linux-kernel - Re: [patch 05/14] percpu: Use a Kconfig variable to configure arch specific percpu setup

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Message-ID: <Pine.LNX.4.64.0711281050470.11968@schroedinger.engr.sgi.com>
Date:	Wed, 28 Nov 2007 10:51:29 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Rusty Russell <rusty@...tcorp.com.au>
cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...e.de>, Ben Elliston <bje@....net.au>
Subject: Re: [patch 05/14] percpu: Use a Kconfig variable to configure arch
 specific percpu setup

On Wed, 28 Nov 2007, Rusty Russell wrote:

> On Wednesday 28 November 2007 05:14:47 Christoph Lameter wrote:
> > On Tue, 27 Nov 2007, Rusty Russell wrote:
> > > Have you considered moving x86-64's setup_per_cpu_areas into generic
> > > code? It's a bit messier because some archs might not have set up NUMA
> > > stuff yet, but it's logically generic...
> >
> > Yes that will happen later. This is just the early cleanup work. I
> > plan to generally bring the two x86 arches in line. The pda will be
> > folded into the per cpu area and after that its easy to do.
> 
> Unfortunately, we tried to get rid of the x86-64 pda (like i386) but you lose 
> the ability to use the stack protection config option.  That's because it 
> assumes that gs:0x68 (or something) is the stack canary; we need a YA gcc 
> change to make this gs:__builtin_stack_canary_off (where gcc can emit 
> __builtin_stack_canary_off as a weak absolute symbol, so we can override it 
> for the kernel.

This works if you rebase the per cpu area at zero. gs:0x68 is still the 
stack canary.

The i386 method does not work because the segment register does not 
directly point to the pda.


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