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object-layout
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object-layout
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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];