Copying part of the stack and using mmap to map it to the current process?

The stack changes (e.g. The return address for the mmap call) after you copied it. I can think of 2 possible ways around this.

The stack changes (e.g. The return address for the mmap call) after you copied it. I can think of 2 possible ways around this: Write asm that doesn't need the stack to perform the new mapping. Call into a function with some huge local data so that the working stack is on a different page from the pages you're mapping over.

Then, you could map over the lower addresses with a second call to mmap once this function returns. Whatever you do, this is a horrible hack and probably a bad idea..

Yeah, I think that's the problem. I did the latter of your two strategies in an earlier draft, which worked, but I had been trying to simplify my code--and forgot the reason for that particular requirement. – Amittai Aviram Dec 12 '10 at 22:12 2 @Amittai Aviram: You could use makecontext() to do the stack copy and mmap in a different, temporary, context which uses a different stack.

– caf Dec 12 '10 at 23:51 You could also use a signal handler with alternate signal stack to avoid the issue of clobbering the stack under running code. – R.. Sep 28 at 0:08.

In any case, the symptom suggests that you've managed to map in over the top of the stack, destroying the return pointer.

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