linux-kernel - Re: [x86] BUG: unable to handle kernel paging request at 00740060

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Message-ID: <20131009181613.GW30970@tucnak.zalov.cz>
Date:	Wed, 9 Oct 2013 20:16:13 +0200
From:	Jakub Jelinek <jakub@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Richard Henderson <rth@...ddle.net>
Subject: Re: [x86] BUG: unable to handle kernel paging request at 00740060

On Wed, Oct 09, 2013 at 04:46:56PM +0200, Peter Zijlstra wrote:
> On Wed, Oct 09, 2013 at 04:33:59PM +0200, Peter Zijlstra wrote:
> > On Wed, Oct 09, 2013 at 04:07:34PM +0200, Peter Zijlstra wrote:
> > > Once I force a x86_64 build using the 'same' config it goes away and
> > > generates 'sensible' code again (although I don't see why L9 isn't
> > > merged with L2):
> > 
> > i386-SMP also generates correct code afaict; a tad stupid but not wrong.
> > 
> > If I remove ftrace from the .config its still broken..
> > If I also remove the likely/unlikely tracer its still broken and lots
> > smaller:
> 
> OK, its -march=winchip2 that's buggered.

Confirmed as gcc bug, filed http://gcc.gnu.org/PR58670
Seems all of 4.[6-9] miscompile it.  Will have a look tomorrow
unless somebody beats me to it.  But historically, the case where
asm goto labels jump to fallthru basic block had numerous problems in the
past.

	Jakub
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