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132 lines
5.8 KiB
HTML
132 lines
5.8 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2018 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Target Structure (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Target Structure (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Target Structure (GNU Compiler Collection (GCC) Internals)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Target-Macros.html#Target-Macros" rel="up" title="Target Macros">
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<link href="Driver.html#Driver" rel="next" title="Driver">
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<link href="Target-Macros.html#Target-Macros" rel="prev" title="Target Macros">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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div.smallexample {margin-left: 3.2em}
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div.smalllisp {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.menu-preformatted {font-family: serif}
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallexample {font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Target-Structure"></a>
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<div class="header">
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<p>
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Next: <a href="Driver.html#Driver" accesskey="n" rel="next">Driver</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</a> [<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>
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</div>
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<hr>
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<a name="The-Global-targetm-Variable"></a>
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<h3 class="section">18.1 The Global <code>targetm</code> Variable</h3>
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<a name="index-target-hooks"></a>
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<a name="index-target-functions"></a>
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<dl>
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<dt><a name="index-targetm"></a>Variable: <em>struct gcc_target</em> <strong>targetm</strong></dt>
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<dd><p>The target <samp>.c</samp> file must define the global <code>targetm</code> variable
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which contains pointers to functions and data relating to the target
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machine. The variable is declared in <samp>target.h</samp>;
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<samp>target-def.h</samp> defines the macro <code>TARGET_INITIALIZER</code> which is
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used to initialize the variable, and macros for the default initializers
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for elements of the structure. The <samp>.c</samp> file should override those
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macros for which the default definition is inappropriate. For example:
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</p><div class="smallexample">
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<pre class="smallexample">#include "target.h"
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#include "target-def.h"
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/* <span class="roman">Initialize the GCC target structure.</span> */
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#undef TARGET_COMP_TYPE_ATTRIBUTES
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#define TARGET_COMP_TYPE_ATTRIBUTES <var>machine</var>_comp_type_attributes
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struct gcc_target targetm = TARGET_INITIALIZER;
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</pre></div>
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</dd></dl>
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<p>Where a macro should be defined in the <samp>.c</samp> file in this manner to
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form part of the <code>targetm</code> structure, it is documented below as a
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“Target Hook” with a prototype. Many macros will change in future
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from being defined in the <samp>.h</samp> file to being part of the
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<code>targetm</code> structure.
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</p>
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<p>Similarly, there is a <code>targetcm</code> variable for hooks that are
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specific to front ends for C-family languages, documented as “C
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Target Hook”. This is declared in <samp>c-family/c-target.h</samp>, the
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initializer <code>TARGETCM_INITIALIZER</code> in
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<samp>c-family/c-target-def.h</samp>. If targets initialize <code>targetcm</code>
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themselves, they should set <code>target_has_targetcm=yes</code> in
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<samp>config.gcc</samp>; otherwise a default definition is used.
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</p>
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<p>Similarly, there is a <code>targetm_common</code> variable for hooks that
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are shared between the compiler driver and the compilers proper,
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documented as “Common Target Hook”. This is declared in
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<samp>common/common-target.h</samp>, the initializer
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<code>TARGETM_COMMON_INITIALIZER</code> in
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<samp>common/common-target-def.h</samp>. If targets initialize
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<code>targetm_common</code> themselves, they should set
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<code>target_has_targetm_common=yes</code> in <samp>config.gcc</samp>; otherwise a
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default definition is used.
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</p>
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</body>
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</html>
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