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@settitle GNAT User's Guide for Native Platforms
@defindex ge
@paragraphindent 0
@exampleindent 4
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@dircategory GNU Ada Tools
@direntry
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@quotation
GNAT User's Guide for Native Platforms , Oct 19, 2021
AdaCore
Copyright @copyright{} 2008-2021, Free Software Foundation
@end quotation
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@titlepage
@title GNAT User's Guide for Native Platforms
@insertcopying
@end titlepage
@contents
@c %** start of user preamble
@c %** end of user preamble
@ifnottex
@node Top
@top GNAT User's Guide for Native Platforms
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@c %**start of body
@anchor{gnat_ugn doc}@anchor{0}
@emph{GNAT, The GNU Ada Development Environment}
@include gcc-common.texi
GCC version @value{version-GCC}@*
AdaCore
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with the Front-Cover Texts being
“GNAT User’s Guide for Native Platforms”,
and with no Back-Cover Texts. A copy of the license is
included in the section entitled @ref{1,,GNU Free Documentation License}.
@menu
* About This Guide::
* Getting Started with GNAT::
* The GNAT Compilation Model::
* Building Executable Programs with GNAT::
* GNAT Utility Programs::
* GNAT and Program Execution::
* Platform-Specific Information::
* Example of Binder Output File::
* Elaboration Order Handling in GNAT::
* Inline Assembler::
* GNU Free Documentation License::
* Index::
@detailmenu
--- The Detailed Node Listing ---
About This Guide
* What This Guide Contains::
* What You Should Know before Reading This Guide::
* Related Information::
* Conventions::
Getting Started with GNAT
* System Requirements::
* Running GNAT::
* Running a Simple Ada Program::
* Running a Program with Multiple Units::
The GNAT Compilation Model
* Source Representation::
* Foreign Language Representation::
* File Naming Topics and Utilities::
* Configuration Pragmas::
* Generating Object Files::
* Source Dependencies::
* The Ada Library Information Files::
* Binding an Ada Program::
* GNAT and Libraries::
* Conditional Compilation::
* Mixed Language Programming::
* GNAT and Other Compilation Models::
* Using GNAT Files with External Tools::
Foreign Language Representation
* Latin-1::
* Other 8-Bit Codes::
* Wide_Character Encodings::
* Wide_Wide_Character Encodings::
File Naming Topics and Utilities
* File Naming Rules::
* Using Other File Names::
* Alternative File Naming Schemes::
* Handling Arbitrary File Naming Conventions with gnatname::
* File Name Krunching with gnatkr::
* Renaming Files with gnatchop::
Handling Arbitrary File Naming Conventions with gnatname
* Arbitrary File Naming Conventions::
* Running gnatname::
* Switches for gnatname::
* Examples of gnatname Usage::
File Name Krunching with gnatkr
* About gnatkr::
* Using gnatkr::
* Krunching Method::
* Examples of gnatkr Usage::
Renaming Files with gnatchop
* Handling Files with Multiple Units::
* Operating gnatchop in Compilation Mode::
* Command Line for gnatchop::
* Switches for gnatchop::
* Examples of gnatchop Usage::
Configuration Pragmas
* Handling of Configuration Pragmas::
* The Configuration Pragmas Files::
GNAT and Libraries
* Introduction to Libraries in GNAT::
* General Ada Libraries::
* Stand-alone Ada Libraries::
* Rebuilding the GNAT Run-Time Library::
General Ada Libraries
* Building a library::
* Installing a library::
* Using a library::
Stand-alone Ada Libraries
* Introduction to Stand-alone Libraries::
* Building a Stand-alone Library::
* Creating a Stand-alone Library to be used in a non-Ada context::
* Restrictions in Stand-alone Libraries::
Conditional Compilation
* Modeling Conditional Compilation in Ada::
* Preprocessing with gnatprep::
* Integrated Preprocessing::
Modeling Conditional Compilation in Ada
* Use of Boolean Constants::
* Debugging - A Special Case::
* Conditionalizing Declarations::
* Use of Alternative Implementations::
* Preprocessing::
Preprocessing with gnatprep
* Preprocessing Symbols::
* Using gnatprep::
* Switches for gnatprep::
* Form of Definitions File::
* Form of Input Text for gnatprep::
Mixed Language Programming
* Interfacing to C::
* Calling Conventions::
* Building Mixed Ada and C++ Programs::
* Generating Ada Bindings for C and C++ headers::
* Generating C Headers for Ada Specifications::
Building Mixed Ada and C++ Programs
* Interfacing to C++::
* Linking a Mixed C++ & Ada Program::
* A Simple Example::
* Interfacing with C++ constructors::
* Interfacing with C++ at the Class Level::
Generating Ada Bindings for C and C++ headers
* Running the Binding Generator::
* Generating Bindings for C++ Headers::
* Switches::
Generating C Headers for Ada Specifications
* Running the C Header Generator::
GNAT and Other Compilation Models
* Comparison between GNAT and C/C++ Compilation Models::
* Comparison between GNAT and Conventional Ada Library Models::
Using GNAT Files with External Tools
* Using Other Utility Programs with GNAT::
* The External Symbol Naming Scheme of GNAT::
Building Executable Programs with GNAT
* Building with gnatmake::
* Compiling with gcc::
* Compiler Switches::
* Linker Switches::
* Binding with gnatbind::
* Linking with gnatlink::
* Using the GNU make Utility::
Building with gnatmake
* Running gnatmake::
* Switches for gnatmake::
* Mode Switches for gnatmake::
* Notes on the Command Line::
* How gnatmake Works::
* Examples of gnatmake Usage::
Compiling with gcc
* Compiling Programs::
* Search Paths and the Run-Time Library (RTL): Search Paths and the Run-Time Library RTL.
* Order of Compilation Issues::
* Examples::
Compiler Switches
* Alphabetical List of All Switches::
* Output and Error Message Control::
* Warning Message Control::
* Debugging and Assertion Control::
* Validity Checking::
* Style Checking::
* Run-Time Checks::
* Using gcc for Syntax Checking::
* Using gcc for Semantic Checking::
* Compiling Different Versions of Ada::
* Character Set Control::
* File Naming Control::
* Subprogram Inlining Control::
* Auxiliary Output Control::
* Debugging Control::
* Exception Handling Control::
* Units to Sources Mapping Files::
* Code Generation Control::
Binding with gnatbind
* Running gnatbind::
* Switches for gnatbind::
* Command-Line Access::
* Search Paths for gnatbind::
* Examples of gnatbind Usage::
Switches for gnatbind
* Consistency-Checking Modes::
* Binder Error Message Control::
* Elaboration Control::
* Output Control::
* Dynamic Allocation Control::
* Binding with Non-Ada Main Programs::
* Binding Programs with No Main Subprogram::
Linking with gnatlink
* Running gnatlink::
* Switches for gnatlink::
Using the GNU make Utility
* Using gnatmake in a Makefile::
* Automatically Creating a List of Directories::
* Generating the Command Line Switches::
* Overcoming Command Line Length Limits::
GNAT Utility Programs
* The File Cleanup Utility gnatclean::
* The GNAT Library Browser gnatls::
The File Cleanup Utility gnatclean
* Running gnatclean::
* Switches for gnatclean::
The GNAT Library Browser gnatls
* Running gnatls::
* Switches for gnatls::
* Example of gnatls Usage::
GNAT and Program Execution
* Running and Debugging Ada Programs::
* Profiling::
* Improving Performance::
* Overflow Check Handling in GNAT::
* Performing Dimensionality Analysis in GNAT::
* Stack Related Facilities::
* Memory Management Issues::
Running and Debugging Ada Programs
* The GNAT Debugger GDB::
* Running GDB::
* Introduction to GDB Commands::
* Using Ada Expressions::
* Calling User-Defined Subprograms::
* Using the next Command in a Function::
* Stopping When Ada Exceptions Are Raised::
* Ada Tasks::
* Debugging Generic Units::
* Remote Debugging with gdbserver::
* GNAT Abnormal Termination or Failure to Terminate::
* Naming Conventions for GNAT Source Files::
* Getting Internal Debugging Information::
* Stack Traceback::
* Pretty-Printers for the GNAT runtime::
Stack Traceback
* Non-Symbolic Traceback::
* Symbolic Traceback::
Profiling
* Profiling an Ada Program with gprof::
Profiling an Ada Program with gprof
* Compilation for profiling::
* Program execution::
* Running gprof::
* Interpretation of profiling results::
Improving Performance
* Performance Considerations::
* Text_IO Suggestions::
* Reducing Size of Executables with Unused Subprogram/Data Elimination::
Performance Considerations
* Controlling Run-Time Checks::
* Use of Restrictions::
* Optimization Levels::
* Debugging Optimized Code::
* Inlining of Subprograms::
* Floating Point Operations::
* Vectorization of loops::
* Other Optimization Switches::
* Optimization and Strict Aliasing::
* Aliased Variables and Optimization::
* Atomic Variables and Optimization::
* Passive Task Optimization::
Reducing Size of Executables with Unused Subprogram/Data Elimination
* About unused subprogram/data elimination::
* Compilation options::
* Example of unused subprogram/data elimination::
Overflow Check Handling in GNAT
* Background::
* Management of Overflows in GNAT::
* Specifying the Desired Mode::
* Default Settings::
* Implementation Notes::
Stack Related Facilities
* Stack Overflow Checking::
* Static Stack Usage Analysis::
* Dynamic Stack Usage Analysis::
Memory Management Issues
* Some Useful Memory Pools::
* The GNAT Debug Pool Facility::
Platform-Specific Information
* Run-Time Libraries::
* Specifying a Run-Time Library::
* GNU/Linux Topics::
* Microsoft Windows Topics::
* Mac OS Topics::
Run-Time Libraries
* Summary of Run-Time Configurations::
Specifying a Run-Time Library
* Choosing the Scheduling Policy::
GNU/Linux Topics
* Required Packages on GNU/Linux::
Microsoft Windows Topics
* Using GNAT on Windows::
* Using a network installation of GNAT::
* CONSOLE and WINDOWS subsystems::
* Temporary Files::
* Disabling Command Line Argument Expansion::
* Windows Socket Timeouts::
* Mixed-Language Programming on Windows::
* Windows Specific Add-Ons::
Mixed-Language Programming on Windows
* Windows Calling Conventions::
* Introduction to Dynamic Link Libraries (DLLs): Introduction to Dynamic Link Libraries DLLs.
* Using DLLs with GNAT::
* Building DLLs with GNAT Project files::
* Building DLLs with GNAT::
* Building DLLs with gnatdll::
* Ada DLLs and Finalization::
* Creating a Spec for Ada DLLs::
* GNAT and Windows Resources::
* Using GNAT DLLs from Microsoft Visual Studio Applications::
* Debugging a DLL::
* Setting Stack Size from gnatlink::
* Setting Heap Size from gnatlink::
Windows Calling Conventions
* C Calling Convention::
* Stdcall Calling Convention::
* Win32 Calling Convention::
* DLL Calling Convention::
Using DLLs with GNAT
* Creating an Ada Spec for the DLL Services::
* Creating an Import Library::
Building DLLs with gnatdll
* Limitations When Using Ada DLLs from Ada::
* Exporting Ada Entities::
* Ada DLLs and Elaboration::
Creating a Spec for Ada DLLs
* Creating the Definition File::
* Using gnatdll::
GNAT and Windows Resources
* Building Resources::
* Compiling Resources::
* Using Resources::
Debugging a DLL
* Program and DLL Both Built with GCC/GNAT::
* Program Built with Foreign Tools and DLL Built with GCC/GNAT::
Windows Specific Add-Ons
* Win32Ada::
* wPOSIX::
Mac OS Topics
* Codesigning the Debugger::
Elaboration Order Handling in GNAT
* Elaboration Code::
* Elaboration Order::
* Checking the Elaboration Order::
* Controlling the Elaboration Order in Ada::
* Controlling the Elaboration Order in GNAT::
* Mixing Elaboration Models::
* ABE Diagnostics::
* SPARK Diagnostics::
* Elaboration Circularities::
* Resolving Elaboration Circularities::
* Elaboration-related Compiler Switches::
* Summary of Procedures for Elaboration Control::
* Inspecting the Chosen Elaboration Order::
Inline Assembler
* Basic Assembler Syntax::
* A Simple Example of Inline Assembler::
* Output Variables in Inline Assembler::
* Input Variables in Inline Assembler::
* Inlining Inline Assembler Code::
* Other Asm Functionality::
Other Asm Functionality
* The Clobber Parameter::
* The Volatile Parameter::
@end detailmenu
@end menu
@node About This Guide,Getting Started with GNAT,Top,Top
@anchor{gnat_ugn/about_this_guide doc}@anchor{2}@anchor{gnat_ugn/about_this_guide about-this-guide}@anchor{3}@anchor{gnat_ugn/about_this_guide gnat-user-s-guide-for-native-platforms}@anchor{4}@anchor{gnat_ugn/about_this_guide id1}@anchor{5}
@chapter About This Guide
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, Ada 2005, Ada 2012, and Ada 202x, and it may also be
invoked in Ada 83 compatibility mode.
By default, GNAT assumes Ada 2012, but you can override with a
compiler switch (@ref{6,,Compiling Different Versions of Ada})
to explicitly specify the language version.
Throughout this manual, references to ‘Ada’ without a year suffix
apply to all Ada versions of the language, starting with Ada 95.
@menu
* What This Guide Contains::
* What You Should Know before Reading This Guide::
* Related Information::
* Conventions::
@end menu
@node What This Guide Contains,What You Should Know before Reading This Guide,,About This Guide
@anchor{gnat_ugn/about_this_guide what-this-guide-contains}@anchor{7}
@section What This Guide Contains
This guide contains the following chapters:
@itemize *
@item
@ref{8,,Getting Started with GNAT} describes how to get started compiling
and running Ada programs with the GNAT Ada programming environment.
@item
@ref{9,,The GNAT Compilation Model} describes the compilation model used
by GNAT.
@item
@ref{a,,Building Executable Programs with GNAT} describes how to use the
main GNAT tools to build executable programs, and it also gives examples of
using the GNU make utility with GNAT.
@item
@ref{b,,GNAT Utility Programs} explains the various utility programs that
are included in the GNAT environment
@item
@ref{c,,GNAT and Program Execution} covers a number of topics related to
running, debugging, and tuning the performace of programs developed
with GNAT
@end itemize
Appendices cover several additional topics:
@itemize *
@item
@ref{d,,Platform-Specific Information} describes the different run-time
library implementations and also presents information on how to use
GNAT on several specific platforms
@item
@ref{e,,Example of Binder Output File} shows the source code for the binder
output file for a sample program.
@item
@ref{f,,Elaboration Order Handling in GNAT} describes how GNAT helps
you deal with elaboration order issues.
@item
@ref{10,,Inline Assembler} shows how to use the inline assembly facility
in an Ada program.
@end itemize
@node What You Should Know before Reading This Guide,Related Information,What This Guide Contains,About This Guide
@anchor{gnat_ugn/about_this_guide what-you-should-know-before-reading-this-guide}@anchor{11}
@section What You Should Know before Reading This Guide
@geindex Ada 95 Language Reference Manual
@geindex Ada 2005 Language Reference Manual
This guide assumes a basic familiarity with the Ada 95 language, as
described in the International Standard ANSI/ISO/IEC-8652:1995, January
1995.
Reference manuals for Ada 95, Ada 2005, and Ada 2012 are included in
the GNAT documentation package.
@node Related Information,Conventions,What You Should Know before Reading This Guide,About This Guide
@anchor{gnat_ugn/about_this_guide related-information}@anchor{12}
@section Related Information
For further information about Ada and related tools, please refer to the
following documents:
@itemize *
@item
@cite{Ada 95 Reference Manual}, @cite{Ada 2005 Reference Manual}, and
@cite{Ada 2012 Reference Manual}, which contain reference
material for the several revisions of the Ada language standard.
@item
@cite{GNAT Reference_Manual}, which contains all reference material for the GNAT
implementation of Ada.
@item
@cite{Using GNAT Studio}, which describes the GNAT Studio
Integrated Development Environment.
@item
@cite{GNAT Studio Tutorial}, which introduces the
main GNAT Studio features through examples.
@item
@cite{Debugging with GDB},
for all details on the use of the GNU source-level debugger.
@item
@cite{GNU Emacs Manual},
for full information on the extensible editor and programming
environment Emacs.
@end itemize
@node Conventions,,Related Information,About This Guide
@anchor{gnat_ugn/about_this_guide conventions}@anchor{13}
@section Conventions
@geindex Conventions
@geindex typographical
@geindex Typographical conventions
Following are examples of the typographical and graphic conventions used
in this guide:
@itemize *
@item
@code{Functions}, @code{utility program names}, @code{standard names},
and @code{classes}.
@item
@code{Option flags}
@item
@code{File names}
@item
@code{Variables}
@item
@emph{Emphasis}
@item
[optional information or parameters]
@item
Examples are described by text
@example
and then shown this way.
@end example
@item
Commands that are entered by the user are shown as preceded by a prompt string
comprising the @code{$} character followed by a space.
@item
Full file names are shown with the ‘/’ character
as the directory separator; e.g., @code{parent-dir/subdir/myfile.adb}.
If you are using GNAT on a Windows platform, please note that
the ‘' character should be used instead.
@end itemize
@node Getting Started with GNAT,The GNAT Compilation Model,About This Guide,Top
@anchor{gnat_ugn/getting_started_with_gnat doc}@anchor{14}@anchor{gnat_ugn/getting_started_with_gnat getting-started-with-gnat}@anchor{8}@anchor{gnat_ugn/getting_started_with_gnat id1}@anchor{15}
@chapter Getting Started with GNAT
This chapter describes how to use GNAT’s command line interface to build
executable Ada programs.
On most platforms a visually oriented Integrated Development Environment
is also available: GNAT Studio.
GNAT Studio offers a graphical “look and feel”, support for development in
other programming languages, comprehensive browsing features, and
many other capabilities.
For information on GNAT Studio please refer to the
@cite{GNAT Studio documentation}.
@menu
* System Requirements::
* Running GNAT::
* Running a Simple Ada Program::
* Running a Program with Multiple Units::
@end menu
@node System Requirements,Running GNAT,,Getting Started with GNAT
@anchor{gnat_ugn/getting_started_with_gnat id2}@anchor{16}@anchor{gnat_ugn/getting_started_with_gnat system-requirements}@anchor{17}
@section System Requirements
Even though any machine can run the GNAT toolset and GNAT Studio IDE, in order
to get the best experience, we recommend using a machine with as many cores
as possible since all individual compilations can run in parallel.
A comfortable setup for a compiler server is a machine with 24 physical cores
or more, with at least 48 GB of memory (2 GB per core).
For a desktop machine, a minimum of 4 cores is recommended (8 preferred),
with at least 2GB per core (so 8 to 16GB).
In addition, for running and navigating sources in GNAT Studio smoothly, we
recommend at least 1.5 GB plus 3 GB of RAM per 1 million source line of code.
In other words, we recommend at least 3 GB for for 500K lines of code and
7.5 GB for 2 million lines of code.
Note that using local and fast drives will also make a difference in terms of
build and link time. Network drives such as NFS, SMB, or worse, configuration
management filesystems (such as ClearCase dynamic views) should be avoided as
much as possible and will produce very degraded performance (typically 2 to 3
times slower than on local fast drives). If such slow drives cannot be avoided
for accessing the source code, then you should at least configure your project
file so that the result of the compilation is stored on a drive local to the
machine performing the run. This can be achieved by setting the @code{Object_Dir}
project file attribute.
@node Running GNAT,Running a Simple Ada Program,System Requirements,Getting Started with GNAT
@anchor{gnat_ugn/getting_started_with_gnat id3}@anchor{18}@anchor{gnat_ugn/getting_started_with_gnat running-gnat}@anchor{19}
@section Running GNAT
Three steps are needed to create an executable file from an Ada source
file:
@itemize *
@item
The source file(s) must be compiled.
@item
The file(s) must be bound using the GNAT binder.
@item
All appropriate object files must be linked to produce an executable.
@end itemize
All three steps are most commonly handled by using the @code{gnatmake}
utility program that, given the name of the main program, automatically
performs the necessary compilation, binding and linking steps.
@node Running a Simple Ada Program,Running a Program with Multiple Units,Running GNAT,Getting Started with GNAT
@anchor{gnat_ugn/getting_started_with_gnat id4}@anchor{1a}@anchor{gnat_ugn/getting_started_with_gnat running-a-simple-ada-program}@anchor{1b}
@section Running a Simple Ada Program
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:
@example
with Ada.Text_IO; use Ada.Text_IO;
procedure Hello is
begin
Put_Line ("Hello WORLD!");
end Hello;
@end example
This file should be named @code{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 @code{ads} for a
spec and @code{adb} for a body.
You can override this default file naming convention by use of the
special pragma @code{Source_File_Name} (for further information please
see @ref{1c,,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 @code{gnatchop} utility
can be used to generate correctly-named source files
(see @ref{1d,,Renaming Files with gnatchop}).
You can compile the program using the following command (@code{$} is used
as the command prompt in the examples in this document):
@example
$ gcc -c hello.adb
@end example
@code{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 @code{.ads} or @code{.adb}, and it will then call
the GNAT compiler to compile the specified file.
The @code{-c} switch is required. It tells @code{gcc} to only do a
compilation. (For C programs, @code{gcc} can also do linking, but this
capability is not used directly for Ada programs, so the @code{-c}
switch must always be present.)
This compile command generates a file
@code{hello.o}, which is the object
file corresponding to your Ada program. It also generates
an ‘Ada Library Information’ file @code{hello.ali},
which contains additional information used to check
that an Ada program is consistent.
To build an executable file, use either @code{gnatmake} or gprbuild with
the name of the main file: these tools are builders that will take care of
all the necessary build steps in the correct order.
In particular, these builders automatically recompile 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.
@geindex Version skew (avoided by `@w{`}gnatmake`@w{`})
@example
$ gnatmake hello.adb
@end example
The result is an executable program called @code{hello}, which can be
run by entering:
@example
$ hello
@end example
assuming that the current directory is on the search path
for executable programs.
and, if all has gone well, you will see:
@example
Hello WORLD!
@end example
appear in response to this command.
@node Running a Program with Multiple Units,,Running a Simple Ada Program,Getting Started with GNAT
@anchor{gnat_ugn/getting_started_with_gnat id5}@anchor{1e}@anchor{gnat_ugn/getting_started_with_gnat running-a-program-with-multiple-units}@anchor{1f}
@section Running a Program with Multiple Units
Consider a slightly more complicated example that has three files: a
main program, and the spec and body of a package:
@example
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;
@end example
Following the one-unit-per-file rule, place this program in the
following three separate files:
@table @asis
@item @emph{greetings.ads}
spec of package @code{Greetings}
@item @emph{greetings.adb}
body of package @code{Greetings}
@item @emph{gmain.adb}
body of main program
@end table
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 @code{-gnatc} switch:
@example
$ gcc -c greetings.ads -gnatc
@end example
Although the compilation can be done in separate steps, in practice it is
almost always more convenient to use the @code{gnatmake} or @code{gprbuild} tools:
@example
$ gnatmake gmain.adb
@end example
@c -- Example: A |withing| unit has a |with| clause, it |withs| a |withed| unit
@node The GNAT Compilation Model,Building Executable Programs with GNAT,Getting Started with GNAT,Top
@anchor{gnat_ugn/the_gnat_compilation_model doc}@anchor{20}@anchor{gnat_ugn/the_gnat_compilation_model id1}@anchor{21}@anchor{gnat_ugn/the_gnat_compilation_model the-gnat-compilation-model}@anchor{9}
@chapter The GNAT Compilation Model
@geindex GNAT compilation model
@geindex Compilation model
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 centralized program library. The chapter covers
the following material:
@itemize *
@item
Topics related to source file makeup and naming
@itemize *
@item
@ref{22,,Source Representation}
@item
@ref{23,,Foreign Language Representation}
@item
@ref{24,,File Naming Topics and Utilities}
@end itemize
@item
@ref{25,,Configuration Pragmas}
@item
@ref{26,,Generating Object Files}
@item
@ref{27,,Source Dependencies}
@item
@ref{28,,The Ada Library Information Files}
@item
@ref{29,,Binding an Ada Program}
@item
@ref{2a,,GNAT and Libraries}
@item
@ref{2b,,Conditional Compilation}
@item
@ref{2c,,Mixed Language Programming}
@item
@ref{2d,,GNAT and Other Compilation Models}
@item
@ref{2e,,Using GNAT Files with External Tools}
@end itemize
@menu
* Source Representation::
* Foreign Language Representation::
* File Naming Topics and Utilities::
* Configuration Pragmas::
* Generating Object Files::
* Source Dependencies::
* The Ada Library Information Files::
* Binding an Ada Program::
* GNAT and Libraries::
* Conditional Compilation::
* Mixed Language Programming::
* GNAT and Other Compilation Models::
* Using GNAT Files with External Tools::
@end menu
@node Source Representation,Foreign Language Representation,,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id2}@anchor{2f}@anchor{gnat_ugn/the_gnat_compilation_model source-representation}@anchor{22}
@section Source Representation
@geindex Latin-1
@geindex VT
@geindex HT
@geindex CR
@geindex LF
@geindex FF
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 @ref{23,,Foreign Language Representation}
for support of non-USA character sets). The format effector characters
are represented using their standard ASCII encodings, as follows:
@quotation
@multitable {xxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxx}
@item
Character
@tab
Effect
@tab
Code
@item
@code{VT}
@tab
Vertical tab
@tab
@code{16#0B#}
@item
@code{HT}
@tab
Horizontal tab
@tab
@code{16#09#}
@item
@code{CR}
@tab
Carriage return
@tab
@code{16#0D#}
@item
@code{LF}
@tab
Line feed
@tab
@code{16#0A#}
@item
@code{FF}
@tab
Form feed
@tab
@code{16#0C#}
@end multitable
@end quotation
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:
@code{LF}, @code{CR}, @code{CR-LF}, or @code{LF-CR}. This is useful
in accommodating files that are imported from other operating systems.
@geindex End of source file; Source file@comma{} end
@geindex SUB (control character)
The end of a source file is normally represented by the physical end of
file. However, the control character @code{16#1A#} (@code{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.
@geindex spec (definition)
@geindex compilation (definition)
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 @emph{spec}) and the corresponding body in
separate files. An Ada @emph{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.
@node Foreign Language Representation,File Naming Topics and Utilities,Source Representation,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model foreign-language-representation}@anchor{23}@anchor{gnat_ugn/the_gnat_compilation_model id3}@anchor{30}
@section Foreign Language Representation
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 (@ref{31,,Character Set Control}).
@menu
* Latin-1::
* Other 8-Bit Codes::
* Wide_Character Encodings::
* Wide_Wide_Character Encodings::
@end menu
@node Latin-1,Other 8-Bit Codes,,Foreign Language Representation
@anchor{gnat_ugn/the_gnat_compilation_model id4}@anchor{32}@anchor{gnat_ugn/the_gnat_compilation_model latin-1}@anchor{33}
@subsection Latin-1
@geindex Latin-1
The basic character set is Latin-1. This character set is defined by ISO
standard 8859, part 1. The lower half (character codes @code{16#00#}
… @code{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.
@geindex Ada.Characters.Latin_1
For a complete list of Latin-1 codes and their encodings, see the source
file of library unit @code{Ada.Characters.Latin_1} in file
@code{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.
@node Other 8-Bit Codes,Wide_Character Encodings,Latin-1,Foreign Language Representation
@anchor{gnat_ugn/the_gnat_compilation_model id5}@anchor{34}@anchor{gnat_ugn/the_gnat_compilation_model other-8-bit-codes}@anchor{35}
@subsection Other 8-Bit Codes
GNAT also supports several other 8-bit coding schemes:
@geindex Latin-2
@geindex ISO 8859-2
@table @asis
@item @emph{ISO 8859-2 (Latin-2)}
Latin-2 letters allowed in identifiers, with uppercase and lowercase
equivalence.
@end table
@geindex Latin-3
@geindex ISO 8859-3
@table @asis
@item @emph{ISO 8859-3 (Latin-3)}
Latin-3 letters allowed in identifiers, with uppercase and lowercase
equivalence.
@end table
@geindex Latin-4
@geindex ISO 8859-4
@table @asis
@item @emph{ISO 8859-4 (Latin-4)}
Latin-4 letters allowed in identifiers, with uppercase and lowercase
equivalence.
@end table
@geindex ISO 8859-5
@geindex Cyrillic
@table @asis
@item @emph{ISO 8859-5 (Cyrillic)}
ISO 8859-5 letters (Cyrillic) allowed in identifiers, with uppercase and
lowercase equivalence.
@end table
@geindex ISO 8859-15
@geindex Latin-9
@table @asis
@item @emph{ISO 8859-15 (Latin-9)}
ISO 8859-15 (Latin-9) letters allowed in identifiers, with uppercase and
lowercase equivalence
@end table
@geindex code page 437 (IBM PC)
@table @asis
@item @emph{IBM PC (code page 437)}
This code page is the normal default for PCs in the U.S. It corresponds
to the original IBM PC character set. This set has some, but not all, of
the extended Latin-1 letters, but these letters do not have the same
encoding as Latin-1. In this mode, these letters are allowed in
identifiers with uppercase and lowercase equivalence.
@end table
@geindex code page 850 (IBM PC)
@table @asis
@item @emph{IBM PC (code page 850)}
This code page is a modification of 437 extended to include all the
Latin-1 letters, but still not with the usual Latin-1 encoding. In this
mode, all these letters are allowed in identifiers with uppercase and
lowercase equivalence.
@item @emph{Full Upper 8-bit}
Any character in the range 80-FF allowed in identifiers, and all are
considered distinct. In other words, there are no uppercase and lowercase
equivalences in this range. This is useful in conjunction with
certain encoding schemes used for some foreign character sets (e.g.,
the typical method of representing Chinese characters on the PC).
@item @emph{No Upper-Half}
No upper-half characters in the range 80-FF are allowed in identifiers.
This gives Ada 83 compatibility for identifier names.
@end table
For precise data on the encodings permitted, and the uppercase and lowercase
equivalences that are recognized, see the file @code{csets.adb} in
the GNAT compiler sources. You will need to obtain a full source release
of GNAT to obtain this file.
@node Wide_Character Encodings,Wide_Wide_Character Encodings,Other 8-Bit Codes,Foreign Language Representation
@anchor{gnat_ugn/the_gnat_compilation_model id6}@anchor{36}@anchor{gnat_ugn/the_gnat_compilation_model wide-character-encodings}@anchor{37}
@subsection Wide_Character Encodings
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:
@table @asis
@item @emph{Hex Coding}
In this encoding, a wide character is represented by the following five
character sequence:
@example
ESC a b c d
@end example
where @code{a}, @code{b}, @code{c}, @code{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
@code{16#A345#}.
This scheme is compatible with use of the full Wide_Character set.
@item @emph{Upper-Half Coding}
@geindex Upper-Half Coding
The wide character with encoding @code{16#abcd#} where the upper bit is on
(in other words, ‘a’ is in the range 8-F) is represented as two bytes,
@code{16#ab#} and @code{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.
@item @emph{Shift JIS Coding}
@geindex Shift JIS Coding
A wide character is represented by a two-character sequence,
@code{16#ab#} and
@code{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.
@item @emph{EUC Coding}
@geindex EUC Coding
A wide character is represented by a two-character sequence
@code{16#ab#} and
@code{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.
@item @emph{UTF-8 Coding}
A wide character is represented using
UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
10646-1/Am.2. Depending on the character value, the representation
is a one, two, or three byte sequence:
@example
16#0000#-16#007f#: 2#0xxxxxxx#
16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx#
16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
@end example
where the @code{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, and in the following section on wide wide
characters, the use of these sequences is documented).
@item @emph{Brackets Coding}
In this encoding, a wide character is represented by the following eight
character sequence:
@example
[ " a b c d " ]
@end example
where @code{a}, @code{b}, @code{c}, @code{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
@code{16#A345#}. It is also possible (though not required) to use the
Brackets coding for upper half characters. For example, the code
@code{16#A3#} can be represented as @code{['A3']}.
This scheme is compatible with use of the full Wide_Character set,
and is also the method used for wide character encoding in some standard
ACATS (Ada Conformity Assessment Test Suite) test suite distributions.
@end table
@cartouche
@quotation 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.
@end quotation
@end cartouche
@node Wide_Wide_Character Encodings,,Wide_Character Encodings,Foreign Language Representation
@anchor{gnat_ugn/the_gnat_compilation_model id7}@anchor{38}@anchor{gnat_ugn/the_gnat_compilation_model wide-wide-character-encodings}@anchor{39}
@subsection Wide_Wide_Character Encodings
GNAT allows wide wide character codes to appear in character and string
literals, and also optionally in identifiers, by means of the following
possible encoding schemes:
@table @asis
@item @emph{UTF-8 Coding}
A wide character is represented using
UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
10646-1/Am.2. Depending on the character value, the representation
of character codes with values greater than 16#FFFF# is a
is a four, five, or six byte sequence:
@example
16#01_0000#-16#10_FFFF#: 11110xxx 10xxxxxx 10xxxxxx
10xxxxxx
16#0020_0000#-16#03FF_FFFF#: 111110xx 10xxxxxx 10xxxxxx
10xxxxxx 10xxxxxx
16#0400_0000#-16#7FFF_FFFF#: 1111110x 10xxxxxx 10xxxxxx
10xxxxxx 10xxxxxx 10xxxxxx
@end example
where the @code{xxx} bits correspond to the left-padded bits of the
32-bit character value.
@item @emph{Brackets Coding}
In this encoding, a wide wide character is represented by the following ten or
twelve byte character sequence:
@example
[ " a b c d e f " ]
[ " a b c d e f g h " ]
@end example
where @code{a-h} are the six or eight hexadecimal
characters (using uppercase letters) of the wide wide character code. For
example, [“1F4567”] is used to represent the wide wide character with code
@code{16#001F_4567#}.
This scheme is compatible with use of the full Wide_Wide_Character set,
and is also the method used for wide wide character encoding in some standard
ACATS (Ada Conformity Assessment Test Suite) test suite distributions.
@end table
@node File Naming Topics and Utilities,Configuration Pragmas,Foreign Language Representation,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model file-naming-topics-and-utilities}@anchor{24}@anchor{gnat_ugn/the_gnat_compilation_model id8}@anchor{3a}
@section File Naming Topics and Utilities
GNAT has a default file naming scheme and also provides the user with
a high degree of control over how the names and extensions of the
source files correspond to the Ada compilation units that they contain.
@menu
* File Naming Rules::
* Using Other File Names::
* Alternative File Naming Schemes::
* Handling Arbitrary File Naming Conventions with gnatname::
* File Name Krunching with gnatkr::
* Renaming Files with gnatchop::
@end menu
@node File Naming Rules,Using Other File Names,,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model file-naming-rules}@anchor{3b}@anchor{gnat_ugn/the_gnat_compilation_model id9}@anchor{3c}
@subsection File Naming Rules
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
@code{a}, @code{g}, @code{i}, or @code{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
@code{s-}, @code{a-}, @code{i-}, and @code{g-},
respectively.
The file extension is @code{.ads} for a spec and
@code{.adb} for a body. The following table shows some
examples of these rules.
@quotation
@multitable {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx}
@item
Source File
@tab
Ada Compilation Unit
@item
@code{main.ads}
@tab
Main (spec)
@item
@code{main.adb}
@tab
Main (body)
@item
@code{arith_functions.ads}
@tab
Arith_Functions (package spec)
@item
@code{arith_functions.adb}
@tab
Arith_Functions (package body)
@item
@code{func-spec.ads}
@tab
Func.Spec (child package spec)
@item
@code{func-spec.adb}
@tab
Func.Spec (child package body)
@item
@code{main-sub.adb}
@tab
Sub (subunit of Main)
@item
@code{a~bad.adb}
@tab
A.Bad (child package body)
@end multitable
@end quotation
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. @ref{3d,,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 @ref{1d,,Renaming Files with gnatchop}.)
Note: in the case of Windows or Mac OS operating systems, case is not
significant. So for example on Windows if the canonical name is
@code{main-sub.adb}, you can use the file name @code{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.
@node Using Other File Names,Alternative File Naming Schemes,File Naming Rules,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model id10}@anchor{3e}@anchor{gnat_ugn/the_gnat_compilation_model using-other-file-names}@anchor{1c}
@subsection Using Other File Names
@geindex File names
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.
@geindex Source_File_Name pragma
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:
@example
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");
@end example
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 @code{gnat.adc}
file used to hold configuration
pragmas that apply to a complete compilation environment.
For more details on how the @code{gnat.adc} file is created and used
see @ref{3f,,Handling of Configuration Pragmas}.
@geindex gnat.adc
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 @code{.ads} or @code{.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 @code{-x} followed by a space and the name
of the language, here @code{ada}, as in:
@example
$ gcc -c -x ada peculiar_file_name.sim
@end example
@code{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 @code{gnatmake} command, it may not
be omitted.
@node Alternative File Naming Schemes,Handling Arbitrary File Naming Conventions with gnatname,Using Other File Names,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model alternative-file-naming-schemes}@anchor{40}@anchor{gnat_ugn/the_gnat_compilation_model id11}@anchor{41}
@subsection Alternative File Naming Schemes
@geindex File naming schemes
@geindex alternative
@geindex File names
The previous section described the use of the @code{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 @code{gnat.adc} files, and also create
a maintenance problem.
@geindex Source_File_Name pragma
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
@code{Source_File_Name} pragmas having the following format:
@example
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
@end example
The @code{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
@code{Casing} indicates
whether the unit name is to be all upper-case letters, all lower-case letters,
or mixed-case. If no
@code{Casing} parameter is used, then the default is all
lower-case.
The optional @code{Dot_Replacement} string is used to replace any periods
that occur in subunit or child unit names. If no @code{Dot_Replacement}
argument is used then separating dots appear unchanged in the resulting
file name.
Although the above syntax indicates that the
@code{Casing} argument must appear
before the @code{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 @code{Subunit_File_Name} rule, and in this case the
@code{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:
@itemize *
@item
If there is a specific @code{Source_File_Name} pragma for the given unit,
then this is always used, and any general pattern rules are ignored.
@item
If there is a pattern type @code{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.
@item
If no pattern type @code{Source_File_Name} pragma that applies to the unit
for which the corresponding file exists, then the standard GNAT default
naming rules are used.
@end itemize
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 @code{.1.ada}, and
bodies end with @code{.2.ada}. GNAT will follow this scheme if the following
two pragmas appear:
@example
pragma Source_File_Name
(Spec_File_Name => ".1.ada");
pragma Source_File_Name
(Body_File_Name => ".2.ada");
@end example
The default GNAT scheme is actually implemented by providing the following
default pragmas internally:
@example
pragma Source_File_Name
(Spec_File_Name => ".ads", Dot_Replacement => "-");
pragma Source_File_Name
(Body_File_Name => ".adb", Dot_Replacement => "-");
@end example
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 @code{_.ADA}, bodies
by adding @code{.ADA}, and subunits by
adding @code{.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.
@example
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);
@end example
@geindex gnatname
@node Handling Arbitrary File Naming Conventions with gnatname,File Name Krunching with gnatkr,Alternative File Naming Schemes,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model handling-arbitrary-file-naming-conventions-with-gnatname}@anchor{42}@anchor{gnat_ugn/the_gnat_compilation_model id12}@anchor{43}
@subsection Handling Arbitrary File Naming Conventions with @code{gnatname}
@geindex File Naming Conventions
@menu
* Arbitrary File Naming Conventions::
* Running gnatname::
* Switches for gnatname::
* Examples of gnatname Usage::
@end menu
@node Arbitrary File Naming Conventions,Running gnatname,,Handling Arbitrary File Naming Conventions with gnatname
@anchor{gnat_ugn/the_gnat_compilation_model arbitrary-file-naming-conventions}@anchor{44}@anchor{gnat_ugn/the_gnat_compilation_model id13}@anchor{45}
@subsubsection Arbitrary File Naming Conventions
The GNAT compiler must be able to know the source file name of a compilation
unit. When using the standard GNAT default file naming conventions
(@code{.ads} for specs, @code{.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 (@ref{25,,Configuration Pragmas})
or a project file.
When the non-standard file naming conventions are well-defined,
a small number of pragmas @code{Source_File_Name} specifying a naming pattern
(@ref{40,,Alternative File Naming Schemes}) may be sufficient. However,
if the file naming conventions are irregular or arbitrary, a number
of pragma @code{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 @code{gnatname} to generate the required pragmas for a
set of files.
@node Running gnatname,Switches for gnatname,Arbitrary File Naming Conventions,Handling Arbitrary File Naming Conventions with gnatname
@anchor{gnat_ugn/the_gnat_compilation_model id14}@anchor{46}@anchor{gnat_ugn/the_gnat_compilation_model running-gnatname}@anchor{47}
@subsubsection Running @code{gnatname}
The usual form of the @code{gnatname} command is:
@example
$ gnatname [ switches ] naming_pattern [ naming_patterns ]
[--and [ switches ] naming_pattern [ naming_patterns ]]
@end example
All of the arguments are optional. If invoked without any argument,
@code{gnatname} will display its usage.
When used with at least one naming pattern, @code{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,
@code{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 @code{gnatname}.
Each Naming Pattern is enclosed between double quotes (or single
quotes on Windows).
A Naming Pattern is a regular expression similar to the wildcard patterns
used in file names by the Unix shells or the DOS prompt.
@code{gnatname} may be called with several sections of directories/patterns.
Sections are separated by the switch @code{--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 if @code{-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:
@example
"*.[12].ada"
"*.ad[sb]*"
"body_*" "spec_*"
@end example
For a more complete description of the syntax of Naming Patterns,
see the second kind of regular expressions described in @code{g-regexp.ads}
(the ‘Glob’ regular expressions).
When invoked without the switch @code{-P}, @code{gnatname} will create a
configuration pragmas file @code{gnat.adc} in the current working directory,
with pragmas @code{Source_File_Name} for each file that contains a valid Ada
unit.
@node Switches for gnatname,Examples of gnatname Usage,Running gnatname,Handling Arbitrary File Naming Conventions with gnatname
@anchor{gnat_ugn/the_gnat_compilation_model id15}@anchor{48}@anchor{gnat_ugn/the_gnat_compilation_model switches-for-gnatname}@anchor{49}
@subsubsection Switches for @code{gnatname}
Switches for @code{gnatname} must precede any specified Naming Pattern.
You may specify any of the following switches to @code{gnatname}:
@geindex --version (gnatname)
@table @asis
@item @code{--version}
Display Copyright and version, then exit disregarding all other options.
@end table
@geindex --help (gnatname)
@table @asis
@item @code{--help}
If @code{--version} was not used, display usage, then exit disregarding
all other options.
@item @code{--subdirs=@emph{dir}}
Real object, library or exec directories are subdirectories <dir> of the
specified ones.
@item @code{--no-backup}
Do not create a backup copy of an existing project file.
@item @code{--and}
Start another section of directories/patterns.
@end table
@geindex -c (gnatname)
@table @asis
@item @code{-c@emph{filename}}
Create a configuration pragmas file @code{filename} (instead of the default
@code{gnat.adc}).
There may be zero, one or more space between @code{-c} and
@code{filename}.
@code{filename} may include directory information. @code{filename} must be
writable. There may be only one switch @code{-c}.
When a switch @code{-c} is
specified, no switch @code{-P} may be specified (see below).
@end table
@geindex -d (gnatname)
@table @asis
@item @code{-d@emph{dir}}
Look for source files in directory @code{dir}. There may be zero, one or more
spaces between @code{-d} and @code{dir}.
@code{dir} may end with @code{/**}, that is it may be of the form
@code{root_dir/**}. In this case, the directory @code{root_dir} and all of its
subdirectories, recursively, have to be searched for sources.
When a switch @code{-d}
is specified, the current working directory will not be searched for source
files, unless it is explicitly specified with a @code{-d}
or @code{-D} switch.
Several switches @code{-d} may be specified.
If @code{dir} is a relative path, it is relative to the directory of
the configuration pragmas file specified with switch
@code{-c},
or to the directory of the project file specified with switch
@code{-P} or,
if neither switch @code{-c}
nor switch @code{-P} are specified, it is relative to the
current working directory. The directory
specified with switch @code{-d} must exist and be readable.
@end table
@geindex -D (gnatname)
@table @asis
@item @code{-D@emph{filename}}
Look for source files in all directories listed in text file @code{filename}.
There may be zero, one or more spaces between @code{-D}
and @code{filename}.
@code{filename} must be an existing, readable text file.
Each nonempty line in @code{filename} must be a directory.
Specifying switch @code{-D} is equivalent to specifying as many
switches @code{-d} as there are nonempty lines in
@code{file}.
@item @code{-eL}
Follow symbolic links when processing project files.
@geindex -f (gnatname)
@item @code{-f@emph{pattern}}
Foreign patterns. Using this switch, it is possible to add sources of languages
other than Ada to the list of sources of a project file.
It is only useful if a -P switch is used.
For example,
@example
gnatname -Pprj -f"*.c" "*.ada"
@end example
will look for Ada units in all files with the @code{.ada} extension,
and will add to the list of file for project @code{prj.gpr} the C files
with extension @code{.c}.
@geindex -h (gnatname)
@item @code{-h}
Output usage (help) information. The output is written to @code{stdout}.
@geindex -P (gnatname)
@item @code{-P@emph{proj}}
Create or update project file @code{proj}. There may be zero, one or more space
between @code{-P} and @code{proj}. @code{proj} may include directory
information. @code{proj} must be writable.
There may be only one switch @code{-P}.
When a switch @code{-P} is specified,
no switch @code{-c} may be specified.
On all platforms, except on VMS, when @code{gnatname} is invoked for an
existing project file <proj>.gpr, a backup copy of the project file is created
in the project directory with file name <proj>.gpr.saved_x. ‘x’ is the first
non negative number that makes this backup copy a new file.
@geindex -v (gnatname)
@item @code{-v}
Verbose mode. Output detailed explanation of behavior to @code{stdout}.
This includes name of the file written, the name of the directories to search
and, for each file in those directories whose name matches at least one of
the Naming Patterns, an indication of whether the file contains a unit,
and if so the name of the unit.
@end table
@geindex -v -v (gnatname)
@table @asis
@item @code{-v -v}
Very Verbose mode. In addition to the output produced in verbose mode,
for each file in the searched directories whose name matches none of
the Naming Patterns, an indication is given that there is no match.
@geindex -x (gnatname)
@item @code{-x@emph{pattern}}
Excluded patterns. Using this switch, it is possible to exclude some files
that would match the name patterns. For example,
@example
gnatname -x "*_nt.ada" "*.ada"
@end example
will look for Ada units in all files with the @code{.ada} extension,
except those whose names end with @code{_nt.ada}.
@end table
@node Examples of gnatname Usage,,Switches for gnatname,Handling Arbitrary File Naming Conventions with gnatname
@anchor{gnat_ugn/the_gnat_compilation_model examples-of-gnatname-usage}@anchor{4a}@anchor{gnat_ugn/the_gnat_compilation_model id16}@anchor{4b}
@subsubsection Examples of @code{gnatname} Usage
@example
$ gnatname -c /home/me/names.adc -d sources "[a-z]*.ada*"
@end example
In this example, the directory @code{/home/me} must already exist
and be writable. In addition, the directory
@code{/home/me/sources} (specified by
@code{-d sources}) must exist and be readable.
Note the optional spaces after @code{-c} and @code{-d}.
@example
$ gnatname -P/home/me/proj -x "*_nt_body.ada"
-dsources -dsources/plus -Dcommon_dirs.txt "body_*" "spec_*"
@end example
Note that several switches @code{-d} may be used,
even in conjunction with one or several switches
@code{-D}. Several Naming Patterns and one excluded pattern
are used in this example.
@node File Name Krunching with gnatkr,Renaming Files with gnatchop,Handling Arbitrary File Naming Conventions with gnatname,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model file-name-krunching-with-gnatkr}@anchor{4c}@anchor{gnat_ugn/the_gnat_compilation_model id17}@anchor{4d}
@subsection File Name Krunching with @code{gnatkr}
@geindex gnatkr
This section 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
@code{gnatkr} utility that can be used to determine the result of
applying this shortening.
@menu
* About gnatkr::
* Using gnatkr::
* Krunching Method::
* Examples of gnatkr Usage::
@end menu
@node About gnatkr,Using gnatkr,,File Name Krunching with gnatkr
@anchor{gnat_ugn/the_gnat_compilation_model about-gnatkr}@anchor{4e}@anchor{gnat_ugn/the_gnat_compilation_model id18}@anchor{4f}
@subsubsection About @code{gnatkr}
The 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:
@itemize *
@item
Take the unit name and replace all dots by hyphens.
@item
If such a replacement occurs in the
second character position of a name, and the first character is
@code{a}, @code{g}, @code{s}, or @code{i},
then replace the dot by the character
@code{~} (tilde)
instead of a minus.
The reason for this exception is to avoid clashes
with the standard names for children of System, Ada, Interfaces,
and GNAT, which use the prefixes
@code{s-}, @code{a-}, @code{i-}, and @code{g-},
respectively.
@end itemize
The @code{-gnatk@emph{nn}}
switch of the compiler activates a ‘krunching’
circuit that limits file names to nn characters (where nn is a decimal
integer).
The @code{gnatkr} utility can be used to determine the krunched name for
a given file, when krunched to a specified maximum length.
@node Using gnatkr,Krunching Method,About gnatkr,File Name Krunching with gnatkr
@anchor{gnat_ugn/the_gnat_compilation_model id19}@anchor{50}@anchor{gnat_ugn/the_gnat_compilation_model using-gnatkr}@anchor{3d}
@subsubsection Using @code{gnatkr}
The @code{gnatkr} command has the form:
@example
$ gnatkr name [ length ]
@end example
@code{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 @code{hellofile.ads}
to eight characters, the result will be hellofil.ads.
Note: for compatibility with previous versions of @code{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 @code{gnatkr} is given an argument
such as @code{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 @code{hellworl.adb}.
Note that the result is always all lower case.
Characters of the other case are folded as required.
@code{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.
@node Krunching Method,Examples of gnatkr Usage,Using gnatkr,File Name Krunching with gnatkr
@anchor{gnat_ugn/the_gnat_compilation_model id20}@anchor{51}@anchor{gnat_ugn/the_gnat_compilation_model krunching-method}@anchor{52}
@subsubsection Krunching Method
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
@code{a}, @code{i}, @code{g}, or @code{s}.
The extension is @code{.ads} for a
spec and @code{.adb} for a body.
Krunching does not affect the extension, but the file name is shortened to
the specified length by following these rules:
@itemize *
@item
The name is divided into segments separated by hyphens, tildes or
underscores and all hyphens, tildes, and underscores are
eliminated. If this leaves the name short enough, we are done.
@item
If the name is too long, the longest segment is located (left-most
if there are two of equal length), and shortened by dropping
its last character. This is repeated until the name is short enough.
As an example, consider the krunching of @code{our-strings-wide_fixed.adb}
to fit the name into 8 characters as required by some operating systems:
@example
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
@end example
@item
The file names for all predefined units are always krunched to eight
characters. The krunching of these predefined units uses the following
special prefix replacements:
@multitable {xxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxx}
@item
Prefix
@tab
Replacement
@item
@code{ada-}
@tab
@code{a-}
@item
@code{gnat-}
@tab
@code{g-}
@item
@code{interfac es-}
@tab
@code{i-}
@item
@code{system-}
@tab
@code{s-}
@end multitable
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
@code{ada-strings-wide_fixed.adb}, which gets krunched as follows:
@example
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
@end example
@end itemize
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 @code{gnatkr} is supplied for conveniently determining the
krunched name of a file.
@node Examples of gnatkr Usage,,Krunching Method,File Name Krunching with gnatkr
@anchor{gnat_ugn/the_gnat_compilation_model examples-of-gnatkr-usage}@anchor{53}@anchor{gnat_ugn/the_gnat_compilation_model id21}@anchor{54}
@subsubsection Examples of @code{gnatkr} Usage
@example
$ 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
@end example
@node Renaming Files with gnatchop,,File Name Krunching with gnatkr,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model id22}@anchor{55}@anchor{gnat_ugn/the_gnat_compilation_model renaming-files-with-gnatchop}@anchor{1d}
@subsection Renaming Files with @code{gnatchop}
@geindex gnatchop
This section discusses how to handle files with multiple units by using
the @code{gnatchop} utility. This utility is also useful in renaming
files to meet the standard GNAT default file naming conventions.
@menu
* Handling Files with Multiple Units::
* Operating gnatchop in Compilation Mode::
* Command Line for gnatchop::
* Switches for gnatchop::
* Examples of gnatchop Usage::
@end menu
@node Handling Files with Multiple Units,Operating gnatchop in Compilation Mode,,Renaming Files with gnatchop
@anchor{gnat_ugn/the_gnat_compilation_model handling-files-with-multiple-units}@anchor{56}@anchor{gnat_ugn/the_gnat_compilation_model id23}@anchor{57}
@subsubsection Handling Files with Multiple Units
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.
If you want to keep your files with multiple units,
perhaps to maintain compatibility with some other Ada compilation system,
you can use @code{gnatname} to generate or update your project files.
Generated or modified project files can be processed by GNAT.
See @ref{42,,Handling Arbitrary File Naming Conventions with gnatname}
for more details on how to use @cite{gnatname}.
Alternatively, 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 @code{gnatchop} once, generate the
new set of files and work with them from that point on.
Note that if your file containing multiple units starts with a byte order
mark (BOM) specifying UTF-8 encoding, then the files generated by gnatchop
will each start with a copy of this BOM, meaning that they can be compiled
automatically in UTF-8 mode without needing to specify an explicit encoding.
@node Operating gnatchop in Compilation Mode,Command Line for gnatchop,Handling Files with Multiple Units,Renaming Files with gnatchop
@anchor{gnat_ugn/the_gnat_compilation_model id24}@anchor{58}@anchor{gnat_ugn/the_gnat_compilation_model operating-gnatchop-in-compilation-mode}@anchor{59}
@subsubsection Operating gnatchop in Compilation Mode
The basic function of @code{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 @code{gnatchop}.
However, using a special option to activate ‘compilation mode’,
@code{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 @code{gnatchop} is given a file that consists of
only configuration pragmas, then this file is appended to the
@code{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
@code{gnat.adc} file is the representation
of a compilation environment. For more information on the
@code{gnat.adc} file, see @ref{3f,,Handling of Configuration Pragmas}.
Second, in compilation mode, if @code{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, @code{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 @code{gnatchop} with the compilation mode
switch provides the required behavior, and is for example the mode
in which GNAT processes the ACVC tests.
@node Command Line for gnatchop,Switches for gnatchop,Operating gnatchop in Compilation Mode,Renaming Files with gnatchop
@anchor{gnat_ugn/the_gnat_compilation_model command-line-for-gnatchop}@anchor{5a}@anchor{gnat_ugn/the_gnat_compilation_model id25}@anchor{5b}
@subsubsection Command Line for @code{gnatchop}
The @code{gnatchop} command has the form:
@example
$ gnatchop switches file_name [file_name ...]
[directory]
@end example
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, @code{gnatchop} generates one output file in
the current directory for each unit in each of the files.
@code{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 @code{hellofiles} containing
@example
procedure Hello;
with Ada.Text_IO; use Ada.Text_IO;
procedure Hello is
begin
Put_Line ("Hello");
end Hello;
@end example
the command
@example
$ gnatchop hellofiles
@end example
generates two files in the current directory, one called
@code{hello.ads} containing the single line that is the procedure spec,
and the other called @code{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 @code{toto.txt} containing
@example
-- Just a comment
@end example
the command
@example
$ gnatchop toto.txt
@end example
will not produce any new file and will result in the following warnings:
@example
toto.txt:1:01: warning: empty file, contains no compilation units
no compilation units found
no source files written
@end example
@node Switches for gnatchop,Examples of gnatchop Usage,Command Line for gnatchop,Renaming Files with gnatchop
@anchor{gnat_ugn/the_gnat_compilation_model id26}@anchor{5c}@anchor{gnat_ugn/the_gnat_compilation_model switches-for-gnatchop}@anchor{5d}
@subsubsection Switches for @code{gnatchop}
@code{gnatchop} recognizes the following switches:
@geindex --version (gnatchop)
@table @asis
@item @code{--version}
Display Copyright and version, then exit disregarding all other options.
@end table
@geindex --help (gnatchop)
@table @asis
@item @code{--help}
If @code{--version} was not used, display usage, then exit disregarding
all other options.
@end table
@geindex -c (gnatchop)
@table @asis
@item @code{-c}
Causes @code{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.
@item @code{-gnat@emph{xxx}}
This passes the given @code{-gnat@emph{xxx}} switch to @code{gnat} which is
used to parse the given file. Not all @emph{xxx} options make sense,
but for example, the use of @code{-gnati2} allows @code{gnatchop} to
process a source file that uses Latin-2 coding for identifiers.
@item @code{-h}
Causes @code{gnatchop} to generate a brief help summary to the standard
output file showing usage information.
@end table
@geindex -k (gnatchop)
@table @asis
@item @code{-k@emph{mm}}
Limit generated file names to the specified number @code{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 @code{-k} and the numeric value. The numeric
value may be omitted in which case a default of @code{-k8},
suitable for use
with DOS-like file systems, is used. If no @code{-k} switch
is present then
there is no limit on the length of file names.
@end table
@geindex -p (gnatchop)
@table @asis
@item @code{-p}
Causes the file modification time stamp of the input file to be
preserved and used for the time stamp of the output file(s). This may be
useful for preserving coherency of time stamps in an environment where
@code{gnatchop} is used as part of a standard build process.
@end table
@geindex -q (gnatchop)
@table @asis
@item @code{-q}
Causes output of informational messages indicating the set of generated
files to be suppressed. Warnings and error messages are unaffected.
@end table
@geindex -r (gnatchop)
@geindex Source_Reference pragmas
@table @asis
@item @code{-r}
Generate @code{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
@code{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 @code{-g} switch of @code{gcc} or @code{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 @code{Source_Reference}
pragma referencing a third file, then gnatchop respects
this pragma, and the generated @code{Source_Reference} pragmas
in the chopped file refer to the original file, with appropriate
line numbers. This is particularly useful when @code{gnatchop}
is used in conjunction with @code{gnatprep} to compile files that
contain preprocessing statements and multiple units.
@end table
@geindex -v (gnatchop)
@table @asis
@item @code{-v}
Causes @code{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.
@end table
@geindex -w (gnatchop)
@table @asis
@item @code{-w}
Overwrite existing file names. Normally @code{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.
@end table
@geindex --GCC= (gnatchop)
@table @asis
@item @code{--GCC=@emph{xxxx}}
Specify the path of the GNAT parser to be used. When this switch is used,
no attempt is made to add the prefix to the GNAT parser executable.
@end table
@node Examples of gnatchop Usage,,Switches for gnatchop,Renaming Files with gnatchop
@anchor{gnat_ugn/the_gnat_compilation_model examples-of-gnatchop-usage}@anchor{5e}@anchor{gnat_ugn/the_gnat_compilation_model id27}@anchor{5f}
@subsubsection Examples of @code{gnatchop} Usage
@example
$ gnatchop -w hello_s.ada prerelease/files
@end example
Chops the source file @code{hello_s.ada}. The output files will be
placed in the directory @code{prerelease/files},
overwriting any
files with matching names in that directory (no files in the current
directory are modified).
@example
$ gnatchop archive
@end example
Chops the source file @code{archive}
into the current directory. One
useful application of @code{gnatchop} is in sending sets of sources
around, for example in email messages. The required sources are simply
concatenated (for example, using a Unix @code{cat}
command), and then
@code{gnatchop} is used at the other end to reconstitute the original
file names.
@example
$ gnatchop file1 file2 file3 direc
@end example
Chops all units in files @code{file1}, @code{file2}, @code{file3}, placing
the resulting files in the directory @code{direc}. Note that if any units
occur more than once anywhere within this set of files, an error message
is generated, and no files are written. To override this check, use the
@code{-w} switch,
in which case the last occurrence in the last file will
be the one that is output, and earlier duplicate occurrences for a given
unit will be skipped.
@node Configuration Pragmas,Generating Object Files,File Naming Topics and Utilities,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model configuration-pragmas}@anchor{25}@anchor{gnat_ugn/the_gnat_compilation_model id28}@anchor{60}
@section Configuration Pragmas
@geindex Configuration pragmas
@geindex Pragmas
@geindex configuration
Configuration pragmas include those pragmas described as
such in the Ada Reference Manual, as well as
implementation-dependent pragmas that are configuration pragmas.
See the @code{Implementation_Defined_Pragmas} chapter in the
@cite{GNAT_Reference_Manual} for details on these
additional GNAT-specific configuration pragmas.
Most notably, the pragma @code{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:
@example
Ada_83
Ada_95
Ada_05
Ada_2005
Ada_12
Ada_2012
Allow_Integer_Address
Annotate
Assertion_Policy
Assume_No_Invalid_Values
C_Pass_By_Copy
Check_Float_Overflow
Check_Name
Check_Policy
Component_Alignment
Convention_Identifier
Debug_Policy
Default_Scalar_Storage_Order
Default_Storage_Pool
Detect_Blocking
Disable_Atomic_Synchronization
Discard_Names
Elaboration_Checks
Eliminate
Enable_Atomic_Synchronization
Extend_System
Extensions_Allowed
External_Name_Casing
Fast_Math
Favor_Top_Level
Ignore_Pragma
Implicit_Packing
Initialize_Scalars
Interrupt_State
License
Locking_Policy
No_Component_Reordering
No_Heap_Finalization
No_Strict_Aliasing
Normalize_Scalars
Optimize_Alignment
Overflow_Mode
Overriding_Renamings
Partition_Elaboration_Policy
Persistent_BSS
Prefix_Exception_Messages
Priority_Specific_Dispatching
Profile
Profile_Warnings
Queuing_Policy
Rename_Pragma
Restrictions
Restriction_Warnings
Reviewable
Short_Circuit_And_Or
Source_File_Name
Source_File_Name_Project
SPARK_Mode
Style_Checks
Suppress
Suppress_Exception_Locations
Task_Dispatching_Policy
Unevaluated_Use_Of_Old
Unsuppress
Use_VADS_Size
Validity_Checks
Warning_As_Error
Warnings
Wide_Character_Encoding
@end example
@menu
* Handling of Configuration Pragmas::
* The Configuration Pragmas Files::
@end menu
@node Handling of Configuration Pragmas,The Configuration Pragmas Files,,Configuration Pragmas
@anchor{gnat_ugn/the_gnat_compilation_model handling-of-configuration-pragmas}@anchor{3f}@anchor{gnat_ugn/the_gnat_compilation_model id29}@anchor{61}
@subsection Handling of Configuration Pragmas
Configuration pragmas may either appear at the start of a compilation
unit, or they can appear in a configuration pragma file to apply to
all compilations performed in a given compilation environment.
GNAT also provides the @code{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 @ref{59,,Operating gnatchop in Compilation Mode} for details.
However, for most purposes, it will be more convenient to edit the
@code{gnat.adc} file that contains configuration pragmas directly,
as described in the following section.
In the case of @code{Restrictions} pragmas appearing as configuration
pragmas in individual compilation units, the exact handling depends on
the type of restriction.
Restrictions that require partition-wide consistency (like
@code{No_Tasking}) are
recognized wherever they appear
and can be freely inherited, e.g. from a @emph{with}ed unit to the @emph{with}ing
unit. This makes sense since the binder will in any case insist on seeing
consistent use, so any unit not conforming to any restrictions that are
anywhere in the partition will be rejected, and you might as well find
that out at compile time rather than at bind time.
For restrictions that do not require partition-wide consistency, e.g.
SPARK or No_Implementation_Attributes, in general the restriction applies
only to the unit in which the pragma appears, and not to any other units.
The exception is No_Elaboration_Code which always applies to the entire
object file from a compilation, i.e. to the body, spec, and all subunits.
This restriction can be specified in a configuration pragma file, or it
can be on the body and/or the spec (in either case it applies to all the
relevant units). It can appear on a subunit only if it has previously
appeared in the body of spec.
@node The Configuration Pragmas Files,,Handling of Configuration Pragmas,Configuration Pragmas
@anchor{gnat_ugn/the_gnat_compilation_model id30}@anchor{62}@anchor{gnat_ugn/the_gnat_compilation_model the-configuration-pragmas-files}@anchor{63}
@subsection The Configuration Pragmas Files
@geindex gnat.adc
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 @code{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 @code{-gnatA} is used, @code{gnat.adc} is not
considered. When taken into account, @code{gnat.adc} is added to the
dependencies, so that if @code{gnat.adc} is modified later, an invocation of
@code{gnatmake} will recompile the source.
Configuration pragmas may be entered into the @code{gnat.adc} file
either by running @code{gnatchop} on a source file that consists only of
configuration pragmas, or more conveniently by direct editing of the
@code{gnat.adc} file, which is a standard format source file.
Besides @code{gnat.adc}, additional files containing configuration
pragmas may be applied to the current compilation using the switch
@code{-gnatec=@emph{path}} where @code{path} must designate an existing file that
contains only configuration pragmas. These configuration pragmas are
in addition to those found in @code{gnat.adc} (provided @code{gnat.adc}
is present and switch @code{-gnatA} is not used).
It is allowable to specify several switches @code{-gnatec=}, all of which
will be taken into account.
Files containing configuration pragmas specified with switches
@code{-gnatec=} are added to the dependencies, unless they are
temporary files. A file is considered temporary if its name ends in
@code{.tmp} or @code{.TMP}. Certain tools follow this naming
convention because they pass information to @code{gcc} via
temporary files that are immediately deleted; it doesn’t make sense to
depend on a file that no longer exists. Such tools include
@code{gprbuild}, @code{gnatmake}, and @code{gnatcheck}.
By default, configuration pragma files are stored by their absolute paths in
ALI files. You can use the @code{-gnateb} switch in order to store them by
their basename instead.
If you are using project file, a separate mechanism is provided using
project attributes.
@c --Comment
@c See :ref:`Specifying_Configuration_Pragmas` for more details.
@node Generating Object Files,Source Dependencies,Configuration Pragmas,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model generating-object-files}@anchor{26}@anchor{gnat_ugn/the_gnat_compilation_model id31}@anchor{64}
@section Generating Object Files
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:
@itemize *
@item
If a package spec has no body, compile the package spec to produce the
object file for the package.
@item
If a package has both a spec and a body, compile the body to produce the
object file for the package. The source file for the package spec need
not be compiled in this case because there is only one object file, which
contains the code for both the spec and body of the package.
@item
For a subprogram, compile the subprogram body to produce the object file
for the subprogram. The spec, if one is present, is as usual in a
separate file, and need not be compiled.
@end itemize
@geindex Subunits
@itemize *
@item
In the case of subunits, only compile the parent unit. A single object
file is generated for the entire subunit tree, which includes all the
subunits.
@item
Compile child units independently of their parent units
(though, of course, the spec of all the ancestor unit must be present in order
to compile a child unit).
@geindex Generics
@item
Compile generic units in the same manner as any other units. The object
files in this case are small dummy files that contain at most the
flag used for elaboration checking. This is because GNAT always handles generic
instantiation by means of macro expansion. However, it is still necessary to
compile generic units, for dependency checking and elaboration purposes.
@end itemize
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
@code{.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 @code{-gnatc} switch.
@node Source Dependencies,The Ada Library Information Files,Generating Object Files,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id32}@anchor{65}@anchor{gnat_ugn/the_gnat_compilation_model source-dependencies}@anchor{27}
@section Source Dependencies
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
@code{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:
@itemize *
@item
If a file being compiled @emph{with}s a unit @code{X}, the object file
depends on the file containing the spec of unit @code{X}. This includes
files that are @emph{with}ed implicitly either because they are parents
of @emph{with}ed child units or they are run-time units required by the
language constructs used in a particular unit.
@item
If a file being compiled instantiates a library level generic unit, the
object file depends on both the spec and body files for this generic
unit.
@item
If a file being compiled instantiates a generic unit defined within a
package, the object file depends on the body file for the package as
well as the spec file.
@end itemize
@geindex Inline
@geindex -gnatn switch
@itemize *
@item
If a file being compiled contains a call to a subprogram for which
pragma @code{Inline} applies and inlining is activated with the
@code{-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.
@geindex -gnatN switch
The use of @code{-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 @code{-gnatn},
the use of this switch generates additional dependencies.
When using a gcc-based back end, then the use of
@code{-gnatN} is deprecated, and the use of @code{-gnatn} is preferred.
Historically front end inlining was more extensive than the gcc back end
inlining, but that is no longer the case.
@item
If an object file @code{O} depends on the proper body of a subunit through
inlining or instantiation, it depends on the parent unit of the subunit.
This means that any modification of the parent unit or one of its subunits
affects the compilation of @code{O}.
@item
The object file for a parent unit depends on all its subunit body files.
@item
The previous two rules meant that for purposes of computing dependencies and
recompilation, a body and all its subunits are treated as an indivisible whole.
These rules are applied transitively: if unit @code{A} @emph{with}s
unit @code{B}, whose elaboration calls an inlined procedure in package
@code{C}, the object file for unit @code{A} will depend on the body of
@code{C}, in file @code{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 @code{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 @code{gnatmake}.
@end itemize
@node The Ada Library Information Files,Binding an Ada Program,Source Dependencies,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id33}@anchor{66}@anchor{gnat_ugn/the_gnat_compilation_model the-ada-library-information-files}@anchor{28}
@section The Ada Library Information Files
@geindex Ada Library Information files
@geindex ALI files
Each compilation actually generates two output files. The first of these
is the normal object file that has a @code{.o} extension. The second is a
text file containing full dependency information. It has the same
name as the source file, but an @code{.ali} extension.
This file is known as the Ada Library Information (@code{ALI}) file.
The following information is contained in the @code{ALI} file.
@itemize *
@item
Version information (indicates which version of GNAT was used to compile
the unit(s) in question)
@item
Main program information (including priority and time slice settings,
as well as the wide character encoding used during compilation).
@item
List of arguments used in the @code{gcc} command for the compilation
@item
Attributes of the unit, including configuration pragmas used, an indication
of whether the compilation was successful, exception model used etc.
@item
A list of relevant restrictions applying to the unit (used for consistency)
checking.
@item
Categorization information (e.g., use of pragma @code{Pure}).
@item
Information on all @emph{with}ed units, including presence of
@code{Elaborate} or @code{Elaborate_All} pragmas.
@item
Information from any @code{Linker_Options} pragmas used in the unit
@item
Information on the use of @code{Body_Version} or @code{Version}
attributes in the unit.
@item
Dependency information. This is a list of files, together with
time stamp and checksum information. These are files on which
the unit depends in the sense that recompilation is required
if any of these units are modified.
@item
Cross-reference data. Contains information on all entities referenced
in the unit. Used by tools like @code{gnatxref} and @code{gnatfind} to
provide cross-reference information.
@end itemize
For a full detailed description of the format of the @code{ALI} file,
see the source of the body of unit @code{Lib.Writ}, contained in file
@code{lib-writ.adb} in the GNAT compiler sources.
@node Binding an Ada Program,GNAT and Libraries,The Ada Library Information Files,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model binding-an-ada-program}@anchor{29}@anchor{gnat_ugn/the_gnat_compilation_model id34}@anchor{67}
@section Binding an Ada Program
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 @code{b~xxx}.adb` (with the corresponding spec
@code{b~xxx}.ads`) where @code{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.
@node GNAT and Libraries,Conditional Compilation,Binding an Ada Program,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model gnat-and-libraries}@anchor{2a}@anchor{gnat_ugn/the_gnat_compilation_model id35}@anchor{68}
@section GNAT and Libraries
@geindex Library building and using
This section 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 the @emph{GNAT_Project_Manager} chapter of the
@emph{GPRbuild User’s Guide}) before reading this chapter.
@menu
* Introduction to Libraries in GNAT::
* General Ada Libraries::
* Stand-alone Ada Libraries::
* Rebuilding the GNAT Run-Time Library::
@end menu
@node Introduction to Libraries in GNAT,General Ada Libraries,,GNAT and Libraries
@anchor{gnat_ugn/the_gnat_compilation_model id36}@anchor{69}@anchor{gnat_ugn/the_gnat_compilation_model introduction-to-libraries-in-gnat}@anchor{6a}
@subsection Introduction to Libraries in GNAT
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:
@itemize *
@item
Source files,
@item
@code{ALI} files (see @ref{28,,The Ada Library Information Files}), and
@item
Object files, an archive or a shared library.
@end itemize
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 @emph{stand-alone libraries} those exposed
units are called @emph{interface units} (@ref{6b,,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 @code{ALI} files and this is why they
constitute a mandatory part of GNAT libraries.
@emph{Stand-alone libraries} are the exception to this rule because a specific
library elaboration routine is produced independently of the application(s)
using the library.
@node General Ada Libraries,Stand-alone Ada Libraries,Introduction to Libraries in GNAT,GNAT and Libraries
@anchor{gnat_ugn/the_gnat_compilation_model general-ada-libraries}@anchor{6c}@anchor{gnat_ugn/the_gnat_compilation_model id37}@anchor{6d}
@subsection General Ada Libraries
@menu
* Building a library::
* Installing a library::
* Using a library::
@end menu
@node Building a library,Installing a library,,General Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model building-a-library}@anchor{6e}@anchor{gnat_ugn/the_gnat_compilation_model id38}@anchor{6f}
@subsubsection Building a library
The easiest way to build a library is to use the Project Manager,
which supports a special type of project called a @emph{Library Project}
(see the @emph{Library Projects} section in the @emph{GNAT Project Manager}
chapter of the @emph{GPRbuild User’s Guide}).
A project is considered a library project, when two project-level attributes
are defined in it: @code{Library_Name} and @code{Library_Dir}. In order to
control different aspects of library configuration, additional optional
project-level attributes can be specified:
@itemize *
@item
@table @asis
@item @code{Library_Kind}
This attribute controls whether the library is to be static or dynamic
@end table
@item
@table @asis
@item @code{Library_Version}
This attribute specifies the library version; this value is used
during dynamic linking of shared libraries to determine if the currently
installed versions of the binaries are compatible.
@end table
@item
@code{Library_Options}
@item
@table @asis
@item @code{Library_GCC}
These attributes specify additional low-level options to be used during
library generation, and redefine the actual application used to generate
library.
@end table
@end itemize
The 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 @code{ALI} files
to the specified location).
Here is a simple library project file:
@example
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;
@end example
and the compilation command to build and install the library:
@example
$ gnatmake -Pmy_lib
@end example
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 (@ref{70,,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
@code{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:
@example
with My_Lib.Service1;
with My_Lib.Service2;
with My_Lib.Service3;
procedure My_Lib_Dummy is
begin
null;
end;
@end example
Here are the generic commands that will build an archive or a shared library.
@example
# 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
@end example
Please note that the library must have a name of the form @code{lib@emph{xxx}.a}
or @code{lib@emph{xxx}.so} (or @code{lib@emph{xxx}.dll} on Windows) in order to
be accessed by the directive @code{-l@emph{xxx}} at link time.
@node Installing a library,Using a library,Building a library,General Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model id39}@anchor{71}@anchor{gnat_ugn/the_gnat_compilation_model installing-a-library}@anchor{72}
@subsubsection Installing a library
@geindex ADA_PROJECT_PATH
@geindex GPR_PROJECT_PATH
If you use project files, library installation is part of the library build
process (see the @emph{Installing a Library with Project Files} section of the
@emph{GNAT Project Manager} chapter of the @emph{GPRbuild User’s Guide}).
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
@ref{73,,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
@code{ada_source_path} and @code{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:
@example
$ gcc -v
@end example
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 @code{ada_source_path} and @code{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 @code{adainclude} (for the sources) and @code{adalib} (for the
objects and @code{ALI} files). When the files exist, the compiler does not
look in @code{adainclude} and @code{adalib}, and thus the
@code{ada_source_path} file
must contain the location for the GNAT run-time sources (which can simply
be @code{adainclude}). In the same way, the @code{ada_object_path} file must
contain the location for the GNAT run-time objects (which can simply
be @code{adalib}).
You can also specify a new default path to the run-time library at compilation
time with the switch @code{--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 @code{gcc}, @code{gnatmake}, @code{gnatbind},
@code{gnatls}, @code{gnatfind} and @code{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.
@node Using a library,,Installing a library,General Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model id40}@anchor{74}@anchor{gnat_ugn/the_gnat_compilation_model using-a-library}@anchor{75}
@subsubsection Using a library
Once again, the project facility greatly simplifies the use of
libraries. In this context, using a library is just a matter of adding a
@emph{with} clause in the user project. For instance, to make use of the
library @code{My_Lib} shown in examples in earlier sections, you can
write:
@example
with "my_lib";
project My_Proj is
...
end My_Proj;
@end example
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 @emph{with}ed by your main project, will link with the
third-party library @code{liba.a}:
@example
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;
@end example
This is an alternative to the use of @code{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 @ref{73,,Search Paths and the Run-Time Library (RTL)}
and @ref{76,,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 @code{mylib} installed in
@code{/dir/my_lib_src} and @code{/dir/my_lib_obj} with the following commands:
@example
$ gnatmake -aI/dir/my_lib_src -aO/dir/my_lib_obj my_appl \\
-largs -lmy_lib
@end example
This can be expressed more simply:
@example
$ gnatmake my_appl
@end example
when the following conditions are met:
@itemize *
@item
@code{/dir/my_lib_src} has been added by the user to the environment
variable
@geindex ADA_INCLUDE_PATH
@geindex environment variable; ADA_INCLUDE_PATH
@code{ADA_INCLUDE_PATH}, or by the administrator to the file
@code{ada_source_path}
@item
@code{/dir/my_lib_obj} has been added by the user to the environment
variable
@geindex ADA_OBJECTS_PATH
@geindex environment variable; ADA_OBJECTS_PATH
@code{ADA_OBJECTS_PATH}, or by the administrator to the file
@code{ada_object_path}
@item
a pragma @code{Linker_Options} has been added to one of the sources.
For example:
@example
pragma Linker_Options ("-lmy_lib");
@end example
@end itemize
Note that you may also load a library dynamically at
run time given its filename, as illustrated in the GNAT @code{plugins} example
in the directory @code{share/examples/gnat/plugins} within the GNAT
install area.
@node Stand-alone Ada Libraries,Rebuilding the GNAT Run-Time Library,General Ada Libraries,GNAT and Libraries
@anchor{gnat_ugn/the_gnat_compilation_model id41}@anchor{77}@anchor{gnat_ugn/the_gnat_compilation_model stand-alone-ada-libraries}@anchor{6b}
@subsection Stand-alone Ada Libraries
@geindex Stand-alone libraries
@menu
* Introduction to Stand-alone Libraries::
* Building a Stand-alone Library::
* Creating a Stand-alone Library to be used in a non-Ada context::
* Restrictions in Stand-alone Libraries::
@end menu
@node Introduction to Stand-alone Libraries,Building a Stand-alone Library,,Stand-alone Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model id42}@anchor{78}@anchor{gnat_ugn/the_gnat_compilation_model introduction-to-stand-alone-libraries}@anchor{79}
@subsubsection Introduction to Stand-alone Libraries
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 @code{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 @code{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 @code{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 @code{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.
@node Building a Stand-alone Library,Creating a Stand-alone Library to be used in a non-Ada context,Introduction to Stand-alone Libraries,Stand-alone Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model building-a-stand-alone-library}@anchor{7a}@anchor{gnat_ugn/the_gnat_compilation_model id43}@anchor{7b}
@subsubsection Building a Stand-alone Library
GNAT’s Project facility provides a simple way of building and installing
stand-alone libraries; see the @emph{Stand-alone Library Projects} section
in the @emph{GNAT Project Manager} chapter of the @emph{GPRbuild User’s Guide}.
To be a Stand-alone Library Project, in addition to the two attributes
that make a project a Library Project (@code{Library_Name} and
@code{Library_Dir}; see the @emph{Library Projects} section in the
@emph{GNAT Project Manager} chapter of the @emph{GPRbuild User’s Guide}),
the attribute @code{Library_Interface} must be defined. For example:
@example
for Library_Dir use "lib_dir";
for Library_Name use "dummy";
for Library_Interface use ("int1", "int1.child");
@end example
Attribute @code{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
(@code{b~dummy.ads/b} in the example above).
This binder-generated package includes initialization and
finalization procedures whose
names depend on the library name (@code{dummyinit} and @code{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 @code{Library_Auto_Init} set to
@code{"false"}.
For a Stand-Alone Library, only the @code{ALI} files of the Interface Units
(those that are listed in attribute @code{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.
It is also possible to build an encapsulated library where not only
the code to elaborate and finalize the library is embedded but also
ensuring that the library is linked only against static
libraries. So an encapsulated library only depends on system
libraries, all other code, including the GNAT runtime, is embedded. To
build an encapsulated library the attribute
@code{Library_Standalone} must be set to @code{encapsulated}:
@example
for Library_Dir use "lib_dir";
for Library_Name use "dummy";
for Library_Kind use "dynamic";
for Library_Interface use ("int1", "int1.child");
for Library_Standalone use "encapsulated";
@end example
The default value for this attribute is @code{standard} in which case
a stand-alone library is built.
The attribute @code{Library_Src_Dir} may be specified for a
Stand-Alone Library. @code{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 @code{Inline} or @code{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:
@itemize *
@item
Compile all library sources.
@item
Invoke the binder with the switch @code{-n} (No Ada main program),
with all the @code{ALI} files of the interfaces, and
with the switch @code{-L} to give specific names to the @code{init}
and @code{final} procedures. For example:
@example
$ gnatbind -n int1.ali int2.ali -Lsal1
@end example
@item
Compile the binder generated file:
@example
$ gcc -c b~int2.adb
@end example
@item
Link the dynamic library with all the necessary object files,
indicating to the linker the names of the @code{init} (and possibly
@code{final}) procedures for automatic initialization (and finalization).
The built library should be placed in a directory different from
the object directory.
@item
Copy the @code{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 @code{SL} on the line in the @code{ALI} file that starts
with letter ‘P’) and make the modified copy of the @code{ALI} file
read-only.