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256 lines
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<title>Installing GCC: Building</title>
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<h1 class="settitle">Installing GCC: Building</h1>
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Now that GCC is configured, you are ready to build the compiler and
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runtime libraries.
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<p>We <strong>highly</strong> recommend that GCC be built using GNU make;
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other versions may work, then again they might not.
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GNU make is required for compiling GNAT (the Ada compiler) and the Java
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runtime library.
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<p>(For example, many broken versions of make will fail if you use the
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recommended setup where <var>objdir</var> is different from <var>srcdir</var>.
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Other broken versions may recompile parts of the compiler when
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installing the compiler.)
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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>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.
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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>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>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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<code>sys/types.h</code>. 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>The solution is not to use such a directory for building GCC.
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<p>When building from CVS or snapshots, or if you modify parser sources,
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you need the Bison parser generator installed. Any version 1.25 or
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later should work; older versions may also work. If you do not modify
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parser sources, releases contain the Bison-generated files and you do
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not need Bison installed to build them.
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<p>When building from CVS or snapshots, or if you modify Texinfo
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documentation, you need version 4.2 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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<h3 class="section"><a name="TOC0"></a>Building a native compiler</h3>
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<p>For a native build issue the command <code>make bootstrap</code>. This
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will build the entire GCC system, which includes the following steps:
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<ul>
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<li>Build host tools necessary to build the compiler such as texinfo, bison,
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gperf.
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<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
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or moved into the top level GCC source tree before configuring.
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<li>Perform a 3-stage bootstrap of the compiler.
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<li>Perform a comparison test of the stage2 and stage3 compilers.
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<li>Build runtime libraries using the stage3 compiler from the previous step.
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</ul>
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<p>If you are short on disk space you might consider <code>make
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bootstrap-lean</code> instead. This is identical to <code>make
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bootstrap</code> except that 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>If you want to save additional space during the bootstrap and in
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the final installation as well, you can build the compiler binaries
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without debugging information as in the following example. This will save
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roughly 40% of disk space both for the bootstrap and the final installation.
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(Libraries will still contain debugging information.)
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<pre class="example"> make CFLAGS='-O' LIBCFLAGS='-g -O2' \
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LIBCXXFLAGS='-g -O2 -fno-implicit-templates' bootstrap
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</pre>
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<p>If you wish to use non-default GCC flags when compiling the stage2 and
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stage3 compilers, set <code>BOOT_CFLAGS</code> on the command line when doing
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<code>make bootstrap</code>. Non-default optimization flags are less well
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tested here than the default of <code>-g -O2</code>, but should still work.
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In a few cases, you may find that you need to specify special flags such
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as <code>-msoft-float</code> here to complete the bootstrap; or, if the
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native compiler miscompiles the stage1 compiler, you may need to work
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around this, by choosing <code>BOOT_CFLAGS</code> to avoid the parts of the
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stage1 compiler that were miscompiled, or by using <code>make
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bootstrap4</code> to increase the number of stages of bootstrap.
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<p>If you used the flag <code>--enable-languages=...</code> 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 <code>make bootstrap</code>
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<strong>does not</strong> work anymore!
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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 <code>Makefile</code>.)
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<h3 class="section"><a name="TOC1"></a>Building a cross compiler</h3>
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<p>We recommend reading the
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<a href="http://www.objsw.com/CrossGCC/">crossgcc FAQ</a>
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for information about building cross compilers.
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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>To build a cross compiler, we first recommend 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>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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<ul>
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<li>Build host tools necessary to build the compiler such as texinfo, bison,
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gperf.
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<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>Build the compiler (single stage only).
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<li>Build runtime libraries using the compiler from the previous step.
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</ul>
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<p>Note that if an error occurs in any step the make process will exit.
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<h3 class="section"><a name="TOC2"></a>Building in parallel</h3>
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<p>You can use <code>make bootstrap MAKE="make -j 2" -j 2</code>, or just
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<code>make -j 2 bootstrap</code> for GNU Make 3.79 and above, instead of
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<code>make bootstrap</code> to build GCC in parallel.
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You can also specify a bigger number, and in most cases using a value
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greater than the number of processors in your machine will result in
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fewer and shorter I/O latency hits, thus improving overall throughput;
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this is especially true for slow drives and network filesystems.
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<h3 class="section"><a name="TOC3"></a>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 (GNAT version 3.13 or later, or GCC version 3.1 or later),
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since the Ada front end is written in Ada (with some
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GNAT-specific extensions), and GNU make.
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<p>However, you do not need a full installation of GNAT, just the GNAT
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binary <code>gnat1</code>, a copy of <code>gnatbind</code>, and a compiler driver
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which can deal with Ada input (by invoking the <code>gnat1</code> binary).
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You can specify this compiler driver by setting the <code>ADAC</code>
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environment variable at the configure step. <code>configure</code> can
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detect the driver automatically if it has got a common name such as
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<code>gcc</code> or <code>gnatgcc</code>. Of course, you still need a working
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C compiler (the compiler driver can be different or not).
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<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 <code>--enable-languages</code> is
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used to disable building the Ada front end.
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<p>Additional build tools (such as <code>gnatmake</code>) or a working GNAT
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run-time library installation are usually <em>not</em> required. However,
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if you want to bootstrap the compiler using a minimal version of GNAT,
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you have to issue the following commands before invoking <code>make
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bootstrap</code> (this assumes that you start with an unmodified and consistent
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source distribution):
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<pre class="example"> cd <var>srcdir</var>/gcc/ada
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touch treeprs.ads [es]info.h nmake.ad[bs]
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</pre>
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<p>At the moment, the GNAT library and several tools for GNAT are not built
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by <code>make bootstrap</code>. You have to invoke
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<code>make gnatlib_and_tools</code> in the <code></code><var>objdir</var><code>/gcc</code>
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subdirectory before proceeding with the next steps.
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<p>For example, you can build a native Ada compiler by issuing the
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following commands (assuming <code>make</code> is GNU make):
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<pre class="example"> cd <var>objdir</var>
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<var>srcdir</var>/configure --enable-languages=c,ada
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cd <var>srcdir</var>/gcc/ada
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touch treeprs.ads [es]info.h nmake.ad[bs]
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cd <var>objdir</var>
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make bootstrap
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cd gcc
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make gnatlib_and_tools
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cd ..
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</pre>
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<p>Currently, when compiling the Ada front end, you cannot use the parallel
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build feature described in the previous section.
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<hr />
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<p>
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<a href="./index.html">Return to the GCC Installation page</a>
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