From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752478AbZGJH2S (ORCPT ); Fri, 10 Jul 2009 03:28:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750848AbZGJH2L (ORCPT ); Fri, 10 Jul 2009 03:28:11 -0400 Received: from cpsmtpm-eml110.kpnxchange.com ([195.121.3.14]:56808 "EHLO CPSMTPM-EML110.kpnxchange.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750765AbZGJH2K (ORCPT ); Fri, 10 Jul 2009 03:28:10 -0400 From: Frans Pop To: Linux Kernel Mailing List Subject: Re: [Bug 13012] 2.6.28.9 causes init to segfault on Debian etch; 2.6.28.8 OK Date: Fri, 10 Jul 2009 09:28:05 +0200 User-Agent: KMail/1.9.9 Cc: akpm@linux-foundation.org, torvalds@linux-foundation.org, linux-kbuild@vger.kernel.org, barryn@pobox.com, bugme-daemon@bugzilla.kernel.org MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200907100928.07369.elendil@planet.nl> X-OriginalArrivalTime: 10 Jul 2009 07:28:08.0596 (UTC) FILETIME=[F8FDE540:01CA012F] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 9 Apr 2009, Linus Torvalds wrote: > On Thu, 9 Apr 2009, Andrew Morton wrote: > > -fwrapv killed Barry's gcc-4.1.2-compiled kernel in 2.6.27.x, > > 2.6.28.x and presumably 2.6.29, 2.6.30. > > Auughh. I hate compiler bugs. They're horrible to debug. > > I _think_ 'fwrapv' only really matters with gcc-4.3, so maybe we could > just enable it for new versions. > > HOWEVER, I also wonder if we could instead of "-fwrapv" use > "-fno-strict-overflow". They are apparently subtly different, and maybe > the bug literally only happens with -fwrapv. > > Barry, can you see if that simple "replace -fwrapv with > -fno-strict-overflow" works for you? > > Or just go with Barry's helpful debugging: > > > I also noticed that the problem only happens with some gcc's: > > > > > > Problem occurs: > > > gcc (GCC) 4.1.2 20061115 (prerelease) (Debian 4.1.1-21) > > > gcc-4.1 (GCC) 4.1.3 20080704 (prerelease) (Debian 4.1.2-25) > > > > > > Problem does not occur (i.e. 2.6.28.9 works and I don't have to > > > revert anything): > > > gcc-4.2 (GCC) 4.2.4 (Debian 4.2.4-6) > > > gcc (Debian 4.3.2-1.1) 4.3.2 > > and consider 4.2 to be the point where it's ok. > > Do we have some gcc developer who > (a) knows what the rules are > and > (b) might even help us figure out where the bug occurs? The discussion on issue looks to have died, but it has bitten Debian stable ("Lenny") [1] as it causes init to die on s390 after a kernel update. Here's a possible patch. The exact gcc version to check for is still a bit open I guess. For the s390 issue I've confirmed that 4.2.4 is OK, but for safety and because of Andrew's comment above I've set the test for 4.3 in the patch. Cheers, FJP [1] http://bugs.debian.org/536354 --- From: Frans Pop Subject: Only add '-fwrapv' to gcc CFLAGS for gcc 4.3 and later This flag has been shown to cause init to segfault for kernels compiled with gcc-4.1. gcc version 4.2.4 has been shown to be OK, but as there is some uncertainty the flag is only added for 4.3 and later. This fixes http://bugzilla.kernel.org/show_bug.cgi?id=13012. Reported-by: Barry K. Nathan Signed-off-by: Frans Pop diff --git a/Makefile b/Makefile index 0aeec59..2f8756e 100644 --- a/Makefile +++ b/Makefile @@ -565,7 +565,8 @@ KBUILD_CFLAGS += $(call cc-option,-Wdeclaration-after-statement,) KBUILD_CFLAGS += $(call cc-option,-Wno-pointer-sign,) # disable invalid "can't wrap" optimizations for signed / pointers -KBUILD_CFLAGS += $(call cc-option,-fwrapv) +KBUILD_CFLAGS += $(shell if [ $(call cc-version) -ge 0430 ]; then \ + echo $(call cc-option,-fwrapv); fi ;) # revert to pre-gcc-4.4 behaviour of .eh_frame KBUILD_CFLAGS += $(call cc-option,-fno-dwarf2-cfi-asm)