linux-kernel - Re: [GIT PULL] Additional x86 fixes for 2.6.31-rc5

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Message-ID: <4A7636DF.8090201@kernel.org>
Date:	Mon, 03 Aug 2009 10:01:19 +0900
From:	Tejun Heo <tj@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Paul Mackerras <paulus@...ba.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] Additional x86 fixes for 2.6.31-rc5

Hello,

H. Peter Anvin wrote:
> You can't actually do "lea %gs:foo,%rbx" (lea doesn't include the
> segment offset, unfortunately; I asked AMD to change that on 64 bits
> but, not too surprisingly, they weren't able to make that change.)
> Getting the address is expensive, but it's obviously possible -- which
> may have similar bad results.  It would be worth experimenting with a
> little bit, though.

Yeap, this part is strange.  I can't understand why it was done that
way.  Interestingly, the segment override doesn't trigger any
exception, it just gets ignored.  Is there a way to retrieve %gs value
without accessing memory?  ie. other than %gs:identity_gs?

Thanks.

-- 
tejun
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