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