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<h3 class="section">17.1 The Global <code>targetm</code> Variable</h3>
<p><a name="index-target-hooks-3854"></a><a name="index-target-functions-3855"></a>
<div class="defun">
— Variable: struct gcc_target <b>targetm</b><var><a name="index-targetm-3856"></a></var><br>
<blockquote><p>The target <samp><span class="file">.c</span></samp> file must define the global <code>targetm</code> variable
which contains pointers to functions and data relating to the target
machine. The variable is declared in <samp><span class="file">target.h</span></samp>;
<samp><span class="file">target-def.h</span></samp> defines the macro <code>TARGET_INITIALIZER</code> which is
used to initialize the variable, and macros for the default initializers
for elements of the structure. The <samp><span class="file">.c</span></samp> file should override those
macros for which the default definition is inappropriate. For example:
<pre class="smallexample"> #include "target.h"
#include "target-def.h"
/* <span class="roman">Initialize the GCC target structure.</span> */
#undef TARGET_COMP_TYPE_ATTRIBUTES
#define TARGET_COMP_TYPE_ATTRIBUTES <var>machine</var>_comp_type_attributes
struct gcc_target targetm = TARGET_INITIALIZER;
</pre>
</blockquote></div>
<p>Where a macro should be defined in the <samp><span class="file">.c</span></samp> file in this manner to
form part of the <code>targetm</code> structure, it is documented below as a
“Target Hook” with a prototype. Many macros will change in future
from being defined in the <samp><span class="file">.h</span></samp> file to being part of the
<code>targetm</code> structure.
<p>Similarly, there is a <code>targetcm</code> variable for hooks that are
specific to front ends for C-family languages, documented as “C
Target Hook”. This is declared in <samp><span class="file">c-family/c-target.h</span></samp>, the
initializer <code>TARGETCM_INITIALIZER</code> in
<samp><span class="file">c-family/c-target-def.h</span></samp>. If targets initialize <code>targetcm</code>
themselves, they should set <code>target_has_targetcm=yes</code> in
<samp><span class="file">config.gcc</span></samp>; otherwise a default definition is used.
<p>Similarly, there is a <code>targetm_common</code> variable for hooks that
are shared between the compiler driver and the compilers proper,
documented as “Common Target Hook”. This is declared in
<samp><span class="file">common/common-target.h</span></samp>, the initializer
<code>TARGETM_COMMON_INITIALIZER</code> in
<samp><span class="file">common/common-target-def.h</span></samp>. If targets initialize
<code>targetm_common</code> themselves, they should set
<code>target_has_targetm_common=yes</code> in <samp><span class="file">config.gcc</span></samp>; otherwise a
default definition is used.
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