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<h1 class="settitle">Installing GCC: Building</h1>
<a name="index-Installing-GCC_003a-Building-1"></a>
Now that GCC is configured, you are ready to build the compiler and
runtime libraries.
<p>Some commands executed when making the compiler may fail (return a
nonzero status) and be ignored by <samp><span class="command">make</span></samp>. These failures, which
are often due to files that were not found, are expected, and can safely
be ignored.
<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><span class="option">--disable-werror</span></samp>.
<p>On certain old systems, defining certain environment variables such as
<samp><span class="env">CC</span></samp> can interfere with the functioning of <samp><span class="command">make</span></samp>.
<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>If you build GCC on a BSD system using a directory stored in an old System
V file system, problems may occur in running <samp><span class="command">fixincludes</span></samp> 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><span class="file">sys/types.h</span></samp>. If you find that <code>size_t</code> is a signed type and
that type mismatches occur, this could be the cause.
<p>The solution is not to use such a directory for building GCC.
<p>When building from SVN or snapshots, or if you modify parser sources,
you need the Bison parser generator installed. If you do not modify
parser sources, releases contain the Bison-generated files and you do
not need Bison installed to build them.
<p>When building from SVN or snapshots, or if you modify Texinfo
documentation, you need version 4.2 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.
<h3 class="section"><a name="TOC0"></a>0.1 Building a native compiler</h3>
<p>For a native build issue the command `<samp><span class="samp">make bootstrap</span></samp>'. This
will build the entire GCC system, which includes the following steps:
<ul>
<li>Build host tools necessary to build the compiler such as texinfo, bison,
gperf.
<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>Perform a 3-stage bootstrap of the compiler.
<li>Perform a comparison test of the stage2 and stage3 compilers.
<li>Build runtime libraries using the stage3 compiler from the previous step.
</ul>
<p>If you are short on disk space you might consider `<samp><span class="samp">make
bootstrap-lean</span></samp>' instead. This is identical to `<samp><span class="samp">make
bootstrap</span></samp>' except that 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>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.)
<pre class="smallexample"> make CFLAGS='-O' LIBCFLAGS='-g -O2' \
LIBCXXFLAGS='-g -O2 -fno-implicit-templates' bootstrap
</pre>
<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><span class="samp">make bootstrap</span></samp>'. Non-default optimization flags are less well
tested here than the default of `<samp><span class="samp">-g -O2</span></samp>', but should still work.
In a few cases, you may find that you need to specify special flags such
as <samp><span class="option">-msoft-float</span></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><span class="samp">make
bootstrap4</span></samp>' to increase the number of stages of bootstrap.
<p>Note that using non-standard <code>CFLAGS</code> can cause bootstrap to fail in
<samp><span class="file">libiberty</span></samp>, if these trigger a warning with the new compiler. For
example using `<samp><span class="samp">-O2 -g -mcpu=i686</span></samp>' on <code>i686-pc-linux-gnu</code> will
cause bootstrap failure as <samp><span class="option">-mcpu=</span></samp> is deprecated in 3.4.0 and above.
<p>If you used the flag <samp><span class="option">--enable-languages=...</span></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 <samp><span class="env">LANGUAGES</span></samp> when calling `<samp><span class="samp">make bootstrap</span></samp>'
<strong>does not</strong> work anymore!
<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><span class="file">Makefile</span></samp>.)
<h3 class="section"><a name="TOC1"></a>0.2 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>To build a cross compiler, we first recommend 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>Assuming you have already installed a native copy of GCC and configured
your cross compiler, issue the command <samp><span class="command">make</span></samp>, which performs the
following steps:
<ul>
<li>Build host tools necessary to build the compiler.
<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>Build the compiler (single stage only).
<li>Build runtime libraries using the compiler from the previous step.
</ul>
<p>Note that if an error occurs in any step the make process will exit.
<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><span class="file">/</span><var>target</var><span class="file">/bin</span></samp>. Here is a table of the tools
you should put in this directory:
<dl>
<dt><samp><span class="file">as</span></samp><dd>This should be the cross-assembler.
<br><dt><samp><span class="file">ld</span></samp><dd>This should be the cross-linker.
<br><dt><samp><span class="file">ar</span></samp><dd>This should be the cross-archiver: a program which can manipulate
archive files (linker libraries) in the target machine's format.
<br><dt><samp><span class="file">ranlib</span></samp><dd>This should be a program to construct a symbol table in an archive file.
</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>The easiest way to provide these files is to build the Binutils package.
Configure it with the same <samp><span class="option">--host</span></samp> and <samp><span class="option">--target</span></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>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><span class="option">--with-sysroot</span></samp> or <samp><span class="option">--with-headers</span></samp> and
<samp><span class="option">--with-libs</span></samp>. Many targets also require “start files” such
as <samp><span class="file">crt0.o</span></samp> and
<samp><span class="file">crtn.o</span></samp> which are linked into each executable. There may be several
alternatives for <samp><span class="file">crt0.o</span></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.
<h3 class="section"><a name="TOC2"></a>0.3 Building in parallel</h3>
<p>You can use `<samp><span class="samp">make bootstrap MAKE="make -j 2" -j 2</span></samp>', or just
`<samp><span class="samp">make -j 2 bootstrap</span></samp>' for GNU Make 3.79 and above, instead of
`<samp><span class="samp">make bootstrap</span></samp>' to build GCC in parallel.
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.
<h3 class="section"><a name="TOC3"></a>0.4 Building the Ada compiler</h3>
<p>In order to build GNAT, the Ada compiler, you need a working GNAT
compiler (GNAT version 3.14 or later, or GCC version 3.1 or later),
including GNAT tools such as <samp><span class="command">gnatmake</span></samp> and <samp><span class="command">gnatlink</span></samp>,
since the Ada front end is written in Ada (with some
GNAT-specific extensions), and GNU make.
<p><samp><span class="command">configure</span></samp> 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><span class="option">--enable-languages</span></samp> is
used to disable building the Ada front end.
<h3 class="section"><a name="TOC4"></a>0.5 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 compiler with profile feedback, use <code>make profiledbootstrap</code>.
<p>When `<samp><span class="samp">make profiledbootstrap</span></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>Unlike `<samp><span class="samp">make bootstrap</span></samp>' 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. Also parallel make is currently
not supported since collisions in profile collecting may occur.
<p><hr />
<p><a href="./index.html">Return to the GCC Installation page</a>
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