The allocator API hands out `*mut u8` so... not really. If you changed the allocator API and everything that uses it and makes assumptions about how it works th

The allocator API hands out `*mut u8` so... not really. If you changed the allocator API and everything that uses it and makes assumptions about how it works then sure, you could make it hand out a pointer to a pointer so you could come in later and update the inner pointer after you've done a GC pass. You couldn't do something like handing out a normal `Box` and keeping track of where it lives so you can patch it later though. Rust doesn't have move or copy constructors so as it gets passed around it'll just be `memcpy`'d and you'll lose track of it.