Generally speaking live patching is done by putting the new code somewhere else entirely and inserting a jump to it at the start of the code to be replaced. So basically you insert a trampoline where one didn't exist before.
If you have some degree of cooperation from the code to be patched (eg hotpatching in Windows), this can be done even though others may be executing the code at the moment. However, if you're going to remove the old code, you need to prevent execution of it regardless (like stopping all CPUs and resuming their execution at a known location).
Biting the hand that feeds IT
