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<head>
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<title>Installing GCC: Building</title>
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Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
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1999, 2000, 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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A GNU Manual
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</head>
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<body>
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<h1 class="settitle">Installing GCC: Building</h1>
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<a name="index-Installing-GCC_003a-Building-1"></a>
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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>Some commands executed when making the compiler may fail (return a
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nonzero status) and be ignored by <samp><span class="command">make</span></samp>. 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. 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><span class="option">--disable-werror</span></samp>.
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<p>On certain old systems, defining certain environment variables such as
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<samp><span class="env">CC</span></samp> can interfere with the functioning of <samp><span class="command">make</span></samp>.
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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 <samp><span class="command">fixincludes</span></samp> 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><span class="file">sys/types.h</span></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>The solution is not to use such a directory for building GCC.
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<p>When building from SVN or snapshots, or if you modify parser sources,
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you need the Bison parser generator installed. 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 SVN 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>0.1 Building a native compiler</h3>
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<p>For a native build issue the command `<samp><span class="samp">make bootstrap</span></samp>'. 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 `<samp><span class="samp">make
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bootstrap-lean</span></samp>' instead. This is identical to `<samp><span class="samp">make
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bootstrap</span></samp>' 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="smallexample"> 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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`<samp><span class="samp">make bootstrap</span></samp>'. Non-default optimization flags are less well
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tested here than the default of `<samp><span class="samp">-g -O2</span></samp>', 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 <samp><span class="option">-msoft-float</span></samp> 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 `<samp><span class="samp">make
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bootstrap4</span></samp>' to increase the number of stages of bootstrap.
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<p>Note that using non-standard <code>CFLAGS</code> can cause bootstrap to fail in
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<samp><span class="file">libiberty</span></samp>, if these trigger a warning with the new compiler. For
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example using `<samp><span class="samp">-O2 -g -mcpu=i686</span></samp>' on <code>i686-pc-linux-gnu</code> will
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cause bootstrap failure as <samp><span class="option">-mcpu=</span></samp> is deprecated in 3.4.0 and above.
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<p>If you used the flag <samp><span class="option">--enable-languages=...</span></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 <samp><span class="env">LANGUAGES</span></samp> when calling `<samp><span class="samp">make bootstrap</span></samp>'
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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 <samp><span class="file">Makefile</span></samp>.)
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<h3 class="section"><a name="TOC1"></a>0.2 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>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 <samp><span class="command">make</span></samp>, 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.
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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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<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><span class="file">/</span><var>target</var><span class="file">/bin</span></samp>. Here is a table of the tools
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you should put in this directory:
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<dl>
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<dt><samp><span class="file">as</span></samp><dd>This should be the cross-assembler.
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<br><dt><samp><span class="file">ld</span></samp><dd>This should be the cross-linker.
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<br><dt><samp><span class="file">ar</span></samp><dd>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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<br><dt><samp><span class="file">ranlib</span></samp><dd>This should be a program to construct a symbol table in an archive file.
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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>The easiest way to provide these files is to build the Binutils package.
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Configure it with the same <samp><span class="option">--host</span></samp> and <samp><span class="option">--target</span></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>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><span class="option">--with-sysroot</span></samp> or <samp><span class="option">--with-headers</span></samp> and
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<samp><span class="option">--with-libs</span></samp>. Many targets also require “start files” such
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as <samp><span class="file">crt0.o</span></samp> and
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<samp><span class="file">crtn.o</span></samp> which are linked into each executable. There may be several
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alternatives for <samp><span class="file">crt0.o</span></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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<h3 class="section"><a name="TOC2"></a>0.3 Building in parallel</h3>
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<p>You can use `<samp><span class="samp">make bootstrap MAKE="make -j 2" -j 2</span></samp>', or just
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`<samp><span class="samp">make -j 2 bootstrap</span></samp>' for GNU Make 3.79 and above, instead of
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`<samp><span class="samp">make bootstrap</span></samp>' 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>0.4 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 3.14 or later, or GCC version 3.1 or later),
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including GNAT tools such as <samp><span class="command">gnatmake</span></samp> and <samp><span class="command">gnatlink</span></samp>,
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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><samp><span class="command">configure</span></samp> 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><span class="option">--enable-languages</span></samp> is
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used to disable building the Ada front end.
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<h3 class="section"><a name="TOC4"></a>0.5 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 compiler with profile feedback, use <code>make profiledbootstrap</code>.
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<p>When `<samp><span class="samp">make profiledbootstrap</span></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>Unlike `<samp><span class="samp">make bootstrap</span></samp>' 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. Also parallel make is currently
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not supported since collisions in profile collecting may occur.
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<p><hr />
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<p><a href="./index.html">Return to the GCC Installation page</a>
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<!-- ***Testing***************************************************************** -->
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<!-- ***Final install*********************************************************** -->
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<!-- ***Binaries**************************************************************** -->
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<!-- ***Specific**************************************************************** -->
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<!-- ***Old documentation****************************************************** -->
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<!-- ***GFDL******************************************************************** -->
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<!-- *************************************************************************** -->
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<!-- Part 6 The End of the Document -->
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</body></html>
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