Re: [x86] Access off the bottom of stack causes a segfault?

[Chris Lattner]

> Any interrupt causes the return address to be pushed onto the
> stack. This will overwrite any data you've put there. In principle,
> in user-mode, you can write below the stack-pointer because an
> interrupt uses the kernel stack. However, your data will still
> get corrupted by signal delivery, etc. So as to not corrupt your
> user-mode stack, the kernel calls your signal code, just like
> a nested call. This means the new return address will be below
> the non-signal user-mode stack-pointer value. This will surely
> corrupt anything you have written below the stack-pointer.

Thanks to everyone for all of the answers. :)  I guess the moral of the
story is to not perform leaf function optimization on X86.  At least
frame-pointer elimination is still safe.

Thanks again,

-Chris

-- 
http://llvm.cs.uiuc.edu/
http://www.nondot.org/~sabre/Projects/

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