From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f67.google.com ([74.125.82.67]:35502 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755772AbcA2Izl (ORCPT ); Fri, 29 Jan 2016 03:55:41 -0500 Received: by mail-wm0-f67.google.com with SMTP id l66so8524015wml.2 for ; Fri, 29 Jan 2016 00:55:41 -0800 (PST) Date: Fri, 29 Jan 2016 09:55:37 +0100 From: Ingo Molnar To: Jakub Jelinek Cc: Jiri Slaby , stable@vger.kernel.org, Steven Noonan , Richard Henderson , Linus Torvalds , Steven Rostedt Subject: Re: [patch added to 3.12-stable] compiler/gcc4+: Remove inaccurate comment about 'asm goto' miscompiles Message-ID: <20160129085537.GA27866@gmail.com> References: <1453978615-20487-1-git-send-email-jslaby@suse.cz> <1453978615-20487-2-git-send-email-jslaby@suse.cz> <20160128110347.GX3017@tucnak.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160128110347.GX3017@tucnak.redhat.com> Sender: stable-owner@vger.kernel.org List-ID: * Jakub Jelinek wrote: > On Thu, Jan 28, 2016 at 11:56:53AM +0100, Jiri Slaby wrote: > > From: Steven Noonan > > > > This patch has been added to the 3.12 stable tree. If you have any > > objections, please let us know. > > > > =============== > > > > commit 5631b8fba640a4ab2f8a954f63a603fa34eda96b upstream. > > > > The bug referenced by the comment in this commit was not > > completely fixed in GCC 4.8.2, as I mentioned in a thread back > > in February: > > > > https://lkml.org/lkml/2014/2/12/797 > > If you suspect a GCC bug, better try to narrow it down to a reasonably sized > testcase, preprocess it and file in GCC bugzilla. Otherwise it will never > be fixed. There's always the hope that someone hits an easier to analyze testcase! ;-) OTOH the Linux kernel might be one of only a handful of large projects making heavy use of 'asm goto', right? Btw., I think Linus complained at least about the debuggability of this: https://lkml.org/lkml/2014/2/12/805 " [...] But I'm sure Jakub&co would love to have a test-case. Sadly, gcc has that really annoying habit of making small changes create *huge* changes in label numbers etc, and that's definitely the case with the extra empty asm - it's basically impossible to compare the generated asm with and without the workaround, because all the label numbers change. I have no idea how gcc people debug things like this, when the output is so unstable. Jakub, any suggestions to how Steven might be able to pinpoint where the code generation problem lies? Linus" Thanks, Ingo