mirror of
https://github.com/golang/go
synced 2024-09-04 23:44:16 +00:00
doc: general update of gccgo_install
Fixes #3325. R=golang-dev, bradfitz, minux.ma, r CC=golang-dev https://golang.org/cl/5858043
This commit is contained in:
parent
65dc7dc90b
commit
a84e3baf9a
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@ -4,36 +4,59 @@
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}-->
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<p>
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This document explains how to use <code>gccgo</code>, a compiler for
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the Go language. The <code>gccgo</code> compiler is a new frontend
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for <code>gcc</code>, the widely used GNU compiler. Although the
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frontend itself is under a BSD-style license, <code>gccgo</code> is
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normally used as part of <code>gcc</code> and is then covered by
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This document explains how to use gccgo, a compiler for
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the Go language. The gccgo compiler is a new frontend
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for GCC, the widely used GNU compiler. Although the
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frontend itself is under a BSD-style license, gccgo is
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normally used as part of GCC and is then covered by
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the <a href="http://www.gnu.org/licenses/gpl.html">GNU General Public
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License</a>.
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License</a> (the license covers gccgo itself as part of GCC; it
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does not cover code generated by gccgo).
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</p>
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<p>
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Note that <code>gccgo</code> is not the <code>6g</code> compiler; see
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the <a href="/doc/install">Installing Go</a> instructions for that
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Note that gccgo is not the <code>gc</code> compiler; see
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the <a href="/doc/install.html">Installing Go</a> instructions for that
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compiler.
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</p>
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<h2 id="Releases">Releases</h2>
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<p>
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The simplest way to install gccgo is to install a GCC binary release
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built to include Go support. GCC binary releases are available from
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<a href="http://gcc.gnu.org/install/binaries.html">various
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websites</a> and are typically included as part of GNU/Linux
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distributions. We expect that most people who build these binaries
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will include Go support.
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</p>
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<p>
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The GCC 4.7.0 release includes Go support that is very close to
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<a href="/doc/go1.html">Go 1</a>. Due to release timing it will not
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include the last few changes to the Go 1 libraries. The GCC 4.7.1
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release should include a complete Go 1 compiler and libraries.
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</p>
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<h2 id="Source_code">Source code</h2>
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<p>
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The <code>gccgo</code> source code is accessible via Subversion. The
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<code>gcc</code> web site
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If you cannot use a release, or prefer to build gccgo for
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yourself,
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the gccgo source code is accessible via Subversion. The
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GCC web site
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has <a href="http://gcc.gnu.org/svn.html">instructions for getting the
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<code>gcc</code> source code</a>. The <code>gccgo</code> source code
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is a branch of the main <code>gcc</code> code
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GCC source code</a>. The gccgo source code is included. As a
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convenience, a stable version of the Go support is available in
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a branch of the main GCC code
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repository: <code>svn://gcc.gnu.org/svn/gcc/branches/gccgo</code>.
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This branch is periodically updated with stable Go compiler sources.
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</p>
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<p>
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Note that although <code>gcc.gnu.org</code> is the most convenient way
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to get the source code for the compiler, that is not where the master
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sources live. If you want to contribute changes to the gccgo
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to get the source code for the Go frontend, it is not where the master
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sources live. If you want to contribute changes to the Go frontend
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compiler, see <a href="/doc/gccgo_contribute.html">Contributing to
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gccgo</a>.
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</p>
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@ -42,29 +65,37 @@ gccgo</a>.
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<h2 id="Building">Building</h2>
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<p>
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Building <code>gccgo</code> is just like building <code>gcc</code>
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Building gccgo is just like building GCC
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with one or two additional options. See
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the <a href="http://gcc.gnu.org/install/">instructions on the gcc web
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site</a>. When you run <code>configure</code>, add the
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option <code>--enable-languages=c,c++,go</code> (along with other
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languages you may want to build). If you are targeting a 32-bit x86,
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then you will want to build <code>gccgo</code> to default to
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then you will want to build gccgo to default to
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supporting locked compare and exchange instructions; do this by also
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using the <code>configure</code> option <code>--with-arch=i586</code>
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(or a newer architecture, depending on where you need your programs to
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run).
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run). If you are targeting a 64-bit x86, but sometimes want to use
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the <code>-m32</code> option, then use the <code>configure</code>
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option <code>--with-arch-32=i586</code>.
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</p>
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<h3 id="Gold">Gold</h3>
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<p>
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On x86 GNU/Linux systems the gccgo compiler is able to
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use a small discontiguous stack for goroutines. This permits programs
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to run many more goroutines, since each goroutine can use a relatively
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small stack. Doing this requires using the gold linker version 2.22
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or later. You can either install GNU binutils 2.22 or later, or you
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can build gold yourself.
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</p>
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<p>
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On x86 GNU/Linux systems the <code>gccgo</code> compiler is able to
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use a small discontiguous stack for goroutines. This permits programs
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to run many more goroutines, since each goroutine can use a relatively
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small stack. Doing this requires using a development version of
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the <code>gold</code> linker. The easiest way to do this is to build
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the GNU binutils, using <code>--enable-gold=default</code> when you run
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the <code>configure</code> script, and to
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use <code>--with-ld=GOLD_BINARY</code> when you
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configure <code>gccgo</code>. A typical sequence would look like
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To build gold yourself, build the GNU binutils,
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using <code>--enable-gold=default</code> when you run
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the <code>configure</code> script. Before building, you must install
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the flex and bison packages. A typical sequence would look like
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this (you can replace <code>/opt/gold</code> with any directory to
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which you have write access):
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</p>
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@ -72,6 +103,7 @@ which you have write access):
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<pre>
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cvs -z 9 -d :pserver:anoncvs@sourceware.org:/cvs/src login
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[password is "anoncvs"]
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[The next command will create a directory named src, not binutils]
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cvs -z 9 -d :pserver:anoncvs@sourceware.org:/cvs/src co binutils
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mkdir binutils-objdir
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cd binutils-objdir
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@ -81,29 +113,69 @@ make install
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</pre>
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<p>
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A number of prerequisites are required to build <code>gcc</code>, as
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described on the <a href="http://gcc.gnu.org/">gcc web site</a>. If
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those are all available, then a typical build and install sequence
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would look like this (only use the <code>--with-ld</code> option if
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you built and installed the gold linker as described above):
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However you install gold, when you configure gccgo, use the
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option <code>--with-ld=<var>GOLD_BINARY</var></code>.
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</p>
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<h3 id="Prerequisites">Prerequisites</h3>
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<p>
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A number of prerequisites are required to build GCC, as
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described on
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the <a href="http://gcc.gnu.org/install/prerequisites.html">gcc web
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site</a>. It is important to install all the prerequisites before
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running the gcc <code>configure</code> script.
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<h3 id="Build_commands">Build commands</h3>
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<p>
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Once all the prerequisites are installed, then a typical build and
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install sequence would look like this (only use
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the <code>--with-ld</code> option if you are using the gold linker as
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described above):
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</p>
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<pre>
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svn checkout svn://gcc.gnu.org/svn/gcc/branches/gccgo gccgo
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mkdir objdir
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cd objdir
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../gccgo/configure --enable-languages=c,c++,go --with-ld=/opt/gold/bin/ld
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../gccgo/configure --prefix=/opt/gccgo --enable-languages=c,c++,go --with-ld=/opt/gold/bin/ld
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make
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make install
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</pre>
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<h3 id="Ubuntu">A note on Ubuntu</h3>
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<p>
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Current versions of Ubuntu and current versions of gcc disagree on
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where system libraries and header files are found. This is not a
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gccgo issue, and we hope this will be resolved soon. Until it is,
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setting these environment variables while configuring and building
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gccgo may fix the problem.
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</p>
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<pre>
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LIBRARY_PATH=/usr/lib/x86_64-linux-gnu
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C_INCLUDE_PATH=/usr/include/x86_64-linux-gnu
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CPLUS_INCLUDE_PATH=/usr/include/x86_64-linux-gnu
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export LIBRARY_PATH C_INCLUDE_PATH CPLUS_INCLUDE_PATH
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</pre>
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<h2 id="Using_gccgo">Using gccgo</h2>
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<p>
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The <code>gccgo</code> compiler works like other gcc frontends.
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The gccgo compiler works like other gcc frontends. The gccgo
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installation does not currently include a version of
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the <code>go</code> command. However if you have the <code>go</code>
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command from an installation of the <code>gc</code> compiler, you can
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use it with gccgo by passing the option <code>-compiler gccgo</code>
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to <code>go build</code> or <code>go install</code> or <code>go
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test</code>.
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</p>
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<p>
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To compile a file:
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To compile a file without using the <code>go</code> command:
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</p>
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<pre>
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gccgo -c file.go
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@ -112,6 +184,7 @@ gccgo -c file.go
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<p>
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That produces <code>file.o</code>. To link files together to form an
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executable:
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</p>
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<pre>
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gccgo -o file file.o
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@ -119,44 +192,68 @@ gccgo -o file file.o
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<p>
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To run the resulting file, you will need to tell the program where to
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find the compiled Go packages. This can be done either by setting
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<code>LD_LIBRARY_PATH</code> in your environment:
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find the compiled Go packages. There are a few ways to do this:
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</p>
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<ul>
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<li>
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<p>
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Set the <code>LD_LIBRARY_PATH</code> environment variable:
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</p>
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<pre>
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LD_LIBRARY_PATH=/usr/lib/gcc/MACHINE/VERSION
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LD_LIBRARY_PATH=${prefix}/lib/gcc/MACHINE/VERSION
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[or]
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LD_LIBRARY_PATH=${prefix}/lib64/gcc/MACHINE/VERSION
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export LD_LIBRARY_PATH
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</pre>
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<p>
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or by passing a <code>-Wl,-R</code> option when you link:
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Here <code>${prefix}</code> is the <code>--prefix</code> option used
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when building gccgo. For a binary install this is
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normally <code>/usr</code>. Whether to use <code>lib</code>
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or <code>lib64</code> depends on the target.
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Typically <code>lib64</code> is correct for x86_64 systems,
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and <code>lib</code> is correct for other systems. The idea is to
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name the directory where <code>libgo.so</code> is found.
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</p>
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</li>
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<li>
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||||
<p>
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Passing a <code>-Wl,-R</code> option when you link:
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</p>
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<pre>
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gccgo -o file file.o -Wl,-R,/usr/lib/gcc/MACHINE/VERSION
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gccgo -o file file.o -Wl,-R,${prefix}/lib/gcc/MACHINE/VERSION
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[or]
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gccgo -o file file.o -Wl,-R,${prefix}/lib64/gcc/MACHINE/VERSION
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</pre>
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</li>
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<li>
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||||
<p>
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or you can use the <code>-static-libgo</code> link-time option to link
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statically against libgo, or you can do a fully static link (static
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linking is the default for the <code>6l</code> Go linker). On most
|
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systems, a static link will look something like:
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|
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<pre>
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gccgo -o file file.o -static -L /usr/lib/nptl -lgobegin -lgo -lpthread
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</pre>
|
||||
Use the <code>-static-libgo</code> option to link statically against
|
||||
the compiled packages.
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||||
</p>
|
||||
</li>
|
||||
|
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<li>
|
||||
<p>
|
||||
You may get a warning about not creating an <code>.eh_frame_hdr</code>
|
||||
section; this has nothing to do with Go, and may be ignored. In the
|
||||
future the requirement of explicitly specifying
|
||||
<code>-L /usr/lib/nptl -lgobegin -lgo -lpthread</code>
|
||||
may be removed.
|
||||
|
||||
Use the <code>-static</code> option to do a fully static link (the
|
||||
default for the <code>gc</code> compiler).
|
||||
</p>
|
||||
</li>
|
||||
</ul>
|
||||
|
||||
<h2 id="Options">Options</h2>
|
||||
|
||||
<p>
|
||||
The <code>gccgo</code> compiler supports all <code>gcc</code> options
|
||||
The gccgo compiler supports all GCC options
|
||||
that are language independent, notably the <code>-O</code>
|
||||
and <code>-g</code> options.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
The <code>-fgo-prefix=PREFIX</code> option may be used to set a unique
|
||||
|
@ -165,28 +262,24 @@ use with large programs that contain many packages, in order to allow
|
|||
multiple packages to use the same identifier as the package name.
|
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The <code>PREFIX</code> may be any string; a good choice for the
|
||||
string is the directory where the package will be installed.
|
||||
|
||||
<p>
|
||||
The <code>-fno-require-return-statement</code> option may be used to
|
||||
disable the compiler error about functions missing return statements.
|
||||
Note that there is no way to disable this error in <code>6g</code>.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
The <code>-I</code> and <code>-L</code> options, which are synonyms
|
||||
for the compiler, may be used to set the search path for finding
|
||||
imports.
|
||||
|
||||
</p>
|
||||
|
||||
<h2 id="Imports">Imports</h2>
|
||||
|
||||
<p>
|
||||
When you compile a file which exports something, the export
|
||||
information will be stored directly in the object file. When
|
||||
you import a package, you must tell <code>gccgo</code> how to
|
||||
When you compile a file that exports something, the export
|
||||
information will be stored directly in the object file. When
|
||||
you import a package, you must tell gccgo how to
|
||||
find the file.
|
||||
|
||||
<p>
|
||||
When you import the package <var>FILE</var> with <code>gccgo</code>,
|
||||
When you import the package <var>FILE</var> with gccgo,
|
||||
it will look for the import data in the following files, and use the
|
||||
first one that it finds.
|
||||
|
||||
|
@ -201,21 +294,25 @@ first one that it finds.
|
|||
<code><var>FILE</var>.gox</code>, when used, will typically contain
|
||||
nothing but export data. This can be generated from
|
||||
<code><var>FILE</var>.o</code> via
|
||||
</p>
|
||||
|
||||
<pre>
|
||||
objcopy -j .go_export FILE.o FILE.gox
|
||||
</pre>
|
||||
|
||||
<p>
|
||||
The <code>gccgo</code> compiler will look in the current
|
||||
directory for import files. In more complex scenarios you
|
||||
The gccgo compiler will look in the current
|
||||
directory for import files. In more complex scenarios you
|
||||
may pass the <code>-I</code> or <code>-L</code> option to
|
||||
<code>gccgo</code>. Both options take directories to search. The
|
||||
gccgo. Both options take directories to search. The
|
||||
<code>-L</code> option is also passed to the linker.
|
||||
</p>
|
||||
|
||||
The <code>gccgo</code> compiler does not currently (2009-11-06) record
|
||||
<p>
|
||||
The gccgo compiler does not currently (2012-03-20) record
|
||||
the file name of imported packages in the object file. You must
|
||||
arrange for the imported data to be linked into the program.
|
||||
</p>
|
||||
|
||||
<pre>
|
||||
gccgo -c mypackage.go # Exports mypackage
|
||||
|
@ -223,48 +320,41 @@ gccgo -c main.go # Imports mypackage
|
|||
gccgo -o main main.o mypackage.o # Explicitly links with mypackage.o
|
||||
</pre>
|
||||
|
||||
<h2 id="Unimplemented">Unimplemented</h2>
|
||||
|
||||
<p>
|
||||
Some Go features are not yet implemented in <code>gccgo</code>. As of
|
||||
2010-08-23, the following are not implemented:
|
||||
|
||||
<ul>
|
||||
<li>goroutines are implemented as NPTL threads. If you can not use
|
||||
the gold linker as described above, they are created with a fixed
|
||||
stack size, and the number of goroutines that may be created at
|
||||
one time is limited.
|
||||
</ul>
|
||||
|
||||
<h2 id="Debugging">Debugging</h2>
|
||||
|
||||
<p>
|
||||
If you use the <code>-g</code> option when you compile, you can run
|
||||
<code>gdb</code> on your executable. The debugger doesn't (yet)
|
||||
know anything about Go. However, you can set breakpoints, single-step,
|
||||
<code>gdb</code> on your executable. The debugger has only limited
|
||||
knowledge about Go. You can set breakpoints, single-step,
|
||||
etc. You can print variables, but they will be printed as though they
|
||||
had C/C++ types. For numeric types this doesn't matter. Go strings
|
||||
will show up as pointers to structures; to see the value
|
||||
<code>print *stringvar</code>. In general Go strings, maps, channels
|
||||
and interfaces are always represented as C pointers.
|
||||
had C/C++ types. For numeric types this doesn't matter. Go strings
|
||||
and interfaces will show up as two-element structures. Go
|
||||
maps and channels are always represented as C pointers to run-time
|
||||
structures.
|
||||
</p>
|
||||
|
||||
<h2 id="C_Interoperability">C Interoperability</h2>
|
||||
|
||||
<p>
|
||||
When using <code>gccgo</code> there is limited interoperability with C,
|
||||
When using gccgo there is limited interoperability with C,
|
||||
or with C++ code compiled using <code>extern "C"</code>.
|
||||
</p>
|
||||
|
||||
<h3 id="Types">Types</h3>
|
||||
|
||||
<p>
|
||||
Basic types map directly: an <code>int</code> in Go is an <code>int</code>
|
||||
in C, etc. Go <code>byte</code> is equivalent to C <code>unsigned char</code>.
|
||||
in C, an <code>int32</code> is an <code>int32_t</code>,
|
||||
etc. Go <code>byte</code> is equivalent to C <code>unsigned
|
||||
char</code>.
|
||||
Pointers in Go are pointers in C. A Go <code>struct</code> is the same as C
|
||||
<code>struct</code> with the same fields and types.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
The Go <code>string</code> type is currently defined as a two-element
|
||||
structure (this is <b style="color: red;">subject to change</b>):
|
||||
</p>
|
||||
|
||||
<pre>
|
||||
struct __go_string {
|
||||
|
@ -279,10 +369,12 @@ array in Go is equivalent to a C pointer to the
|
|||
equivalent of the element type.
|
||||
For example, Go <code>*[10]int</code> is equivalent to C <code>int*</code>,
|
||||
assuming that the C pointer does point to 10 elements.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
A slice in Go is a structure. The current definition is
|
||||
(this is <b style="color: red;">subject to change</b>):
|
||||
</p>
|
||||
|
||||
<pre>
|
||||
struct __go_slice {
|
||||
|
@ -294,9 +386,10 @@ struct __go_slice {
|
|||
|
||||
<p>
|
||||
The type of a Go function with no receiver is equivalent to a C function
|
||||
whose parameter types are equivalent. When a Go function returns more
|
||||
than one value, the C function returns a struct. For example, these
|
||||
whose parameter types are equivalent. When a Go function returns more
|
||||
than one value, the C function returns a struct. For example, these
|
||||
functions have equivalent types:
|
||||
</p>
|
||||
|
||||
<pre>
|
||||
func GoFunction(int) (int, float64)
|
||||
|
@ -305,7 +398,9 @@ struct { int i; float64 f; } CFunction(int)
|
|||
|
||||
<p>
|
||||
A pointer to a Go function is equivalent to a pointer to a C function
|
||||
when the functions have equivalent types.
|
||||
when the functions have equivalent types (this is
|
||||
<b style="color: red;">subject to change</b>).
|
||||
</p>
|
||||
|
||||
<p>
|
||||
Go <code>interface</code>, <code>channel</code>, and <code>map</code>
|
||||
|
@ -317,6 +412,7 @@ which one is difficult to predict in general; use a cast. C <code>union</code>
|
|||
types have no corresponding Go type. C <code>struct</code> types containing
|
||||
bitfields have no corresponding Go type. C++ <code>class</code> types have
|
||||
no corresponding Go type.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
Memory allocation is completely different between C and Go, as Go uses
|
||||
|
@ -328,33 +424,38 @@ while the Go side still has a copy the program will fail. When passing a
|
|||
pointer from Go to C, the Go function must retain a visible copy of it in
|
||||
some Go variable. Otherwise the Go garbage collector may delete the
|
||||
pointer while the C function is still using it.
|
||||
</p>
|
||||
|
||||
<h3 id="Function_names">Function names</h3>
|
||||
|
||||
<p>
|
||||
Go code can call C functions directly using a Go extension implemented
|
||||
in <code>gccgo</code>: a function declaration may be followed by
|
||||
<code>__asm__("NAME")</code>. For example, here is how the C function
|
||||
in gccgo: a function declaration may be preceded by
|
||||
<code>//extern NAME</code>. For example, here is how the C function
|
||||
<code>open</code> can be declared in Go:
|
||||
</p>
|
||||
|
||||
<pre>
|
||||
func c_open(name *byte, mode int, perm int) int __asm__ ("open");
|
||||
//extern open
|
||||
func c_open(name *byte, mode int, perm int) int
|
||||
</pre>
|
||||
|
||||
<p>
|
||||
The C function naturally expects a NUL-terminated string, which in
|
||||
Go is equivalent to a pointer to an array (not a slice!) of
|
||||
<code>byte</code> with a terminating zero byte. So a sample call
|
||||
from Go would look like (after importing the <code>os</code> package):
|
||||
from Go would look like (after importing the <code>syscall</code> package):
|
||||
</p>
|
||||
|
||||
<pre>
|
||||
var name = [4]byte{'f', 'o', 'o', 0};
|
||||
i := c_open(&name[0], os.O_RDONLY, 0);
|
||||
i := c_open(&name[0], syscall.O_RDONLY, 0);
|
||||
</pre>
|
||||
|
||||
<p>
|
||||
(this serves as an example only, to open a file in Go please use Go's
|
||||
<code>os.Open</code> function instead).
|
||||
</p>
|
||||
|
||||
<p>
|
||||
The name of Go functions accessed from C is subject to change. At present
|
||||
|
@ -363,8 +464,8 @@ the name of a Go function that does not have a receiver is
|
|||
the <code>-fgo-prefix</code> option used when the package is compiled;
|
||||
if the option is not used, the default is <code>go</code>.
|
||||
To call the function from C you must set the name using
|
||||
a <code>gcc</code> extension similar to the <code>gccgo</code>
|
||||
extension.
|
||||
a GCC extension.
|
||||
</p>
|
||||
|
||||
<pre>
|
||||
extern int go_function(int) __asm__ ("myprefix.mypackage.Function");
|
||||
|
@ -374,37 +475,35 @@ extern int go_function(int) __asm__ ("myprefix.mypackage.Function");
|
|||
Automatic generation of Go declarations from C source code</h3>
|
||||
|
||||
<p>
|
||||
The Go version of <code>gcc</code> supports automatically generating
|
||||
Go declarations from C code. The facility is rather awkward at present,
|
||||
and a better mechanism is under development.
|
||||
The Go version of GCC supports automatically generating
|
||||
Go declarations from C code. The facility is rather awkward, and most
|
||||
users should use the <a href="/cmd/cgo">cgo</a> program with
|
||||
the <code>-gccgo</code> option instead.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
Compile your C code as usual, but replace <code>-c</code> with
|
||||
<code>-S -ggo</code>. The result will be an assembler file
|
||||
with a <code>.s</code> extension. This assembler file will contain
|
||||
comments beginning with #GO. Those comments are declarations in the Go
|
||||
language for the C types, variables and functions declared in the C code.
|
||||
C types which can not be represented in Go will contain the string INVALID.
|
||||
Unsupported macro definitions will be recorded as <code>unknowndefine</code>,
|
||||
and uses of <code>#undef</code> will be recorded as <code>undef</code>.
|
||||
So it is very approximately possible to get Go code by running
|
||||
|
||||
<pre>
|
||||
gcc -S -ggo foo.c
|
||||
grep '#GO' foo.s | grep -v INVALID | grep -v unknowndefine | grep -v undef > foo.go
|
||||
</pre>
|
||||
Compile your C code as usual, and add the option
|
||||
<code>-fdump-go-spec=<var>FILENAME</var></code>. This will create the
|
||||
file <code><var>FILENAME</var></code> as a side effect of the
|
||||
compilation. This file will contain Go declarations for the types,
|
||||
variables and functions declared in the C code. C types that can not
|
||||
be represented in Go will be recorded as comments in the Go code. The
|
||||
generated file will not have a <code>package</code> declaration, but
|
||||
can otherwise be compiled directly by gccgo.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
This procedure is full of unstated caveats and restrictions and we make no
|
||||
guarantee that it will not change in the future. It is more useful as a
|
||||
starting point for real Go code than as a regular procedure.
|
||||
</p>
|
||||
|
||||
<h2 id="RTEMS_Port">RTEMS Port</h2>
|
||||
<p>
|
||||
The <code>gccgo</code> compiler has been ported to <a href="http://www.rtems.com/">
|
||||
The gccgo compiler has been ported to <a href="http://www.rtems.com/">
|
||||
<code>RTEMS</code></a>. <code>RTEMS</code> is a real-time executive
|
||||
that provides a high performance environment for embedded applications
|
||||
on a range of processors and embedded hardware. The current <code>gccgo</code>
|
||||
on a range of processors and embedded hardware. The current gccgo
|
||||
port is for x86. The goal is to extend the port to most of the
|
||||
<a href="http://www.rtems.org/wiki/index.php/SupportedCPUs">
|
||||
architectures supported by <code>RTEMS</code></a>. For more information on the port,
|
||||
|
|
Loading…
Reference in a new issue