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

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Message-ID: <486AD6BD.9080600@sgi.com>
Date:	Tue, 01 Jul 2008 18:15:41 -0700
From:	Mike Travis <travis@....com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jack Steiner <steiner@....com>
Subject: Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu
 area

H. Peter Anvin wrote:
> Jeremy Fitzhardinge wrote:
>>
>> Yes, and there's no reason we couldn't do the same on 64-bit, aside
>> from the stack-protector's use of %gs:40.  There's no code-size cost
>> in large offsets, since they're always 32-bits anyway (there's no
>> short absolute addressing mode).
>>
>> If we manually generate %gs-relative references to percpu data, then
>> it's no different to what we do with 32-bit, whether it be a specific
>> symbol address or using the TLS relocations.
>>
> 
> If we think the problem is the zero-basing triggering linker bugs, we
> should probably just use a small offset, like 64 (put a small dummy
> section before the .percpu.data section to occupy this section.)
> 
> I'm going to play with this a bit and see if I come up with something
> sanish.
> 
>     -hpa

One interesting thing I've discovered is the gcc --version may make a
difference.

The kernel panic that occurred from Ingo's config, I was able to replicate
with GCC 4.2.0 (which is on our devel server).  But this one complained
about not being able to handle the STACK-PROTECTOR option so I moved
everything to another machine that has 4.2.4, and now it seems that it
works fine.  I'm still re-verifying that the source bits and config options 
are identical (it was a later git-remote update), and that in fact it is
the gcc --version, but that may be the conclusion.  (My code also has some
patches submitted but not yet included in the tip/master tree.  Curiously
just enabling some debug options changed the footprint of the panic.)

Are we allowed to insist on a specific level of GCC for compiling the
kernel?

Thanks,
Mike
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