Do you know ALL_INTERIOR_POINTERS? In gc/doc/README:
"Any objects not intended to be collected must be pointed to either from other such accessible objects, or from the registers, stack, data, or statically allocated bss segments. Pointers from the stack or registers may point to anywhere inside an object. The same is true for heap pointers if the collector is compiled with ALL_INTERIOR_POINTERS defined, or GC_all_interior_pointers is otherwise set, as is now the default."
