On Wednesday 28 December 2005 15:14, linux-os (Dick Johnson) wrote:
> >> Anyway, getting down to 20 bytes of stack-space available
> >> seems to be pretty scary.
> >
> > + movl %esp, %edi
> > + movl %edi, %ecx
> > + andl $~0x1000, %edi
> > + subl %edi, %ecx
> >
> > ecx will be equal to ?
>
> Whatever the stack was minus that value ANDed with NOT 0x1000,
> i.e. 0x1000 minus the stack already in use. The code assumes
> that the stack starts and ends on a 0x1000 (page) boundary.
> If that's not true, then all bets are off.
Hmm. I must be thick today. (esp - (esp & 0xffffefff))
is always equal to (esp & 0x00001000). Which is either 0 or 0x1000.
--
vda
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