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<!-- Created by GNU Texinfo 6.1, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Installing GCC</title>
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<meta name="description" content="Installing GCC">
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<meta name="keywords" content="Installing GCC">
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</style>
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</head>
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<body lang="en">
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<h1 class="settitle" align="center">Installing GCC</h1>
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<a name="index-Installing-GCC_003a-Building"></a>
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<p>Now that GCC is configured, you are ready to build the compiler and
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runtime libraries.
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</p>
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<p>Some commands executed when making the compiler may fail (return a
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nonzero status) and be ignored by <code>make</code>. These failures, which
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are often due to files that were not found, are expected, and can safely
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be ignored.
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</p>
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<p>It is normal to have compiler warnings when compiling certain files.
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Unless you are a GCC developer, you can generally ignore these warnings
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unless they cause compilation to fail. Developers should attempt to fix
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any warnings encountered, however they can temporarily continue past
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warnings-as-errors by specifying the configure flag
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<samp>--disable-werror</samp>.
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</p>
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<p>On certain old systems, defining certain environment variables such as
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<code>CC</code> can interfere with the functioning of <code>make</code>.
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</p>
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<p>If you encounter seemingly strange errors when trying to build the
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compiler in a directory other than the source directory, it could be
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because you have previously configured the compiler in the source
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directory. Make sure you have done all the necessary preparations.
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</p>
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<p>If you build GCC on a BSD system using a directory stored in an old System
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V file system, problems may occur in running <code>fixincludes</code> if the
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System V file system doesn’t support symbolic links. These problems
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result in a failure to fix the declaration of <code>size_t</code> in
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<samp>sys/types.h</samp>. If you find that <code>size_t</code> is a signed type and
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that type mismatches occur, this could be the cause.
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</p>
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<p>The solution is not to use such a directory for building GCC.
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</p>
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<p>Similarly, when building from SVN or snapshots, or if you modify
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<samp>*.l</samp> files, you need the Flex lexical analyzer generator
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installed. If you do not modify <samp>*.l</samp> files, releases contain
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the Flex-generated files and you do not need Flex installed to build
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them. There is still one Flex-based lexical analyzer (part of the
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build machinery, not of GCC itself) that is used even if you only
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build the C front end.
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</p>
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<p>When building from SVN or snapshots, or if you modify Texinfo
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documentation, you need version 4.7 or later of Texinfo installed if you
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want Info documentation to be regenerated. Releases contain Info
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documentation pre-built for the unmodified documentation in the release.
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</p>
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<a name="Building-a-native-compiler"></a>
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<h3 class="section">Building a native compiler</h3>
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<p>For a native build, the default configuration is to perform
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a 3-stage bootstrap of the compiler when ‘<samp>make</samp>’ is invoked.
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This will build the entire GCC system and ensure that it compiles
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itself correctly. It can be disabled with the <samp>--disable-bootstrap</samp>
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parameter to ‘<samp>configure</samp>’, but bootstrapping is suggested because
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the compiler will be tested more completely and could also have
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better performance.
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</p>
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<p>The bootstrapping process will complete the following steps:
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</p>
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<ul>
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<li> Build tools necessary to build the compiler.
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</li><li> Perform a 3-stage bootstrap of the compiler. This includes building
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three times the target tools for use by the compiler such as binutils
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(bfd, binutils, gas, gprof, ld, and opcodes) if they have been
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individually linked or moved into the top level GCC source tree before
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configuring.
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</li><li> Perform a comparison test of the stage2 and stage3 compilers.
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</li><li> Build runtime libraries using the stage3 compiler from the previous step.
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</li></ul>
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<p>If you are short on disk space you might consider ‘<samp>make
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bootstrap-lean</samp>’ instead. The sequence of compilation is the
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same described above, but object files from the stage1 and
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stage2 of the 3-stage bootstrap of the compiler are deleted as
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soon as they are no longer needed.
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</p>
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<p>If you wish to use non-default GCC flags when compiling the stage2
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and stage3 compilers, set <code>BOOT_CFLAGS</code> on the command line when
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doing ‘<samp>make</samp>’. For example, if you want to save additional space
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during the bootstrap and in the final installation as well, you can
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build the compiler binaries without debugging information as in the
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following example. This will save roughly 40% of disk space both for
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the bootstrap and the final installation. (Libraries will still contain
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debugging information.)
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</p>
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<div class="smallexample">
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<pre class="smallexample">make BOOT_CFLAGS='-O' bootstrap
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</pre></div>
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<p>You can place non-default optimization flags into <code>BOOT_CFLAGS</code>; they
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are less well tested here than the default of ‘<samp>-g -O2</samp>’, but should
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still work. In a few cases, you may find that you need to specify special
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flags such as <samp>-msoft-float</samp> here to complete the bootstrap; or,
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if the native compiler miscompiles the stage1 compiler, you may need
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to work around this, by choosing <code>BOOT_CFLAGS</code> to avoid the parts
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of the stage1 compiler that were miscompiled, or by using ‘<samp>make
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bootstrap4</samp>’ to increase the number of stages of bootstrap.
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</p>
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<p><code>BOOT_CFLAGS</code> does not apply to bootstrapped target libraries.
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Since these are always compiled with the compiler currently being
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bootstrapped, you can use <code>CFLAGS_FOR_TARGET</code> to modify their
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compilation flags, as for non-bootstrapped target libraries.
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Again, if the native compiler miscompiles the stage1 compiler, you may
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need to work around this by avoiding non-working parts of the stage1
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compiler. Use <code>STAGE1_TFLAGS</code> to this end.
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</p>
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<p>If you used the flag <samp>--enable-languages=…</samp> to restrict
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the compilers to be built, only those you’ve actually enabled will be
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built. This will of course only build those runtime libraries, for
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which the particular compiler has been built. Please note,
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that re-defining <code>LANGUAGES</code> when calling ‘<samp>make</samp>’
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<strong>does not</strong> work anymore!
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</p>
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<p>If the comparison of stage2 and stage3 fails, this normally indicates
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that the stage2 compiler has compiled GCC incorrectly, and is therefore
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a potentially serious bug which you should investigate and report. (On
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a few systems, meaningful comparison of object files is impossible; they
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always appear “different”. If you encounter this problem, you will
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need to disable comparison in the <samp>Makefile</samp>.)
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</p>
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<p>If you do not want to bootstrap your compiler, you can configure with
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<samp>--disable-bootstrap</samp>. In particular cases, you may want to
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bootstrap your compiler even if the target system is not the same as
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the one you are building on: for example, you could build a
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<code>powerpc-unknown-linux-gnu</code> toolchain on a
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<code>powerpc64-unknown-linux-gnu</code> host. In this case, pass
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<samp>--enable-bootstrap</samp> to the configure script.
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</p>
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<p><code>BUILD_CONFIG</code> can be used to bring in additional customization
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to the build. It can be set to a whitespace-separated list of names.
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For each such <code>NAME</code>, top-level <samp>config/<code>NAME</code>.mk</samp> will
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be included by the top-level <samp>Makefile</samp>, bringing in any settings
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it contains. The default <code>BUILD_CONFIG</code> can be set using the
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configure option <samp>--with-build-config=<code>NAME</code>...</samp>. Some
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examples of supported build configurations are:
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</p>
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<dl compact="compact">
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<dt>‘<samp>bootstrap-O1</samp>’</dt>
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<dd><p>Removes any <samp>-O</samp>-started option from <code>BOOT_CFLAGS</code>, and adds
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<samp>-O1</samp> to it. ‘<samp>BUILD_CONFIG=bootstrap-O1</samp>’ is equivalent to
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‘<samp>BOOT_CFLAGS='-g -O1'</samp>’.
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</p>
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</dd>
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<dt>‘<samp>bootstrap-O3</samp>’</dt>
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<dd><p>Analogous to <code>bootstrap-O1</code>.
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</p>
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</dd>
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<dt>‘<samp>bootstrap-lto</samp>’</dt>
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<dd><p>Enables Link-Time Optimization for host tools during bootstrapping.
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‘<samp>BUILD_CONFIG=bootstrap-lto</samp>’ is equivalent to adding
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<samp>-flto</samp> to ‘<samp>BOOT_CFLAGS</samp>’. This option assumes that the host
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supports the linker plugin (e.g. GNU ld version 2.21 or later or GNU gold
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version 2.21 or later).
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</p>
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</dd>
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<dt>‘<samp>bootstrap-lto-noplugin</samp>’</dt>
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<dd><p>This option is similar to <code>bootstrap-lto</code>, but is intended for
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hosts that do not support the linker plugin. Without the linker plugin
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static libraries are not compiled with link-time optimizations. Since
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the GCC middle end and back end are in <samp>libbackend.a</samp> this means
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that only the front end is actually LTO optimized.
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</p>
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</dd>
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<dt>‘<samp>bootstrap-debug</samp>’</dt>
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<dd><p>Verifies that the compiler generates the same executable code, whether
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or not it is asked to emit debug information. To this end, this
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option builds stage2 host programs without debug information, and uses
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<samp>contrib/compare-debug</samp> to compare them with the stripped stage3
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object files. If <code>BOOT_CFLAGS</code> is overridden so as to not enable
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debug information, stage2 will have it, and stage3 won’t. This option
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is enabled by default when GCC bootstrapping is enabled, if
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<code>strip</code> can turn object files compiled with and without debug
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info into identical object files. In addition to better test
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coverage, this option makes default bootstraps faster and leaner.
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</p>
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</dd>
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<dt>‘<samp>bootstrap-debug-big</samp>’</dt>
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<dd><p>Rather than comparing stripped object files, as in
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<code>bootstrap-debug</code>, this option saves internal compiler dumps
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during stage2 and stage3 and compares them as well, which helps catch
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additional potential problems, but at a great cost in terms of disk
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space. It can be specified in addition to ‘<samp>bootstrap-debug</samp>’.
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</p>
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</dd>
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<dt>‘<samp>bootstrap-debug-lean</samp>’</dt>
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<dd><p>This option saves disk space compared with <code>bootstrap-debug-big</code>,
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but at the expense of some recompilation. Instead of saving the dumps
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of stage2 and stage3 until the final compare, it uses
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<samp>-fcompare-debug</samp> to generate, compare and remove the dumps
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during stage3, repeating the compilation that already took place in
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stage2, whose dumps were not saved.
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</p>
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</dd>
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<dt>‘<samp>bootstrap-debug-lib</samp>’</dt>
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<dd><p>This option tests executable code invariance over debug information
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generation on target libraries, just like <code>bootstrap-debug-lean</code>
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tests it on host programs. It builds stage3 libraries with
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<samp>-fcompare-debug</samp>, and it can be used along with any of the
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<code>bootstrap-debug</code> options above.
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</p>
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<p>There aren’t <code>-lean</code> or <code>-big</code> counterparts to this option
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because most libraries are only build in stage3, so bootstrap compares
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would not get significant coverage. Moreover, the few libraries built
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in stage2 are used in stage3 host programs, so we wouldn’t want to
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compile stage2 libraries with different options for comparison purposes.
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</p>
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</dd>
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<dt>‘<samp>bootstrap-debug-ckovw</samp>’</dt>
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<dd><p>Arranges for error messages to be issued if the compiler built on any
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stage is run without the option <samp>-fcompare-debug</samp>. This is
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useful to verify the full <samp>-fcompare-debug</samp> testing coverage. It
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must be used along with <code>bootstrap-debug-lean</code> and
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<code>bootstrap-debug-lib</code>.
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</p>
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</dd>
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<dt>‘<samp>bootstrap-time</samp>’</dt>
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<dd><p>Arranges for the run time of each program started by the GCC driver,
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built in any stage, to be logged to <samp>time.log</samp>, in the top level of
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the build tree.
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</p>
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</dd>
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</dl>
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<a name="Building-a-cross-compiler"></a>
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<h3 class="section">Building a cross compiler</h3>
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<p>When building a cross compiler, it is not generally possible to do a
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3-stage bootstrap of the compiler. This makes for an interesting problem
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as parts of GCC can only be built with GCC.
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</p>
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<p>To build a cross compiler, we recommend first building and installing a
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native compiler. You can then use the native GCC compiler to build the
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cross compiler. The installed native compiler needs to be GCC version
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2.95 or later.
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</p>
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<p>If the cross compiler is to be built with support for the Java
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programming language and the ability to compile .java source files is
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desired, the installed native compiler used to build the cross
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compiler needs to be the same GCC version as the cross compiler. In
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addition the cross compiler needs to be configured with
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<samp>--with-ecj-jar=…</samp>.
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</p>
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<p>Assuming you have already installed a native copy of GCC and configured
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your cross compiler, issue the command <code>make</code>, which performs the
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following steps:
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</p>
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<ul>
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<li> Build host tools necessary to build the compiler.
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</li><li> Build target tools for use by the compiler such as binutils (bfd,
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binutils, gas, gprof, ld, and opcodes)
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if they have been individually linked or moved into the top level GCC source
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tree before configuring.
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</li><li> Build the compiler (single stage only).
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</li><li> Build runtime libraries using the compiler from the previous step.
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</li></ul>
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<p>Note that if an error occurs in any step the make process will exit.
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</p>
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<p>If you are not building GNU binutils in the same source tree as GCC,
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you will need a cross-assembler and cross-linker installed before
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configuring GCC. Put them in the directory
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<samp><var>prefix</var>/<var>target</var>/bin</samp>. Here is a table of the tools
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you should put in this directory:
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</p>
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<dl compact="compact">
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<dt><samp>as</samp></dt>
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<dd><p>This should be the cross-assembler.
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</p>
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</dd>
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<dt><samp>ld</samp></dt>
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<dd><p>This should be the cross-linker.
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</p>
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</dd>
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<dt><samp>ar</samp></dt>
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<dd><p>This should be the cross-archiver: a program which can manipulate
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archive files (linker libraries) in the target machine’s format.
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</p>
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</dd>
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<dt><samp>ranlib</samp></dt>
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<dd><p>This should be a program to construct a symbol table in an archive file.
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</p></dd>
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</dl>
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<p>The installation of GCC will find these programs in that directory,
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and copy or link them to the proper place to for the cross-compiler to
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find them when run later.
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</p>
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<p>The easiest way to provide these files is to build the Binutils package.
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Configure it with the same <samp>--host</samp> and <samp>--target</samp>
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options that you use for configuring GCC, then build and install
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them. They install their executables automatically into the proper
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directory. Alas, they do not support all the targets that GCC
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supports.
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</p>
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<p>If you are not building a C library in the same source tree as GCC,
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you should also provide the target libraries and headers before
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configuring GCC, specifying the directories with
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<samp>--with-sysroot</samp> or <samp>--with-headers</samp> and
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<samp>--with-libs</samp>. Many targets also require “start files” such
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as <samp>crt0.o</samp> and
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<samp>crtn.o</samp> which are linked into each executable. There may be several
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alternatives for <samp>crt0.o</samp>, for use with profiling or other
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compilation options. Check your target’s definition of
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<code>STARTFILE_SPEC</code> to find out what start files it uses.
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</p>
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<a name="Building-in-parallel"></a>
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<h3 class="section">Building in parallel</h3>
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<p>GNU Make 3.80 and above, which is necessary to build GCC, support
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building in parallel. To activate this, you can use ‘<samp>make -j 2</samp>’
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instead of ‘<samp>make</samp>’. You can also specify a bigger number, and
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in most cases using a value greater than the number of processors in
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your machine will result in fewer and shorter I/O latency hits, thus
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improving overall throughput; this is especially true for slow drives
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and network filesystems.
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</p>
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<a name="Building-the-Ada-compiler"></a>
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<h3 class="section">Building the Ada compiler</h3>
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<p>In order to build GNAT, the Ada compiler, you need a working GNAT
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compiler (GCC version 4.0 or later).
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This includes GNAT tools such as <code>gnatmake</code> and
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<code>gnatlink</code>, since the Ada front end is written in Ada and
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uses some GNAT-specific extensions.
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</p>
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<p>In order to build a cross compiler, it is suggested to install
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the new compiler as native first, and then use it to build the cross
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compiler.
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</p>
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<p><code>configure</code> does not test whether the GNAT installation works
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and has a sufficiently recent version; if too old a GNAT version is
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installed, the build will fail unless <samp>--enable-languages</samp> is
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used to disable building the Ada front end.
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</p>
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<p><code>ADA_INCLUDE_PATH</code> and <code>ADA_OBJECT_PATH</code> environment variables
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must not be set when building the Ada compiler, the Ada tools, or the
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Ada runtime libraries. You can check that your build environment is clean
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by verifying that ‘<samp>gnatls -v</samp>’ lists only one explicit path in each
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section.
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</p>
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<a name="Building-with-profile-feedback"></a>
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<h3 class="section">Building with profile feedback</h3>
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<p>It is possible to use profile feedback to optimize the compiler itself. This
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|
should result in a faster compiler binary. Experiments done on x86 using gcc
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|
3.3 showed approximately 7 percent speedup on compiling C programs. To
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bootstrap the compiler with profile feedback, use <code>make profiledbootstrap</code>.
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</p>
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<p>When ‘<samp>make profiledbootstrap</samp>’ is run, it will first build a <code>stage1</code>
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compiler. This compiler is used to build a <code>stageprofile</code> compiler
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|
instrumented to collect execution counts of instruction and branch
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|
probabilities. Then runtime libraries are compiled with profile collected.
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|
Finally a <code>stagefeedback</code> compiler is built using the information collected.
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</p>
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<p>Unlike standard bootstrap, several additional restrictions apply. The
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compiler used to build <code>stage1</code> needs to support a 64-bit integral type.
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It is recommended to only use GCC for this.
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</p>
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<hr />
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<p>
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<p><a href="./index.html">Return to the GCC Installation page</a>
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</p>
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