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     42 <h1 class="settitle">Installing GCC: Building</h1>
     43 <a name="index-Installing-GCC_003a-Building-1"></a>
     44 Now that GCC is configured, you are ready to build the compiler and
     45 runtime libraries.
     46 
     47    <p>Some commands executed when making the compiler may fail (return a
     48 nonzero status) and be ignored by <samp><span class="command">make</span></samp>.  These failures, which
     49 are often due to files that were not found, are expected, and can safely
     50 be ignored.
     51 
     52    <p>It is normal to have compiler warnings when compiling certain files. 
     53 Unless you are a GCC developer, you can generally ignore these warnings
     54 unless they cause compilation to fail.  Developers should attempt to fix
     55 any warnings encountered, however they can temporarily continue past
     56 warnings-as-errors by specifying the configure flag
     57 <samp><span class="option">--disable-werror</span></samp>.
     58 
     59    <p>On certain old systems, defining certain environment variables such as
     60 <samp><span class="env">CC</span></samp> can interfere with the functioning of <samp><span class="command">make</span></samp>.
     61 
     62    <p>If you encounter seemingly strange errors when trying to build the
     63 compiler in a directory other than the source directory, it could be
     64 because you have previously configured the compiler in the source
     65 directory.  Make sure you have done all the necessary preparations.
     66 
     67    <p>If you build GCC on a BSD system using a directory stored in an old System
     68 V file system, problems may occur in running <samp><span class="command">fixincludes</span></samp> if the
     69 System V file system doesn't support symbolic links.  These problems
     70 result in a failure to fix the declaration of <code>size_t</code> in
     71 <samp><span class="file">sys/types.h</span></samp>.  If you find that <code>size_t</code> is a signed type and
     72 that type mismatches occur, this could be the cause.
     73 
     74    <p>The solution is not to use such a directory for building GCC.
     75 
     76    <p>Similarly, when building from SVN or snapshots, or if you modify
     77 <samp><span class="file">*.l</span></samp> files, you need the Flex lexical analyzer generator
     78 installed.  If you do not modify <samp><span class="file">*.l</span></samp> files, releases contain
     79 the Flex-generated files and you do not need Flex installed to build
     80 them.  There is still one Flex-based lexical analyzer (part of the
     81 build machinery, not of GCC itself) that is used even if you only
     82 build the C front end.
     83 
     84    <p>When building from SVN or snapshots, or if you modify Texinfo
     85 documentation, you need version 4.7 or later of Texinfo installed if you
     86 want Info documentation to be regenerated.  Releases contain Info
     87 documentation pre-built for the unmodified documentation in the release.
     88 
     89 <h3 class="section"><a name="TOC0"></a>Building a native compiler</h3>
     90 
     91 <p>For a native build, the default configuration is to perform
     92 a 3-stage bootstrap of the compiler when &lsquo;<samp><span class="samp">make</span></samp>&rsquo; is invoked. 
     93 This will build the entire GCC system and ensure that it compiles
     94 itself correctly.  It can be disabled with the <samp><span class="option">--disable-bootstrap</span></samp>
     95 parameter to &lsquo;<samp><span class="samp">configure</span></samp>&rsquo;, but bootstrapping is suggested because
     96 the compiler will be tested more completely and could also have
     97 better performance.
     98 
     99    <p>The bootstrapping process will complete the following steps:
    100 
    101      <ul>
    102 <li>Build tools necessary to build the compiler.
    103 
    104      <li>Perform a 3-stage bootstrap of the compiler.  This includes building
    105 three times the target tools for use by the compiler such as binutils
    106 (bfd, binutils, gas, gprof, ld, and opcodes) if they have been
    107 individually linked or moved into the top level GCC source tree before
    108 configuring.
    109 
    110      <li>Perform a comparison test of the stage2 and stage3 compilers.
    111 
    112      <li>Build runtime libraries using the stage3 compiler from the previous step.
    113 
    114    </ul>
    115 
    116    <p>If you are short on disk space you might consider &lsquo;<samp><span class="samp">make
    117 bootstrap-lean</span></samp>&rsquo; instead.  The sequence of compilation is the
    118 same described above, but object files from the stage1 and
    119 stage2 of the 3-stage bootstrap of the compiler are deleted as
    120 soon as they are no longer needed.
    121 
    122    <p>If you wish to use non-default GCC flags when compiling the stage2
    123 and stage3 compilers, set <code>BOOT_CFLAGS</code> on the command line when
    124 doing &lsquo;<samp><span class="samp">make</span></samp>&rsquo;.  For example, if you want to save additional space
    125 during the bootstrap and in the final installation as well, you can
    126 build the compiler binaries without debugging information as in the
    127 following example.  This will save roughly 40% of disk space both for
    128 the bootstrap and the final installation.  (Libraries will still contain
    129 debugging information.)
    130 
    131 <pre class="smallexample">     make BOOT_CFLAGS='-O' bootstrap
    132 </pre>
    133    <p>You can place non-default optimization flags into <code>BOOT_CFLAGS</code>; they
    134 are less well tested here than the default of &lsquo;<samp><span class="samp">-g -O2</span></samp>&rsquo;, but should
    135 still work.  In a few cases, you may find that you need to specify special
    136 flags such as <samp><span class="option">-msoft-float</span></samp> here to complete the bootstrap; or,
    137 if the native compiler miscompiles the stage1 compiler, you may need
    138 to work around this, by choosing <code>BOOT_CFLAGS</code> to avoid the parts
    139 of the stage1 compiler that were miscompiled, or by using &lsquo;<samp><span class="samp">make
    140 bootstrap4</span></samp>&rsquo; to increase the number of stages of bootstrap.
    141 
    142    <p><code>BOOT_CFLAGS</code> does not apply to bootstrapped target libraries. 
    143 Since these are always compiled with the compiler currently being
    144 bootstrapped, you can use <code>CFLAGS_FOR_TARGET</code> to modify their
    145 compilation flags, as for non-bootstrapped target libraries. 
    146 Again, if the native compiler miscompiles the stage1 compiler, you may
    147 need to work around this by avoiding non-working parts of the stage1
    148 compiler.  Use <code>STAGE1_TFLAGS</code> to this end.
    149 
    150    <p>If you used the flag <samp><span class="option">--enable-languages=...</span></samp> to restrict
    151 the compilers to be built, only those you've actually enabled will be
    152 built.  This will of course only build those runtime libraries, for
    153 which the particular compiler has been built.  Please note,
    154 that re-defining <samp><span class="env">LANGUAGES</span></samp> when calling &lsquo;<samp><span class="samp">make</span></samp>&rsquo;
    155 <strong>does not</strong> work anymore!
    156 
    157    <p>If the comparison of stage2 and stage3 fails, this normally indicates
    158 that the stage2 compiler has compiled GCC incorrectly, and is therefore
    159 a potentially serious bug which you should investigate and report.  (On
    160 a few systems, meaningful comparison of object files is impossible; they
    161 always appear &ldquo;different&rdquo;.  If you encounter this problem, you will
    162 need to disable comparison in the <samp><span class="file">Makefile</span></samp>.)
    163 
    164    <p>If you do not want to bootstrap your compiler, you can configure with
    165 <samp><span class="option">--disable-bootstrap</span></samp>.  In particular cases, you may want to
    166 bootstrap your compiler even if the target system is not the same as
    167 the one you are building on: for example, you could build a
    168 <code>powerpc-unknown-linux-gnu</code> toolchain on a
    169 <code>powerpc64-unknown-linux-gnu</code> host.  In this case, pass
    170 <samp><span class="option">--enable-bootstrap</span></samp> to the configure script.
    171 
    172    <p><code>BUILD_CONFIG</code> can be used to bring in additional customization
    173 to the build.  It can be set to a whitespace-separated list of names. 
    174 For each such <code>NAME</code>, top-level <samp><span class="file">config/</span><code>NAME</code><span class="file">.mk</span></samp> will
    175 be included by the top-level <samp><span class="file">Makefile</span></samp>, bringing in any settings
    176 it contains.  The default <code>BUILD_CONFIG</code> can be set using the
    177 configure option <samp><span class="option">--with-build-config=</span><code>NAME</code><span class="option">...</span></samp>.  Some
    178 examples of supported build configurations are:
    179 
    180      <dl>
    181 <dt>&lsquo;<samp><span class="samp">bootstrap-O1</span></samp>&rsquo;<dd>Removes any <samp><span class="option">-O</span></samp>-started option from <code>BOOT_CFLAGS</code>, and adds
    182 <samp><span class="option">-O1</span></samp> to it.  &lsquo;<samp><span class="samp">BUILD_CONFIG=bootstrap-O1</span></samp>&rsquo; is equivalent to
    183 &lsquo;<samp><span class="samp">BOOT_CFLAGS='-g -O1'</span></samp>&rsquo;.
    184 
    185      <br><dt>&lsquo;<samp><span class="samp">bootstrap-O3</span></samp>&rsquo;<dd>Analogous to <code>bootstrap-O1</code>.
    186 
    187      <br><dt>&lsquo;<samp><span class="samp">bootstrap-lto</span></samp>&rsquo;<dd>Enables Link-Time Optimization for host tools during bootstrapping. 
    188 &lsquo;<samp><span class="samp">BUILD_CONFIG=bootstrap-lto</span></samp>&rsquo; is equivalent to adding
    189 <samp><span class="option">-flto</span></samp> to &lsquo;<samp><span class="samp">BOOT_CFLAGS</span></samp>&rsquo;.
    190 
    191      <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug</span></samp>&rsquo;<dd>Verifies that the compiler generates the same executable code, whether
    192 or not it is asked to emit debug information.  To this end, this
    193 option builds stage2 host programs without debug information, and uses
    194 <samp><span class="file">contrib/compare-debug</span></samp> to compare them with the stripped stage3
    195 object files.  If <code>BOOT_CFLAGS</code> is overridden so as to not enable
    196 debug information, stage2 will have it, and stage3 won't.  This option
    197 is enabled by default when GCC bootstrapping is enabled, if
    198 <code>strip</code> can turn object files compiled with and without debug
    199 info into identical object files.  In addition to better test
    200 coverage, this option makes default bootstraps faster and leaner.
    201 
    202      <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug-big</span></samp>&rsquo;<dd>Rather than comparing stripped object files, as in
    203 <code>bootstrap-debug</code>, this option saves internal compiler dumps
    204 during stage2 and stage3 and compares them as well, which helps catch
    205 additional potential problems, but at a great cost in terms of disk
    206 space.  It can be specified in addition to &lsquo;<samp><span class="samp">bootstrap-debug</span></samp>&rsquo;.
    207 
    208      <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug-lean</span></samp>&rsquo;<dd>This option saves disk space compared with <code>bootstrap-debug-big</code>,
    209 but at the expense of some recompilation.  Instead of saving the dumps
    210 of stage2 and stage3 until the final compare, it uses
    211 <samp><span class="option">-fcompare-debug</span></samp> to generate, compare and remove the dumps
    212 during stage3, repeating the compilation that already took place in
    213 stage2, whose dumps were not saved.
    214 
    215      <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug-lib</span></samp>&rsquo;<dd>This option tests executable code invariance over debug information
    216 generation on target libraries, just like <code>bootstrap-debug-lean</code>
    217 tests it on host programs.  It builds stage3 libraries with
    218 <samp><span class="option">-fcompare-debug</span></samp>, and it can be used along with any of the
    219 <code>bootstrap-debug</code> options above.
    220 
    221      <p>There aren't <code>-lean</code> or <code>-big</code> counterparts to this option
    222 because most libraries are only build in stage3, so bootstrap compares
    223 would not get significant coverage.  Moreover, the few libraries built
    224 in stage2 are used in stage3 host programs, so we wouldn't want to
    225 compile stage2 libraries with different options for comparison purposes.
    226 
    227      <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug-ckovw</span></samp>&rsquo;<dd>Arranges for error messages to be issued if the compiler built on any
    228 stage is run without the option <samp><span class="option">-fcompare-debug</span></samp>.  This is
    229 useful to verify the full <samp><span class="option">-fcompare-debug</span></samp> testing coverage.  It
    230 must be used along with <code>bootstrap-debug-lean</code> and
    231 <code>bootstrap-debug-lib</code>.
    232 
    233      <br><dt>&lsquo;<samp><span class="samp">bootstrap-time</span></samp>&rsquo;<dd>Arranges for the run time of each program started by the GCC driver,
    234 built in any stage, to be logged to <samp><span class="file">time.log</span></samp>, in the top level of
    235 the build tree.
    236 
    237    </dl>
    238 
    239 <h3 class="section"><a name="TOC1"></a>Building a cross compiler</h3>
    240 
    241 <p>When building a cross compiler, it is not generally possible to do a
    242 3-stage bootstrap of the compiler.  This makes for an interesting problem
    243 as parts of GCC can only be built with GCC.
    244 
    245    <p>To build a cross compiler, we recommend first building and installing a
    246 native compiler.  You can then use the native GCC compiler to build the
    247 cross compiler.  The installed native compiler needs to be GCC version
    248 2.95 or later.
    249 
    250    <p>If the cross compiler is to be built with support for the Java
    251 programming language and the ability to compile .java source files is
    252 desired, the installed native compiler used to build the cross
    253 compiler needs to be the same GCC version as the cross compiler.  In
    254 addition the cross compiler needs to be configured with
    255 <samp><span class="option">--with-ecj-jar=...</span></samp>.
    256 
    257    <p>Assuming you have already installed a native copy of GCC and configured
    258 your cross compiler, issue the command <samp><span class="command">make</span></samp>, which performs the
    259 following steps:
    260 
    261      <ul>
    262 <li>Build host tools necessary to build the compiler.
    263 
    264      <li>Build target tools for use by the compiler such as binutils (bfd,
    265 binutils, gas, gprof, ld, and opcodes)
    266 if they have been individually linked or moved into the top level GCC source
    267 tree before configuring.
    268 
    269      <li>Build the compiler (single stage only).
    270 
    271      <li>Build runtime libraries using the compiler from the previous step. 
    272 </ul>
    273 
    274    <p>Note that if an error occurs in any step the make process will exit.
    275 
    276    <p>If you are not building GNU binutils in the same source tree as GCC,
    277 you will need a cross-assembler and cross-linker installed before
    278 configuring GCC.  Put them in the directory
    279 <samp><var>prefix</var><span class="file">/</span><var>target</var><span class="file">/bin</span></samp>.  Here is a table of the tools
    280 you should put in this directory:
    281 
    282      <dl>
    283 <dt><samp><span class="file">as</span></samp><dd>This should be the cross-assembler.
    284 
    285      <br><dt><samp><span class="file">ld</span></samp><dd>This should be the cross-linker.
    286 
    287      <br><dt><samp><span class="file">ar</span></samp><dd>This should be the cross-archiver: a program which can manipulate
    288 archive files (linker libraries) in the target machine's format.
    289 
    290      <br><dt><samp><span class="file">ranlib</span></samp><dd>This should be a program to construct a symbol table in an archive file. 
    291 </dl>
    292 
    293    <p>The installation of GCC will find these programs in that directory,
    294 and copy or link them to the proper place to for the cross-compiler to
    295 find them when run later.
    296 
    297    <p>The easiest way to provide these files is to build the Binutils package. 
    298 Configure it with the same <samp><span class="option">--host</span></samp> and <samp><span class="option">--target</span></samp>
    299 options that you use for configuring GCC, then build and install
    300 them.  They install their executables automatically into the proper
    301 directory.  Alas, they do not support all the targets that GCC
    302 supports.
    303 
    304    <p>If you are not building a C library in the same source tree as GCC,
    305 you should also provide the target libraries and headers before
    306 configuring GCC, specifying the directories with
    307 <samp><span class="option">--with-sysroot</span></samp> or <samp><span class="option">--with-headers</span></samp> and
    308 <samp><span class="option">--with-libs</span></samp>.  Many targets also require &ldquo;start files&rdquo; such
    309 as <samp><span class="file">crt0.o</span></samp> and
    310 <samp><span class="file">crtn.o</span></samp> which are linked into each executable.  There may be several
    311 alternatives for <samp><span class="file">crt0.o</span></samp>, for use with profiling or other
    312 compilation options.  Check your target's definition of
    313 <code>STARTFILE_SPEC</code> to find out what start files it uses.
    314 
    315 <h3 class="section"><a name="TOC2"></a>Building in parallel</h3>
    316 
    317 <p>GNU Make 3.80 and above, which is necessary to build GCC, support
    318 building in parallel.  To activate this, you can use &lsquo;<samp><span class="samp">make -j 2</span></samp>&rsquo;
    319 instead of &lsquo;<samp><span class="samp">make</span></samp>&rsquo;.  You can also specify a bigger number, and
    320 in most cases using a value greater than the number of processors in
    321 your machine will result in fewer and shorter I/O latency hits, thus
    322 improving overall throughput; this is especially true for slow drives
    323 and network filesystems.
    324 
    325 <h3 class="section"><a name="TOC3"></a>Building the Ada compiler</h3>
    326 
    327 <p>In order to build GNAT, the Ada compiler, you need a working GNAT
    328 compiler (GCC version 4.0 or later). 
    329 This includes GNAT tools such as <samp><span class="command">gnatmake</span></samp> and
    330 <samp><span class="command">gnatlink</span></samp>, since the Ada front end is written in Ada and
    331 uses some GNAT-specific extensions.
    332 
    333    <p>In order to build a cross compiler, it is suggested to install
    334 the new compiler as native first, and then use it to build the cross
    335 compiler.
    336 
    337    <p><samp><span class="command">configure</span></samp> does not test whether the GNAT installation works
    338 and has a sufficiently recent version; if too old a GNAT version is
    339 installed, the build will fail unless <samp><span class="option">--enable-languages</span></samp> is
    340 used to disable building the Ada front end.
    341 
    342    <p><samp><span class="env">ADA_INCLUDE_PATH</span></samp> and <samp><span class="env">ADA_OBJECT_PATH</span></samp> environment variables
    343 must not be set when building the Ada compiler, the Ada tools, or the
    344 Ada runtime libraries. You can check that your build environment is clean
    345 by verifying that &lsquo;<samp><span class="samp">gnatls -v</span></samp>&rsquo; lists only one explicit path in each
    346 section.
    347 
    348 <h3 class="section"><a name="TOC4"></a>Building with profile feedback</h3>
    349 
    350 <p>It is possible to use profile feedback to optimize the compiler itself.  This
    351 should result in a faster compiler binary.  Experiments done on x86 using gcc
    352 3.3 showed approximately 7 percent speedup on compiling C programs.  To
    353 bootstrap the compiler with profile feedback, use <code>make profiledbootstrap</code>.
    354 
    355    <p>When &lsquo;<samp><span class="samp">make profiledbootstrap</span></samp>&rsquo; is run, it will first build a <code>stage1</code>
    356 compiler.  This compiler is used to build a <code>stageprofile</code> compiler
    357 instrumented to collect execution counts of instruction and branch
    358 probabilities.  Then runtime libraries are compiled with profile collected. 
    359 Finally a <code>stagefeedback</code> compiler is built using the information collected.
    360 
    361    <p>Unlike standard bootstrap, several additional restrictions apply.  The
    362 compiler used to build <code>stage1</code> needs to support a 64-bit integral type. 
    363 It is recommended to only use GCC for this.  Also parallel make is currently
    364 not supported since collisions in profile collecting may occur.
    365 
    366    <p><hr />
    367 <p><a href="./index.html">Return to the GCC Installation page</a>
    368 
    369 <!-- ***Testing***************************************************************** -->
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    371 <!-- ***Binaries**************************************************************** -->
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    373 <!-- ***Old documentation****************************************************** -->
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    375 <!-- *************************************************************************** -->
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