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

[H. Peter Anvin]

Followup to:  <Pine.LNX.4.53.0310141510590.2211@chaos>
By author:    "Richard B. Johnson" <root@xxxxxxxxxxxxxxxxxx>
In newsgroup: linux.dev.kernel
> 
> > main:
> >         mov DWORD PTR [%ESP - 16004], %EBP    # Save EBP to stack
> 
> BAM **INTERRUPT** writes return address below stack-pointer.
> 

Since we're in user mode, interrupts don't matter, but signals have
the same effect.

Note that this is a matter of the ABI definition.  For example, in the
x86-64 ABI there is a designated region of well-defined size below
%rsp called the redzone, which signals aren't allowed to clobber.

	-hpa
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