Message-ID: <486912C4.8070705@sgi.com>
Date: Mon, 30 Jun 2008 10:07:16 -0700
From: Mike Travis <travis@sgi.com>
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To: "Eric W. Biederman" <ebiederm@xmission.com>
CC: Jeremy Fitzhardinge <jeremy@goop.org>,
       Christoph Lameter <clameter@sgi.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu
 area
References: <20080604003018.538497000@polaris-admin.engr.sgi.com>	<20080605102222.GA21319@elte.hu> <484EF29C.7080100@sgi.com>	<485947A8.8060801@goop.org> <4859511E.5050605@sgi.com>	<48596315.6020104@goop.org> <48596893.4040908@sgi.com>	<485AADAC.3070301@sgi.com> <485AB78B.5090904@goop.org>	<485AC120.6010202@sgi.com> <485AC5D4.6040302@goop.org>	<485ACA8F.10006@sgi.com> <485ACD92.8050109@sgi.com>	<485AD138.4010404@goop.org> <485ADA12.5010505@sgi.com>	<485ADC73.60009@goop.org> <485BDB04.4090709@sgi.com>	<485BE80E.10209@goop.org>	<Pine.LNX.4.64.0806201045460.15874@schroedinger.engr.sgi.com>	<485BF8F5.6010802@goop.org> <485BFFC5.6020404@sgi.com> <m1skv7onvh.fsf@frodo.ebiederm.org>
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Eric W. Biederman wrote:
> Mike Travis <travis@sgi.com> writes:
...
>> Can we generate a new symbol which would account for LOAD_OFFSET?
> 
> Ouch.  Absolute symbols indeed.  On the 32bit kernel that may play havoc
> with the relocatable kernel, although we have had similar absolute logic
> for the last year. With __per_cpu_start and __per_cpu_end so it may
> not be a problem.
> 
> To initialize the percpu data you do want to talk to the virtual address
> at __per_coup_load.  But it is absolute Ugh.  
> 
> It might be worth saying something like.
> .data.percpu.start : AT(.data.percpu.dummy - LOAD_OFFSET) {
> 	DATA(0)                   
> 	. = ALIGN(align);
>         __per_cpu_load = . ;                   
> }
> To make __per_cpu_load a relative symbol. ld has a bad habit of taking
> symbols out of empty sections and making them absolute.  Which is why
> I added the DATA(0).
> 
> Still I don't think that would be the 64bit problem.
> 
> Eric

FYI, I did try this out and it caused the bootloader to scramble the
loaded data.  The first corruption I found was the .x86cpuvendor.init
section contained all zeroes.

Mike
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