Re: [patch 4/6] Convert PDA into the percpu section

Rusty Russell
2007-03-31T02:54:43Z

On Sat, 2007-03-31 at 04:35 +0200, Andi Kleen wrote:
> On Saturday 31 March 2007 04:00, Jeremy Fitzhardinge wrote:
> > Currently x86 (similar to x84-64) has a special per-cpu structure
> > called "i386_pda" which can be easily and efficiently referenced via
> > the %fs register. An ELF section is more flexible than a structure,
> > allowing any piece of code to use this area. Indeed, such a section
> > already exists: the per-cpu area.
>
> Hmm, I'm a little reluctant. This moves i386 more away from x86-64
> again. If we ever merge them it would mean more work. Do you really need it?

Well, I think the merge should go the other way in this case: this
really does simplify things.

The only thing stopping x86-64 from doing the same as i386 is the
stack-protector stuff. And that can be fixed (unfortunately requires a
gcc patch to change the %gs:40 to %gs:__gcc_stack_protector_offset and
emit a weak absolute symbol __gss_stack_protector_offset = 40).

I shall prepare a patch for that next week; I've been busy Kleening up
lguest 8)

Rusty.