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@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,

@c 1999, 2000, 2001, 2003, 2004, 2005, 2008, 2011

@c Free Software Foundation, Inc.

@c This is part of the GCC manual.

@c For copying conditions, see the file gcc.texi.

@node Fragments

@chapter Makefile Fragments

@cindex makefile fragment

When you configure GCC using the @file{configure} script, it will

construct the file @file{Makefile} from the template file

@file{Makefile.in}.  When it does this, it can incorporate makefile

fragments from the @file{config} directory.  These are used to set

Makefile parameters that are not amenable to being calculated by

autoconf.  The list of fragments to incorporate is set by

@file{config.gcc} (and occasionally @file{config.build}

and @file{config.host}); @xref{System Config}.

Fragments are named either @file{t-@var{target}} or @file{x-@var{host}},

depending on whether they are relevant to configuring GCC to produce

code for a particular target, or to configuring GCC to run on a

particular host.  Here @var{target} and @var{host} are mnemonics

which usually have some relationship to the canonical system name, but

no formal connection.

If these files do not exist, it means nothing needs to be added for a

given target or host.  Most targets need a few @file{t-@var{target}}

fragments, but needing @file{x-@var{host}} fragments is rare.

@menu

* Target Fragment:: Writing @file{t-@var{target}} files.

* Host Fragment::   Writing @file{x-@var{host}} files.

@end menu

@node Target Fragment

@section Target Makefile Fragments

@cindex target makefile fragment

@cindex @file{t-@var{target}}

Target makefile fragments can set these Makefile variables.

@table @code

@findex LIBGCC2_CFLAGS

@item LIBGCC2_CFLAGS

Compiler flags to use when compiling @file{libgcc2.c}.

@findex LIB2FUNCS_EXTRA

@item LIB2FUNCS_EXTRA

A list of source file names to be compiled or assembled and inserted

into @file{libgcc.a}.

@findex CRTSTUFF_T_CFLAGS

@item CRTSTUFF_T_CFLAGS

Special flags used when compiling @file{crtstuff.c}.

@xref{Initialization}.

@findex CRTSTUFF_T_CFLAGS_S

@item CRTSTUFF_T_CFLAGS_S

Special flags used when compiling @file{crtstuff.c} for shared

linking.  Used if you use @file{crtbeginS.o} and @file{crtendS.o}

in @code{EXTRA-PARTS}.

@xref{Initialization}.

@findex MULTILIB_OPTIONS

@item MULTILIB_OPTIONS

For some targets, invoking GCC in different ways produces objects

that can not be linked together.  For example, for some targets GCC

produces both big and little endian code.  For these targets, you must

arrange for multiple versions of @file{libgcc.a} to be compiled, one for

each set of incompatible options.  When GCC invokes the linker, it

arranges to link in the right version of @file{libgcc.a}, based on

the command line options used.

The @code{MULTILIB_OPTIONS} macro lists the set of options for which

special versions of @file{libgcc.a} must be built.  Write options that

are mutually incompatible side by side, separated by a slash.  Write

options that may be used together separated by a space.  The build

procedure will build all combinations of compatible options.

For example, if you set @code{MULTILIB_OPTIONS} to @samp{m68000/m68020

msoft-float}, @file{Makefile} will build special versions of

@file{libgcc.a} using the following sets of options:  @option{-m68000},

@option{-m68020}, @option{-msoft-float}, @samp{-m68000 -msoft-float}, and

@samp{-m68020 -msoft-float}.

@findex MULTILIB_DIRNAMES

@item MULTILIB_DIRNAMES

If @code{MULTILIB_OPTIONS} is used, this variable specifies the

directory names that should be used to hold the various libraries.

Write one element in @code{MULTILIB_DIRNAMES} for each element in

@code{MULTILIB_OPTIONS}.  If @code{MULTILIB_DIRNAMES} is not used, the

default value will be @code{MULTILIB_OPTIONS}, with all slashes treated

as spaces.

For example, if @code{MULTILIB_OPTIONS} is set to @samp{m68000/m68020

msoft-float}, then the default value of @code{MULTILIB_DIRNAMES} is

@samp{m68000 m68020 msoft-float}.  You may specify a different value if

you desire a different set of directory names.

@findex MULTILIB_MATCHES

@item MULTILIB_MATCHES

Sometimes the same option may be written in two different ways.  If an

option is listed in @code{MULTILIB_OPTIONS}, GCC needs to know about

any synonyms.  In that case, set @code{MULTILIB_MATCHES} to a list of

items of the form @samp{option=option} to describe all relevant

synonyms.  For example, @samp{m68000=mc68000 m68020=mc68020}.

@findex MULTILIB_EXCEPTIONS

@item MULTILIB_EXCEPTIONS

Sometimes when there are multiple sets of @code{MULTILIB_OPTIONS} being

specified, there are combinations that should not be built.  In that

case, set @code{MULTILIB_EXCEPTIONS} to be all of the switch exceptions

in shell case syntax that should not be built.

For example the ARM processor cannot execute both hardware floating

point instructions and the reduced size THUMB instructions at the same

time, so there is no need to build libraries with both of these

options enabled.  Therefore @code{MULTILIB_EXCEPTIONS} is set to:

@smallexample

*mthumb/*mhard-float*

@end smallexample

@findex MULTILIB_EXTRA_OPTS

@item MULTILIB_EXTRA_OPTS

Sometimes it is desirable that when building multiple versions of

@file{libgcc.a} certain options should always be passed on to the

compiler.  In that case, set @code{MULTILIB_EXTRA_OPTS} to be the list

of options to be used for all builds.  If you set this, you should

probably set @code{CRTSTUFF_T_CFLAGS} to a dash followed by it.

@findex SPECS

@item SPECS

Unfortunately, setting @code{MULTILIB_EXTRA_OPTS} is not enough, since

it does not affect the build of target libraries, at least not the

build of the default multilib.  One possible work-around is to use

@code{DRIVER_SELF_SPECS} to bring options from the @file{specs} file

as if they had been passed in the compiler driver command line.

However, you don't want to be adding these options after the toolchain

is installed, so you can instead tweak the @file{specs} file that will

be used during the toolchain build, while you still install the

original, built-in @file{specs}.  The trick is to set @code{SPECS} to

some other filename (say @file{specs.install}), that will then be

created out of the built-in specs, and introduce a @file{Makefile}

rule to generate the @file{specs} file that's going to be used at

build time out of your @file{specs.install}.

@item T_CFLAGS

These are extra flags to pass to the C compiler.  They are used both

when building GCC, and when compiling things with the just-built GCC@.

This variable is deprecated and should not be used.

@end table

@node Host Fragment

@section Host Makefile Fragments

@cindex host makefile fragment

@cindex @file{x-@var{host}}

The use of @file{x-@var{host}} fragments is discouraged.  You should only

use it for makefile dependencies.