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<title>GNU Compiler Collection (GCC) Internals: Plugins attr</title>

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<a name="Plugins-attr"></a>
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<p>
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<a name="Registering-custom-attributes-or-pragmas"></a>
<h3 class="section">23.6 Registering custom attributes or pragmas</h3>

<p>For analysis (or other) purposes it is useful to be able to add custom
attributes or pragmas.
</p>
<p>The <code>PLUGIN_ATTRIBUTES</code> callback is called during attribute
registration. Use the <code>register_attribute</code> function to register
custom attributes.
</p>
<div class="smallexample">
<pre class="smallexample">/* Attribute handler callback */
static tree
handle_user_attribute (tree *node, tree name, tree args,
                       int flags, bool *no_add_attrs)
{
  return NULL_TREE;
}

/* Attribute definition */
static struct attribute_spec user_attr =
  { &quot;user&quot;, 1, 1, false,  false, false, handle_user_attribute, false };

/* Plugin callback called during attribute registration.
Registered with register_callback (plugin_name, PLUGIN_ATTRIBUTES, register_attributes, NULL)
*/
static void
register_attributes (void *event_data, void *data)
{
  warning (0, G_(&quot;Callback to register attributes&quot;));
  register_attribute (&amp;user_attr);
}

</pre></div>


<p>The <i>PLUGIN_PRAGMAS</i> callback is called once during pragmas
registration. Use the <code>c_register_pragma</code>,
<code>c_register_pragma_with_data</code>,
<code>c_register_pragma_with_expansion</code>,
<code>c_register_pragma_with_expansion_and_data</code> functions to register
custom pragmas and their handlers (which often want to call
<code>pragma_lex</code>) from <samp>c-family/c-pragma.h</samp>.
</p>
<div class="smallexample">
<pre class="smallexample">/* Plugin callback called during pragmas registration. Registered with
     register_callback (plugin_name, PLUGIN_PRAGMAS,
                        register_my_pragma, NULL);
*/
static void
register_my_pragma (void *event_data, void *data)
{
  warning (0, G_(&quot;Callback to register pragmas&quot;));
  c_register_pragma (&quot;GCCPLUGIN&quot;, &quot;sayhello&quot;, handle_pragma_sayhello);
}
</pre></div>

<p>It is suggested to pass <code>&quot;GCCPLUGIN&quot;</code> (or a short name identifying
your plugin) as the &ldquo;space&rdquo; argument of your pragma.
</p>
<p>Pragmas registered with <code>c_register_pragma_with_expansion</code> or
<code>c_register_pragma_with_expansion_and_data</code> support
preprocessor expansions. For example:
</p>
<div class="smallexample">
<pre class="smallexample">#define NUMBER 10
#pragma GCCPLUGIN foothreshold (NUMBER)
</pre></div>


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