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| <title>Installing GCC</title> |
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| <h1 class="settitle" align="center">Installing GCC</h1> |
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| <a name="index-Installing-GCC_003a-Building"></a> |
| |
| <p>Now that GCC is configured, you are ready to build the compiler and |
| runtime libraries. |
| </p> |
| <p>Some commands executed when making the compiler may fail (return a |
| nonzero status) and be ignored by <code>make</code>. These failures, which |
| are often due to files that were not found, are expected, and can safely |
| be ignored. |
| </p> |
| <p>It is normal to have compiler warnings when compiling certain files. |
| Unless you are a GCC developer, you can generally ignore these warnings |
| unless they cause compilation to fail. Developers should attempt to fix |
| any warnings encountered, however they can temporarily continue past |
| warnings-as-errors by specifying the configure flag |
| <samp>--disable-werror</samp>. |
| </p> |
| <p>On certain old systems, defining certain environment variables such as |
| <code>CC</code> can interfere with the functioning of <code>make</code>. |
| </p> |
| <p>If you encounter seemingly strange errors when trying to build the |
| compiler in a directory other than the source directory, it could be |
| because you have previously configured the compiler in the source |
| directory. Make sure you have done all the necessary preparations. |
| </p> |
| <p>If you build GCC on a BSD system using a directory stored in an old System |
| V file system, problems may occur in running <code>fixincludes</code> if the |
| System V file system doesn’t support symbolic links. These problems |
| result in a failure to fix the declaration of <code>size_t</code> in |
| <samp>sys/types.h</samp>. If you find that <code>size_t</code> is a signed type and |
| that type mismatches occur, this could be the cause. |
| </p> |
| <p>The solution is not to use such a directory for building GCC. |
| </p> |
| <p>Similarly, when building from SVN or snapshots, or if you modify |
| <samp>*.l</samp> files, you need the Flex lexical analyzer generator |
| installed. If you do not modify <samp>*.l</samp> files, releases contain |
| the Flex-generated files and you do not need Flex installed to build |
| them. There is still one Flex-based lexical analyzer (part of the |
| build machinery, not of GCC itself) that is used even if you only |
| build the C front end. |
| </p> |
| <p>When building from SVN or snapshots, or if you modify Texinfo |
| documentation, you need version 4.7 or later of Texinfo installed if you |
| want Info documentation to be regenerated. Releases contain Info |
| documentation pre-built for the unmodified documentation in the release. |
| </p> |
| <a name="Building-a-native-compiler"></a> |
| <h3 class="section">Building a native compiler</h3> |
| |
| <p>For a native build, the default configuration is to perform |
| a 3-stage bootstrap of the compiler when ‘<samp>make</samp>’ is invoked. |
| This will build the entire GCC system and ensure that it compiles |
| itself correctly. It can be disabled with the <samp>--disable-bootstrap</samp> |
| parameter to ‘<samp>configure</samp>’, but bootstrapping is suggested because |
| the compiler will be tested more completely and could also have |
| better performance. |
| </p> |
| <p>The bootstrapping process will complete the following steps: |
| </p> |
| <ul> |
| <li> Build tools necessary to build the compiler. |
| |
| </li><li> Perform a 3-stage bootstrap of the compiler. This includes building |
| three times the target tools for use by the compiler such as binutils |
| (bfd, binutils, gas, gprof, ld, and opcodes) if they have been |
| individually linked or moved into the top level GCC source tree before |
| configuring. |
| |
| </li><li> Perform a comparison test of the stage2 and stage3 compilers. |
| |
| </li><li> Build runtime libraries using the stage3 compiler from the previous step. |
| |
| </li></ul> |
| |
| <p>If you are short on disk space you might consider ‘<samp>make |
| bootstrap-lean</samp>’ instead. The sequence of compilation is the |
| same described above, but object files from the stage1 and |
| stage2 of the 3-stage bootstrap of the compiler are deleted as |
| soon as they are no longer needed. |
| </p> |
| <p>If you wish to use non-default GCC flags when compiling the stage2 |
| and stage3 compilers, set <code>BOOT_CFLAGS</code> on the command line when |
| doing ‘<samp>make</samp>’. For example, if you want to save additional space |
| during the bootstrap and in the final installation as well, you can |
| build the compiler binaries without debugging information as in the |
| following example. This will save roughly 40% of disk space both for |
| the bootstrap and the final installation. (Libraries will still contain |
| debugging information.) |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">make BOOT_CFLAGS='-O' bootstrap |
| </pre></div> |
| |
| <p>You can place non-default optimization flags into <code>BOOT_CFLAGS</code>; they |
| are less well tested here than the default of ‘<samp>-g -O2</samp>’, but should |
| still work. In a few cases, you may find that you need to specify special |
| flags such as <samp>-msoft-float</samp> here to complete the bootstrap; or, |
| if the native compiler miscompiles the stage1 compiler, you may need |
| to work around this, by choosing <code>BOOT_CFLAGS</code> to avoid the parts |
| of the stage1 compiler that were miscompiled, or by using ‘<samp>make |
| bootstrap4</samp>’ to increase the number of stages of bootstrap. |
| </p> |
| <p><code>BOOT_CFLAGS</code> does not apply to bootstrapped target libraries. |
| Since these are always compiled with the compiler currently being |
| bootstrapped, you can use <code>CFLAGS_FOR_TARGET</code> to modify their |
| compilation flags, as for non-bootstrapped target libraries. |
| Again, if the native compiler miscompiles the stage1 compiler, you may |
| need to work around this by avoiding non-working parts of the stage1 |
| compiler. Use <code>STAGE1_TFLAGS</code> to this end. |
| </p> |
| <p>If you used the flag <samp>--enable-languages=…</samp> to restrict |
| the compilers to be built, only those you’ve actually enabled will be |
| built. This will of course only build those runtime libraries, for |
| which the particular compiler has been built. Please note, |
| that re-defining <code>LANGUAGES</code> when calling ‘<samp>make</samp>’ |
| <strong>does not</strong> work anymore! |
| </p> |
| <p>If the comparison of stage2 and stage3 fails, this normally indicates |
| that the stage2 compiler has compiled GCC incorrectly, and is therefore |
| a potentially serious bug which you should investigate and report. (On |
| a few systems, meaningful comparison of object files is impossible; they |
| always appear “different”. If you encounter this problem, you will |
| need to disable comparison in the <samp>Makefile</samp>.) |
| </p> |
| <p>If you do not want to bootstrap your compiler, you can configure with |
| <samp>--disable-bootstrap</samp>. In particular cases, you may want to |
| bootstrap your compiler even if the target system is not the same as |
| the one you are building on: for example, you could build a |
| <code>powerpc-unknown-linux-gnu</code> toolchain on a |
| <code>powerpc64-unknown-linux-gnu</code> host. In this case, pass |
| <samp>--enable-bootstrap</samp> to the configure script. |
| </p> |
| <p><code>BUILD_CONFIG</code> can be used to bring in additional customization |
| to the build. It can be set to a whitespace-separated list of names. |
| For each such <code>NAME</code>, top-level <samp>config/<code>NAME</code>.mk</samp> will |
| be included by the top-level <samp>Makefile</samp>, bringing in any settings |
| it contains. The default <code>BUILD_CONFIG</code> can be set using the |
| configure option <samp>--with-build-config=<code>NAME</code>...</samp>. Some |
| examples of supported build configurations are: |
| </p> |
| <dl compact="compact"> |
| <dt>‘<samp>bootstrap-O1</samp>’</dt> |
| <dd><p>Removes any <samp>-O</samp>-started option from <code>BOOT_CFLAGS</code>, and adds |
| <samp>-O1</samp> to it. ‘<samp>BUILD_CONFIG=bootstrap-O1</samp>’ is equivalent to |
| ‘<samp>BOOT_CFLAGS='-g -O1'</samp>’. |
| </p> |
| </dd> |
| <dt>‘<samp>bootstrap-O3</samp>’</dt> |
| <dd><p>Analogous to <code>bootstrap-O1</code>. |
| </p> |
| </dd> |
| <dt>‘<samp>bootstrap-lto</samp>’</dt> |
| <dd><p>Enables Link-Time Optimization for host tools during bootstrapping. |
| ‘<samp>BUILD_CONFIG=bootstrap-lto</samp>’ is equivalent to adding |
| <samp>-flto</samp> to ‘<samp>BOOT_CFLAGS</samp>’. This option assumes that the host |
| supports the linker plugin (e.g. GNU ld version 2.21 or later or GNU gold |
| version 2.21 or later). |
| </p> |
| </dd> |
| <dt>‘<samp>bootstrap-lto-noplugin</samp>’</dt> |
| <dd><p>This option is similar to <code>bootstrap-lto</code>, but is intended for |
| hosts that do not support the linker plugin. Without the linker plugin |
| static libraries are not compiled with link-time optimizations. Since |
| the GCC middle end and back end are in <samp>libbackend.a</samp> this means |
| that only the front end is actually LTO optimized. |
| </p> |
| </dd> |
| <dt>‘<samp>bootstrap-debug</samp>’</dt> |
| <dd><p>Verifies that the compiler generates the same executable code, whether |
| or not it is asked to emit debug information. To this end, this |
| option builds stage2 host programs without debug information, and uses |
| <samp>contrib/compare-debug</samp> to compare them with the stripped stage3 |
| object files. If <code>BOOT_CFLAGS</code> is overridden so as to not enable |
| debug information, stage2 will have it, and stage3 won’t. This option |
| is enabled by default when GCC bootstrapping is enabled, if |
| <code>strip</code> can turn object files compiled with and without debug |
| info into identical object files. In addition to better test |
| coverage, this option makes default bootstraps faster and leaner. |
| </p> |
| </dd> |
| <dt>‘<samp>bootstrap-debug-big</samp>’</dt> |
| <dd><p>Rather than comparing stripped object files, as in |
| <code>bootstrap-debug</code>, this option saves internal compiler dumps |
| during stage2 and stage3 and compares them as well, which helps catch |
| additional potential problems, but at a great cost in terms of disk |
| space. It can be specified in addition to ‘<samp>bootstrap-debug</samp>’. |
| </p> |
| </dd> |
| <dt>‘<samp>bootstrap-debug-lean</samp>’</dt> |
| <dd><p>This option saves disk space compared with <code>bootstrap-debug-big</code>, |
| but at the expense of some recompilation. Instead of saving the dumps |
| of stage2 and stage3 until the final compare, it uses |
| <samp>-fcompare-debug</samp> to generate, compare and remove the dumps |
| during stage3, repeating the compilation that already took place in |
| stage2, whose dumps were not saved. |
| </p> |
| </dd> |
| <dt>‘<samp>bootstrap-debug-lib</samp>’</dt> |
| <dd><p>This option tests executable code invariance over debug information |
| generation on target libraries, just like <code>bootstrap-debug-lean</code> |
| tests it on host programs. It builds stage3 libraries with |
| <samp>-fcompare-debug</samp>, and it can be used along with any of the |
| <code>bootstrap-debug</code> options above. |
| </p> |
| <p>There aren’t <code>-lean</code> or <code>-big</code> counterparts to this option |
| because most libraries are only build in stage3, so bootstrap compares |
| would not get significant coverage. Moreover, the few libraries built |
| in stage2 are used in stage3 host programs, so we wouldn’t want to |
| compile stage2 libraries with different options for comparison purposes. |
| </p> |
| </dd> |
| <dt>‘<samp>bootstrap-debug-ckovw</samp>’</dt> |
| <dd><p>Arranges for error messages to be issued if the compiler built on any |
| stage is run without the option <samp>-fcompare-debug</samp>. This is |
| useful to verify the full <samp>-fcompare-debug</samp> testing coverage. It |
| must be used along with <code>bootstrap-debug-lean</code> and |
| <code>bootstrap-debug-lib</code>. |
| </p> |
| </dd> |
| <dt>‘<samp>bootstrap-time</samp>’</dt> |
| <dd><p>Arranges for the run time of each program started by the GCC driver, |
| built in any stage, to be logged to <samp>time.log</samp>, in the top level of |
| the build tree. |
| </p> |
| </dd> |
| </dl> |
| |
| <a name="Building-a-cross-compiler"></a> |
| <h3 class="section">Building a cross compiler</h3> |
| |
| <p>When building a cross compiler, it is not generally possible to do a |
| 3-stage bootstrap of the compiler. This makes for an interesting problem |
| as parts of GCC can only be built with GCC. |
| </p> |
| <p>To build a cross compiler, we recommend first building and installing a |
| native compiler. You can then use the native GCC compiler to build the |
| cross compiler. The installed native compiler needs to be GCC version |
| 2.95 or later. |
| </p> |
| <p>If the cross compiler is to be built with support for the Java |
| programming language and the ability to compile .java source files is |
| desired, the installed native compiler used to build the cross |
| compiler needs to be the same GCC version as the cross compiler. In |
| addition the cross compiler needs to be configured with |
| <samp>--with-ecj-jar=…</samp>. |
| </p> |
| <p>Assuming you have already installed a native copy of GCC and configured |
| your cross compiler, issue the command <code>make</code>, which performs the |
| following steps: |
| </p> |
| <ul> |
| <li> Build host tools necessary to build the compiler. |
| |
| </li><li> Build target tools for use by the compiler such as binutils (bfd, |
| binutils, gas, gprof, ld, and opcodes) |
| if they have been individually linked or moved into the top level GCC source |
| tree before configuring. |
| |
| </li><li> Build the compiler (single stage only). |
| |
| </li><li> Build runtime libraries using the compiler from the previous step. |
| </li></ul> |
| |
| <p>Note that if an error occurs in any step the make process will exit. |
| </p> |
| <p>If you are not building GNU binutils in the same source tree as GCC, |
| you will need a cross-assembler and cross-linker installed before |
| configuring GCC. Put them in the directory |
| <samp><var>prefix</var>/<var>target</var>/bin</samp>. Here is a table of the tools |
| you should put in this directory: |
| </p> |
| <dl compact="compact"> |
| <dt><samp>as</samp></dt> |
| <dd><p>This should be the cross-assembler. |
| </p> |
| </dd> |
| <dt><samp>ld</samp></dt> |
| <dd><p>This should be the cross-linker. |
| </p> |
| </dd> |
| <dt><samp>ar</samp></dt> |
| <dd><p>This should be the cross-archiver: a program which can manipulate |
| archive files (linker libraries) in the target machine’s format. |
| </p> |
| </dd> |
| <dt><samp>ranlib</samp></dt> |
| <dd><p>This should be a program to construct a symbol table in an archive file. |
| </p></dd> |
| </dl> |
| |
| <p>The installation of GCC will find these programs in that directory, |
| and copy or link them to the proper place to for the cross-compiler to |
| find them when run later. |
| </p> |
| <p>The easiest way to provide these files is to build the Binutils package. |
| Configure it with the same <samp>--host</samp> and <samp>--target</samp> |
| options that you use for configuring GCC, then build and install |
| them. They install their executables automatically into the proper |
| directory. Alas, they do not support all the targets that GCC |
| supports. |
| </p> |
| <p>If you are not building a C library in the same source tree as GCC, |
| you should also provide the target libraries and headers before |
| configuring GCC, specifying the directories with |
| <samp>--with-sysroot</samp> or <samp>--with-headers</samp> and |
| <samp>--with-libs</samp>. Many targets also require “start files” such |
| as <samp>crt0.o</samp> and |
| <samp>crtn.o</samp> which are linked into each executable. There may be several |
| alternatives for <samp>crt0.o</samp>, for use with profiling or other |
| compilation options. Check your target’s definition of |
| <code>STARTFILE_SPEC</code> to find out what start files it uses. |
| </p> |
| <a name="Building-in-parallel"></a> |
| <h3 class="section">Building in parallel</h3> |
| |
| <p>GNU Make 3.80 and above, which is necessary to build GCC, support |
| building in parallel. To activate this, you can use ‘<samp>make -j 2</samp>’ |
| instead of ‘<samp>make</samp>’. You can also specify a bigger number, and |
| in most cases using a value greater than the number of processors in |
| your machine will result in fewer and shorter I/O latency hits, thus |
| improving overall throughput; this is especially true for slow drives |
| and network filesystems. |
| </p> |
| <a name="Building-the-Ada-compiler"></a> |
| <h3 class="section">Building the Ada compiler</h3> |
| |
| <p>In order to build GNAT, the Ada compiler, you need a working GNAT |
| compiler (GCC version 4.0 or later). |
| This includes GNAT tools such as <code>gnatmake</code> and |
| <code>gnatlink</code>, since the Ada front end is written in Ada and |
| uses some GNAT-specific extensions. |
| </p> |
| <p>In order to build a cross compiler, it is suggested to install |
| the new compiler as native first, and then use it to build the cross |
| compiler. |
| </p> |
| <p><code>configure</code> does not test whether the GNAT installation works |
| and has a sufficiently recent version; if too old a GNAT version is |
| installed, the build will fail unless <samp>--enable-languages</samp> is |
| used to disable building the Ada front end. |
| </p> |
| <p><code>ADA_INCLUDE_PATH</code> and <code>ADA_OBJECT_PATH</code> environment variables |
| must not be set when building the Ada compiler, the Ada tools, or the |
| Ada runtime libraries. You can check that your build environment is clean |
| by verifying that ‘<samp>gnatls -v</samp>’ lists only one explicit path in each |
| section. |
| </p> |
| <a name="Building-with-profile-feedback"></a> |
| <h3 class="section">Building with profile feedback</h3> |
| |
| <p>It is possible to use profile feedback to optimize the compiler itself. This |
| should result in a faster compiler binary. Experiments done on x86 using gcc |
| 3.3 showed approximately 7 percent speedup on compiling C programs. To |
| bootstrap the compiler with profile feedback, use <code>make profiledbootstrap</code>. |
| </p> |
| <p>When ‘<samp>make profiledbootstrap</samp>’ is run, it will first build a <code>stage1</code> |
| compiler. This compiler is used to build a <code>stageprofile</code> compiler |
| instrumented to collect execution counts of instruction and branch |
| probabilities. Then runtime libraries are compiled with profile collected. |
| Finally a <code>stagefeedback</code> compiler is built using the information collected. |
| </p> |
| <p>Unlike standard bootstrap, several additional restrictions apply. The |
| compiler used to build <code>stage1</code> needs to support a 64-bit integral type. |
| It is recommended to only use GCC for this. |
| </p> |
| <hr /> |
| <p><p><a href="./index.html">Return to the GCC Installation page</a> |
| </p> |
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