Object and VTable layout ======================== The first pointer inside an Object points to a MonoClass structure. Objects also contains a MonoThreadsSync structure which is used by the mono Thread implementation. typedef struct { MonoClass *class; MonoThreadsSync synchronisation; /* object specific data goes here */ } MonoObject; The MonoClass contains all Class infos, the VTable and a pointer to static class data. typedef struct { /* various class infos */ MonoClass *parent; const char *name; const char *name_space; ... /* interface offset table */ gint *interface_offsets; gpointer data; /* a pointer to static data */ /* the variable sized vtable is included at the end */ gpointer vtable [vtable_size]; } MonoClass; Calling virtual functions: ========================== Each MonoMethod (if virtual) has an associated slot, which is an index into the VTable. So we can use the following code to compute the address of a virtual function: method_addr = object->class->vtable [method->slot]; Calling interface methods: ========================== Each interface class is associated with an unique ID. The following code computes the address of an interface function: offset_into_vtable = object->class->interface_offsets [interface_id]; method_addr = object->class->vtable [offset_into_vtable + method->slot];