gcc/doc/sourcebuild.texi

@c Copyright (C) 2002, 2003, 2004 Free Software Foundation, Inc.
@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.

@node Source Tree
@chapter Source Tree Structure and Build System

This chapter describes the structure of the GCC source tree, and how
GCC is built.  The user documentation for building and installing GCC
is in a separate manual (@uref{http://gcc.gnu.org/install/}), with
which it is presumed that you are familiar.

@menu
* Configure Terms:: Configuration terminology and history.
* Top Level::       The top level source directory.
* gcc Directory::   The @file{gcc} subdirectory.
* Testsuites::      The GCC testsuites.
@end menu

@include configterms.texi

@node Top Level
@section Top Level Source Directory

The top level source directory in a GCC distribution contains several
files and directories that are shared with other software
distributions such as that of GNU Binutils.  It also contains several
subdirectories that contain parts of GCC and its runtime libraries:

@table @file
@item boehm-gc
The Boehm conservative garbage collector, used as part of the Java
runtime library.

@item contrib
Contributed scripts that may be found useful in conjunction with GCC@.
One of these, @file{contrib/texi2pod.pl}, is used to generate man
pages from Texinfo manuals as part of the GCC build process.

@item fastjar
An implementation of the @command{jar} command, used with the Java
front end.

@item gcc
The main sources of GCC itself (except for runtime libraries),
including optimizers, support for different target architectures,
language front ends, and testsuites.  @xref{gcc Directory, , The
@file{gcc} Subdirectory}, for details.

@item include
Headers for the @code{libiberty} library.

@item libf2c
The Fortran runtime library.

@item libffi
The @code{libffi} library, used as part of the Java runtime library.

@item libiberty
The @code{libiberty} library, used for portability and for some
generally useful data structures and algorithms.  @xref{Top, ,
Introduction, libiberty, @sc{gnu} libiberty}, for more information
about this library.

@item libjava
The Java runtime library.

@item libobjc
The Objective-C runtime library.

@item libstdc++-v3
The C++ runtime library.

@item maintainer-scripts
Scripts used by the @code{gccadmin} account on @code{gcc.gnu.org}.

@item zlib
The @code{zlib} compression library, used by the Java front end and as
part of the Java runtime library.
@end table

The build system in the top level directory, including how recursion
into subdirectories works and how building runtime libraries for
multilibs is handled, is documented in a separate manual, included
with GNU Binutils.  @xref{Top, , GNU configure and build system,
configure, The GNU configure and build system}, for details.

@node gcc Directory
@section The @file{gcc} Subdirectory

The @file{gcc} directory contains many files that are part of the C
sources of GCC, other files used as part of the configuration and
build process, and subdirectories including documentation and a
testsuite.  The files that are sources of GCC are documented in a
separate chapter.  @xref{Passes, , Passes and Files of the Compiler}.

@menu
* Subdirectories:: Subdirectories of @file{gcc}.
* Configuration::  The configuration process, and the files it uses.
* Build::          The build system in the @file{gcc} directory.
* Makefile::       Targets in @file{gcc/Makefile}.
* Library Files::  Library source files and headers under @file{gcc/}.
* Headers::        Headers installed by GCC.
* Documentation::  Building documentation in GCC.
* Front End::      Anatomy of a language front end.
* Back End::       Anatomy of a target back end.
@end menu

@node Subdirectories
@subsection Subdirectories of @file{gcc}

The @file{gcc} directory contains the following subdirectories:

@table @file
@item @var{language}
Subdirectories for various languages.  Directories containing a file
@file{config-lang.in} are language subdirectories.  The contents of
the subdirectories @file{cp} (for C++) and @file{objc} (for
Objective-C) are documented in this manual (@pxref{Passes, , Passes
and Files of the Compiler}); those for other languages are not.
@xref{Front End, , Anatomy of a Language Front End}, for details of
the files in these directories.

@item config
Configuration files for supported architectures and operating
systems.  @xref{Back End, , Anatomy of a Target Back End}, for
details of the files in this directory.

@item doc
Texinfo documentation for GCC, together with automatically generated
man pages and support for converting the installation manual to
HTML@.  @xref{Documentation}.

@item fixinc
The support for fixing system headers to work with GCC@.  See
@file{fixinc/README} for more information.  The headers fixed by this
mechanism are installed in @file{@var{libsubdir}/include}.  Along with
those headers, @file{README-fixinc} is also installed, as
@file{@var{libsubdir}/include/README}.

@item ginclude
System headers installed by GCC, mainly those required by the C
standard of freestanding implementations.  @xref{Headers, , Headers
Installed by GCC}, for details of when these and other headers are
installed.

@item intl
GNU @code{libintl}, from GNU @code{gettext}, for systems which do not
include it in libc.  Properly, this directory should be at top level,
parallel to the @file{gcc} directory.

@item po
Message catalogs with translations of messages produced by GCC into
various languages, @file{@var{language}.po}.  This directory also
contains @file{gcc.pot}, the template for these message catalogues,
@file{exgettext}, a wrapper around @command{gettext} to extract the
messages from the GCC sources and create @file{gcc.pot}, which is run
by @samp{make gcc.pot}, and @file{EXCLUDES}, a list of files from
which messages should not be extracted.

@item testsuite
The GCC testsuites (except for those for runtime libraries).
@xref{Testsuites}.
@end table

@node Configuration
@subsection Configuration in the @file{gcc} Directory

The @file{gcc} directory is configured with an Autoconf-generated
script @file{configure}.  The @file{configure} script is generated
from @file{configure.ac} and @file{aclocal.m4}.  From the files
@file{configure.ac} and @file{acconfig.h}, Autoheader generates the
file @file{config.in}.  The file @file{cstamp-h.in} is used as a
timestamp.

@menu
* Config Fragments::     Scripts used by @file{configure}.
* System Config::        The @file{config.build}, @file{config.host}, and
                         @file{config.gcc} files.
* Configuration Files::  Files created by running @file{configure}.
@end menu

@node Config Fragments
@subsubsection Scripts Used by @file{configure}

@file{configure} uses some other scripts to help in its work:

@itemize @bullet
@item The standard GNU @file{config.sub} and @file{config.guess}
files, kept in the top level directory, are used.  FIXME: when is the
@file{config.guess} file in the @file{gcc} directory (that just calls
the top level one) used?

@item The file @file{config.gcc} is used to handle configuration
specific to the particular target machine.  The file
@file{config.build} is used to handle configuration specific to the
particular build machine.  The file @file{config.host} is used to handle
configuration specific to the particular host machine.  (In general,
these should only be used for features that cannot reasonably be tested in
Autoconf feature tests.)
@xref{System Config, , The @file{config.build}; @file{config.host};
and @file{config.gcc} Files}, for details of the contents of these files.

@item Each language subdirectory has a file
@file{@var{language}/config-lang.in} that is used for
front-end-specific configuration.  @xref{Front End Config, , The Front
End @file{config-lang.in} File}, for details of this file.

@item A helper script @file{configure.frag} is used as part of
creating the output of @file{configure}.
@end itemize

@node System Config
@subsubsection The @file{config.build}; @file{config.host}; and @file{config.gcc} Files

The @file{config.build} file contains specific rules for particular systems
which GCC is built on.  This should be used as rarely as possible, as the
behavior of the build system can always be detected by autoconf.

The @file{config.host} file contains specific rules for particular systems
which GCC will run on.  This is rarely needed.

The @file{config.gcc} file contains specific rules for particular systems
which GCC will generate code for.  This is usually needed.

Each file has a list of the shell variables it sets, with descriptions, at the
top of the file.

FIXME: document the contents of these files, and what variables should
be set to control build, host and target configuration.

@include configfiles.texi

@node Build
@subsection Build System in the @file{gcc} Directory

FIXME: describe the build system, including what is built in what
stages.  Also list the various source files that are used in the build
process but aren't source files of GCC itself and so aren't documented
below (@pxref{Passes}).

@include makefile.texi

@node Library Files
@subsection Library Source Files and Headers under the @file{gcc} Directory

FIXME: list here, with explanation, all the C source files and headers
under the @file{gcc} directory that aren't built into the GCC
executable but rather are part of runtime libraries and object files,
such as @file{crtstuff.c} and @file{unwind-dw2.c}.  @xref{Headers, ,
Headers Installed by GCC}, for more information about the
@file{ginclude} directory.

@node Headers
@subsection Headers Installed by GCC

In general, GCC expects the system C library to provide most of the
headers to be used with it.  However, GCC will fix those headers if
necessary to make them work with GCC, and will install some headers
required of freestanding implementations.  These headers are installed
in @file{@var{libsubdir}/include}.  Headers for non-C runtime
libraries are also installed by GCC; these are not documented here.
(FIXME: document them somewhere.)

Several of the headers GCC installs are in the @file{ginclude}
directory.  These headers, @file{iso646.h},
@file{stdarg.h}, @file{stdbool.h}, and @file{stddef.h},
are installed in @file{@var{libsubdir}/include},
unless the target Makefile fragment (@pxref{Target Fragment})
overrides this by setting @code{USER_H}.

In addition to these headers and those generated by fixing system
headers to work with GCC, some other headers may also be installed in
@file{@var{libsubdir}/include}.  @file{config.gcc} may set
@code{extra_headers}; this specifies additional headers under
@file{config} to be installed on some systems.

GCC installs its own version of @code{<float.h>}, from @file{ginclude/float.h}.
This is done to cope with command-line options that change the
representation of floating point numbers.

GCC also installs its own version of @code{<limits.h>}; this is generated
from @file{glimits.h}, together with @file{limitx.h} and
@file{limity.h} if the system also has its own version of
@code{<limits.h>}.  (GCC provides its own header because it is
required of ISO C freestanding implementations, but needs to include
the system header from its own header as well because other standards
such as POSIX specify additional values to be defined in
@code{<limits.h>}.)  The system's @code{<limits.h>} header is used via
@file{@var{libsubdir}/include/syslimits.h}, which is copied from
@file{gsyslimits.h} if it does not need fixing to work with GCC; if it
needs fixing, @file{syslimits.h} is the fixed copy.

@node Documentation
@subsection Building Documentation

The main GCC documentation is in the form of manuals in Texinfo
format.  These are installed in Info format, and DVI versions may be
generated by @samp{make dvi}.  In addition, some man pages are
generated from the Texinfo manuals, there are some other text files
with miscellaneous documentation, and runtime libraries have their own
documentation outside the @file{gcc} directory.  FIXME: document the
documentation for runtime libraries somewhere.

@menu
* Texinfo Manuals::      GCC manuals in Texinfo format.
* Man Page Generation::  Generating man pages from Texinfo manuals.
* Miscellaneous Docs::   Miscellaneous text files with documentation.
@end menu

@node Texinfo Manuals
@subsubsection Texinfo Manuals

The manuals for GCC as a whole, and the C and C++ front ends, are in
files @file{doc/*.texi}.  Other front ends have their own manuals in
files @file{@var{language}/*.texi}.  Common files
@file{doc/include/*.texi} are provided which may be included in
multiple manuals; the following files are in @file{doc/include}:

@table @file
@item fdl.texi
The GNU Free Documentation License.
@item funding.texi
The section ``Funding Free Software''.
@item gcc-common.texi
Common definitions for manuals.
@item gpl.texi
The GNU General Public License.
@item texinfo.tex
A copy of @file{texinfo.tex} known to work with the GCC manuals.
@end table

DVI formatted manuals are generated by @samp{make dvi}, which uses
@command{texi2dvi} (via the Makefile macro @code{$(TEXI2DVI)}).  Info
manuals are generated by @samp{make info} (which is run as part of
a bootstrap); this generates the manuals in the source directory,
using @command{makeinfo} via the Makefile macro @code{$(MAKEINFO)},
and they are included in release distributions.

Manuals are also provided on the GCC web site, in both HTML and
PostScript forms.  This is done via the script
@file{maintainer-scripts/update_web_docs}.  Each manual to be
provided online must be listed in the definition of @code{MANUALS} in
that file; a file @file{@var{name}.texi} must only appear once in the
source tree, and the output manual must have the same name as the
source file.  (However, other Texinfo files, included in manuals but
not themselves the root files of manuals, may have names that appear
more than once in the source tree.)  The manual file
@file{@var{name}.texi} should only include other files in its own
directory or in @file{doc/include}.  HTML manuals will be generated by
@samp{makeinfo --html} and PostScript manuals by @command{texi2dvi}
and @command{dvips}.  All Texinfo files that are parts of manuals must
be checked into CVS, even if they are generated files, for the
generation of online manuals to work.

The installation manual, @file{doc/install.texi}, is also provided on
the GCC web site.  The HTML version is generated by the script
@file{doc/install.texi2html}.

@node Man Page Generation
@subsubsection Man Page Generation

Because of user demand, in addition to full Texinfo manuals, man pages
are provided which contain extracts from those manuals.  These man
pages are generated from the Texinfo manuals using
@file{contrib/texi2pod.pl} and @command{pod2man}.  (The man page for
@command{g++}, @file{cp/g++.1}, just contains a @samp{.so} reference
to @file{gcc.1}, but all the other man pages are generated from
Texinfo manuals.)

Because many systems may not have the necessary tools installed to
generate the man pages, they are only generated if the
@file{configure} script detects that recent enough tools are
installed, and the Makefiles allow generating man pages to fail
without aborting the build.  Man pages are also included in release
distributions.  They are generated in the source directory.

Magic comments in Texinfo files starting @samp{@@c man} control what
parts of a Texinfo file go into a man page.  Only a subset of Texinfo
is supported by @file{texi2pod.pl}, and it may be necessary to add
support for more Texinfo features to this script when generating new
man pages.  To improve the man page output, some special Texinfo
macros are provided in @file{doc/include/gcc-common.texi} which
@file{texi2pod.pl} understands:

@table @code
@item @@gcctabopt
Use in the form @samp{@@table @@gcctabopt} for tables of options,
where for printed output the effect of @samp{@@code} is better than
that of @samp{@@option} but for man page output a different effect is
wanted.
@item @@gccoptlist
Use for summary lists of options in manuals.
@item @@gol
Use at the end of each line inside @samp{@@gccoptlist}.  This is
necessary to avoid problems with differences in how the
@samp{@@gccoptlist} macro is handled by different Texinfo formatters.
@end table

FIXME: describe the @file{texi2pod.pl} input language and magic
comments in more detail.

@node Miscellaneous Docs
@subsubsection Miscellaneous Documentation

In addition to the formal documentation that is installed by GCC,
there are several other text files with miscellaneous documentation:

@table @file
@item ABOUT-GCC-NLS
Notes on GCC's Native Language Support.  FIXME: this should be part of
this manual rather than a separate file.
@item ABOUT-NLS
Notes on the Free Translation Project.
@item COPYING
The GNU General Public License.
@item COPYING.LIB
The GNU Lesser General Public License.
@item *ChangeLog*
@itemx */ChangeLog*
Change log files for various parts of GCC@.
@item LANGUAGES
Details of a few changes to the GCC front-end interface.  FIXME: the
information in this file should be part of general documentation of
the front-end interface in this manual.
@item ONEWS
Information about new features in old versions of GCC@.  (For recent
versions, the information is on the GCC web site.)
@item README.Portability
Information about portability issues when writing code in GCC@.  FIXME:
why isn't this part of this manual or of the GCC Coding Conventions?
@item SERVICE
A pointer to the GNU Service Directory.
@end table

FIXME: document such files in subdirectories, at least @file{config},
@file{cp}, @file{objc}, @file{testsuite}.

@node Front End
@subsection Anatomy of a Language Front End

A front end for a language in GCC has the following parts:

@itemize @bullet
@item
A directory @file{@var{language}} under @file{gcc} containing source
files for that front end.  @xref{Front End Directory, , The Front End
@file{@var{language}} Directory}, for details.
@item
A mention of the language in the list of supported languages in
@file{gcc/doc/install.texi}.
@item
A mention of the name under which the language's runtime library is
recognized by @option{--enable-shared=@var{package}} in the
documentation of that option in @file{gcc/doc/install.texi}.
@item
A mention of any special prerequisites for building the front end in
the documentation of prerequisites in @file{gcc/doc/install.texi}.
@item
Details of contributors to that front end in
@file{gcc/doc/contrib.texi}.  If the details are in that front end's
own manual then there should be a link to that manual's list in
@file{contrib.texi}.
@item
Information about support for that language in
@file{gcc/doc/frontends.texi}.
@item
Information about standards for that language, and the front end's
support for them, in @file{gcc/doc/standards.texi}.  This may be a
link to such information in the front end's own manual.
@item
Details of source file suffixes for that language and @option{-x
@var{lang}} options supported, in @file{gcc/doc/invoke.texi}.
@item
Entries in @code{default_compilers} in @file{gcc.c} for source file
suffixes for that language.
@item
Preferably testsuites, which may be under @file{gcc/testsuite} or
runtime library directories.  FIXME: document somewhere how to write
testsuite harnesses.
@item
Probably a runtime library for the language, outside the @file{gcc}
directory.  FIXME: document this further.
@item
Details of the directories of any runtime libraries in
@file{gcc/doc/sourcebuild.texi}.
@end itemize

If the front end is added to the official GCC CVS repository, the
following are also necessary:

@itemize @bullet
@item
At least one Bugzilla component for bugs in that front end and runtime
libraries.  This category needs to be mentioned in
@file{gcc/gccbug.in}, as well as being added to the Bugzilla database.
@item
Normally, one or more maintainers of that front end listed in
@file{MAINTAINERS}.
@item
Mentions on the GCC web site in @file{index.html} and
@file{frontends.html}, with any relevant links on
@file{readings.html}.  (Front ends that are not an official part of
GCC may also be listed on @file{frontends.html}, with relevant links.)
@item
A news item on @file{index.html}, and possibly an announcement on the
@email{gcc-announce@@gcc.gnu.org} mailing list.
@item
The front end's manuals should be mentioned in
@file{maintainer-scripts/update_web_docs} (@pxref{Texinfo Manuals})
and the online manuals should be linked to from
@file{onlinedocs/index.html}.
@item
Any old releases or CVS repositories of the front end, before its
inclusion in GCC, should be made available on the GCC FTP site
@uref{ftp://gcc.gnu.org/pub/gcc/old-releases/}.
@item
The release and snapshot script @file{maintainer-scripts/gcc_release}
should be updated to generate appropriate tarballs for this front end.
The associated @file{maintainer-scripts/snapshot-README} and
@file{maintainer-scripts/snapshot-index.html} files should be updated
to list the tarballs and diffs for this front end.
@item
If this front end includes its own version files that include the
current date, @file{maintainer-scripts/update_version} should be
updated accordingly.
@item
@file{CVSROOT/modules} in the GCC CVS repository should be updated.
@end itemize

@menu
* Front End Directory::  The front end @file{@var{language}} directory.
* Front End Config::     The front end @file{config-lang.in} file.
@end menu

@node Front End Directory
@subsubsection The Front End @file{@var{language}} Directory

A front end @file{@var{language}} directory contains the source files
of that front end (but not of any runtime libraries, which should be
outside the @file{gcc} directory).  This includes documentation, and
possibly some subsidiary programs build alongside the front end.
Certain files are special and other parts of the compiler depend on
their names:

@table @file
@item config-lang.in
This file is required in all language subdirectories.  @xref{Front End
Config, , The Front End @file{config-lang.in} File}, for details of
its contents
@item Make-lang.in
This file is required in all language subdirectories.  It contains
targets @code{@var{lang}.@var{hook}} (where @code{@var{lang}} is the
setting of @code{language} in @file{config-lang.in}) for the following
values of @code{@var{hook}}, and any other Makefile rules required to
build those targets (which may if necessary use other Makefiles
specified in @code{outputs} in @file{config-lang.in}, although this is
deprecated).  Some hooks are defined by using a double-colon rule for
@code{@var{hook}}, rather than by using a target of form
@code{@var{lang}.@var{hook}}.  These hooks are called ``double-colon
hooks'' below.  It also adds any testsuite targets that can use the
standard rule in @file{gcc/Makefile.in} to the variable
@code{lang_checks}.

@table @code
@item all.build
@itemx all.cross
@itemx start.encap
@itemx rest.encap
FIXME: exactly what goes in each of these targets?
@item tags
Build an @command{etags} @file{TAGS} file in the language subdirectory
in the source tree.
@item info
Build info documentation for the front end, in the build directory.
This target is only called by @samp{make bootstrap} if a suitable
version of @command{makeinfo} is available, so does not need to check
for this, and should fail if an error occurs.
@item dvi
Build DVI documentation for the front end, in the build directory.
This should be done using @code{$(TEXI2DVI)}, with appropriate
@option{-I} arguments pointing to directories of included files.
This hook is a double-colon hook.
@item man
Build generated man pages for the front end from Texinfo manuals
(@pxref{Man Page Generation}), in the build directory.  This target
is only called if the necessary tools are available, but should ignore
errors so as not to stop the build if errors occur; man pages are
optional and the tools involved may be installed in a broken way.
@item install-normal
FIXME: what is this target for?
@item install-common
Install everything that is part of the front end, apart from the
compiler executables listed in @code{compilers} in
@file{config-lang.in}.
@item install-info
Install info documentation for the front end, if it is present in the
source directory.  This target should have dependencies on info files
that should be installed.  This hook is a double-colon hook.
@item install-man
Install man pages for the front end.  This target should ignore
errors.
@item srcextra
Copies its dependencies into the source directory.  This generally should
be used for generated files such as @file{gcc/c-parse.c} which are not
present in CVS, but should be included in any release tarballs.  This
target will be executed during a bootstrap if
@samp{--enable-generated-files-in-srcdir} was specified as a
@file{configure} option.
@item srcinfo
@itemx srcman
Copies its dependencies into the source directory.  These targets will be
executed during a bootstrap if @samp{--enable-generated-files-in-srcdir}
was specified as a @file{configure} option.
@item uninstall
Uninstall files installed by installing the compiler.  This is
currently documented not to be supported, so the hook need not do
anything.
@item mostlyclean
@itemx clean
@itemx distclean
@itemx maintainer-clean
The language parts of the standard GNU
@samp{*clean} targets. @xref{Standard Targets, , Standard Targets for
Users, standards, GNU Coding Standards}, for details of the standard
targets.  For GCC, @code{maintainer-clean} should delete
all generated files in the source directory that are not checked into
CVS, but should not delete anything checked into CVS@.
@item stage1
@itemx stage2
@itemx stage3
@itemx stage4
@itemx stageprofile
@itemx stagefeedback
Move to the stage directory files not included in @code{stagestuff} in
@file{config-lang.in} or otherwise moved by the main @file{Makefile}.
@end table

@item lang.opt
This file registers the set of switches that the front end accepts on
the command line, and their --help text.  The file format is
documented in the file @file{c.opt}.  These files are processed by the
script @file{opts.sh}.
@item lang-specs.h
This file provides entries for @code{default_compilers} in
@file{gcc.c} which override the default of giving an error that a
compiler for that language is not installed.
@item @var{language}-tree.def
This file, which need not exist, defines any language-specific tree
codes.
@end table

@node Front End Config
@subsubsection The Front End @file{config-lang.in} File

Each language subdirectory contains a @file{config-lang.in} file.  In
addition the main directory contains @file{c-config-lang.in}, which
contains limited information for the C language.  This file is a shell
script that may define some variables describing the language:

@table @code
@item language
This definition must be present, and gives the name of the language
for some purposes such as arguments to @option{--enable-languages}.
@item lang_requires
If defined, this variable lists (space-separated) language front ends
other than C that this front end requires to be enabled (with the
names given being their @code{language} settings).  For example, the
Java front end depends on the C++ front end, so sets
@samp{lang_requires=c++}.
@item target_libs
If defined, this variable lists (space-separated) targets in the top
level @file{Makefile} to build the runtime libraries for this
language, such as @code{target-libobjc}.
@item lang_dirs
If defined, this variable lists (space-separated) top level
directories (parallel to @file{gcc}), apart from the runtime libraries,
that should not be configured if this front end is not built.
@item build_by_default
If defined to @samp{no}, this language front end is not built unless
enabled in a @option{--enable-languages} argument.  Otherwise, front
ends are built by default, subject to any special logic in
@file{configure.ac} (as is present to disable the Ada front end if the
Ada compiler is not already installed).
@item boot_language
If defined to @samp{yes}, this front end is built in stage 1 of the
bootstrap.  This is only relevant to front ends written in their own
languages.
@item compilers
If defined, a space-separated list of compiler executables that will
be run by the driver.  The names here will each end
with @samp{\$(exeext)}.
@item stagestuff
If defined, a space-separated list of files that should be moved to
the @file{stage@var{n}} directories in each stage of bootstrap.
@item outputs
If defined, a space-separated list of files that should be generated
by @file{configure} substituting values in them.  This mechanism can
be used to create a file @file{@var{language}/Makefile} from
@file{@var{language}/Makefile.in}, but this is deprecated, building
everything from the single @file{gcc/Makefile} is preferred.
@item gtfiles
If defined, a space-separated list of files that should be scanned by
gengtype.c to generate the garbage collection tables and routines for
this language.  This excludes the files that are common to all front
ends. @xref{Type Information}.

@end table

@node Back End
@subsection Anatomy of a Target Back End

A back end for a target architecture in GCC has the following parts:

@itemize @bullet
@item
A directory @file{@var{machine}} under @file{gcc/config}, containing a
machine description @file{@var{machine}.md} file (@pxref{Machine Desc,
, Machine Descriptions}), header files @file{@var{machine}.h} and
@file{@var{machine}-protos.h} and a source file @file{@var{machine}.c}
(@pxref{Target Macros, , Target Description Macros and Functions}),
possibly a target Makefile fragment @file{t-@var{machine}}
(@pxref{Target Fragment, , The Target Makefile Fragment}), and maybe
some other files.  The names of these files may be changed from the
defaults given by explicit specifications in @file{config.gcc}.
@item
If necessary, a file @file{@var{machine}-modes.def} in the
@file{@var{machine}} directory, containing additional machine modes to
represent condition codes.  @xref{Condition Code}, for further details.
@item
Entries in @file{config.gcc} (@pxref{System Config, , The
@file{config.gcc} File}) for the systems with this target
architecture.
@item
Documentation in @file{gcc/doc/invoke.texi} for any command-line
options supported by this target (@pxref{Run-time Target, , Run-time
Target Specification}).  This means both entries in the summary table
of options and details of the individual options.
@item
Documentation in @file{gcc/doc/extend.texi} for any target-specific
attributes supported (@pxref{Target Attributes, , Defining
target-specific uses of @code{__attribute__}}), including where the
same attribute is already supported on some targets, which are
enumerated in the manual.
@item
Documentation in @file{gcc/doc/extend.texi} for any target-specific
pragmas supported.
@item
Documentation in @file{gcc/doc/extend.texi} of any target-specific
built-in functions supported.
@item
Documentation in @file{gcc/doc/md.texi} of any target-specific
constraint letters (@pxref{Machine Constraints, , Constraints for
Particular Machines}).
@item
A note in @file{gcc/doc/contrib.texi} under the person or people who
contributed the target support.
@item
Entries in @file{gcc/doc/install.texi} for all target triplets
supported with this target architecture, giving details of any special
notes about installation for this target, or saying that there are no
special notes if there are none.
@item
Possibly other support outside the @file{gcc} directory for runtime
libraries.  FIXME: reference docs for this.  The libstdc++ porting
manual needs to be installed as info for this to work, or to be a
chapter of this manual.
@end itemize

If the back end is added to the official GCC CVS repository, the
following are also necessary:

@itemize @bullet
@item
An entry for the target architecture in @file{readings.html} on the
GCC web site, with any relevant links.
@item
Details of the properties of the back end and target architecture in
@file{backends.html} on the GCC web site.
@item
A news item about the contribution of support for that target
architecture, in @file{index.html} on the GCC web site.
@item
Normally, one or more maintainers of that target listed in
@file{MAINTAINERS}.  Some existing architectures may be unmaintained,
but it would be unusual to add support for a target that does not have
a maintainer when support is added.
@end itemize

@node Testsuites
@section Testsuites

GCC contains several testsuites to help maintain compiler quality.
Most of the runtime libraries and language front ends in GCC have
testsuites.  Currently only the C language testsuites are documented
here; FIXME: document the others.

@menu
* Test Idioms::     Idioms used in testsuite code.
* Ada Tests::       The Ada language testsuites.
* C Tests::         The C language testsuites.
* libgcj Tests::    The Java library testsuites.
* gcov Testing::    Support for testing gcov.
* profopt Testing:: Support for testing profile-directed optimizations.
* compat Testing::  Support for testing binary compatibility.
@end menu

@node Test Idioms
@subsection Idioms Used in Testsuite Code

In general C testcases have a trailing @file{-@var{n}.c}, starting
with @file{-1.c}, in case other testcases with similar names are added
later.  If the test is a test of some well-defined feature, it should
have a name referring to that feature such as
@file{@var{feature}-1.c}.  If it does not test a well-defined feature
but just happens to exercise a bug somewhere in the compiler, and a
bug report has been filed for this bug in the GCC bug database,
@file{pr@var{bug-number}-1.c} is the appropriate form of name.
Otherwise (for miscellaneous bugs not filed in the GCC bug database),
and previously more generally, test cases are named after the date on
which they were added.  This allows people to tell at a glance whether
a test failure is because of a recently found bug that has not yet
been fixed, or whether it may be a regression, but does not give any
other information about the bug or where discussion of it may be
found.  Some other language testsuites follow similar conventions.

Test cases should use @code{abort ()} to indicate failure and
@code{exit (0)} for success; on some targets these may be redefined to
indicate failure and success in other ways.

In the @file{gcc.dg} testsuite, it is often necessary to test that an
error is indeed a hard error and not just a warning---for example,
where it is a constraint violation in the C standard, which must
become an error with @option{-pedantic-errors}.  The following idiom,
where the first line shown is line @var{line} of the file and the line
that generates the error, is used for this:

@smallexample
/* @{ dg-bogus "warning" "warning in place of error" @} */
/* @{ dg-error "@var{regexp}" "@var{message}" @{ target *-*-* @} @var{line} @} */
@end smallexample

It may be necessary to check that an expression is an integer constant
expression and has a certain value.  To check that @code{@var{E}} has
value @code{@var{V}}, an idiom similar to the following is used:

@smallexample
char x[((E) == (V) ? 1 : -1)];
@end smallexample

In @file{gcc.dg} tests, @code{__typeof__} is sometimes used to make
assertions about the types of expressions.  See, for example,
@file{gcc.dg/c99-condexpr-1.c}.  The more subtle uses depend on the
exact rules for the types of conditional expressions in the C
standard; see, for example, @file{gcc.dg/c99-intconst-1.c}.

It is useful to be able to test that optimizations are being made
properly.  This cannot be done in all cases, but it can be done where
the optimization will lead to code being optimized away (for example,
where flow analysis or alias analysis should show that certain code
cannot be called) or to functions not being called because they have
been expanded as built-in functions.  Such tests go in
@file{gcc.c-torture/execute}.  Where code should be optimized away, a
call to a nonexistent function such as @code{link_failure ()} may be
inserted; a definition

@smallexample
#ifndef __OPTIMIZE__
void
link_failure (void)
@{
  abort ();
@}
#endif
@end smallexample

@noindent
will also be needed so that linking still succeeds when the test is
run without optimization.  When all calls to a built-in function
should have been optimized and no calls to the non-built-in version of
the function should remain, that function may be defined as
@code{static} to call @code{abort ()} (although redeclaring a function
as static may not work on all targets).

All testcases must be portable.  Target-specific testcases must have
appropriate code to avoid causing failures on unsupported systems;
unfortunately, the mechanisms for this differ by directory.

FIXME: discuss non-C testsuites here.

@node Ada Tests
@subsection Ada Language Testsuites

The Ada testsuite includes executable tests from the ACATS 2.5
testsuite, publicly available at
@uref{http://www.adaic.org/compilers/acats/2.5}

These tests are integrated in the GCC testsuite in the
@file{gcc/testsuite/ada/acats} directory, and
enabled automatically when running @code{make check}, assuming
the Ada language has been enabled when configuring GCC.

You can also run the Ada testsuite independently, using
@code{make check-ada}, or run a subset of the tests by specifying which
chapter to run, e.g:

@smallexample
$ make check-ada CHAPTERS="c3 c9"
@end smallexample

The tests are organized by directory, each directory corresponding to
a chapter of the Ada Reference Manual. So for example, c9 corresponds
to chapter 9, which deals with tasking features of the language.

There is also an extra chapter called @file{gcc} containing a template for
creating new executable tests.

The tests are run using two 'sh' scripts: run_acats and run_all.sh
To run the tests using a simulator or a cross target, see the small
customization section at the top of run_all.sh

These tests are run using the build tree: they can be run without doing
a @code{make install}.

@node C Tests
@subsection C Language Testsuites

GCC contains the following C language testsuites, in the
@file{gcc/testsuite} directory:

@table @file
@item gcc.dg
This contains tests of particular features of the C compiler, using the
more modern @samp{dg} harness.  Correctness tests for various compiler
features should go here if possible.

Magic comments determine whether the file
is preprocessed, compiled, linked or run.  In these tests, error and warning
message texts are compared against expected texts or regular expressions
given in comments.  These tests are run with the options @samp{-ansi -pedantic}
unless other options are given in the test.  Except as noted below they
are not run with multiple optimization options.
@item gcc.dg/compat
This subdirectory contains tests for binary compatibility using
@file{compat.exp}, which in turn uses the language-independent support
(@pxref{compat Testing, , Support for testing binary compatibility}).
@item gcc.dg/cpp
This subdirectory contains tests of the preprocessor.
@item gcc.dg/debug
This subdirectory contains tests for debug formats.  Tests in this
subdirectory are run for each debug format that the compiler supports.
@item gcc.dg/format
This subdirectory contains tests of the @option{-Wformat} format
checking.  Tests in this directory are run with and without
@option{-DWIDE}.
@item gcc.dg/noncompile
This subdirectory contains tests of code that should not compile and
does not need any special compilation options.  They are run with
multiple optimization options, since sometimes invalid code crashes
the compiler with optimization.
@item gcc.dg/special
FIXME: describe this.

@item gcc.c-torture
This contains particular code fragments which have historically broken easily.
These tests are run with multiple optimization options, so tests for features
which only break at some optimization levels belong here.  This also contains
tests to check that certain optimizations occur.  It might be worthwhile to
separate the correctness tests cleanly from the code quality tests, but
it hasn't been done yet.

@item gcc.c-torture/compat
FIXME: describe this.

This directory should probably not be used for new tests.
@item gcc.c-torture/compile
This testsuite contains test cases that should compile, but do not
need to link or run.  These test cases are compiled with several
different combinations of optimization options.  All warnings are
disabled for these test cases, so this directory is not suitable if
you wish to test for the presence or absence of compiler warnings.
While special options can be set, and tests disabled on specific
platforms, by the use of @file{.x} files, mostly these test cases
should not contain platform dependencies.  FIXME: discuss how defines
such as @code{NO_LABEL_VALUES} and @code{STACK_SIZE} are used.
@item gcc.c-torture/execute
This testsuite contains test cases that should compile, link and run;
otherwise the same comments as for @file{gcc.c-torture/compile} apply.
@item gcc.c-torture/execute/ieee
This contains tests which are specific to IEEE floating point.
@item gcc.c-torture/unsorted
FIXME: describe this.

This directory should probably not be used for new tests.
@item gcc.c-torture/misc-tests
This directory contains C tests that require special handling.  Some
of these tests have individual expect files, and others share
special-purpose expect files:

@table @file
@item @code{bprob*.c}
Test @option{-fbranch-probabilities} using @file{bprob.exp}, which
in turn uses the generic, language-independent framework
(@pxref{profopt Testing, , Support for testing profile-directed
optimizations}).

@item @code{dg-*.c}
Test the testsuite itself using @file{dg-test.exp}.

@item @code{gcov*.c}
Test @command{gcov} output using @file{gcov.exp}, which in turn uses the
language-independent support (@pxref{gcov Testing, , Support for testing gcov}).

@item @code{i386-pf-*.c}
Test i386-specific support for data prefetch using @file{i386-prefetch.exp}.
@end table

@end table

FIXME: merge in @file{testsuite/README.gcc} and discuss the format of
test cases and magic comments more.

@node libgcj Tests
@subsection The Java library testsuites.

Runtime tests are executed via @samp{make check} in the
@file{@var{target}/libjava/testsuite} directory in the build
tree.  Additional runtime tests can be checked into this testsuite.

Regression testing of the core packages in libgcj is also covered by the
Mauve testsuite.  The @uref{http://sources.redhat.com/mauve/,,Mauve Project}
develops tests for the Java Class Libraries.  These tests are run as part
of libgcj testing by placing the Mauve tree within the libjava testsuite
sources at @file{libjava/testsuite/libjava.mauve/mauve}, or by specifying
the location of that tree when invoking @samp{make}, as in
@samp{make MAUVEDIR=~/mauve check}.

To detect regressions, a mechanism in @file{mauve.exp} compares the
failures for a test run against the list of expected failures in
@file{libjava/testsuite/libjava.mauve/xfails} from the source hierarchy.
Update this file when adding new failing tests to Mauve, or when fixing
bugs in libgcj that had caused Mauve test failures.

The @uref{http://oss.software.ibm.com/developerworks/opensource/jacks/,,
Jacks} project provides a testsuite for Java compilers that can be used
to test changes that affect the GCJ front end.  This testsuite is run as
part of Java testing by placing the Jacks tree within the the libjava
testsuite sources at @file{libjava/testsuite/libjava.jacks/jacks}.

We encourage developers to contribute test cases to Mauve and Jacks.

@node gcov Testing
@subsection Support for testing @command{gcov}

Language-independent support for testing @command{gcov}, and for checking
that branch profiling produces expected values, is provided by the
expect file @file{gcov.exp}.  @command{gcov} tests also rely on procedures
in @file{gcc.dg.exp} to compile and run the test program.  A typical
@command{gcov} test contains the following DejaGNU commands within comments:

@smallexample
@{ dg-options "-fprofile-arcs -ftest-coverage" @}
@{ dg-do run @{ target native @} @}
@{ dg-final @{ run-gcov sourcefile @} @}
@end smallexample

Checks of @command{gcov} output can include line counts, branch percentages,
and call return percentages.  All of these checks are requested via
commands that appear in comments in the test's source file.
Commands to check line counts are processed by default.
Commands to check branch percentages and call return percentages are
processed if the @command{run-gcov} command has arguments @code{branches}
or @code{calls}, respectively.  For example, the following specifies
checking both, as well as passing @code{-b} to @command{gcov}:

@smallexample
@{ dg-final @{ run-gcov branches calls @{ -b sourcefile @} @} @}
@end smallexample

A line count command appears within a comment on the source line
that is expected to get the specified count and has the form
@code{count(@var{cnt})}.  A test should only check line counts for
lines that will get the same count for any architecture.

Commands to check branch percentages (@code{branch}) and call
return percentages (@code{returns}) are very similar to each other.
A beginning command appears on or before the first of a range of
lines that will report the percentage, and the ending command
follows that range of lines.  The beginning command can include a
list of percentages, all of which are expected to be found within
the range.  A range is terminated by the next command of the same
kind.  A command @code{branch(end)} or @code{returns(end)} marks
the end of a range without starting a new one.  For example:

@smallexample
if (i > 10 && j > i && j < 20)  /* branch(27 50 75) */
                                /* branch(end) */
  foo (i, j);
@end smallexample

For a call return percentage, the value specified is the
percentage of calls reported to return.  For a branch percentage,
the value is either the expected percentage or 100 minus that
value, since the direction of a branch can differ depending on the
target or the optimization level.

Not all branches and calls need to be checked.  A test should not
check for branches that might be optimized away or replaced with
predicated instructions.  Don't check for calls inserted by the
compiler or ones that might be inlined or optimized away.

A single test can check for combinations of line counts, branch
percentages, and call return percentages.  The command to check a
line count must appear on the line that will report that count, but
commands to check branch percentages and call return percentages can
bracket the lines that report them.

@node profopt Testing
@subsection Support for testing profile-directed optimizations

The file @file{profopt.exp} provides language-independent support for
checking correct execution of a test built with profile-directed
optimization.  This testing requires that a test program be built and
executed twice.  The first time it is compiled to generate profile
data, and the second time it is compiled to use the data that was
generated during the first execution.  The second execution is to
verify that the test produces the expected results.

To check that the optimization actually generated better code, a
test can be built and run a third time with normal optimizations to
verify that the performance is better with the profile-directed
optimizations.  @file{profopt.exp} has the beginnings of this kind
of support.

@file{profopt.exp} provides generic support for profile-directed
optimizations.  Each set of tests that uses it provides information
about a specific optimization:

@table @code
@item tool
tool being tested, e.g., @command{gcc}

@item profile_option
options used to generate profile data

@item feedback_option
options used to optimize using that profile data

@item prof_ext
suffix of profile data files

@item PROFOPT_OPTIONS
list of options with which to run each test, similar to the lists for
torture tests
@end table

@node compat Testing
@subsection Support for testing binary compatibility

The file @file{compat.exp} provides language-independent support for
binary compatibility testing.  It supports testing interoperability of
two compilers that follow the same ABI, or of multiple sets of
compiler options that should not affect binary compatibility.  It is
intended to be used for testsuites that complement ABI testsuites.

A test supported by this framework has three parts, each in a
separate source file: a main program and two pieces that interact
with each other to split up the functionality being tested.

@table @file
@item @var{testname}_main.@var{suffix}
Contains the main program, which calls a function in file
@file{@var{testname}_x.@var{suffix}}.

@item @var{testname}_x.@var{suffix}
Contains at least one call to a function in
@file{@var{testname}_y.@var{suffix}}.

@item @var{testname}_y.@var{suffix}
Shares data with, or gets arguments from,
@file{@var{testname}_x.@var{suffix}}.
@end table

Within each test, the main program and one functional piece are
compiled by the GCC under test.  The other piece can be compiled by
an alternate compiler.  If no alternate compiler is specified,
then all three source files are all compiled by the GCC under test.
It's also possible to specify a pair of lists of compiler options,
one list for each compiler, so that each test will be compiled with
each pair of options.

@file{compat.exp} defines default pairs of compiler options.
These can be overridden by defining the environment variable
@env{COMPAT_OPTIONS} as:

@smallexample
COMPAT_OPTIONS="[list [list @{@var{tst1}@} @{@var{alt1}@}]
  ...[list @{@var{tstn}@} @{@var{altn}@}]]"
@end smallexample

where @var{tsti} and @var{alti} are lists of options, with @var{tsti}
used by the compiler under test and @var{alti} used by the alternate
compiler.  For example, with
@code{[list [list @{-g -O0@} @{-O3@}] [list @{-fpic@} @{-fPIC -O2@}]]},
the test is first built with @code{-g -O0} by the compiler under
test and with @code{-O3} by the alternate compiler.  The test is
built a second time using @code{-fpic} by the compiler under test
and @code{-fPIC -O2} by the alternate compiler.

An alternate compiler is specified by defining an environment
variable; for C++ define @env{ALT_CXX_UNDER_TEST} to be the full
pathname of an installed compiler.  That will be written to the
@file{site.exp} file used by DejaGNU.  The default is to build each
test with the compiler under test using the first of each pair of
compiler options from @env{COMPAT_OPTIONS}.  When
@env{ALT_CXX_UNDER_TEST} is @code{same}, each test is built using
the compiler under test but with combinations of the options from
@env{COMPAT_OPTIONS}.

To run only the C++ compatibility suite using the compiler under test
and another version of GCC using specific compiler options, do the
following from @file{@var{objdir}/gcc}:

@smallexample
rm site.exp
make -k \
  ALT_CXX_UNDER_TEST=$@{alt_prefix@}/bin/g++ \
  COMPAT_OPTIONS="lists as shown above" \
  check-c++ \
  RUNTESTFLAGS="compat.exp"
@end smallexample

A test that fails when the source files are compiled with different
compilers, but passes when the files are compiled with the same
compiler, demonstrates incompatibility of the generated code or
runtime support.  A test that fails for the alternate compiler but
passes for the compiler under test probably tests for a bug that was
fixed in the compiler under test but is present in the alternate
compiler.