[$] Running code within another process's address space

One of the key resources that defines a process is its address space — the
set of mappings that determines what any specific memory address means
within that process. An address space is normally private
to the process it belongs to, but there are situations where one process
needs to make changes to another process's memory; an interactive debugger
would be one case in point. The ptrace()
system call makes such changes possible, but it is slow and not always easy
to use, so there has been a longstanding quest for better alternatives.
One possibility, process_vm_exec()
from Andrei Vagin, was recently posted for review.