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23.6 Registering custom attributes or pragmas

For analysis (or other) purposes it is useful to be able to add custom attributes or pragmas.

The PLUGIN_ATTRIBUTES callback is called during attribute registration. Use the register_attribute function to register custom attributes.

     /* 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 =
       { "user", 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_("Callback to register attributes"));
       register_attribute (&user_attr);

The PLUGIN_PRAGMAS callback is called once during pragmas registration. Use the c_register_pragma, c_register_pragma_with_data, c_register_pragma_with_expansion, c_register_pragma_with_expansion_and_data functions to register custom pragmas and their handlers (which often want to call pragma_lex) from c-family/c-pragma.h.

     /* 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_("Callback to register pragmas"));
       c_register_pragma ("GCCPLUGIN", "sayhello", handle_pragma_sayhello);

It is suggested to pass "GCCPLUGIN" (or a short name identifying your plugin) as the “space” argument of your pragma.

Pragmas registered with c_register_pragma_with_expansion or c_register_pragma_with_expansion_and_data support preprocessor expansions. For example:

     #define NUMBER 10
     #pragma GCCPLUGIN foothreshold (NUMBER)