linux-kernel - Re: [crash, bisected] Re: [PATCH 3/4] x86

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Message-ID: <486AC9D9.9030506@zytor.com>
Date:	Tue, 01 Jul 2008 17:20:41 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Mike Travis <travis@....com>,
	Christoph Lameter <clameter@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu
 area

Jeremy Fitzhardinge wrote:
> 
> Yes, and there's no reason we couldn't do the same on 64-bit, aside from 
> the stack-protector's use of %gs:40.  There's no code-size cost in large 
> offsets, since they're always 32-bits anyway (there's no short absolute 
> addressing mode).
> 
> If we manually generate %gs-relative references to percpu data, then 
> it's no different to what we do with 32-bit, whether it be a specific 
> symbol address or using the TLS relocations.
> 

If we think the problem is the zero-basing triggering linker bugs, we 
should probably just use a small offset, like 64 (put a small dummy 
section before the .percpu.data section to occupy this section.)

I'm going to play with this a bit and see if I come up with something 
sanish.

	-hpa
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