add callback invocation from OP_DEBUG

include/mruby.h

@@ -156,6 +156,7 @@ typedef struct mrb_state {
 
 #ifdef ENABLE_DEBUG
   void (*code_fetch_hook)(struct mrb_state* mrb, struct mrb_irep *irep, mrb_code *pc, mrb_value *regs);
+  void (*debug_op_hook)(struct mrb_state* mrb, struct mrb_irep *irep, mrb_code *pc, mrb_value *regs);
 #endif
 
   struct RClass *eException_class;

src/vm.c

@@ -2113,10 +2113,14 @@ mrb_context_run(mrb_state *mrb, struct RProc *proc, mrb_value self, unsigned int
 
     CASE(OP_DEBUG) {
       /* A      debug print R(A),R(B),R(C) */
+#ifdef ENABLE_DEBUG
+      mrb->debug_op_hook(mrb, irep, pc, regs);
+#else
 #ifdef ENABLE_STDIO
       printf("OP_DEBUG %d %d %d\n", GETARG_A(i), GETARG_B(i), GETARG_C(i));
 #else
       abort();
+#endif
 #endif
       NEXT;
     }