Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752824Ab3JJGWo (ORCPT ); Thu, 10 Oct 2013 02:22:44 -0400 Received: from mail-ee0-f45.google.com ([74.125.83.45]:42743 "EHLO mail-ee0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751598Ab3JJGWm (ORCPT ); Thu, 10 Oct 2013 02:22:42 -0400 Date: Thu, 10 Oct 2013 08:22:38 +0200 From: Ingo Molnar To: Jakub Jelinek Cc: Peter Zijlstra , Oleg Nesterov , Fengguang Wu , Linus Torvalds , Linux Kernel Mailing List , Richard Henderson Subject: Re: [x86] BUG: unable to handle kernel paging request at 00740060 Message-ID: <20131010062238.GB9853@gmail.com> References: <20131008143400.GA14721@redhat.com> <20131009080459.GA2298@localhost> <20131009124310.GA11769@redhat.com> <20131009140734.GH3081@twins.programming.kicks-ass.net> <20131009143359.GU26785@twins.programming.kicks-ass.net> <20131009144656.GV26785@twins.programming.kicks-ass.net> <20131009181613.GW30970@tucnak.zalov.cz> <20131009190231.GI13848@laptop.programming.kicks-ass.net> <20131009190851.GX30970@tucnak.zalov.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131009190851.GX30970@tucnak.zalov.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1391 Lines: 32 * Jakub Jelinek wrote: > On Wed, Oct 09, 2013 at 09:02:31PM +0200, Peter Zijlstra wrote: > > On Wed, Oct 09, 2013 at 08:16:13PM +0200, Jakub Jelinek wrote: > > > > > 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. > > > > That bug lists the component as middle end; this suggests x86_64 would > > be vulnerable too, can you confirm? So far we've only observed the > > wrong code on i386 targets, x86_64 targets appeared correct. > > Any target, the testcase in the bugzilla aborts on x86_64 with -O2, and > even say on ppc64 (sure, one would have to rewrite the asm to have it > fail at runtime). Please let us know once you know enough about the bug to suggest workarounds. Because it's a nice optimization even extra instruction(s) would be acceptable I suspect: we could perhaps put a NOP into a slowpath, with an (unused) goto to it, or something like that? Thanks, Ingo -- 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/