From: ebiederm@xmission.com (Eric W. Biederman)
To: Mike Travis <travis@sgi.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Jeremy Fitzhardinge <jeremy@goop.org>,
       Christoph Lameter <cl@linux-foundation.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>,
       Jack Steiner <steiner@sgi.com>
References: <20080604003018.538497000@polaris-admin.engr.sgi.com>
	<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> <486912C4.8070705@sgi.com>
	<48691556.2080208@zytor.com> <48691E8B.4040605@sgi.com>
	<m14p7asl3x.fsf@frodo.ebiederm.org> <48694B3B.3010600@goop.org>
	<m1skuuov4t.fsf@frodo.ebiederm.org> <486A61A7.1000902@zytor.com>
	<486A68DD.80702@goop.org> <m1d4lxgwxj.fsf@frodo.ebiederm.org>
	<486A9D4F.8010508@goop.org> <m1skutffn4.fsf@frodo.ebiederm.org>
	<486AA72B.6010401@goop.org> <486AC9D9.9030506@zytor.com>
	<486AD6BD.9080600@sgi.com>
Date: Tue, 01 Jul 2008 18:32:38 -0700
In-Reply-To: <486AD6BD.9080600@sgi.com> (Mike Travis's message of "Tue, 01 Jul
	2008 18:15:41 -0700")
Message-ID: <m17ic5f4uh.fsf@frodo.ebiederm.org>
User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Subject: Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu area
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2202
Lines: 51

Mike Travis <travis@sgi.com> writes:

> 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?

Depends on the root cause.  If it turns out to be something that is buggy
in gcc and we can't work around.  We might do something.  I don't recall
that kind of thing happening often.  I think our minimum gcc is currently
gcc-3.4.

Eric
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/