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

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Date:	Mon, 30 Jun 2008 10:43:01 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Mike Travis <travis@....com>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	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

Mike Travis wrote:
> 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.

Well, that's what appeared to be happening with the pre-initialized GDT 
as well, so I'm not sure that's a new symptom.

    J
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