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104 lines
5.0 KiB
HTML
104 lines
5.0 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Target Structure - GNU Compiler Collection (GCC) Internals</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="GNU Compiler Collection (GCC) Internals">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Target-Macros.html#Target-Macros" title="Target Macros">
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<link rel="next" href="Driver.html#Driver" title="Driver">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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Copyright (C) 1988-2015 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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<style type="text/css"><!--
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pre.display { font-family:inherit }
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pre.format { font-family:inherit }
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span.sc { font-variant:small-caps }
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span.roman { font-family:serif; font-weight:normal; }
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span.sansserif { font-family:sans-serif; font-weight:normal; }
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--></style>
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</head>
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<body>
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<div class="node">
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<a name="Target-Structure"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Driver.html#Driver">Driver</a>,
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Up: <a rel="up" accesskey="u" href="Target-Macros.html#Target-Macros">Target Macros</a>
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<hr>
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</div>
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<h3 class="section">17.1 The Global <code>targetm</code> Variable</h3>
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<p><a name="index-target-hooks-3854"></a><a name="index-target-functions-3855"></a>
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<div class="defun">
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— Variable: struct gcc_target <b>targetm</b><var><a name="index-targetm-3856"></a></var><br>
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<blockquote><p>The target <samp><span class="file">.c</span></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><span class="file">target.h</span></samp>;
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<samp><span class="file">target-def.h</span></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><span class="file">.c</span></samp> file should override those
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macros for which the default definition is inappropriate. For example:
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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>
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</blockquote></div>
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<p>Where a macro should be defined in the <samp><span class="file">.c</span></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><span class="file">.h</span></samp> file to being part of the
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<code>targetm</code> structure.
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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><span class="file">c-family/c-target.h</span></samp>, the
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initializer <code>TARGETCM_INITIALIZER</code> in
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<samp><span class="file">c-family/c-target-def.h</span></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><span class="file">config.gcc</span></samp>; otherwise a default definition is used.
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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><span class="file">common/common-target.h</span></samp>, the initializer
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<code>TARGETM_COMMON_INITIALIZER</code> in
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<samp><span class="file">common/common-target-def.h</span></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><span class="file">config.gcc</span></samp>; otherwise a
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default definition is used.
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</body></html>
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