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     44 <h1 class="settitle">Installing GCC: Building</h1>
     45 <a name="index-Installing-GCC_003a-Building-1"></a>
     46 Now that GCC is configured, you are ready to build the compiler and
     47 runtime libraries.
     48 
     49    <p>Some commands executed when making the compiler may fail (return a
     50 nonzero status) and be ignored by <samp><span class="command">make</span></samp>.  These failures, which
     51 are often due to files that were not found, are expected, and can safely
     52 be ignored.
     53 
     54    <p>It is normal to have compiler warnings when compiling certain files. 
     55 Unless you are a GCC developer, you can generally ignore these warnings
     56 unless they cause compilation to fail.  Developers should attempt to fix
     57 any warnings encountered, however they can temporarily continue past
     58 warnings-as-errors by specifying the configure flag
     59 <samp><span class="option">--disable-werror</span></samp>.
     60 
     61    <p>On certain old systems, defining certain environment variables such as
     62 <samp><span class="env">CC</span></samp> can interfere with the functioning of <samp><span class="command">make</span></samp>.
     63 
     64    <p>If you encounter seemingly strange errors when trying to build the
     65 compiler in a directory other than the source directory, it could be
     66 because you have previously configured the compiler in the source
     67 directory.  Make sure you have done all the necessary preparations.
     68 
     69    <p>If you build GCC on a BSD system using a directory stored in an old System
     70 V file system, problems may occur in running <samp><span class="command">fixincludes</span></samp> if the
     71 System V file system doesn't support symbolic links.  These problems
     72 result in a failure to fix the declaration of <code>size_t</code> in
     73 <samp><span class="file">sys/types.h</span></samp>.  If you find that <code>size_t</code> is a signed type and
     74 that type mismatches occur, this could be the cause.
     75 
     76    <p>The solution is not to use such a directory for building GCC.
     77 
     78    <p>Similarly, when building from SVN or snapshots, or if you modify
     79 <samp><span class="file">*.l</span></samp> files, you need the Flex lexical analyzer generator
     80 installed.  If you do not modify <samp><span class="file">*.l</span></samp> files, releases contain
     81 the Flex-generated files and you do not need Flex installed to build
     82 them.  There is still one Flex-based lexical analyzer (part of the
     83 build machinery, not of GCC itself) that is used even if you only
     84 build the C front end.
     85 
     86    <p>When building from SVN or snapshots, or if you modify Texinfo
     87 documentation, you need version 4.7 or later of Texinfo installed if you
     88 want Info documentation to be regenerated.  Releases contain Info
     89 documentation pre-built for the unmodified documentation in the release.
     90 
     91 <h3 class="section"><a name="TOC0"></a>Building a native compiler</h3>
     92 
     93 <p>For a native build, the default configuration is to perform
     94 a 3-stage bootstrap of the compiler when &lsquo;<samp><span class="samp">make</span></samp>&rsquo; is invoked. 
     95 This will build the entire GCC system and ensure that it compiles
     96 itself correctly.  It can be disabled with the <samp><span class="option">--disable-bootstrap</span></samp>
     97 parameter to &lsquo;<samp><span class="samp">configure</span></samp>&rsquo;, but bootstrapping is suggested because
     98 the compiler will be tested more completely and could also have
     99 better performance.
    100 
    101    <p>The bootstrapping process will complete the following steps:
    102 
    103      <ul>
    104 <li>Build tools necessary to build the compiler.
    105 
    106      <li>Perform a 3-stage bootstrap of the compiler.  This includes building
    107 three times the target tools for use by the compiler such as binutils
    108 (bfd, binutils, gas, gprof, ld, and opcodes) if they have been
    109 individually linked or moved into the top level GCC source tree before
    110 configuring.
    111 
    112      <li>Perform a comparison test of the stage2 and stage3 compilers.
    113 
    114      <li>Build runtime libraries using the stage3 compiler from the previous step.
    115 
    116    </ul>
    117 
    118    <p>If you are short on disk space you might consider &lsquo;<samp><span class="samp">make
    119 bootstrap-lean</span></samp>&rsquo; instead.  The sequence of compilation is the
    120 same described above, but object files from the stage1 and
    121 stage2 of the 3-stage bootstrap of the compiler are deleted as
    122 soon as they are no longer needed.
    123 
    124    <p>If you wish to use non-default GCC flags when compiling the stage2
    125 and stage3 compilers, set <code>BOOT_CFLAGS</code> on the command line when
    126 doing &lsquo;<samp><span class="samp">make</span></samp>&rsquo;.  For example, if you want to save additional space
    127 during the bootstrap and in the final installation as well, you can
    128 build the compiler binaries without debugging information as in the
    129 following example.  This will save roughly 40% of disk space both for
    130 the bootstrap and the final installation.  (Libraries will still contain
    131 debugging information.)
    132 
    133 <pre class="smallexample">          make BOOT_CFLAGS='-O' bootstrap
    134 </pre>
    135    <p>You can place non-default optimization flags into <code>BOOT_CFLAGS</code>; they
    136 are less well tested here than the default of &lsquo;<samp><span class="samp">-g -O2</span></samp>&rsquo;, but should
    137 still work.  In a few cases, you may find that you need to specify special
    138 flags such as <samp><span class="option">-msoft-float</span></samp> here to complete the bootstrap; or,
    139 if the native compiler miscompiles the stage1 compiler, you may need
    140 to work around this, by choosing <code>BOOT_CFLAGS</code> to avoid the parts
    141 of the stage1 compiler that were miscompiled, or by using &lsquo;<samp><span class="samp">make
    142 bootstrap4</span></samp>&rsquo; to increase the number of stages of bootstrap.
    143 
    144    <p><code>BOOT_CFLAGS</code> does not apply to bootstrapped target libraries. 
    145 Since these are always compiled with the compiler currently being
    146 bootstrapped, you can use <code>CFLAGS_FOR_TARGET</code> to modify their
    147 compilation flags, as for non-bootstrapped target libraries. 
    148 Again, if the native compiler miscompiles the stage1 compiler, you may
    149 need to work around this by avoiding non-working parts of the stage1
    150 compiler.  Use <code>STAGE1_TFLAGS</code> to this end.
    151 
    152    <p>If you used the flag <samp><span class="option">--enable-languages=...</span></samp> to restrict
    153 the compilers to be built, only those you've actually enabled will be
    154 built.  This will of course only build those runtime libraries, for
    155 which the particular compiler has been built.  Please note,
    156 that re-defining <samp><span class="env">LANGUAGES</span></samp> when calling &lsquo;<samp><span class="samp">make</span></samp>&rsquo;
    157 <strong>does not</strong> work anymore!
    158 
    159    <p>If the comparison of stage2 and stage3 fails, this normally indicates
    160 that the stage2 compiler has compiled GCC incorrectly, and is therefore
    161 a potentially serious bug which you should investigate and report.  (On
    162 a few systems, meaningful comparison of object files is impossible; they
    163 always appear &ldquo;different&rdquo;.  If you encounter this problem, you will
    164 need to disable comparison in the <samp><span class="file">Makefile</span></samp>.)
    165 
    166    <p>If you do not want to bootstrap your compiler, you can configure with
    167 <samp><span class="option">--disable-bootstrap</span></samp>.  In particular cases, you may want to
    168 bootstrap your compiler even if the target system is not the same as
    169 the one you are building on: for example, you could build a
    170 <code>powerpc-unknown-linux-gnu</code> toolchain on a
    171 <code>powerpc64-unknown-linux-gnu</code> host.  In this case, pass
    172 <samp><span class="option">--enable-bootstrap</span></samp> to the configure script.
    173 
    174    <p><code>BUILD_CONFIG</code> can be used to bring in additional customization
    175 to the build.  It can be set to a whitespace-separated list of names. 
    176 For each such <code>NAME</code>, top-level <samp><span class="file">config/</span><code>NAME</code><span class="file">.mk</span></samp> will
    177 be included by the top-level <samp><span class="file">Makefile</span></samp>, bringing in any settings
    178 it contains.  The default <code>BUILD_CONFIG</code> can be set using the
    179 configure option <samp><span class="option">--with-build-config=</span><code>NAME</code><span class="option">...</span></samp>.  Some
    180 examples of supported build configurations are:
    181 
    182      <dl>
    183 <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
    184 <samp><span class="option">-O1</span></samp> to it.  &lsquo;<samp><span class="samp">BUILD_CONFIG=bootstrap-O1</span></samp>&rsquo; is equivalent to
    185 &lsquo;<samp><span class="samp">BOOT_CFLAGS='-g -O1'</span></samp>&rsquo;.
    186 
    187      <br><dt>&lsquo;<samp><span class="samp">bootstrap-O3</span></samp>&rsquo;<dd>Analogous to <code>bootstrap-O1</code>.
    188 
    189      <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug</span></samp>&rsquo;<dd>Verifies that the compiler generates the same executable code, whether
    190 or not it is asked to emit debug information.  To this end, this
    191 option builds stage2 host programs without debug information, and uses
    192 <samp><span class="file">contrib/compare-debug</span></samp> to compare them with the stripped stage3
    193 object files.  If <code>BOOT_CFLAGS</code> is overridden so as to not enable
    194 debug information, stage2 will have it, and stage3 won't.  This option
    195 is enabled by default when GCC bootstrapping is enabled, if
    196 <code>strip</code> can turn object files compiled with and without debug
    197 info into identical object files.  In addition to better test
    198 coverage, this option makes default bootstraps faster and leaner.
    199 
    200      <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug-big</span></samp>&rsquo;<dd>Rather than comparing stripped object files, as in
    201 <code>bootstrap-debug</code>, this option saves internal compiler dumps
    202 during stage2 and stage3 and compares them as well, which helps catch
    203 additional potential problems, but at a great cost in terms of disk
    204 space.  It can be specified in addition to &lsquo;<samp><span class="samp">bootstrap-debug</span></samp>&rsquo;.
    205 
    206      <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>,
    207 but at the expense of some recompilation.  Instead of saving the dumps
    208 of stage2 and stage3 until the final compare, it uses
    209 <samp><span class="option">-fcompare-debug</span></samp> to generate, compare and remove the dumps
    210 during stage3, repeating the compilation that already took place in
    211 stage2, whose dumps were not saved.
    212 
    213      <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug-lib</span></samp>&rsquo;<dd>This option tests executable code invariance over debug information
    214 generation on target libraries, just like <code>bootstrap-debug-lean</code>
    215 tests it on host programs.  It builds stage3 libraries with
    216 <samp><span class="option">-fcompare-debug</span></samp>, and it can be used along with any of the
    217 <code>bootstrap-debug</code> options above.
    218 
    219      <p>There aren't <code>-lean</code> or <code>-big</code> counterparts to this option
    220 because most libraries are only build in stage3, so bootstrap compares
    221 would not get significant coverage.  Moreover, the few libraries built
    222 in stage2 are used in stage3 host programs, so we wouldn't want to
    223 compile stage2 libraries with different options for comparison purposes.
    224 
    225      <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
    226 stage is run without the option <samp><span class="option">-fcompare-debug</span></samp>.  This is
    227 useful to verify the full <samp><span class="option">-fcompare-debug</span></samp> testing coverage.  It
    228 must be used along with <code>bootstrap-debug-lean</code> and
    229 <code>bootstrap-debug-lib</code>.
    230 
    231      <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,
    232 built in any stage, to be logged to <samp><span class="file">time.log</span></samp>, in the top level of
    233 the build tree.
    234 
    235    </dl>
    236 
    237 <h3 class="section"><a name="TOC1"></a>Building a cross compiler</h3>
    238 
    239 <p>When building a cross compiler, it is not generally possible to do a
    240 3-stage bootstrap of the compiler.  This makes for an interesting problem
    241 as parts of GCC can only be built with GCC.
    242 
    243    <p>To build a cross compiler, we recommend first building and installing a
    244 native compiler.  You can then use the native GCC compiler to build the
    245 cross compiler.  The installed native compiler needs to be GCC version
    246 2.95 or later.
    247 
    248    <p>If the cross compiler is to be built with support for the Java
    249 programming language and the ability to compile .java source files is
    250 desired, the installed native compiler used to build the cross
    251 compiler needs to be the same GCC version as the cross compiler.  In
    252 addition the cross compiler needs to be configured with
    253 <samp><span class="option">--with-ecj-jar=...</span></samp>.
    254 
    255    <p>Assuming you have already installed a native copy of GCC and configured
    256 your cross compiler, issue the command <samp><span class="command">make</span></samp>, which performs the
    257 following steps:
    258 
    259      <ul>
    260 <li>Build host tools necessary to build the compiler.
    261 
    262      <li>Build target tools for use by the compiler such as binutils (bfd,
    263 binutils, gas, gprof, ld, and opcodes)
    264 if they have been individually linked or moved into the top level GCC source
    265 tree before configuring.
    266 
    267      <li>Build the compiler (single stage only).
    268 
    269      <li>Build runtime libraries using the compiler from the previous step. 
    270 </ul>
    271 
    272    <p>Note that if an error occurs in any step the make process will exit.
    273 
    274    <p>If you are not building GNU binutils in the same source tree as GCC,
    275 you will need a cross-assembler and cross-linker installed before
    276 configuring GCC.  Put them in the directory
    277 <samp><var>prefix</var><span class="file">/</span><var>target</var><span class="file">/bin</span></samp>.  Here is a table of the tools
    278 you should put in this directory:
    279 
    280      <dl>
    281 <dt><samp><span class="file">as</span></samp><dd>This should be the cross-assembler.
    282 
    283      <br><dt><samp><span class="file">ld</span></samp><dd>This should be the cross-linker.
    284 
    285      <br><dt><samp><span class="file">ar</span></samp><dd>This should be the cross-archiver: a program which can manipulate
    286 archive files (linker libraries) in the target machine's format.
    287 
    288      <br><dt><samp><span class="file">ranlib</span></samp><dd>This should be a program to construct a symbol table in an archive file. 
    289 </dl>
    290 
    291    <p>The installation of GCC will find these programs in that directory,
    292 and copy or link them to the proper place to for the cross-compiler to
    293 find them when run later.
    294 
    295    <p>The easiest way to provide these files is to build the Binutils package. 
    296 Configure it with the same <samp><span class="option">--host</span></samp> and <samp><span class="option">--target</span></samp>
    297 options that you use for configuring GCC, then build and install
    298 them.  They install their executables automatically into the proper
    299 directory.  Alas, they do not support all the targets that GCC
    300 supports.
    301 
    302    <p>If you are not building a C library in the same source tree as GCC,
    303 you should also provide the target libraries and headers before
    304 configuring GCC, specifying the directories with
    305 <samp><span class="option">--with-sysroot</span></samp> or <samp><span class="option">--with-headers</span></samp> and
    306 <samp><span class="option">--with-libs</span></samp>.  Many targets also require &ldquo;start files&rdquo; such
    307 as <samp><span class="file">crt0.o</span></samp> and
    308 <samp><span class="file">crtn.o</span></samp> which are linked into each executable.  There may be several
    309 alternatives for <samp><span class="file">crt0.o</span></samp>, for use with profiling or other
    310 compilation options.  Check your target's definition of
    311 <code>STARTFILE_SPEC</code> to find out what start files it uses.
    312 
    313 <h3 class="section"><a name="TOC2"></a>Building in parallel</h3>
    314 
    315 <p>GNU Make 3.80 and above, which is necessary to build GCC, support
    316 building in parallel.  To activate this, you can use &lsquo;<samp><span class="samp">make -j 2</span></samp>&rsquo;
    317 instead of &lsquo;<samp><span class="samp">make</span></samp>&rsquo;.  You can also specify a bigger number, and
    318 in most cases using a value greater than the number of processors in
    319 your machine will result in fewer and shorter I/O latency hits, thus
    320 improving overall throughput; this is especially true for slow drives
    321 and network filesystems.
    322 
    323 <h3 class="section"><a name="TOC3"></a>Building the Ada compiler</h3>
    324 
    325 <p>In order to build GNAT, the Ada compiler, you need a working GNAT
    326 compiler (GCC version 3.4 or later). 
    327 This includes GNAT tools such as <samp><span class="command">gnatmake</span></samp> and
    328 <samp><span class="command">gnatlink</span></samp>, since the Ada front end is written in Ada and
    329 uses some GNAT-specific extensions.
    330 
    331    <p>In order to build a cross compiler, it is suggested to install
    332 the new compiler as native first, and then use it to build the cross
    333 compiler.
    334 
    335    <p><samp><span class="command">configure</span></samp> does not test whether the GNAT installation works
    336 and has a sufficiently recent version; if too old a GNAT version is
    337 installed, the build will fail unless <samp><span class="option">--enable-languages</span></samp> is
    338 used to disable building the Ada front end.
    339 
    340    <p><samp><span class="env">ADA_INCLUDE_PATH</span></samp> and <samp><span class="env">ADA_OBJECT_PATH</span></samp> environment variables
    341 must not be set when building the Ada compiler, the Ada tools, or the
    342 Ada runtime libraries. You can check that your build environment is clean
    343 by verifying that &lsquo;<samp><span class="samp">gnatls -v</span></samp>&rsquo; lists only one explicit path in each
    344 section.
    345 
    346 <h3 class="section"><a name="TOC4"></a>Building with profile feedback</h3>
    347 
    348 <p>It is possible to use profile feedback to optimize the compiler itself.  This
    349 should result in a faster compiler binary.  Experiments done on x86 using gcc
    350 3.3 showed approximately 7 percent speedup on compiling C programs.  To
    351 bootstrap the compiler with profile feedback, use <code>make profiledbootstrap</code>.
    352 
    353    <p>When &lsquo;<samp><span class="samp">make profiledbootstrap</span></samp>&rsquo; is run, it will first build a <code>stage1</code>
    354 compiler.  This compiler is used to build a <code>stageprofile</code> compiler
    355 instrumented to collect execution counts of instruction and branch
    356 probabilities.  Then runtime libraries are compiled with profile collected. 
    357 Finally a <code>stagefeedback</code> compiler is built using the information collected.
    358 
    359    <p>Unlike standard bootstrap, several additional restrictions apply.  The
    360 compiler used to build <code>stage1</code> needs to support a 64-bit integral type. 
    361 It is recommended to only use GCC for this.  Also parallel make is currently
    362 not supported since collisions in profile collecting may occur.
    363 
    364    <p><hr />
    365 <p><a href="./index.html">Return to the GCC Installation page</a>
    366 
    367 <!-- ***Testing***************************************************************** -->
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    373 <!-- *************************************************************************** -->
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