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+<html lang="en">
+<head>
+<title>Installing GCC: Building</title>
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+<body>
+<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>Similarly, when building from SVN or snapshots, or if you modify
+<samp><span class="file">*.l</span></samp> files, you need the Flex lexical analyzer generator
+installed. If you do not modify <samp><span class="file">*.l</span></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>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.
+
+<h3 class="section"><a name="TOC0"></a>Building a native compiler</h3>
+
+<p>For a native build, the default configuration is to perform
+a 3-stage bootstrap of the compiler when &lsquo;<samp><span class="samp">make</span></samp>&rsquo; is invoked.
+This will build the entire GCC system and ensure that it compiles
+itself correctly. It can be disabled with the <samp><span class="option">--disable-bootstrap</span></samp>
+parameter to &lsquo;<samp><span class="samp">configure</span></samp>&rsquo;, but bootstrapping is suggested because
+the compiler will be tested more completely and could also have
+better performance.
+
+ <p>The bootstrapping process will complete the following steps:
+
+ <ul>
+<li>Build tools necessary to build the compiler.
+
+ <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>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 &lsquo;<samp><span class="samp">make
+bootstrap-lean</span></samp>&rsquo; 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>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 &lsquo;<samp><span class="samp">make</span></samp>&rsquo;. 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.)
+
+<pre class="smallexample"> make BOOT_CFLAGS='-O' bootstrap
+</pre>
+ <p>You can place non-default optimization flags into <code>BOOT_CFLAGS</code>; they
+are less well tested here than the default of &lsquo;<samp><span class="samp">-g -O2</span></samp>&rsquo;, 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 &lsquo;<samp><span class="samp">make
+bootstrap4</span></samp>&rsquo; to increase the number of stages of bootstrap.
+
+ <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>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 &lsquo;<samp><span class="samp">make</span></samp>&rsquo;
+<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 &ldquo;different&rdquo;. If you encounter this problem, you will
+need to disable comparison in the <samp><span class="file">Makefile</span></samp>.)
+
+ <p>If you do not want to bootstrap your compiler, you can configure with
+<samp><span class="option">--disable-bootstrap</span></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><span class="option">--enable-bootstrap</span></samp> to the configure script.
+
+ <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><span class="file">config/</span><code>NAME</code><span class="file">.mk</span></samp> will
+be included by the top-level <samp><span class="file">Makefile</span></samp>, bringing in any settings
+it contains. The default <code>BUILD_CONFIG</code> can be set using the
+configure option <samp><span class="option">--with-build-config=</span><code>NAME</code><span class="option">...</span></samp>. Some
+examples of supported build configurations are:
+
+ <dl>
+<dt>&lsquo;<samp><span class="samp">bootstrap-O1</span></samp>&rsquo;<dd>Removes any <samp><span class="option">-O</span></samp>-started option from <code>BOOT_CFLAGS</code>, and adds
+<samp><span class="option">-O1</span></samp> to it. &lsquo;<samp><span class="samp">BUILD_CONFIG=bootstrap-O1</span></samp>&rsquo; is equivalent to
+&lsquo;<samp><span class="samp">BOOT_CFLAGS='-g -O1'</span></samp>&rsquo;.
+
+ <br><dt>&lsquo;<samp><span class="samp">bootstrap-O3</span></samp>&rsquo;<dd>Analogous to <code>bootstrap-O1</code>.
+
+ <br><dt>&lsquo;<samp><span class="samp">bootstrap-lto</span></samp>&rsquo;<dd>Enables Link-Time Optimization for host tools during bootstrapping.
+&lsquo;<samp><span class="samp">BUILD_CONFIG=bootstrap-lto</span></samp>&rsquo; is equivalent to adding
+<samp><span class="option">-flto</span></samp> to &lsquo;<samp><span class="samp">BOOT_CFLAGS</span></samp>&rsquo;.
+
+ <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug</span></samp>&rsquo;<dd>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><span class="file">contrib/compare-debug</span></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.
+
+ <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug-big</span></samp>&rsquo;<dd>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 &lsquo;<samp><span class="samp">bootstrap-debug</span></samp>&rsquo;.
+
+ <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug-lean</span></samp>&rsquo;<dd>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><span class="option">-fcompare-debug</span></samp> to generate, compare and remove the dumps
+during stage3, repeating the compilation that already took place in
+stage2, whose dumps were not saved.
+
+ <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug-lib</span></samp>&rsquo;<dd>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><span class="option">-fcompare-debug</span></samp>, and it can be used along with any of the
+<code>bootstrap-debug</code> options above.
+
+ <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.
+
+ <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug-ckovw</span></samp>&rsquo;<dd>Arranges for error messages to be issued if the compiler built on any
+stage is run without the option <samp><span class="option">-fcompare-debug</span></samp>. This is
+useful to verify the full <samp><span class="option">-fcompare-debug</span></samp> testing coverage. It
+must be used along with <code>bootstrap-debug-lean</code> and
+<code>bootstrap-debug-lib</code>.
+
+ <br><dt>&lsquo;<samp><span class="samp">bootstrap-time</span></samp>&rsquo;<dd>Arranges for the run time of each program started by the GCC driver,
+built in any stage, to be logged to <samp><span class="file">time.log</span></samp>, in the top level of
+the build tree.
+
+ </dl>
+
+<h3 class="section"><a name="TOC1"></a>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 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>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><span class="option">--with-ecj-jar=...</span></samp>.
+
+ <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 &ldquo;start files&rdquo; 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>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 &lsquo;<samp><span class="samp">make -j 2</span></samp>&rsquo;
+instead of &lsquo;<samp><span class="samp">make</span></samp>&rsquo;. 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>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 <samp><span class="command">gnatmake</span></samp> and
+<samp><span class="command">gnatlink</span></samp>, since the Ada front end is written in Ada and
+uses some GNAT-specific extensions.
+
+ <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><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.
+
+ <p><samp><span class="env">ADA_INCLUDE_PATH</span></samp> and <samp><span class="env">ADA_OBJECT_PATH</span></samp> 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 &lsquo;<samp><span class="samp">gnatls -v</span></samp>&rsquo; lists only one explicit path in each
+section.
+
+<h3 class="section"><a name="TOC4"></a>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>When &lsquo;<samp><span class="samp">make profiledbootstrap</span></samp>&rsquo; 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 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. 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>
+
+<!-- ***Testing***************************************************************** -->
+<!-- ***Final install*********************************************************** -->
+<!-- ***Binaries**************************************************************** -->
+<!-- ***Specific**************************************************************** -->
+<!-- ***Old documentation****************************************************** -->
+<!-- ***GFDL******************************************************************** -->
+<!-- *************************************************************************** -->
+<!-- Part 6 The End of the Document -->
+</body></html>
+