334 lines
16 KiB
HTML
334 lines
16 KiB
HTML
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A GNU Manual
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<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>GNU Compiler Collection (GCC) Internals: Target Fragment</title>
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<meta name="description" content="GNU Compiler Collection (GCC) Internals: Target Fragment">
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<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Target Fragment">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Fragments.html#Fragments" rel="up" title="Fragments">
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</head>
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Target-Fragment"></a>
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<div class="header">
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<p>
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Next: <a href="Host-Fragment.html#Host-Fragment" accesskey="n" rel="next">Host Fragment</a>, Up: <a href="Fragments.html#Fragments" accesskey="u" rel="up">Fragments</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Target-Makefile-Fragments"></a>
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<h3 class="section">19.1 Target Makefile Fragments</h3>
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<a name="index-target-makefile-fragment"></a>
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<a name="index-t_002dtarget"></a>
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<p>Target makefile fragments can set these Makefile variables.
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</p>
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<dl compact="compact">
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<dd><a name="index-LIBGCC2_005fCFLAGS"></a>
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</dd>
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<dt><code>LIBGCC2_CFLAGS</code></dt>
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<dd><p>Compiler flags to use when compiling <samp>libgcc2.c</samp>.
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</p>
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<a name="index-LIB2FUNCS_005fEXTRA"></a>
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</dd>
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<dt><code>LIB2FUNCS_EXTRA</code></dt>
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<dd><p>A list of source file names to be compiled or assembled and inserted
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into <samp>libgcc.a</samp>.
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</p>
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<a name="index-CRTSTUFF_005fT_005fCFLAGS"></a>
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</dd>
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<dt><code>CRTSTUFF_T_CFLAGS</code></dt>
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<dd><p>Special flags used when compiling <samp>crtstuff.c</samp>.
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See <a href="Initialization.html#Initialization">Initialization</a>.
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</p>
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<a name="index-CRTSTUFF_005fT_005fCFLAGS_005fS"></a>
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</dd>
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<dt><code>CRTSTUFF_T_CFLAGS_S</code></dt>
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<dd><p>Special flags used when compiling <samp>crtstuff.c</samp> for shared
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linking. Used if you use <samp>crtbeginS.o</samp> and <samp>crtendS.o</samp>
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in <code>EXTRA-PARTS</code>.
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See <a href="Initialization.html#Initialization">Initialization</a>.
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</p>
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<a name="index-MULTILIB_005fOPTIONS"></a>
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</dd>
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<dt><code>MULTILIB_OPTIONS</code></dt>
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<dd><p>For some targets, invoking GCC in different ways produces objects
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that can not be linked together. For example, for some targets GCC
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produces both big and little endian code. For these targets, you must
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arrange for multiple versions of <samp>libgcc.a</samp> to be compiled, one for
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each set of incompatible options. When GCC invokes the linker, it
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arranges to link in the right version of <samp>libgcc.a</samp>, based on
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the command line options used.
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</p>
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<p>The <code>MULTILIB_OPTIONS</code> macro lists the set of options for which
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special versions of <samp>libgcc.a</samp> must be built. Write options that
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are mutually incompatible side by side, separated by a slash. Write
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options that may be used together separated by a space. The build
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procedure will build all combinations of compatible options.
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</p>
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<p>For example, if you set <code>MULTILIB_OPTIONS</code> to ‘<samp>m68000/m68020
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msoft-float</samp>’, <samp>Makefile</samp> will build special versions of
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<samp>libgcc.a</samp> using the following sets of options: <samp>-m68000</samp>,
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<samp>-m68020</samp>, <samp>-msoft-float</samp>, ‘<samp>-m68000 -msoft-float</samp>’, and
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‘<samp>-m68020 -msoft-float</samp>’.
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</p>
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<a name="index-MULTILIB_005fDIRNAMES"></a>
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</dd>
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<dt><code>MULTILIB_DIRNAMES</code></dt>
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<dd><p>If <code>MULTILIB_OPTIONS</code> is used, this variable specifies the
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directory names that should be used to hold the various libraries.
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Write one element in <code>MULTILIB_DIRNAMES</code> for each element in
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<code>MULTILIB_OPTIONS</code>. If <code>MULTILIB_DIRNAMES</code> is not used, the
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default value will be <code>MULTILIB_OPTIONS</code>, with all slashes treated
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as spaces.
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</p>
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<p><code>MULTILIB_DIRNAMES</code> describes the multilib directories using GCC
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conventions and is applied to directories that are part of the GCC
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installation. When multilib-enabled, the compiler will add a
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subdirectory of the form <var>prefix</var>/<var>multilib</var> before each
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directory in the search path for libraries and crt files.
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</p>
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<p>For example, if <code>MULTILIB_OPTIONS</code> is set to ‘<samp>m68000/m68020
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msoft-float</samp>’, then the default value of <code>MULTILIB_DIRNAMES</code> is
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‘<samp>m68000 m68020 msoft-float</samp>’. You may specify a different value if
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you desire a different set of directory names.
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</p>
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<a name="index-MULTILIB_005fMATCHES"></a>
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</dd>
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<dt><code>MULTILIB_MATCHES</code></dt>
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<dd><p>Sometimes the same option may be written in two different ways. If an
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option is listed in <code>MULTILIB_OPTIONS</code>, GCC needs to know about
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any synonyms. In that case, set <code>MULTILIB_MATCHES</code> to a list of
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items of the form ‘<samp>option=option</samp>’ to describe all relevant
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synonyms. For example, ‘<samp>m68000=mc68000 m68020=mc68020</samp>’.
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</p>
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<a name="index-MULTILIB_005fEXCEPTIONS"></a>
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</dd>
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<dt><code>MULTILIB_EXCEPTIONS</code></dt>
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<dd><p>Sometimes when there are multiple sets of <code>MULTILIB_OPTIONS</code> being
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specified, there are combinations that should not be built. In that
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case, set <code>MULTILIB_EXCEPTIONS</code> to be all of the switch exceptions
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in shell case syntax that should not be built.
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</p>
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<p>For example the ARM processor cannot execute both hardware floating
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point instructions and the reduced size THUMB instructions at the same
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time, so there is no need to build libraries with both of these
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options enabled. Therefore <code>MULTILIB_EXCEPTIONS</code> is set to:
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</p><div class="smallexample">
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<pre class="smallexample">*mthumb/*mhard-float*
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</pre></div>
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<a name="index-MULTILIB_005fREQUIRED"></a>
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</dd>
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<dt><code>MULTILIB_REQUIRED</code></dt>
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<dd><p>Sometimes when there are only a few combinations are required, it would
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be a big effort to come up with a <code>MULTILIB_EXCEPTIONS</code> list to
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cover all undesired ones. In such a case, just listing all the required
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combinations in <code>MULTILIB_REQUIRED</code> would be more straightforward.
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</p>
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<p>The way to specify the entries in <code>MULTILIB_REQUIRED</code> is same with
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the way used for <code>MULTILIB_EXCEPTIONS</code>, only this time what are
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required will be specified. Suppose there are multiple sets of
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<code>MULTILIB_OPTIONS</code> and only two combinations are required, one
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for ARMv7-M and one for ARMv7-R with hard floating-point ABI and FPU, the
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<code>MULTILIB_REQUIRED</code> can be set to:
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</p><div class="smallexample">
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<pre class="smallexample"><code>MULTILIB_REQUIRED</code> = mthumb/march=armv7-m
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<code>MULTILIB_REQUIRED</code> += march=armv7-r/mfloat-abi=hard/mfpu=vfpv3-d16
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</pre></div>
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<p>The <code>MULTILIB_REQUIRED</code> can be used together with
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<code>MULTILIB_EXCEPTIONS</code>. The option combinations generated from
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<code>MULTILIB_OPTIONS</code> will be filtered by <code>MULTILIB_EXCEPTIONS</code>
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and then by <code>MULTILIB_REQUIRED</code>.
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</p>
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<a name="index-MULTILIB_005fREUSE"></a>
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</dd>
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<dt><code>MULTILIB_REUSE</code></dt>
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<dd><p>Sometimes it is desirable to reuse one existing multilib for different
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sets of options. Such kind of reuse can minimize the number of multilib
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variants. And for some targets it is better to reuse an existing multilib
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than to fall back to default multilib when there is no corresponding multilib.
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This can be done by adding reuse rules to <code>MULTILIB_REUSE</code>.
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</p>
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<p>A reuse rule is comprised of two parts connected by equality sign. The left
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part is the option set used to build multilib and the right part is the option
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set that will reuse this multilib. Both parts should only use options
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specified in <code>MULTILIB_OPTIONS</code> and the equality signs found in options
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name should be replaced with periods. The order of options in the left part
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matters and should be same with those specified in <code>MULTILIB_REQUIRED</code> or
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aligned with the order in <code>MULTILIB_OPTIONS</code>. There is no such limitation
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for options in the right part as we don’t build multilib from them.
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</p>
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<p><code>MULTILIB_REUSE</code> is different from <code>MULTILIB_MATCHES</code> in that it
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sets up relations between two option sets rather than two options. Here is an
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example to demo how we reuse libraries built in Thumb mode for applications built
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in ARM mode:
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</p><div class="smallexample">
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<pre class="smallexample"><code>MULTILIB_REUSE</code> = mthumb/march.armv7-r=marm/march.armv7-r
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</pre></div>
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<p>Before the advent of <code>MULTILIB_REUSE</code>, GCC select multilib by comparing command
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line options with options used to build multilib. The <code>MULTILIB_REUSE</code> is
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complementary to that way. Only when the original comparison matches nothing it will
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work to see if it is OK to reuse some existing multilib.
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</p>
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<a name="index-MULTILIB_005fEXTRA_005fOPTS"></a>
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</dd>
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<dt><code>MULTILIB_EXTRA_OPTS</code></dt>
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<dd><p>Sometimes it is desirable that when building multiple versions of
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<samp>libgcc.a</samp> certain options should always be passed on to the
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compiler. In that case, set <code>MULTILIB_EXTRA_OPTS</code> to be the list
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of options to be used for all builds. If you set this, you should
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probably set <code>CRTSTUFF_T_CFLAGS</code> to a dash followed by it.
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</p>
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<a name="index-MULTILIB_005fOSDIRNAMES"></a>
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</dd>
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<dt><code>MULTILIB_OSDIRNAMES</code></dt>
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<dd><p>If <code>MULTILIB_OPTIONS</code> is used, this variable specifies
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a list of subdirectory names, that are used to modify the search
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path depending on the chosen multilib. Unlike <code>MULTILIB_DIRNAMES</code>,
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<code>MULTILIB_OSDIRNAMES</code> describes the multilib directories using
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operating systems conventions, and is applied to the directories such as
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<code>lib</code> or those in the <code>LIBRARY_PATH</code> environment variable.
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The format is either the same as of
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<code>MULTILIB_DIRNAMES</code>, or a set of mappings. When it is the same
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as <code>MULTILIB_DIRNAMES</code>, it describes the multilib directories
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using operating system conventions, rather than GCC conventions. When it is a set
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of mappings of the form <var>gccdir</var>=<var>osdir</var>, the left side gives
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the GCC convention and the right gives the equivalent OS defined
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location. If the <var>osdir</var> part begins with a ‘<samp>!</samp>’,
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GCC will not search in the non-multilib directory and use
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exclusively the multilib directory. Otherwise, the compiler will
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examine the search path for libraries and crt files twice; the first
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time it will add <var>multilib</var> to each directory in the search path,
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the second it will not.
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</p>
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<p>For configurations that support both multilib and multiarch,
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<code>MULTILIB_OSDIRNAMES</code> also encodes the multiarch name, thus
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subsuming <code>MULTIARCH_DIRNAME</code>. The multiarch name is appended to
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each directory name, separated by a colon (e.g.
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‘<samp>../lib32:i386-linux-gnu</samp>’).
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</p>
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<p>Each multiarch subdirectory will be searched before the corresponding OS
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multilib directory, for example ‘<samp>/lib/i386-linux-gnu</samp>’ before
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‘<samp>/lib/../lib32</samp>’. The multiarch name will also be used to modify the
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system header search path, as explained for <code>MULTIARCH_DIRNAME</code>.
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</p>
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<a name="index-MULTIARCH_005fDIRNAME"></a>
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</dd>
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<dt><code>MULTIARCH_DIRNAME</code></dt>
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<dd><p>This variable specifies the multiarch name for configurations that are
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multiarch-enabled but not multilibbed configurations.
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</p>
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<p>The multiarch name is used to augment the search path for libraries, crt
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files and system header files with additional locations. The compiler
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will add a multiarch subdirectory of the form
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<var>prefix</var>/<var>multiarch</var> before each directory in the library and
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crt search path. It will also add two directories
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<code>LOCAL_INCLUDE_DIR</code>/<var>multiarch</var> and
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<code>NATIVE_SYSTEM_HEADER_DIR</code>/<var>multiarch</var>) to the system header
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search path, respectively before <code>LOCAL_INCLUDE_DIR</code> and
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<code>NATIVE_SYSTEM_HEADER_DIR</code>.
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</p>
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<p><code>MULTIARCH_DIRNAME</code> is not used for configurations that support
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both multilib and multiarch. In that case, multiarch names are encoded
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in <code>MULTILIB_OSDIRNAMES</code> instead.
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</p>
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<p>More documentation about multiarch can be found at
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<a href="https://wiki.debian.org/Multiarch">https://wiki.debian.org/Multiarch</a>.
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</p>
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<a name="index-SPECS"></a>
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</dd>
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<dt><code>SPECS</code></dt>
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<dd><p>Unfortunately, setting <code>MULTILIB_EXTRA_OPTS</code> is not enough, since
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it does not affect the build of target libraries, at least not the
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build of the default multilib. One possible work-around is to use
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<code>DRIVER_SELF_SPECS</code> to bring options from the <samp>specs</samp> file
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as if they had been passed in the compiler driver command line.
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However, you don’t want to be adding these options after the toolchain
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is installed, so you can instead tweak the <samp>specs</samp> file that will
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be used during the toolchain build, while you still install the
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original, built-in <samp>specs</samp>. The trick is to set <code>SPECS</code> to
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some other filename (say <samp>specs.install</samp>), that will then be
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created out of the built-in specs, and introduce a <samp>Makefile</samp>
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rule to generate the <samp>specs</samp> file that’s going to be used at
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build time out of your <samp>specs.install</samp>.
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</p>
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</dd>
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<dt><code>T_CFLAGS</code></dt>
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<dd><p>These are extra flags to pass to the C compiler. They are used both
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when building GCC, and when compiling things with the just-built GCC.
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This variable is deprecated and should not be used.
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</p></dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Host-Fragment.html#Host-Fragment" accesskey="n" rel="next">Host Fragment</a>, Up: <a href="Fragments.html#Fragments" accesskey="u" rel="up">Fragments</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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