> if we can identify what memory the child will need to access before calling _exit or exec (say, "the current function and its local variables") I mean, a goo

> if we can identify what memory the child will need to access before calling _exit or exec (say, "the current function and its local variables") I mean, a good deal of the parameters you need for the relevant syscalls are strings, which means it's not sufficient to copy just the stack frame, but all the memory reachable from the stack frame. Which is a nontrivial problem if you're assuming C/C++-style code.