+++ /dev/null
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
- "http://www.w3.org/TR/html4/strict.dtd">
-<html>
-<head>
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
- <title>LLVM gold plugin</title>
- <link rel="stylesheet" href="_static/llvm.css" type="text/css">
-</head>
-<body>
-
-<h1>LLVM gold plugin</h1>
-<ol>
- <li><a href="#introduction">Introduction</a></li>
- <li><a href="#build">How to build it</a></li>
- <li><a href="#usage">Usage</a>
- <ul>
- <li><a href="#example1">Example of link time optimization</a></li>
- <li><a href="#lto_autotools">Quickstart for using LTO with autotooled projects</a></li>
- </ul></li>
- <li><a href="#licensing">Licensing</a></li>
-</ol>
-<div class="doc_author">Written by Nick Lewycky</div>
-
-<!--=========================================================================-->
-<h2><a name="introduction">Introduction</a></h2>
-<!--=========================================================================-->
-<div>
- <p>Building with link time optimization requires cooperation from the
-system linker. LTO support on Linux systems requires that you use
-the <a href="http://sourceware.org/binutils">gold linker</a> which supports
-LTO via plugins. This is the same mechanism used by the
-<a href="http://gcc.gnu.org/wiki/LinkTimeOptimization">GCC LTO</a>
-project.</p>
- <p>The LLVM gold plugin implements the
-<a href="http://gcc.gnu.org/wiki/whopr/driver">gold plugin interface</a>
-on top of
-<a href="LinkTimeOptimization.html#lto">libLTO</a>.
-The same plugin can also be used by other tools such as <tt>ar</tt> and
-<tt>nm</tt>.
-</div>
-<!--=========================================================================-->
-<h2><a name="build">How to build it</a></h2>
-<!--=========================================================================-->
-<div>
- <p>You need to have gold with plugin support and build the LLVMgold
-plugin. Check whether you have gold running <tt>/usr/bin/ld -v</tt>. It will
-report “GNU gold” or else “GNU ld” if not. If you have
-gold, check for plugin support by running <tt>/usr/bin/ld -plugin</tt>. If it
-complains “missing argument” then you have plugin support. If not,
-such as an “unknown option” error then you will either need to
-build gold or install a version with plugin support.</p>
-<ul>
- <li>To build gold with plugin support:
- <pre class="doc_code">
-mkdir binutils
-cd binutils
-cvs -z 9 -d :pserver:anoncvs@sourceware.org:/cvs/src login
-<em>{enter "anoncvs" as the password}</em>
-cvs -z 9 -d :pserver:anoncvs@sourceware.org:/cvs/src co binutils
-mkdir build
-cd build
-../src/configure --enable-gold --enable-plugins
-make all-gold
-</pre>
- That should leave you with <tt>binutils/build/gold/ld-new</tt> which supports the <tt>-plugin</tt> option. It also built would have
-<tt>binutils/build/binutils/ar</tt> and <tt>nm-new</tt> which support plugins
-but don't have a visible -plugin option, instead relying on the gold plugin
-being present in <tt>../lib/bfd-plugins</tt> relative to where the binaries are
-placed.
- <li>Build the LLVMgold plugin: Configure LLVM with
- <tt>--with-binutils-include=/path/to/binutils/src/include</tt> and run
- <tt>make</tt>.
-</ul>
-</div>
-<!--=========================================================================-->
-<h2><a name="usage">Usage</a></h2>
-<!--=========================================================================-->
-<div>
-
- <p>The linker takes a <tt>-plugin</tt> option that points to the path of
- the plugin <tt>.so</tt> file. To find out what link command <tt>gcc</tt>
- would run in a given situation, run <tt>gcc -v <em>[...]</em></tt> and look
- for the line where it runs <tt>collect2</tt>. Replace that with
- <tt>ld-new -plugin /path/to/LLVMgold.so</tt> to test it out. Once you're
- ready to switch to using gold, backup your existing <tt>/usr/bin/ld</tt>
- then replace it with <tt>ld-new</tt>.</p>
-
- <p>You can produce bitcode files from <tt>clang</tt> using
- <tt>-emit-llvm</tt> or <tt>-flto</tt>, or the <tt>-O4</tt> flag which is
- synonymous with <tt>-O3 -flto</tt>.</p>
-
- <p>Any of these flags will also cause <tt>clang</tt> to look for the
- gold plugin in the <tt>lib</tt> directory under its prefix and pass the
- <tt>-plugin</tt> option to <tt>ld</tt>. It will not look for an alternate
- linker, which is why you need gold to be the installed system linker in
- your path.</p>
-
- <p>If you want <tt>ar</tt> and <tt>nm</tt> to work seamlessly as well, install
- <tt>LLVMgold.so</tt> to <tt>/usr/lib/bfd-plugins</tt>. If you built your
- own gold, be sure to install the <tt>ar</tt> and <tt>nm-new</tt> you built to
- <tt>/usr/bin</tt>.<p>
-
-<!-- ======================================================================= -->
-<h3>
- <a name="example1">Example of link time optimization</a>
-</h3>
-
-<div>
- <p>The following example shows a worked example of the gold plugin mixing
- LLVM bitcode and native code.
-<pre class="doc_code">
---- a.c ---
-#include <stdio.h>
-
-extern void foo1(void);
-extern void foo4(void);
-
-void foo2(void) {
- printf("Foo2\n");
-}
-
-void foo3(void) {
- foo4();
-}
-
-int main(void) {
- foo1();
-}
-
---- b.c ---
-#include <stdio.h>
-
-extern void foo2(void);
-
-void foo1(void) {
- foo2();
-}
-
-void foo4(void) {
- printf("Foo4");
-}
-
---- command lines ---
-$ clang -flto a.c -c -o a.o # <-- a.o is LLVM bitcode file
-$ ar q a.a a.o # <-- a.a is an archive with LLVM bitcode
-$ clang b.c -c -o b.o # <-- b.o is native object file
-$ clang -flto a.a b.o -o main # <-- link with LLVMgold plugin
-</pre>
-
- <p>Gold informs the plugin that foo3 is never referenced outside the IR,
- leading LLVM to delete that function. However, unlike in the
- <a href="LinkTimeOptimization.html#example1">libLTO
- example</a> gold does not currently eliminate foo4.</p>
-</div>
-
-</div>
-
-<!--=========================================================================-->
-<h2>
- <a name="lto_autotools">
- Quickstart for using LTO with autotooled projects
- </a>
-</h2>
-<!--=========================================================================-->
-<div>
- <p>Once your system <tt>ld</tt>, <tt>ar</tt>, and <tt>nm</tt> all support LLVM
- bitcode, everything is in place for an easy to use LTO build of autotooled
- projects:</p>
-
- <ul>
- <li>Follow the instructions <a href="#build">on how to build LLVMgold.so</a>.</li>
- <li>Install the newly built binutils to <tt>$PREFIX</tt></li>
- <li>Copy <tt>Release/lib/LLVMgold.so</tt> to
- <tt>$PREFIX/lib/bfd-plugins/</tt></li>
- <li>Set environment variables (<tt>$PREFIX</tt> is where you installed clang and
- binutils):
-<pre class="doc_code">
-export CC="$PREFIX/bin/clang -flto"
-export CXX="$PREFIX/bin/clang++ -flto"
-export AR="$PREFIX/bin/ar"
-export NM="$PREFIX/bin/nm"
-export RANLIB=/bin/true #ranlib is not needed, and doesn't support .bc files in .a
-export CFLAGS="-O4"
-</pre>
- </li>
- <li>Or you can just set your path:
-<pre class="doc_code">
-export PATH="$PREFIX/bin:$PATH"
-export CC="clang -flto"
-export CXX="clang++ -flto"
-export RANLIB=/bin/true
-export CFLAGS="-O4"
-</pre></li>
- <li>Configure & build the project as usual:
-<pre class="doc_code">
-% ./configure && make && make check
-</pre></li>
- </ul>
-
- <p>The environment variable settings may work for non-autotooled projects
- too, but you may need to set the <tt>LD</tt> environment variable as
- well.</p>
-</div>
-
-<!--=========================================================================-->
-<h2><a name="licensing">Licensing</a></h2>
-<!--=========================================================================-->
-<div>
- <p>Gold is licensed under the GPLv3. LLVMgold uses the interface file
-<tt>plugin-api.h</tt> from gold which means that the resulting LLVMgold.so
-binary is also GPLv3. This can still be used to link non-GPLv3 programs just
-as much as gold could without the plugin.</p>
-</div>
-
-<!-- *********************************************************************** -->
-<hr>
-<address>
- <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
- src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
- <a href="http://validator.w3.org/check/referer"><img
- src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
- <a href="mailto:nicholas@metrix.on.ca">Nick Lewycky</a><br>
- <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
- Last modified: $Date: 2010-04-16 23:58:21 -0800 (Fri, 16 Apr 2010) $
-</address>
-</body>
-</html>
--- /dev/null
+.. _gold-plugin:
+
+====================
+The LLVM gold plugin
+====================
+
+.. sectionauthor:: Nick Lewycky
+
+Introduction
+============
+
+Building with link time optimization requires cooperation from
+the system linker. LTO support on Linux systems requires that you use the
+`gold linker`_ which supports LTO via plugins. This is the same mechanism
+used by the `GCC LTO`_ project.
+
+The LLVM gold plugin implements the gold plugin interface on top of
+:ref:`libLTO`. The same plugin can also be used by other tools such as
+``ar`` and ``nm``.
+
+.. _`gold linker`: http://sourceware.org/binutils
+.. _`GCC LTO`: http://gcc.gnu.org/wiki/LinkTimeOptimization
+.. _`gold plugin interface`: http://gcc.gnu.org/wiki/whopr/driver
+
+.. _lto-how-to-build:
+
+How to build it
+===============
+
+You need to have gold with plugin support and build the LLVMgold plugin.
+Check whether you have gold running ``/usr/bin/ld -v``. It will report "GNU
+gold" or else "GNU ld" if not. If you have gold, check for plugin support
+by running ``/usr/bin/ld -plugin``. If it complains "missing argument" then
+you have plugin support. If not, such as an "unknown option" error then you
+will either need to build gold or install a version with plugin support.
+
+* To build gold with plugin support:
+
+ .. code-block:: bash
+
+ $ mkdir binutils
+ $ cd binutils
+ $ cvs -z 9 -d :pserver:anoncvs@sourceware.org:/cvs/src login
+ {enter "anoncvs" as the password}
+ $ cvs -z 9 -d :pserver:anoncvs@sourceware.org:/cvs/src co binutils
+ $ mkdir build
+ $ cd build
+ $ ../src/configure --enable-gold --enable-plugins
+ $ make all-gold
+
+ That should leave you with ``binutils/build/gold/ld-new`` which supports
+ the ``-plugin`` option. It also built would have
+ ``binutils/build/binutils/ar`` and ``nm-new`` which support plugins but
+ don't have a visible -plugin option, instead relying on the gold plugin
+ being present in ``../lib/bfd-plugins`` relative to where the binaries
+ are placed.
+
+* Build the LLVMgold plugin: Configure LLVM with
+ ``--with-binutils-include=/path/to/binutils/src/include`` and run
+ ``make``.
+
+Usage
+=====
+
+The linker takes a ``-plugin`` option that points to the path of
+the plugin ``.so`` file. To find out what link command ``gcc``
+would run in a given situation, run ``gcc -v [...]`` and
+look for the line where it runs ``collect2``. Replace that with
+``ld-new -plugin /path/to/LLVMgold.so`` to test it out. Once you're
+ready to switch to using gold, backup your existing ``/usr/bin/ld``
+then replace it with ``ld-new``.
+
+You can produce bitcode files from ``clang`` using ``-emit-llvm`` or
+``-flto``, or the ``-O4`` flag which is synonymous with ``-O3 -flto``.
+
+Any of these flags will also cause ``clang`` to look for the gold plugin in
+the ``lib`` directory under its prefix and pass the ``-plugin`` option to
+``ld``. It will not look for an alternate linker, which is why you need
+gold to be the installed system linker in your path.``
+
+If you want ``ar`` and ``nm`` to work seamlessly as well, install
+``LLVMgold.so`` to ``/usr/lib/bfd-plugins``. If you built your own gold, be
+sure to install the ``ar`` and ``nm-new`` you built to ``/usr/bin``
+
+
+Example of link time optimization
+---------------------------------
+
+The following example shows a worked example of the gold plugin mixing LLVM
+bitcode and native code.
+
+.. code-block:: c
+
+ --- a.c ---
+ #include <stdio.h>
+
+ extern void foo1(void);
+ extern void foo4(void);
+
+ void foo2(void) {
+ printf("Foo2\n");
+ }
+
+ void foo3(void) {
+ foo4();
+ }
+
+ int main(void) {
+ foo1();
+ }
+
+ --- b.c ---
+ #include <stdio.h>
+
+ extern void foo2(void);
+
+ void foo1(void) {
+ foo2();
+ }
+
+ void foo4(void) {
+ printf("Foo4");
+ }
+
+.. code-block:: bash
+
+ --- command lines ---
+ $ clang -flto a.c -c -o a.o # <-- a.o is LLVM bitcode file
+ $ ar q a.a a.o # <-- a.a is an archive with LLVM bitcode
+ $ clang b.c -c -o b.o # <-- b.o is native object file
+ $ clang -flto a.a b.o -o main # <-- link with LLVMgold plugin
+
+Gold informs the plugin that foo3 is never referenced outside the IR,
+leading LLVM to delete that function. However, unlike in the :ref:`libLTO
+example <libLTO-example>` gold does not currently eliminate foo4.
+
+Quickstart for using LTO with autotooled projects
+=================================================
+
+Once your system ``ld``, ``ar``, and ``nm`` all support LLVM bitcode,
+everything is in place for an easy to use LTO build of autotooled projects:
+
+* Follow the instructions :ref:`on how to build LLVMgold.so
+ <lto-how-to-build>`.
+
+* Install the newly built binutils to ``$PREFIX``
+
+* Copy ``Release/lib/LLVMgold.so`` to ``$PREFIX/lib/bfd-plugins/``
+
+* Set environment variables (``$PREFIX`` is where you installed clang and
+ binutils):
+
+ .. code-block:: bash
+
+ export CC="$PREFIX/bin/clang -flto"
+ export CXX="$PREFIX/bin/clang++ -flto"
+ export AR="$PREFIX/bin/ar"
+ export NM="$PREFIX/bin/nm"
+ export RANLIB=/bin/true #ranlib is not needed, and doesn't support .bc files in .a
+ export CFLAGS="-O4"
+
+* Or you can just set your path:
+
+ .. code-block:: bash
+
+ export PATH="$PREFIX/bin:$PATH"
+ export CC="clang -flto"
+ export CXX="clang++ -flto"
+ export RANLIB=/bin/true
+ export CFLAGS="-O4"
+* Configure and build the project as usual:
+
+ .. code-block:: bash
+
+ % ./configure && make && make check
+
+The environment variable settings may work for non-autotooled projects too,
+but you may need to set the ``LD`` environment variable as well.
+
+Licensing
+=========
+
+Gold is licensed under the GPLv3. LLVMgold uses the interface file
+``plugin-api.h`` from gold which means that the resulting LLVMgold.so
+binary is also GPLv3. This can still be used to link non-GPLv3 programs
+just as much as gold could without the plugin.
projects / oota-llvm.git / commitdiff