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

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Message-ID: <485C0341.3090302@zytor.com>
Date:	Fri, 20 Jun 2008 12:21:37 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Christoph Lameter <clameter@....com>, Mike Travis <travis@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu
 area

Jeremy Fitzhardinge wrote:
>>
>> Its loaded at __per_cpu_load but the symbols have addresses starting 
>> at 0.
> 
> Yes, which leads to an odd-looking ELF file where the Phdrs aren't 
> sorted by virtual address order.  I'm wondering what would happen if a 
> bootloader that actually understood ELF files tried to load it as an 
> actual ELF file...
> 

If it is implemented correctly, it will work.  It might trigger bugs in 
such loaders, however.

>> Hmmm.... we could add the relocation offset to __per_cpu_load? 
>> __per_cpu_load is used very sparingly. Basically only useful during 
>> early boot and when a new per cpu area has to be setup. In that case 
>> we want to copy from __per_cpu_load to the newly allocated percpu area.
> 
> Yes, it should be fairly easy to manually relocate it by applying the 
> (load - link) offset to it.

Seems easy enough, and as already stated, this is not 
performance-critical so a few extra instructions is pretty much a non-issue.

	-hpa
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