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     25  1.13    mrg <title>Installing GCC: Building</title>
     26  1.10    mrg 
     27  1.13    mrg <meta name="description" content="Installing GCC: Building">
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     69  1.19    mrg 
     70  1.20    mrg <a class="index-entry-id" id="index-Installing-GCC_003a-Building"></a>
     71  1.10    mrg 
     72  1.10    mrg <p>Now that GCC is configured, you are ready to build the compiler and
     73   1.9    mrg runtime libraries.
     74  1.10    mrg </p>
     75  1.10    mrg <p>Some commands executed when making the compiler may fail (return a
     76  1.20    mrg nonzero status) and be ignored by <code class="command">make</code>.  These failures, which
     77   1.1    mrg are often due to files that were not found, are expected, and can safely
     78   1.1    mrg be ignored.
     79  1.10    mrg </p>
     80  1.10    mrg <p>It is normal to have compiler warnings when compiling certain files.
     81   1.1    mrg Unless you are a GCC developer, you can generally ignore these warnings
     82   1.1    mrg unless they cause compilation to fail.  Developers should attempt to fix
     83   1.1    mrg any warnings encountered, however they can temporarily continue past
     84   1.1    mrg warnings-as-errors by specifying the configure flag
     85  1.20    mrg <samp class="option">--disable-werror</samp>.
     86  1.10    mrg </p>
     87  1.10    mrg <p>On certain old systems, defining certain environment variables such as
     88  1.20    mrg <code class="env">CC</code> can interfere with the functioning of <code class="command">make</code>.
     89  1.10    mrg </p>
     90  1.10    mrg <p>If you encounter seemingly strange errors when trying to build the
     91   1.1    mrg compiler in a directory other than the source directory, it could be
     92   1.1    mrg because you have previously configured the compiler in the source
     93   1.1    mrg directory.  Make sure you have done all the necessary preparations.
     94  1.10    mrg </p>
     95  1.10    mrg <p>If you build GCC on a BSD system using a directory stored in an old System
     96  1.20    mrg V file system, problems may occur in running <code class="command">fixincludes</code> if the
     97  1.10    mrg System V file system doesn&rsquo;t support symbolic links.  These problems
     98  1.20    mrg result in a failure to fix the declaration of <code class="code">size_t</code> in
     99  1.20    mrg <samp class="file">sys/types.h</samp>.  If you find that <code class="code">size_t</code> is a signed type and
    100   1.1    mrg that type mismatches occur, this could be the cause.
    101  1.10    mrg </p>
    102  1.10    mrg <p>The solution is not to use such a directory for building GCC.
    103  1.10    mrg </p>
    104  1.11    mrg <p>Similarly, when building from the source repository or snapshots, or if you modify
    105  1.20    mrg <samp class="file">*.l</samp> files, you need the Flex lexical analyzer generator
    106  1.20    mrg installed.  If you do not modify <samp class="file">*.l</samp> files, releases contain
    107   1.1    mrg the Flex-generated files and you do not need Flex installed to build
    108   1.1    mrg them.  There is still one Flex-based lexical analyzer (part of the
    109   1.1    mrg build machinery, not of GCC itself) that is used even if you only
    110   1.1    mrg build the C front end.
    111  1.10    mrg </p>
    112  1.11    mrg <p>When building from the source repository or snapshots, or if you modify Texinfo
    113   1.1    mrg documentation, you need version 4.7 or later of Texinfo installed if you
    114   1.1    mrg want Info documentation to be regenerated.  Releases contain Info
    115   1.1    mrg documentation pre-built for the unmodified documentation in the release.
    116  1.10    mrg </p>
    117  1.20    mrg <div class="section-level-extent" id="Building-a-native-compiler">
    118  1.20    mrg <h3 class="section"><span>Building a native compiler<a class="copiable-link" href="#Building-a-native-compiler"> &para;</a></span></h3>
    119   1.1    mrg 
    120   1.1    mrg <p>For a native build, the default configuration is to perform
    121  1.20    mrg a 3-stage bootstrap of the compiler when &lsquo;<samp class="samp">make</samp>&rsquo; is invoked.
    122   1.1    mrg This will build the entire GCC system and ensure that it compiles
    123  1.20    mrg itself correctly.  It can be disabled with the <samp class="option">--disable-bootstrap</samp>
    124  1.20    mrg parameter to &lsquo;<samp class="samp">configure</samp>&rsquo;, but bootstrapping is suggested because
    125   1.1    mrg the compiler will be tested more completely and could also have
    126   1.1    mrg better performance.
    127  1.10    mrg </p>
    128  1.10    mrg <p>The bootstrapping process will complete the following steps:
    129  1.10    mrg </p>
    130  1.20    mrg <ul class="itemize mark-bullet">
    131  1.20    mrg <li>Build tools necessary to build the compiler.
    132   1.1    mrg 
    133  1.20    mrg </li><li>Perform a 3-stage bootstrap of the compiler.  This includes building
    134   1.1    mrg three times the target tools for use by the compiler such as binutils
    135   1.1    mrg (bfd, binutils, gas, gprof, ld, and opcodes) if they have been
    136   1.1    mrg individually linked or moved into the top level GCC source tree before
    137   1.1    mrg configuring.
    138   1.1    mrg 
    139  1.20    mrg </li><li>Perform a comparison test of the stage2 and stage3 compilers.
    140   1.1    mrg 
    141  1.20    mrg </li><li>Build runtime libraries using the stage3 compiler from the previous step.
    142   1.1    mrg 
    143  1.10    mrg </li></ul>
    144   1.1    mrg 
    145  1.20    mrg <p>If you are short on disk space you might consider &lsquo;<samp class="samp">make
    146  1.10    mrg bootstrap-lean</samp>&rsquo; instead.  The sequence of compilation is the
    147   1.1    mrg same described above, but object files from the stage1 and
    148   1.1    mrg stage2 of the 3-stage bootstrap of the compiler are deleted as
    149   1.1    mrg soon as they are no longer needed.
    150  1.10    mrg </p>
    151  1.10    mrg <p>If you wish to use non-default GCC flags when compiling the stage2
    152  1.20    mrg and stage3 compilers, set <code class="code">BOOT_CFLAGS</code> on the command line when
    153  1.20    mrg doing &lsquo;<samp class="samp">make</samp>&rsquo;.  For example, if you want to save additional space
    154   1.1    mrg during the bootstrap and in the final installation as well, you can
    155   1.1    mrg build the compiler binaries without debugging information as in the
    156   1.1    mrg following example.  This will save roughly 40% of disk space both for
    157   1.1    mrg the bootstrap and the final installation.  (Libraries will still contain
    158   1.1    mrg debugging information.)
    159  1.10    mrg </p>
    160  1.20    mrg <div class="example smallexample">
    161  1.20    mrg <pre class="example-preformatted">make BOOT_CFLAGS='-O' bootstrap
    162  1.10    mrg </pre></div>
    163   1.1    mrg 
    164  1.20    mrg <p>You can place non-default optimization flags into <code class="code">BOOT_CFLAGS</code>; they
    165  1.20    mrg are less well tested here than the default of &lsquo;<samp class="samp">-g -O2</samp>&rsquo;, but should
    166   1.1    mrg still work.  In a few cases, you may find that you need to specify special
    167  1.20    mrg flags such as <samp class="option">-msoft-float</samp> here to complete the bootstrap; or,
    168   1.1    mrg if the native compiler miscompiles the stage1 compiler, you may need
    169  1.20    mrg to work around this, by choosing <code class="code">BOOT_CFLAGS</code> to avoid the parts
    170  1.20    mrg of the stage1 compiler that were miscompiled, or by using &lsquo;<samp class="samp">make
    171  1.10    mrg bootstrap4</samp>&rsquo; to increase the number of stages of bootstrap.
    172  1.10    mrg </p>
    173  1.20    mrg <p><code class="code">BOOT_CFLAGS</code> does not apply to bootstrapped target libraries.
    174   1.1    mrg Since these are always compiled with the compiler currently being
    175  1.20    mrg bootstrapped, you can use <code class="code">CFLAGS_FOR_TARGET</code> to modify their
    176  1.10    mrg compilation flags, as for non-bootstrapped target libraries.
    177   1.1    mrg Again, if the native compiler miscompiles the stage1 compiler, you may
    178   1.1    mrg need to work around this by avoiding non-working parts of the stage1
    179  1.20    mrg compiler.  Use <code class="code">STAGE1_TFLAGS</code> to this end.
    180  1.10    mrg </p>
    181  1.20    mrg <p>If you used the flag <samp class="option">--enable-languages=&hellip;</samp> to restrict
    182  1.10    mrg the compilers to be built, only those you&rsquo;ve actually enabled will be
    183   1.1    mrg built.  This will of course only build those runtime libraries, for
    184   1.1    mrg which the particular compiler has been built.  Please note,
    185  1.20    mrg that re-defining <code class="env">LANGUAGES</code> when calling &lsquo;<samp class="samp">make</samp>&rsquo;
    186  1.20    mrg <strong class="strong">does not</strong> work anymore!
    187  1.10    mrg </p>
    188  1.10    mrg <p>If the comparison of stage2 and stage3 fails, this normally indicates
    189   1.1    mrg that the stage2 compiler has compiled GCC incorrectly, and is therefore
    190   1.1    mrg a potentially serious bug which you should investigate and report.  (On
    191   1.1    mrg a few systems, meaningful comparison of object files is impossible; they
    192   1.1    mrg always appear &ldquo;different&rdquo;.  If you encounter this problem, you will
    193  1.20    mrg need to disable comparison in the <samp class="file">Makefile</samp>.)
    194  1.10    mrg </p>
    195  1.10    mrg <p>If you do not want to bootstrap your compiler, you can configure with
    196  1.20    mrg <samp class="option">--disable-bootstrap</samp>.  In particular cases, you may want to
    197   1.1    mrg bootstrap your compiler even if the target system is not the same as
    198   1.1    mrg the one you are building on: for example, you could build a
    199  1.20    mrg <code class="code">powerpc-unknown-linux-gnu</code> toolchain on a
    200  1.20    mrg <code class="code">powerpc64-unknown-linux-gnu</code> host.  In this case, pass
    201  1.20    mrg <samp class="option">--enable-bootstrap</samp> to the configure script.
    202  1.10    mrg </p>
    203  1.20    mrg <p><code class="code">BUILD_CONFIG</code> can be used to bring in additional customization
    204  1.10    mrg to the build.  It can be set to a whitespace-separated list of names.
    205  1.20    mrg For each such <code class="code">NAME</code>, top-level <samp class="file">config/<code class="code">NAME</code>.mk</samp> will
    206  1.20    mrg be included by the top-level <samp class="file">Makefile</samp>, bringing in any settings
    207  1.20    mrg it contains.  The default <code class="code">BUILD_CONFIG</code> can be set using the
    208  1.20    mrg configure option <samp class="option">--with-build-config=<code class="code">NAME</code>...</samp>.  Some
    209   1.1    mrg examples of supported build configurations are:
    210  1.10    mrg </p>
    211  1.20    mrg <dl class="table">
    212  1.20    mrg <dt>&lsquo;<samp class="samp">bootstrap-O1</samp>&rsquo;</dt>
    213  1.20    mrg <dd><p>Removes any <samp class="option">-O</samp>-started option from <code class="code">BOOT_CFLAGS</code>, and adds
    214  1.20    mrg <samp class="option">-O1</samp> to it.  &lsquo;<samp class="samp">BUILD_CONFIG=bootstrap-O1</samp>&rsquo; is equivalent to
    215  1.20    mrg &lsquo;<samp class="samp">BOOT_CFLAGS='-g -O1'</samp>&rsquo;.
    216  1.10    mrg </p>
    217  1.10    mrg </dd>
    218  1.20    mrg <dt>&lsquo;<samp class="samp">bootstrap-O3</samp>&rsquo;</dt>
    219  1.20    mrg <dt>&lsquo;<samp class="samp">bootstrap-Og</samp>&rsquo;</dt>
    220  1.20    mrg <dd><p>Analogous to <code class="code">bootstrap-O1</code>.
    221  1.10    mrg </p>
    222  1.10    mrg </dd>
    223  1.20    mrg <dt>&lsquo;<samp class="samp">bootstrap-lto</samp>&rsquo;</dt>
    224  1.10    mrg <dd><p>Enables Link-Time Optimization for host tools during bootstrapping.
    225  1.20    mrg &lsquo;<samp class="samp">BUILD_CONFIG=bootstrap-lto</samp>&rsquo; is equivalent to adding
    226  1.20    mrg <samp class="option">-flto</samp> to &lsquo;<samp class="samp">BOOT_CFLAGS</samp>&rsquo;.  This option assumes that the host
    227   1.5    mrg supports the linker plugin (e.g. GNU ld version 2.21 or later or GNU gold
    228   1.5    mrg version 2.21 or later).
    229  1.10    mrg </p>
    230  1.10    mrg </dd>
    231  1.20    mrg <dt>&lsquo;<samp class="samp">bootstrap-lto-noplugin</samp>&rsquo;</dt>
    232  1.20    mrg <dd><p>This option is similar to <code class="code">bootstrap-lto</code>, but is intended for
    233  1.10    mrg hosts that do not support the linker plugin.  Without the linker plugin 
    234  1.10    mrg static libraries are not compiled with link-time optimizations.  Since 
    235  1.20    mrg the GCC middle end and back end are in <samp class="file">libbackend.a</samp> this means
    236   1.5    mrg that only the front end is actually LTO optimized.
    237  1.10    mrg </p>
    238  1.10    mrg </dd>
    239  1.20    mrg <dt>&lsquo;<samp class="samp">bootstrap-lto-lean</samp>&rsquo;</dt>
    240  1.20    mrg <dd><p>This option is similar to <code class="code">bootstrap-lto</code>, but is intended for
    241  1.12    mrg faster build by only using LTO in the final bootstrap stage.
    242  1.20    mrg With &lsquo;<samp class="samp">make profiledbootstrap</samp>&rsquo; the LTO frontend
    243  1.12    mrg is trained only on generator files.
    244  1.12    mrg </p>
    245  1.12    mrg </dd>
    246  1.20    mrg <dt>&lsquo;<samp class="samp">bootstrap-debug</samp>&rsquo;</dt>
    247  1.10    mrg <dd><p>Verifies that the compiler generates the same executable code, whether
    248   1.1    mrg or not it is asked to emit debug information.  To this end, this
    249   1.1    mrg option builds stage2 host programs without debug information, and uses
    250  1.20    mrg <samp class="file">contrib/compare-debug</samp> to compare them with the stripped stage3
    251  1.20    mrg object files.  If <code class="code">BOOT_CFLAGS</code> is overridden so as to not enable
    252  1.10    mrg debug information, stage2 will have it, and stage3 won&rsquo;t.  This option
    253   1.1    mrg is enabled by default when GCC bootstrapping is enabled, if
    254  1.20    mrg <code class="code">strip</code> can turn object files compiled with and without debug
    255   1.1    mrg info into identical object files.  In addition to better test
    256   1.1    mrg coverage, this option makes default bootstraps faster and leaner.
    257  1.10    mrg </p>
    258  1.10    mrg </dd>
    259  1.20    mrg <dt>&lsquo;<samp class="samp">bootstrap-debug-big</samp>&rsquo;</dt>
    260  1.10    mrg <dd><p>Rather than comparing stripped object files, as in
    261  1.20    mrg <code class="code">bootstrap-debug</code>, this option saves internal compiler dumps
    262   1.1    mrg during stage2 and stage3 and compares them as well, which helps catch
    263   1.1    mrg additional potential problems, but at a great cost in terms of disk
    264  1.20    mrg space.  It can be specified in addition to &lsquo;<samp class="samp">bootstrap-debug</samp>&rsquo;.
    265  1.10    mrg </p>
    266  1.10    mrg </dd>
    267  1.20    mrg <dt>&lsquo;<samp class="samp">bootstrap-debug-lean</samp>&rsquo;</dt>
    268  1.20    mrg <dd><p>This option saves disk space compared with <code class="code">bootstrap-debug-big</code>,
    269   1.1    mrg but at the expense of some recompilation.  Instead of saving the dumps
    270   1.1    mrg of stage2 and stage3 until the final compare, it uses
    271  1.20    mrg <samp class="option">-fcompare-debug</samp> to generate, compare and remove the dumps
    272   1.1    mrg during stage3, repeating the compilation that already took place in
    273   1.1    mrg stage2, whose dumps were not saved.
    274  1.10    mrg </p>
    275  1.10    mrg </dd>
    276  1.20    mrg <dt>&lsquo;<samp class="samp">bootstrap-debug-lib</samp>&rsquo;</dt>
    277  1.10    mrg <dd><p>This option tests executable code invariance over debug information
    278  1.20    mrg generation on target libraries, just like <code class="code">bootstrap-debug-lean</code>
    279   1.1    mrg tests it on host programs.  It builds stage3 libraries with
    280  1.20    mrg <samp class="option">-fcompare-debug</samp>, and it can be used along with any of the
    281  1.20    mrg <code class="code">bootstrap-debug</code> options above.
    282  1.10    mrg </p>
    283  1.20    mrg <p>There aren&rsquo;t <code class="code">-lean</code> or <code class="code">-big</code> counterparts to this option
    284   1.1    mrg because most libraries are only build in stage3, so bootstrap compares
    285   1.1    mrg would not get significant coverage.  Moreover, the few libraries built
    286  1.10    mrg in stage2 are used in stage3 host programs, so we wouldn&rsquo;t want to
    287   1.1    mrg compile stage2 libraries with different options for comparison purposes.
    288  1.10    mrg </p>
    289  1.10    mrg </dd>
    290  1.20    mrg <dt>&lsquo;<samp class="samp">bootstrap-debug-ckovw</samp>&rsquo;</dt>
    291  1.10    mrg <dd><p>Arranges for error messages to be issued if the compiler built on any
    292  1.20    mrg stage is run without the option <samp class="option">-fcompare-debug</samp>.  This is
    293  1.20    mrg useful to verify the full <samp class="option">-fcompare-debug</samp> testing coverage.  It
    294  1.20    mrg must be used along with <code class="code">bootstrap-debug-lean</code> and
    295  1.20    mrg <code class="code">bootstrap-debug-lib</code>.
    296  1.10    mrg </p>
    297  1.10    mrg </dd>
    298  1.20    mrg <dt>&lsquo;<samp class="samp">bootstrap-cet</samp>&rsquo;</dt>
    299  1.10    mrg <dd><p>This option enables Intel CET for host tools during bootstrapping.
    300  1.20    mrg &lsquo;<samp class="samp">BUILD_CONFIG=bootstrap-cet</samp>&rsquo; is equivalent to adding
    301  1.20    mrg <samp class="option">-fcf-protection</samp> to &lsquo;<samp class="samp">BOOT_CFLAGS</samp>&rsquo;.  This option
    302  1.10    mrg assumes that the host supports Intel CET (e.g. GNU assembler version
    303  1.10    mrg 2.30 or later).
    304  1.10    mrg </p>
    305  1.10    mrg </dd>
    306  1.20    mrg <dt>&lsquo;<samp class="samp">bootstrap-time</samp>&rsquo;</dt>
    307  1.10    mrg <dd><p>Arranges for the run time of each program started by the GCC driver,
    308  1.20    mrg built in any stage, to be logged to <samp class="file">time.log</samp>, in the top level of
    309   1.1    mrg the build tree.
    310  1.10    mrg </p>
    311  1.10    mrg </dd>
    312  1.20    mrg <dt>&lsquo;<samp class="samp">bootstrap-asan</samp>&rsquo;</dt>
    313  1.13    mrg <dd><p>Compiles GCC itself using Address Sanitization in order to catch invalid memory
    314  1.13    mrg accesses within the GCC code.
    315  1.13    mrg </p>
    316  1.13    mrg </dd>
    317  1.20    mrg <dt>&lsquo;<samp class="samp">bootstrap-hwasan</samp>&rsquo;</dt>
    318  1.16    mrg <dd><p>Compiles GCC itself using HWAddress Sanitization in order to catch invalid
    319  1.16    mrg memory accesses within the GCC code.  This option is only available on AArch64
    320  1.16    mrg systems that are running Linux kernel version 5.4 or later.
    321  1.16    mrg </p>
    322  1.16    mrg </dd>
    323  1.10    mrg </dl>
    324   1.1    mrg 
    325  1.20    mrg </div>
    326  1.20    mrg <div class="section-level-extent" id="Building-a-cross-compiler">
    327  1.20    mrg <h3 class="section"><span>Building a cross compiler<a class="copiable-link" href="#Building-a-cross-compiler"> &para;</a></span></h3>
    328   1.1    mrg 
    329   1.1    mrg <p>When building a cross compiler, it is not generally possible to do a
    330   1.1    mrg 3-stage bootstrap of the compiler.  This makes for an interesting problem
    331   1.1    mrg as parts of GCC can only be built with GCC.
    332  1.10    mrg </p>
    333  1.10    mrg <p>To build a cross compiler, we recommend first building and installing a
    334   1.1    mrg native compiler.  You can then use the native GCC compiler to build the
    335   1.1    mrg cross compiler.  The installed native compiler needs to be GCC version
    336   1.1    mrg 2.95 or later.
    337  1.10    mrg </p>
    338  1.10    mrg <p>Assuming you have already installed a native copy of GCC and configured
    339  1.20    mrg your cross compiler, issue the command <code class="command">make</code>, which performs the
    340   1.1    mrg following steps:
    341  1.10    mrg </p>
    342  1.20    mrg <ul class="itemize mark-bullet">
    343  1.20    mrg <li>Build host tools necessary to build the compiler.
    344   1.1    mrg 
    345  1.20    mrg </li><li>Build target tools for use by the compiler such as binutils (bfd,
    346   1.1    mrg binutils, gas, gprof, ld, and opcodes)
    347   1.1    mrg if they have been individually linked or moved into the top level GCC source
    348   1.1    mrg tree before configuring.
    349   1.1    mrg 
    350  1.20    mrg </li><li>Build the compiler (single stage only).
    351   1.9    mrg 
    352  1.20    mrg </li><li>Build runtime libraries using the compiler from the previous step.
    353  1.10    mrg </li></ul>
    354   1.1    mrg 
    355  1.10    mrg <p>Note that if an error occurs in any step the make process will exit.
    356  1.10    mrg </p>
    357  1.10    mrg <p>If you are not building GNU binutils in the same source tree as GCC,
    358   1.1    mrg you will need a cross-assembler and cross-linker installed before
    359   1.1    mrg configuring GCC.  Put them in the directory
    360  1.20    mrg <samp class="file"><var class="var">prefix</var>/<var class="var">target</var>/bin</samp>.  Here is a table of the tools
    361   1.1    mrg you should put in this directory:
    362  1.10    mrg </p>
    363  1.20    mrg <dl class="table">
    364  1.20    mrg <dt><samp class="file">as</samp></dt>
    365  1.10    mrg <dd><p>This should be the cross-assembler.
    366  1.10    mrg </p>
    367  1.10    mrg </dd>
    368  1.20    mrg <dt><samp class="file">ld</samp></dt>
    369  1.10    mrg <dd><p>This should be the cross-linker.
    370  1.10    mrg </p>
    371  1.10    mrg </dd>
    372  1.20    mrg <dt><samp class="file">ar</samp></dt>
    373  1.10    mrg <dd><p>This should be the cross-archiver: a program which can manipulate
    374  1.10    mrg archive files (linker libraries) in the target machine&rsquo;s format.
    375  1.10    mrg </p>
    376  1.10    mrg </dd>
    377  1.20    mrg <dt><samp class="file">ranlib</samp></dt>
    378  1.10    mrg <dd><p>This should be a program to construct a symbol table in an archive file.
    379  1.10    mrg </p></dd>
    380   1.1    mrg </dl>
    381   1.1    mrg 
    382  1.10    mrg <p>The installation of GCC will find these programs in that directory,
    383   1.1    mrg and copy or link them to the proper place to for the cross-compiler to
    384   1.1    mrg find them when run later.
    385  1.10    mrg </p>
    386  1.10    mrg <p>The easiest way to provide these files is to build the Binutils package.
    387  1.20    mrg Configure it with the same <samp class="option">--host</samp> and <samp class="option">--target</samp>
    388   1.1    mrg options that you use for configuring GCC, then build and install
    389   1.1    mrg them.  They install their executables automatically into the proper
    390   1.1    mrg directory.  Alas, they do not support all the targets that GCC
    391   1.1    mrg supports.
    392  1.10    mrg </p>
    393  1.10    mrg <p>If you are not building a C library in the same source tree as GCC,
    394   1.1    mrg you should also provide the target libraries and headers before
    395   1.1    mrg configuring GCC, specifying the directories with
    396  1.20    mrg <samp class="option">--with-sysroot</samp> or <samp class="option">--with-headers</samp> and
    397  1.20    mrg <samp class="option">--with-libs</samp>.  Many targets also require &ldquo;start files&rdquo; such
    398  1.20    mrg as <samp class="file">crt0.o</samp> and
    399  1.20    mrg <samp class="file">crtn.o</samp> which are linked into each executable.  There may be several
    400  1.20    mrg alternatives for <samp class="file">crt0.o</samp>, for use with profiling or other
    401  1.10    mrg compilation options.  Check your target&rsquo;s definition of
    402  1.20    mrg <code class="code">STARTFILE_SPEC</code> to find out what start files it uses.
    403  1.10    mrg </p>
    404  1.20    mrg </div>
    405  1.20    mrg <div class="section-level-extent" id="Building-in-parallel">
    406  1.20    mrg <h3 class="section"><span>Building in parallel<a class="copiable-link" href="#Building-in-parallel"> &para;</a></span></h3>
    407   1.1    mrg 
    408   1.1    mrg <p>GNU Make 3.80 and above, which is necessary to build GCC, support
    409  1.20    mrg building in parallel.  To activate this, you can use &lsquo;<samp class="samp">make -j 2</samp>&rsquo;
    410  1.20    mrg instead of &lsquo;<samp class="samp">make</samp>&rsquo;.  You can also specify a bigger number, and
    411   1.1    mrg in most cases using a value greater than the number of processors in
    412   1.1    mrg your machine will result in fewer and shorter I/O latency hits, thus
    413   1.1    mrg improving overall throughput; this is especially true for slow drives
    414   1.1    mrg and network filesystems.
    415  1.10    mrg </p>
    416  1.20    mrg </div>
    417  1.20    mrg <div class="section-level-extent" id="Building-the-Ada-compiler">
    418  1.20    mrg <h3 class="section"><span>Building the Ada compiler<a class="copiable-link" href="#Building-the-Ada-compiler"> &para;</a></span></h3>
    419   1.1    mrg 
    420  1.20    mrg <p><a class="uref" href="prerequisites.html#GNAT-prerequisite">GNAT prerequisites</a>.
    421  1.10    mrg </p>
    422  1.20    mrg </div>
    423  1.20    mrg <div class="section-level-extent" id="Building-the-D-compiler">
    424  1.20    mrg <h3 class="section"><span>Building the D compiler<a class="copiable-link" href="#Building-the-D-compiler"> &para;</a></span></h3>
    425  1.16    mrg 
    426  1.20    mrg <p><a class="uref" href="prerequisites.html#GDC-prerequisite">GDC prerequisites</a>.
    427  1.16    mrg </p>
    428  1.20    mrg </div>
    429  1.20    mrg <div class="section-level-extent" id="Building-with-profile-feedback">
    430  1.20    mrg <h3 class="section"><span>Building with profile feedback<a class="copiable-link" href="#Building-with-profile-feedback"> &para;</a></span></h3>
    431   1.1    mrg 
    432   1.1    mrg <p>It is possible to use profile feedback to optimize the compiler itself.  This
    433   1.1    mrg should result in a faster compiler binary.  Experiments done on x86 using gcc
    434   1.1    mrg 3.3 showed approximately 7 percent speedup on compiling C programs.  To
    435  1.20    mrg bootstrap the compiler with profile feedback, use <code class="code">make profiledbootstrap</code>.
    436  1.10    mrg </p>
    437  1.20    mrg <p>When &lsquo;<samp class="samp">make profiledbootstrap</samp>&rsquo; is run, it will first build a <code class="code">stage1</code>
    438  1.20    mrg compiler.  This compiler is used to build a <code class="code">stageprofile</code> compiler
    439   1.1    mrg instrumented to collect execution counts of instruction and branch
    440  1.20    mrg probabilities.  Training run is done by building <code class="code">stagetrain</code>
    441  1.20    mrg compiler.  Finally a <code class="code">stagefeedback</code> compiler is built
    442  1.10    mrg using the information collected.
    443  1.10    mrg </p>
    444  1.10    mrg <p>Unlike standard bootstrap, several additional restrictions apply.  The
    445  1.20    mrg compiler used to build <code class="code">stage1</code> needs to support a 64-bit integral type.
    446   1.8    mrg It is recommended to only use GCC for this.
    447  1.10    mrg </p>
    448  1.10    mrg <p>On Linux/x86_64 hosts with some restrictions (no virtualization) it is
    449  1.20    mrg also possible to do autofdo build with &lsquo;<samp class="samp">make
    450  1.19    mrg autoprofiledbootstrap</samp>&rsquo;. This uses Linux perf to sample branches in the
    451  1.10    mrg binary and then rebuild it with feedback derived from the profile.
    452  1.20    mrg Linux perf and the <code class="code">autofdo</code> toolkit needs to be installed for
    453   1.9    mrg this.
    454  1.10    mrg </p>
    455  1.10    mrg <p>Only the profile from the current build is used, so when an error
    456   1.9    mrg occurs it is recommended to clean before restarting. Otherwise
    457   1.9    mrg the code quality may be much worse.
    458  1.10    mrg </p>
    459  1.10    mrg <hr />
    460  1.10    mrg <p>
    461  1.20    mrg <p><a class="uref" href="./index.html">Return to the GCC Installation page</a>
    462  1.10    mrg </p>
    463  1.10    mrg 
    464  1.10    mrg 
    465  1.10    mrg 
    466  1.10    mrg 
    467  1.10    mrg 
    468  1.10    mrg 
    469  1.20    mrg </div>
    470   1.8    mrg 
    471   1.8    mrg 
    472   1.7    mrg 
    473  1.10    mrg </body>
    474  1.10    mrg </html>
    475