What is the object structure in Mono?

Question

Mono

Where can I read about the structure of an object in mono, i.e. how many bytes are allocated for the invoke index, for different flags, for the virtual method table, etc.?
I ask because the structure of the object in mono apparently differs from the structure of the object in .net and IL code that works correctly under .net works fine under mono as well, then as soon as gc works in mono, the application crashes.