example, the previous package could be written as
follows:
| package API is Count : Integer := 0; function Factorial (Val : Integer) return Integer; procedure Initialize_API; procedure Finalize_API; -- Initialization and Finalization routines. end API; |
| package body API is function Factorial (Val : Integer) return Integer is Fact : Integer := 1; begin Count := Count + 1; for K in 1 .. Val loop Fact := Fact * K; end loop; return Fact; end Factorial; ... -- The remainder of this package body is unchanged. end API; |
Note that if you do not export the Ada entities with a C or
Stdcall convention you will have to provide the mangled Ada names
in the definition file of the Ada DLL
(see Creating the Definition File).
The DLL that you are building contains your Ada code as well as all the routines in the Ada library that are needed by it. The first thing a user of your DLL must do is elaborate the Ada code (see Elaboration Order Handling in GNAT).
To achieve this you must export an initialization routine
(Initialize_API in the previous example), which must be invoked
before using any of the DLL services. This elaboration routine must call
the Ada elaboration routine adainit generated by the GNAT binder
(see Binding with Non-Ada Main Programs). See the body of
Initialize_Api for an example. Note that the GNAT binder is
automatically invoked during the DLL build process by the gnatdll
tool (see Using gnatdll).
When a DLL is loaded, Windows systematically invokes a routine called
DllMain. It would therefore be possible to call adainit
directly from DllMain without having to provide an explicit
initialization routine. Unfortunately, it is not possible to call
adainit from the DllMain if your program has library level
tasks because access to the DllMain entry point is serialized by
the system (that is, only a single thread can execute “through” it at a
time), which means that the GNAT run time will deadlock waiting for the
newly created task to complete its initialization.
When the services of an Ada DLL are no longer needed, the client code should
invoke the DLL finalization routine, if available. The DLL finalization
routine is in charge of releasing all resources acquired by the DLL. In the
case of the Ada code contained in the DLL, this is achieved by calling
routine adafinal generated by the GNAT binder
(see Binding with Non-Ada Main Programs).
See the body of Finalize_Api for an
example. As already pointed out the GNAT binder is automatically invoked
during the DLL build process by the gnatdll tool
(see Using gnatdll).
To use the services exported by the Ada DLL from another programming
language (e.g. C), you have to translate the specs of the exported Ada
entities in that language. For instance in the case of API.dll,
the corresponding C header file could look like:
| extern int *_imp__count; #define count (*_imp__count) int factorial (int); |
It is important to understand that when building an Ada DLL to be used by
other Ada applications, you need two different specs for the packages
contained in the DLL: one for building the DLL and the other for using
the DLL. This is because the DLL calling convention is needed to
use a variable defined in a DLL, but when building the DLL, the variable
must have either the Ada or C calling convention. As an
example consider a DLL comprising the following package API:
| package API is Count : Integer := 0; ... -- Remainder of the package omitted. end API; |
After producing a DLL containing package API, the spec that
must be used to import API.Count from Ada code outside of the
DLL is:
| package API is Count : Integer; pragma Import (DLL, Count); end API; |
The definition file is the last file needed to build the DLL. It lists
the exported symbols. As an example, the definition file for a DLL
containing only package API (where all the entities are exported
with a C calling convention) is:
| EXPORTS count factorial finalize_api initialize_api |
If the C calling convention is missing from package API,
then the definition file contains the mangled Ada names of the above
entities, which in this case are:
| EXPORTS api__count api__factorial api__finalize_api api__initialize_api |
gnatdllgnatdll is a tool to automate the DLL build process once all the Ada
and non-Ada sources that make up your DLL have been compiled.
gnatdll is actually in charge of two distinct tasks: build the
static import library for the DLL and the actual DLL. The form of the
gnatdll command is
| $ gnatdll [switches] list-of-files [-largs opts] |
where list-of-files is a list of ALI and object files. The object file list must be the exact list of objects corresponding to the non-Ada sources whose services are to be included in the DLL. The ALI file list must be the exact list of ALI files for the corresponding Ada sources whose services are to be included in the DLL. If list-of-files is missing, only the static import library is generated.
You may specify any of the following switches to gnatdll:
-a[address]gnatdll builds relocatable DLL. We
advise the reader to build relocatable DLL.
-b address0x11000000.
-bargs opts-d dllfilegnatdll to do anything. The name of the generated import library is
obtained algorithmically from dllfile as shown in the following
example: if dllfile is xyz.dll, the import library name is
libxyz.dll.a. The name of the definition file to use (if not specified
by option -e) is obtained algorithmically from dllfile
as shown in the following example:
if dllfile is xyz.dll, the definition
file used is xyz.def.
-e deffile-g-hgnatdll switch usage information.
-Idirgnatdll to search the dir directory for source and
object files needed to build the DLL.
(see Search Paths and the Run-Time Library (RTL)).
-k@nn suffix from the import library's exported
names, but keeps them for the link names. You must specify this
option if you want to use a Stdcall function in a DLL for which
the @nn suffix has been removed. This is the case for most
of the Windows NT DLL for example. This option has no effect when
-n option is specified.
-l file-n-q-v-largs optsgnatdll ExampleAs an example the command to build a relocatable DLL from api.adb once api.adb has been compiled and api.def created is
$ gnatdll -d api.dll api.ali
The above command creates two files: libapi.dll.a (the import library) and api.dll (the actual DLL). If you want to create only the DLL, just type:
$ gnatdll -d api.dll -n api.ali
Alternatively if you want to create just the import library, type:
$ gnatdll -d api.dll
gnatdll behind the ScenesThis section details the steps involved in creating a DLL. gnatdll
does these steps for you. Unless you are interested in understanding what
goes on behind the scenes, you should skip this section.
We use the previous example of a DLL containing the Ada package API,
to illustrate the steps necessary to build a DLL. The starting point is a
set of objects that will make up the DLL and the corresponding ALI
files. In the case of this example this means that api.o and
api.ali are available. To build a relocatable DLL, gnatdll does
the following:
gnatdll builds the base file (api.base). A base file gives
the information necessary to generate relocation information for the
DLL.
$ gnatbind -n api
$ gnatlink api -o api.jnk -mdll -Wl,--base-file,api.base
In addition to the base file, the gnatlink command generates an
output file api.jnk which can be discarded. The -mdll switch
asks gnatlink to generate the routines DllMain and
DllMainCRTStartup that are called by the Windows loader when the DLL
is loaded into memory.
gnatdll uses dlltool (see Using dlltool) to build the
export table (api.exp). The export table contains the relocation
information in a form which can be used during the final link to ensure
that the Windows loader is able to place the DLL anywhere in memory.
$ dlltool --dllname api.dll --def api.def --base-file api.base \
--output-exp api.exp
gnatdll builds the base file using the new export table. Note that
gnatbind must be called once again since the binder generated file
has been deleted during the previous call to gnatlink.
$ gnatbind -n api
$ gnatlink api -o api.jnk api.exp -mdll
-Wl,--base-file,api.base
gnatdll builds the new export table using the new base file and
generates the DLL import library libAPI.dll.a.
$ dlltool --dllname api.dll --def api.def --base-file api.base \
--output-exp api.exp --output-lib libAPI.a
gnatdll builds the relocatable DLL using the final export
table.
$ gnatbind -n api
$ gnatlink api api.exp -o api.dll -mdll
dlltooldlltool is the low-level tool used by gnatdll to build
DLLs and static import libraries. This section summarizes the most
common dlltool switches. The form of the dlltool command
is
$ dlltool [switches]
dlltool switches include:
dlltool with switch
--output-lib.
@nn from exported names
(see Windows Calling Conventions
for a discussion about Stdcall-style symbols.
dlltool switches with a concise description.
as.
Resources are an easy way to add Windows specific objects to your application. The objects that can be added as resources include:
This section explains how to build, compile and use resources.
A resource file is an ASCII file. By convention resource files have an
.rc extension.
The easiest way to build a resource file is to use Microsoft tools
such as imagedit.exe to build bitmaps, icons and cursors and
dlgedit.exe to build dialogs.
It is always possible to build an .rc file yourself by writing a
resource script.
It is not our objective to explain how to write a resource file. A complete description of the resource script language can be found in the Microsoft documentation.
This section describes how to build a GNAT-compatible (COFF) object file
containing the resources. This is done using the Resource Compiler
windres as follows:
$ windres -i myres.rc -o myres.o
By default windres will run gcc to preprocess the .rc
file. You can specify an alternate preprocessor (usually named
cpp.exe) using the windres --preprocessor
parameter. A list of all possible options may be obtained by entering
the command windres --help.
It is also possible to use the Microsoft resource compiler rc.exe
to produce a .res file (binary resource file). See the
corresponding Microsoft documentation for further details. In this case
you need to use windres to translate the .res file to a
GNAT-compatible object file as follows:
$ windres -i myres.res -o myres.o
To include the resource file in your program just add the GNAT-compatible object file for the resource(s) to the linker arguments. With gnatmake this is done by using the -largs option:
$ gnatmake myprog -largs myres.o
Debugging a DLL is similar to debugging a standard program. But we have to deal with two different executable parts: the DLL and the program that uses it. We have the following four possibilities:
GCC/GNAT.
GCC/GNAT.
GCC/GNAT and the DLL is built with
foreign tools.
In this section we address only cases one and two above.
There is no point in trying to debug
a DLL with GNU/GDB, if there is no GDB-compatible debugging
information in it. To do so you must use a debugger compatible with the
tools suite used to build the DLL.
This is the simplest case. Both the DLL and the program have GDB
compatible debugging information. It is then possible to break anywhere in
the process. Let's suppose here that the main procedure is named
ada_main and that in the DLL there is an entry point named
ada_dll.
The DLL (see Introduction to Dynamic Link Libraries (DLLs)) and program must have been built with the debugging information (see GNAT -g switch). Here are the step-by-step instructions for debugging it:
GDB on the main program.
$ gdb -nw ada_main
(gdb) start
This step is required to be able to set a breakpoint inside the DLL. As long as the program is not run, the DLL is not loaded. This has the consequence that the DLL debugging information is also not loaded, so it is not possible to set a breakpoint in the DLL.
(gdb) break ada_dll
(gdb) cont
At this stage a breakpoint is set inside the DLL. From there on you can use the standard approach to debug the whole program (see Running and Debugging Ada Programs).
In this case things are slightly more complex because it is not possible to
start the main program and then break at the beginning to load the DLL and the
associated DLL debugging information. It is not possible to break at the
beginning of the program because there is no GDB debugging information,
and therefore there is no direct way of getting initial control. This
section addresses this issue by describing some methods that can be used
to break somewhere in the DLL to debug it.
First suppose that the main procedure is named main (this is for
example some C code built with Microsoft Visual C) and that there is a
DLL named test.dll containing an Ada entry point named
ada_dll.
The DLL (see Introduction to Dynamic Link Libraries (DLLs)) must have been built with debugging information (see GNAT -g option).
$ objdump --file-header main.exe
The starting address is reported on the last line. For example:
main.exe: file format pei-i386
architecture: i386, flags 0x0000010a:
EXEC_P, HAS_DEBUG, D_PAGED
start address 0x00401010
$ gdb main.exe
$ (gdb) break *0x00401010
$ (gdb) run
The program will stop at the given address.
(gdb) break ada_dll.adb:45
Or if you want to break using a symbol on the DLL, you need first to select the Ada language (language used by the DLL).
(gdb) set language ada
(gdb) break ada_dll
(gdb) cont
This will run the program until it reaches the breakpoint that has been set. From that point you can use the standard way to debug a program as described in (see Running and Debugging Ada Programs).
It is also possible to debug the DLL by attaching to a running process.
With GDB it is always possible to debug a running process by
attaching to it. It is possible to debug a DLL this way. The limitation
of this approach is that the DLL must run long enough to perform the
attach operation. It may be useful for instance to insert a time wasting
loop in the code of the DLL to meet this criterion.
$ main
$ gdb
(gdb) attach 208
(gdb) symbol-file main.exe
(gdb) break ada_dll
(gdb) cont
This last step will resume the process execution, and stop at the breakpoint we have set. From there you can use the standard approach to debug a program as described in (see Running and Debugging Ada Programs).
It is possible to specify the program stack size at link time. On modern versions of Windows, starting with XP, this is mostly useful to set the size of the main stack (environment task). The other task stacks are set with pragma Storage_Size or with the gnatbind -d command.
Since older versions of Windows (2000, NT4, etc.) do not allow setting the reserve size of individual tasks, the link-time stack size applies to all tasks, and pragma Storage_Size has no effect. In particular, Stack Overflow checks are made against this link-time specified size.
This setting can be done with gnatlink using either:
$ gnatlink hello -Xlinker --stack=0x10000,0x1000
This sets the stack reserve size to 0x10000 bytes and the stack commit size to 0x1000 bytes.
$ gnatlink hello -Wl,--stack=0x1000000
This sets the stack reserve size to 0x1000000 bytes. Note that with -Wl option it is not possible to set the stack commit size because the coma is a separator for this option.
Under Windows systems, it is possible to specify the program heap size from gnatlink using either:
$ gnatlink hello -Xlinker --heap=0x10000,0x1000
This sets the heap reserve size to 0x10000 bytes and the heap commit size to 0x1000 bytes.
$ gnatlink hello -Wl,--heap=0x1000000
This sets the heap reserve size to 0x1000000 bytes. Note that with -Wl option it is not possible to set the heap commit size because the coma is a separator for this option.
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Permission is granted to copy, distribute and/or modify this document
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with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
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If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.
gprof): Running gprofgnatpp): Output File Controlgnatchop): Switches for gnatchopgnatbind): Switches for gnatbindgnatls): Switches for gnatlsgnatpp): Setting the Source Search Pathgnathtml): Converting Ada Files to html with gnathtmlgnatbind): Output Controlgnatdll): Using gnatdllgnatls): Switches for gnatlsgnatls): Switches for gnatlsgnatclean): Switches for gnatcleangnatls): Switches for gnatlsgnatbind): Binder Error Message Controlgnatdll): Using gnatdllgnatmem): Switches for gnatmemgnatdll): Using gnatdllgnatbind): Output Controlgnatbind): Output Controlgnatchop): Switches for gnatchopgnatclean): Switches for gnatcleangnatname): Switches for gnatnamegnathtml): Converting Ada Files to html with gnathtmlgnatclean): Switches for gnatcleangnatdll): Using gnatdllgnatfind): gnatfind Switchesgnathtml): Converting Ada Files to html with gnathtmlgnathtml): Converting Ada Files to html with gnathtmlgnatls): Switches for gnatlsgnatname): Switches for gnatnamegnatname): Switches for gnatnamegnatmetric): Other gnatmetric Switchesgnatbind): Output Controlgnatdll): Using gnatdllgprof): Running gprofgprof): Running gprofgnathtml): Converting Ada Files to html with gnathtmlgnatclean): Switches for gnatcleangnathtml): Converting Ada Files to html with gnathtmlgnatname): Switches for gnatnamegprof): Running gprofgprof): Running gprofgnatls): Switches for gnatlsgnatmetric): Other gnatmetric Switchesgnatpp): Other gnatpp Switchesgnatdll): Using gnatdllgnatpp): Setting the Source Search Pathgnatbind): Output Controlgnatclean): Switches for gnatcleangnatdll): Using gnatdllgnatls): Switches for gnatlsgnatname): Switches for gnatnamegnatclean): Switches for gnatcleangnatdll): Using gnatdllgnathtml): Converting Ada Files to html with gnathtmlgnatls): Switches for gnatlsgnatmem): Switches for gnatmemgnatpp): Setting the Source Search Pathgnatclean): Switches for gnatcleangnatls): Switches for gnatlsgnatpp): Setting the Source Search Pathgnatbind): Output Controlgnatchop): Switches for gnatchopgnatdll): Using gnatdllgnatbind): Output Controlgnatdll): Using gnatdllgnathtml): Converting Ada Files to html with gnathtmlgnatdll): Using gnatdllgnatbind): Binder Error Message Controlgnatbind): Binder Error Message Controlgnatmem): Switches for gnatmemgnatbind): Binding with Non-Ada Main Programsgnatclean): Switches for gnatcleangnatdll): Using gnatdllgnatbind): Output Controlgnatbind): Output Controlgnathtml): Converting Ada Files to html with gnathtmlgnatls): Switches for gnatlsgnatpp): Output File Controlgnatpp): Output File Controlgnatbind): Elaboration Controlgnatchop): Switches for gnatchopgnatclean): Switches for gnatcleangnathtml): Converting Ada Files to html with gnathtmlgnatname): Switches for gnatnamegnatpp): Output File Controlgnatchop): Switches for gnatchopgnatclean): Switches for gnatcleangnatdll): Using gnatdllgnatmem): Switches for gnatmemgnatmetric): Other gnatmetric Switchesgnatbind): Output Controlgnatchop): Switches for gnatchopgnatclean): Switches for gnatcleangnatpp): Output File Controlgnatpp): Output File Controlgnatpp): Output File Controlgnatbind): Consistency-Checking Modesgnatls): Switches for gnatlsgnatmem): Switches for gnatmemgnathtml): Converting Ada Files to html with gnathtmlgnatbind): Switches for gnatbindgnatbind): Switches for gnatbindgnatbind): Binder Error Message Controlgnatbind): Switches for gnatbindgnatbind): Switches for gnatbindgnathtml): Converting Ada Files to html with gnathtmlgnatbind): Switches for gnatbindgnatls): Switches for gnatlsgnatbind): Binder Error Message Controlgnatbind): Switches for gnatbindgnatchop): Switches for gnatchopgnatclean): Switches for gnatcleangnatdll): Using gnatdllgnatls): Switches for gnatlsgnatmetric): Other gnatmetric Switchesgnatname): Switches for gnatnamegnatpp): Other gnatpp Switchesgnatname): Switches for gnatnamegnatclean): Switches for gnatcleangnatbind): Switches for gnatbindgnatchop): Switches for gnatchopgnatpp): Other gnatpp Switchesgnatbind): Binder Error Message Controlgnatbind): Binder Error Message Controlgnatbind): Consistency-Checking Modesgnatbind): Switches for gnatbindgnatbind): Consistency-Checking Modesgnatbind): Switches for gnatbindgnatclean): Switches for gnatcleangnatname): Switches for gnatnamegnatbind): Switches for gnatbindgnatbind): Binding Programs with No Main Subprogramgnatbind): Switches for gnatbind.def: The Definition File__gnat_finalize: Example of Binder Output File__gnat_initialize: Example of Binder Output File__gnat_set_globals: Example of Binder Output File_main: The External Symbol Naming Scheme of GNATAbstract_Type_Declarations rule (for gnatcheck): Abstract_Type_DeclarationsAda: Naming Conventions for GNAT Source FilesAda: Search Paths for gnatbindAda.Characters.Latin_1: Latin-1ADA_INCLUDE_PATH: Search Paths and the Run-Time Library (RTL)ADA_OBJECTS_PATH: Search Paths for gnatbindADA_PRJ_INCLUDE_FILE: Search Paths and the Run-Time Library (RTL)ADA_PRJ_OBJECTS_FILE: Search Paths for gnatbindADA_PROJECT_PATH: Installing a libraryADA_PROJECT_PATH: Importing ProjectsADA_PROJECT_PATH: Importing Other Projectsadafinal: Example of Binder Output Fileadafinal: Binding with Non-Ada Main Programsadainit: Example of Binder Output Fileadainit: Binding with Non-Ada Main ProgramsAnonymous_Arrays rule (for gnatcheck): Anonymous_ArraysAnonymous_Subtypes rule (for gnatcheck): Anonymous_SubtypesAPIENTRY: Windows Calling ConventionsAsm: Calling ConventionsAssert: Debugging and Assertion ControlBlocks rule (for gnatcheck): BlocksBoolean_Relational_Operators rule (for gnatcheck): Boolean_Relational_OperatorsC: Calling ConventionsC varargs function: Calling ConventionsC++: Calling Conventionscase statement (effect of -mbig-switch option): Switches for gccCeiling_Locking (under rts-pthread): Solaris Threads IssuesCOBOL: Calling ConventionsControlled_Type_Declarations rule (for gnatcheck): Controlled_Type_DeclarationsCR: Source RepresentationDebug: Debugging and Assertion ControlDebug Pool: The GNAT Debug Pool FacilityDeclarations_In_Blocks rule (for gnatcheck): Declarations_In_BlocksDefault: Calling ConventionsDefault_Parameters rule (for gnatcheck): Default_ParametersDiscriminated_Records rule (for gnatcheck): Discriminated_RecordsDLL: Introduction to Dynamic Link Libraries (DLLs)DLL: Calling ConventionsElaborate: Controlling the Elaboration OrderElaborate_All: Controlling the Elaboration OrderElaborate_Body: Controlling the Elaboration OrderEnumeration_Ranges_In_CASE_Statements (for gnatcheck): Enumeration_Ranges_In_CASE_StatementsExceptions_As_Control_Flow (for gnatcheck): Exceptions_As_Control_FlowEXIT_Statements_With_No_Loop_Name (for gnatcheck): EXIT_Statements_With_No_Loop_NameExpanded_Loop_Exit_Names rule (for gnatcheck): Expanded_Loop_Exit_NamesExplicit_Full_Discrete_Ranges rule (for gnatcheck): Explicit_Full_Discrete_RangesExport: The External Symbol Naming Scheme of GNATExternal: Calling ConventionsFF: Source RepresentationFloat_Equality_Checks rule (for gnatcheck): Float_Equality_ChecksForbidden_Pragmas rule (for gnatcheck): Forbidden_PragmasFortran: Calling ConventionsFunction_Style_Procedures rule (for gnatcheck): Function_Style_Proceduresgdb: Running and Debugging Ada ProgramsGenerics_In_Subprograms rule (for gnatcheck): Generics_In_SubprogramsGNAT: Naming Conventions for GNAT Source FilesGNAT: Search Paths for gnatbindgnat1: Compiling Programsgnat_argc: Command-Line Accessgnat_argv: Command-Line Accessgnatbind: Binding Using gnatbindgnatcheck: Verifying Properties Using gnatcheckgnatchop: Renaming Files Using gnatchopgnatclean: Cleaning Up Using gnatcleangnatdll: Using gnatdllgnatelim: Reducing Size of Ada Executables with gnatelimgnatfind: The Cross-Referencing Tools gnatxref and gnatfindgnatkr: File Name Krunching Using gnatkrgnatlink: Linking Using gnatlinkgnatls: The GNAT Library Browser gnatlsgnatmake: The GNAT Make Program gnatmakegnatmem: The gnatmem Toolgnatmetric: The GNAT Metric Tool gnatmetricgnatpp: The GNAT Pretty-Printer gnatppgnatprep: Preprocessinggnatprep: Preprocessing Using gnatprepgnatstub: Creating Sample Bodies Using gnatstubgnatxref: The Cross-Referencing Tools gnatxref and gnatfindGOTO_Statements rule (for gnatcheck): GOTO_StatementsHT: Source RepresentationImplicit_IN_Mode_Parameters rule (for gnatcheck): Implicit_IN_Mode_ParametersImplicit_SMALL_For_Fixed_Point_Types rule (for gnatcheck): Implicit_SMALL_For_Fixed_Point_TypesImproper_Returns rule (for gnatcheck): Improper_ReturnsImproperly_Located_Instantiations rule (for gnatcheck): Improperly_Located_InstantiationsInheritance_Locking (under rts-pthread): Solaris Threads IssuesInline: Inlining of SubprogramsInline: Source DependenciesInterfaces: Naming Conventions for GNAT Source FilesInterfaces: Search Paths for gnatbindLF: Source RepresentationLibrary_Level_Subprograms rule (for gnatcheck): Library_Level_SubprogramsLocal_Packages rule (for gnatcheck): Local_PackagesMachine_Overflows: Run-Time ChecksMain Program: Example of Binder Output Filemake: Using the GNU make Utilitymakefile: Using gnatmake in a MakefileMemory Pool: Some Useful Memory PoolsMetrics rule (for gnatcheck): MetricsMisnamed_Identifiers rule (for gnatcheck): Misnamed_IdentifiersMultiple_Entries_In_Protected_Definitions rule (for gnatcheck): Multiple_Entries_In_Protected_Definitionsgnatmem): Switches for gnatmemName_Clashes rule (for gnatcheck): Name_ClashesNon_Qualified_Aggregates rule (for gnatcheck): Non_Qualified_AggregatesNon_Short_Circuit_Operators rule (for gnatcheck): Non_Short_Circuit_OperatorsNon_SPARK_Attributes rule (for gnatcheck): Non_SPARK_AttributesNon_Tagged_Derived_Types rule (for gnatcheck): Non_Tagged_Derived_TypesNon_Visible_Exceptions rule (for gnatcheck): Non_Visible_ExceptionsNumeric_Literals rule (for gnatcheck): Numeric_LiteralsObject file list: Example of Binder Output FileOTHERS_In_Aggregates rule (for gnatcheck): OTHERS_In_AggregatesOTHERS_In_CASE_Statements rule (for gnatcheck): OTHERS_In_CASE_StatementsOTHERS_In_Exception_Handlers rule (for gnatcheck): OTHERS_In_Exception_HandlersOuter_Loop_Exits rule (for gnatcheck): Outer_Loop_ExitsOverloaded_Operators rule (for gnatcheck): Overloaded_OperatorsOverly_Nested_Control_Structures rule (for gnatcheck): Overly_Nested_Control_StructuresParameters_Out_Of_Order rule (for gnatcheck): Parameters_Out_Of_OrderPositional_Actuals_For_Defaulted_Generic_Parameters rule (for gnatcheck): Positional_Actuals_For_Defaulted_Generic_ParametersPositional_Actuals_For_Defaulted_Parameters rule (for gnatcheck): Positional_Actuals_For_Defaulted_ParametersPositional_Components rule (for gnatcheck): Positional_ComponentsPositional_Generic_Parameters rule (for gnatcheck): Positional_Generic_ParametersPositional_Parameters rule (for gnatcheck): Positional_ParametersAssert: Debugging - A Special CaseAssertion_Policy: Debugging - A Special CaseDebug: Debugging - A Special CaseDebug_Policy: Debugging - A Special CasePredefined_Numeric_Types rule (for gnatcheck): Predefined_Numeric_TypesPreelaborate: Controlling the Elaboration OrderPTHREAD_PRIO_INHERIT policy (under rts-pthread): Solaris Threads IssuesPTHREAD_PRIO_PROTECT policy (under rts-pthread): Solaris Threads IssuesPure: Controlling the Elaboration OrderRaising_External_Exceptions rule (for gnatcheck): Raising_External_ExceptionsRaising_Predefined_Exceptions rule (for gnatcheck): Raising_Predefined_Exceptionsrc: Compiling Resourcesgnatcheck): Format of the Report Filegnatcheck): gnatcheck Rule OptionsSCHED_FIFO scheduling policy: Choosing the Scheduling PolicySCHED_OTHER scheduling policy: Choosing the Scheduling PolicySCHED_RR scheduling policy: Choosing the Scheduling PolicySDP_Table_Build: Example of Binder Output FileSeparate_Numeric_Error_Handlers rule (for gnatcheck): Separate_Numeric_Error_HandlersSlices rule (for gnatcheck): SlicesSource_Reference: Switches for gnatchopStdcall: Windows Calling ConventionsStdcall: Calling Conventionsstderr: Output and Error Message Controlstdout: Output and Error Message ControlStubbed: Calling ConventionsStyle checking: Style CheckingSUB: Source RepresentationSuppress: Controlling Run-Time ChecksSuppress: Run-Time ChecksSystem: Naming Conventions for GNAT Source FilesSystem: Search Paths for gnatbindSystem.IO: Search Paths and the Run-Time Library (RTL)Text_IO and performance: Text_IO SuggestionsUnassigned_OUT_Parameters rule (for gnatcheck): Unassigned_OUT_ParametersUncommented_BEGIN_In_Package_Bodies rule (for gnatcheck): Uncommented_BEGIN_In_Package_BodiesUnconstrained_Array_Returns rule (for gnatcheck): Unconstrained_Array_ReturnsUniversal_Ranges rule (for gnatcheck): Universal_RangesUnnamed_Blocks_And_Loops rule (for gnatcheck): Unnamed_Blocks_And_LoopsUnsuppress: Controlling Run-Time ChecksUnsuppress: Run-Time Checksunused subprogram/data elimination: Reducing Size of Executables with unused subprogram/data eliminationUSE_PACKAGE_Clauses rule (for gnatcheck): USE_PACKAGE_ClausesValidity Checking: Validity CheckingVolatile_Objects_Without_Address_Clauses rule (for gnatcheck): Volatile_Objects_Without_Address_ClausesVT: Source RepresentationWin32: Calling Conventionswindres: Compiling ResourcesZero Cost Exceptions: Example of Binder Output Filegnatbind
gnatchop
gnatname
gnatxref and gnatfind
gnatkr
gnatprep
gnatls
gnatclean
make Utility
Abstract_Type_Declarations
Anonymous_Arrays
Anonymous_Subtypes
Blocks
Boolean_Relational_Operators
Controlled_Type_Declarations
Declarations_In_Blocks
Default_Parameters
Discriminated_Records
Enumeration_Ranges_In_CASE_Statements
Exceptions_As_Control_Flow
EXIT_Statements_With_No_Loop_Name
Expanded_Loop_Exit_Names
Explicit_Full_Discrete_Ranges
Float_Equality_Checks
Forbidden_Pragmas
Function_Style_Procedures
Generics_In_Subprograms
GOTO_Statements
Implicit_IN_Mode_Parameters
Implicit_SMALL_For_Fixed_Point_Types
Improperly_Located_Instantiations
Improper_Returns
Library_Level_Subprograms
Local_Packages
Metrics
Misnamed_Identifiers
Multiple_Entries_In_Protected_Definitions
Name_Clashes
Non_Qualified_Aggregates
Non_Short_Circuit_Operators
Non_SPARK_Attributes
Non_Tagged_Derived_Types
Non_Visible_Exceptions
Numeric_Literals
OTHERS_In_Aggregates
OTHERS_In_CASE_Statements
OTHERS_In_Exception_Handlers
Outer_Loop_Exits
Overloaded_Operators
Overly_Nested_Control_Structures
Parameters_Out_Of_Order
Positional_Actuals_For_Defaulted_Generic_Parameters
Positional_Actuals_For_Defaulted_Parameters
Positional_Components
Positional_Generic_Parameters
Positional_Parameters
Predefined_Numeric_Types
Raising_External_Exceptions
Raising_Predefined_Exceptions
Separate_Numeric_Error_Handlers
Slices
Unassigned_OUT_Parameters
Uncommented_BEGIN_In_Package_Bodies
Unconstrained_Array_Returns
Universal_Ranges
Unnamed_Blocks_And_Loops
USE_PACKAGE_Clauses
Volatile_Objects_Without_Address_Clauses
[1] Most programs should experience a substantial speed improvement by being compiled with a ZCX run-time. This is especially true for tasking applications or applications with many exception handlers.