<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- Copyright (C) 1988-2015 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Funding Free Software", the Front-Cover
Texts being (a) (see below), and with the Back-Cover Texts being (b)
(see below).  A copy of the license is included in the section entitled
"GNU Free Documentation License".

(a) The FSF's Front-Cover Text is:

A GNU Manual

(b) The FSF's Back-Cover Text is:

You have freedom to copy and modify this GNU Manual, like GNU
     software.  Copies published by the Free Software Foundation raise
     funds for GNU development. -->
<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
<head>
<title>GNU Compiler Collection (GCC) Internals: Back End</title>

<meta name="description" content="GNU Compiler Collection (GCC) Internals: Back End">
<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Back End">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link href="index.html#Top" rel="start" title="Top">
<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="gcc-Directory.html#gcc-Directory" rel="up" title="gcc Directory">
<link href="Testsuites.html#Testsuites" rel="next" title="Testsuites">
<link href="Front-End-Makefile.html#Front-End-Makefile" rel="prev" title="Front End Makefile">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.indentedblock {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
div.smalllisp {margin-left: 3.2em}
kbd {font-style:oblique}
pre.display {font-family: inherit}
pre.format {font-family: inherit}
pre.menu-comment {font-family: serif}
pre.menu-preformatted {font-family: serif}
pre.smalldisplay {font-family: inherit; font-size: smaller}
pre.smallexample {font-size: smaller}
pre.smallformat {font-family: inherit; font-size: smaller}
pre.smalllisp {font-size: smaller}
span.nocodebreak {white-space:nowrap}
span.nolinebreak {white-space:nowrap}
span.roman {font-family:serif; font-weight:normal}
span.sansserif {font-family:sans-serif; font-weight:normal}
ul.no-bullet {list-style: none}
-->
</style>


</head>

<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
<a name="Back-End"></a>
<div class="header">
<p>
Previous: <a href="Front-End.html#Front-End" accesskey="p" rel="prev">Front End</a>, Up: <a href="gcc-Directory.html#gcc-Directory" accesskey="u" rel="up">gcc Directory</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Anatomy-of-a-Target-Back-End"></a>
<h4 class="subsection">6.3.9 Anatomy of a Target Back End</h4>

<p>A back end for a target architecture in GCC has the following parts:
</p>
<ul>
<li> A directory <samp><var>machine</var></samp> under <samp>gcc/config</samp>, containing a
machine description <samp><var>machine</var>.md</samp> file (see <a href="Machine-Desc.html#Machine-Desc">Machine Descriptions</a>), header files <samp><var>machine</var>.h</samp> and
<samp><var>machine</var>-protos.h</samp> and a source file <samp><var>machine</var>.c</samp>
(see <a href="Target-Macros.html#Target-Macros">Target Description Macros and Functions</a>),
possibly a target Makefile fragment <samp>t-<var>machine</var></samp>
(see <a href="Target-Fragment.html#Target-Fragment">The Target Makefile Fragment</a>), and maybe
some other files.  The names of these files may be changed from the
defaults given by explicit specifications in <samp>config.gcc</samp>.
</li><li> If necessary, a file <samp><var>machine</var>-modes.def</samp> in the
<samp><var>machine</var></samp> directory, containing additional machine modes to
represent condition codes.  See <a href="Condition-Code.html#Condition-Code">Condition Code</a>, for further details.
</li><li> An optional <samp><var>machine</var>.opt</samp> file in the <samp><var>machine</var></samp>
directory, containing a list of target-specific options.  You can also
add other option files using the <code>extra_options</code> variable in
<samp>config.gcc</samp>.  See <a href="Options.html#Options">Options</a>.
</li><li> Entries in <samp>config.gcc</samp> (see <a href="System-Config.html#System-Config">The
<samp>config.gcc</samp> File</a>) for the systems with this target
architecture.
</li><li> Documentation in <samp>gcc/doc/invoke.texi</samp> for any command-line
options supported by this target (see <a href="Run_002dtime-Target.html#Run_002dtime-Target">Run-time
Target Specification</a>).  This means both entries in the summary table
of options and details of the individual options.
</li><li> Documentation in <samp>gcc/doc/extend.texi</samp> for any target-specific
attributes supported (see <a href="Target-Attributes.html#Target-Attributes">Defining
target-specific uses of <code>__attribute__</code></a>), including where the
same attribute is already supported on some targets, which are
enumerated in the manual.
</li><li> Documentation in <samp>gcc/doc/extend.texi</samp> for any target-specific
pragmas supported.
</li><li> Documentation in <samp>gcc/doc/extend.texi</samp> of any target-specific
built-in functions supported.
</li><li> Documentation in <samp>gcc/doc/extend.texi</samp> of any target-specific
format checking styles supported.
</li><li> Documentation in <samp>gcc/doc/md.texi</samp> of any target-specific
constraint letters (see <a href="Machine-Constraints.html#Machine-Constraints">Constraints for
Particular Machines</a>).
</li><li> A note in <samp>gcc/doc/contrib.texi</samp> under the person or people who
contributed the target support.
</li><li> Entries in <samp>gcc/doc/install.texi</samp> for all target triplets
supported with this target architecture, giving details of any special
notes about installation for this target, or saying that there are no
special notes if there are none.
</li><li> Possibly other support outside the <samp>gcc</samp> directory for runtime
libraries.  FIXME: reference docs for this.  The <code>libstdc++</code> porting
manual needs to be installed as info for this to work, or to be a
chapter of this manual.
</li></ul>

<p>If the back end is added to the official GCC source repository, the
following are also necessary:
</p>
<ul>
<li> An entry for the target architecture in <samp>readings.html</samp> on the
GCC web site, with any relevant links.
</li><li> Details of the properties of the back end and target architecture in
<samp>backends.html</samp> on the GCC web site.
</li><li> A news item about the contribution of support for that target
architecture, in <samp>index.html</samp> on the GCC web site.
</li><li> Normally, one or more maintainers of that target listed in
<samp>MAINTAINERS</samp>.  Some existing architectures may be unmaintained,
but it would be unusual to add support for a target that does not have
a maintainer when support is added.
</li><li> Target triplets covering all <samp>config.gcc</samp> stanzas for the target,
in the list in <samp>contrib/config-list.mk</samp>.
</li></ul>

<hr>
<div class="header">
<p>
Previous: <a href="Front-End.html#Front-End" accesskey="p" rel="prev">Front End</a>, Up: <a href="gcc-Directory.html#gcc-Directory" accesskey="u" rel="up">gcc Directory</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
</div>


</body>
</html>