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<h3 class="section">23.2 Plugin API</h3>
<p>Plugins are activated by the compiler at specific events as defined in
<samp><span class="file">gcc-plugin.h</span></samp>. For each event of interest, the plugin should
call <code>register_callback</code> specifying the name of the event and
address of the callback function that will handle that event.
<p>The header <samp><span class="file">gcc-plugin.h</span></samp> must be the first gcc header to be included.
<h4 class="subsection">23.2.1 Plugin license check</h4>
<p>Every plugin should define the global symbol <code>plugin_is_GPL_compatible</code>
to assert that it has been licensed under a GPL-compatible license.
If this symbol does not exist, the compiler will emit a fatal error
and exit with the error message:
<pre class="smallexample"> fatal error: plugin <var>name</var> is not licensed under a GPL-compatible license
<var>name</var>: undefined symbol: plugin_is_GPL_compatible
compilation terminated
</pre>
<p>The declared type of the symbol should be int, to match a forward declaration
in <samp><span class="file">gcc-plugin.h</span></samp> that suppresses C++ mangling. It does not need to be in
any allocated section, though. The compiler merely asserts that
the symbol exists in the global scope. Something like this is enough:
<pre class="smallexample"> int plugin_is_GPL_compatible;
</pre>
<h4 class="subsection">23.2.2 Plugin initialization</h4>
<p>Every plugin should export a function called <code>plugin_init</code> that
is called right after the plugin is loaded. This function is
responsible for registering all the callbacks required by the plugin
and do any other required initialization.
<p>This function is called from <code>compile_file</code> right before invoking
the parser. The arguments to <code>plugin_init</code> are:
<ul>
<li><code>plugin_info</code>: Plugin invocation information.
<li><code>version</code>: GCC version.
</ul>
<p>The <code>plugin_info</code> struct is defined as follows:
<pre class="smallexample"> struct plugin_name_args
{
char *base_name; /* Short name of the plugin
(filename without .so suffix). */
const char *full_name; /* Path to the plugin as specified with
-fplugin=. */
int argc; /* Number of arguments specified with
-fplugin-arg-.... */
struct plugin_argument *argv; /* Array of ARGC key-value pairs. */
const char *version; /* Version string provided by plugin. */
const char *help; /* Help string provided by plugin. */
}
</pre>
<p>If initialization fails, <code>plugin_init</code> must return a non-zero
value. Otherwise, it should return 0.
<p>The version of the GCC compiler loading the plugin is described by the
following structure:
<pre class="smallexample"> struct plugin_gcc_version
{
const char *basever;
const char *datestamp;
const char *devphase;
const char *revision;
const char *configuration_arguments;
};
</pre>
<p>The function <code>plugin_default_version_check</code> takes two pointers to
such structure and compare them field by field. It can be used by the
plugin's <code>plugin_init</code> function.
<p>The version of GCC used to compile the plugin can be found in the symbol
<code>gcc_version</code> defined in the header <samp><span class="file">plugin-version.h</span></samp>. The
recommended version check to perform looks like
<pre class="smallexample"> #include "plugin-version.h"
...
int
plugin_init (struct plugin_name_args *plugin_info,
struct plugin_gcc_version *version)
{
if (!plugin_default_version_check (version, &gcc_version))
return 1;
}
</pre>
<p>but you can also check the individual fields if you want a less strict check.
<h4 class="subsection">23.2.3 Plugin callbacks</h4>
<p>Callback functions have the following prototype:
<pre class="smallexample"> /* The prototype for a plugin callback function.
gcc_data - event-specific data provided by GCC
user_data - plugin-specific data provided by the plug-in. */
typedef void (*plugin_callback_func)(void *gcc_data, void *user_data);
</pre>
<p>Callbacks can be invoked at the following pre-determined events:
<pre class="smallexample"> enum plugin_event
{
PLUGIN_PASS_MANAGER_SETUP, /* To hook into pass manager. */
PLUGIN_FINISH_TYPE, /* After finishing parsing a type. */
PLUGIN_FINISH_DECL, /* After finishing parsing a declaration. */
PLUGIN_FINISH_UNIT, /* Useful for summary processing. */
PLUGIN_PRE_GENERICIZE, /* Allows to see low level AST in C and C++ frontends. */
PLUGIN_FINISH, /* Called before GCC exits. */
PLUGIN_INFO, /* Information about the plugin. */
PLUGIN_GGC_START, /* Called at start of GCC Garbage Collection. */
PLUGIN_GGC_MARKING, /* Extend the GGC marking. */
PLUGIN_GGC_END, /* Called at end of GGC. */
PLUGIN_REGISTER_GGC_ROOTS, /* Register an extra GGC root table. */
PLUGIN_ATTRIBUTES, /* Called during attribute registration */
PLUGIN_START_UNIT, /* Called before processing a translation unit. */
PLUGIN_PRAGMAS, /* Called during pragma registration. */
/* Called before first pass from all_passes. */
PLUGIN_ALL_PASSES_START,
/* Called after last pass from all_passes. */
PLUGIN_ALL_PASSES_END,
/* Called before first ipa pass. */
PLUGIN_ALL_IPA_PASSES_START,
/* Called after last ipa pass. */
PLUGIN_ALL_IPA_PASSES_END,
/* Allows to override pass gate decision for current_pass. */
PLUGIN_OVERRIDE_GATE,
/* Called before executing a pass. */
PLUGIN_PASS_EXECUTION,
/* Called before executing subpasses of a GIMPLE_PASS in
execute_ipa_pass_list. */
PLUGIN_EARLY_GIMPLE_PASSES_START,
/* Called after executing subpasses of a GIMPLE_PASS in
execute_ipa_pass_list. */
PLUGIN_EARLY_GIMPLE_PASSES_END,
/* Called when a pass is first instantiated. */
PLUGIN_NEW_PASS,
/* Called when a file is #include-d or given via the #line directive.
This could happen many times. The event data is the included file path,
as a const char* pointer. */
PLUGIN_INCLUDE_FILE,
PLUGIN_EVENT_FIRST_DYNAMIC /* Dummy event used for indexing callback
array. */
};
</pre>
<p>In addition, plugins can also look up the enumerator of a named event,
and / or generate new events dynamically, by calling the function
<code>get_named_event_id</code>.
<p>To register a callback, the plugin calls <code>register_callback</code> with
the arguments:
<ul>
<li><code>char *name</code>: Plugin name.
<li><code>int event</code>: The event code.
<li><code>plugin_callback_func callback</code>: The function that handles <code>event</code>.
<li><code>void *user_data</code>: Pointer to plugin-specific data.
</ul>
<p>For the <i>PLUGIN_PASS_MANAGER_SETUP</i>, <i>PLUGIN_INFO</i>, and
<i>PLUGIN_REGISTER_GGC_ROOTS</i> pseudo-events the <code>callback</code> should be null,
and the <code>user_data</code> is specific.
<p>When the <i>PLUGIN_PRAGMAS</i> event is triggered (with a null pointer as
data from GCC), plugins may register their own pragmas. Notice that
pragmas are not available from <samp><span class="file">lto1</span></samp>, so plugins used with
<code>-flto</code> option to GCC during link-time optimization cannot use
pragmas and do not even see functions like <code>c_register_pragma</code> or
<code>pragma_lex</code>.
<p>The <i>PLUGIN_INCLUDE_FILE</i> event, with a <code>const char*</code> file path as
GCC data, is triggered for processing of <code>#include</code> or
<code>#line</code> directives.
<p>The <i>PLUGIN_FINISH</i> event is the last time that plugins can call GCC
functions, notably emit diagnostics with <code>warning</code>, <code>error</code>
etc.
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