Template:GNU C Compiler Internals/When to Instrument 4 1

• Add new function and type declarations in hook gem_c_common_nodes_and_builtins.
• Instrument an AST after it is parsed in hook gem_finish_function.
• Modify attributes of a declaration in hooks gem_start_decl and gem_finish_decl. Let us say we would like to replace local array declarations char arr[10] with a heap array char *arr=(char*)malloc(10);

 void l2h_start_decl(void *p_decl, void *p_declspecs, init initialized, void *p_attr) {
   struct c_declarator *decl = *((struct c_declarator**)p_decl);
   if (current_function_decl == NULL_TREE) return;
   if (decl->kind == cdk_array) {
     decl->kind = cdk_pointer;
     decl->u.pointer_quals = 0;
   }
 }

 void l2h_finish_decl(tree decl, tree *init, tree spec) {
   ...
   gem_find_symtab(&t_malloc, "malloc");
   BUILD_FUNC_CALL1(t_call, t_malloc, build_int_cst(NULL_TREE, size), NULL_TREE);
   *init = build1(NOP_EXPR, build_pointer_type(char_type_node), t_call);
   DECL(decl) = build_int_cst(NULL_TREE, 0); // if this field is NULL the init is ignored
 }

• Replace function call with a proxy function