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<title>GNU Compiler Collection (GCC) Internals: Target Structure</title>
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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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<a name="Target-Structure"></a>
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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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<a name="The-Global-targetm-Variable"></a>
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<h3 class="section">17.1 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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