mono/docs/object-layout

Object and VTable layout
========================

The first pointer inside an Object points to a MonoVtable structure. Objects
also contains a MonoThreadsSync structure which is used by the mono Thread
implementation. 
 
typedef struct {
	MonoVTable *vtable;
	MonoThreadsSync synchronisation;
	
	/* object specific data goes here */
} MonoObject;

The MonoVtable contains the vtable, interface offsets and a pointer to static
class data. Each object/vtable belongs to exactly one AppDomain.

typedef struct {
	MonoClass  *klass;
	MonoDomain *domain;  
        gpointer   *interface_offsets;   
	/* a pointer to static data */
        gpointer    data;
	/* the variable sized vtable is included at the end */
        gpointer    vtable [0];	
} MonoVTable;

The MonoClass contains domain independent Class infos.

typedef struct {
	/* various class infos */
	MonoClass  *parent;
	const char *name;
	const char *name_space;
	...
} 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->vtable->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:

method_addr = *(object->vtable->interface_offsets [interface_id] + method->slot*4);