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

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Date:	Mon, 30 Jun 2008 10:07:16 -0700
From:	Mike Travis <travis@....com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Christoph Lameter <clameter@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu
 area

Eric W. Biederman wrote:
> Mike Travis <travis@....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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