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

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Message-Id: <1175309657.12230.420.camel@localhost.localdomain>
Date:	Sat, 31 Mar 2007 12:54:17 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Andi Kleen <ak@...e.de>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	virtualization@...ts.osdl.org, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [patch 4/6] Convert PDA into the percpu section

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.


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