Re: i386 ABI and the stack

[Albert Cahalan]

On 6/23/06, Linus Torvalds <torvalds@xxxxxxxx> wrote:
> On Fri, 23 Jun 2006, H. Peter Anvin wrote:
> > >
> > > The x86-64 ABI has a 128-byte(*) zone that is safe from signals etc, so you
> > > can use a small amount of stack below the stackpointer safely. Not so on
> > > x86.
> >
> > Adding a small redzone like this to i386 would be easy, though -- just drop
> > the stack pointer by that much when creating a signal frame.  128 bytes isn't
> > enough to interfere with libraries.
>
> However, any binaries created with that in mind would be
> buggy-by-definition on older kernels, so I don't think it's worth it.

Since gcc-2.96 would access 256 bytes below the stack pointer
(according to the valgrind man page), the kernel needs to allow
for this in signal handlers anyway.

I'm pretty sure I saw that code in the kernel in fact, but I
can't find it now. Perhaps it got lost in a cleanup accident?
(it sure would be nice to have continuous source control history)
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