Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759913Ab2BJTAN (ORCPT ); Fri, 10 Feb 2012 14:00:13 -0500 Received: from mail-pw0-f46.google.com ([209.85.160.46]:46477 "EHLO mail-pw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759670Ab2BJTAL (ORCPT ); Fri, 10 Feb 2012 14:00:11 -0500 MIME-Version: 1.0 In-Reply-To: <1328895795.25989.29.camel@laptop> References: <1328873119-21553-1-git-send-email-jolsa@redhat.com> <1328895795.25989.29.camel@laptop> From: Linus Torvalds Date: Fri, 10 Feb 2012 10:59:51 -0800 X-Google-Sender-Auth: LdwD0Vj6jymhu3MSXAnmsUWNSEI Message-ID: Subject: Re: [RFC 0/5] kernel: backtrace unwind support To: Peter Zijlstra Cc: Jiri Olsa , acme@redhat.com, mingo@elte.hu, paulus@samba.org, cjashfor@linux.vnet.ibm.com, fweisbec@gmail.com, linux-kernel@vger.kernel.org, "James E.J. Bottomley" , Jan Blunck Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1824 Lines: 38 On Fri, Feb 10, 2012 at 9:43 AM, Peter Zijlstra wrote: > > So I CC'ed Linus who has a strong here, jejb since he's the one that > told me several time there's a number of literate dwarfs already in the > kernel and Jan because I think it was him that tried last on x86. I never *ever* want to see this code ever again. Sorry, but last time was too f*cking painful. The whole (and *only*) point of unwinders is to make debugging easy when a bug occurs. But the f*cking dwarf unwinder had bugs itself, or our dwarf information had bugs, and in either case it actually turned several "trivial" bugs into a total undebuggable hell. It was made doubly painful by the developers involved then several times ignoring the problem, and claiming the code was bug-free when it clearly wasn't, or trying to claim that the problem was that we set up some random dwarf information wrong, when THAT GOES WITHOUT SAYING (since dwarf is a complex mess that never gets any actual testing except when things go wrong - at which point the code had better work regardless of whether the dwarf info was correct or not). So no. An unwinder that is several hundred lines long is simply not even *remotely* interesting to me. If you can mathematically prove that the unwinder is correct - even in the presence of bogus and actively incorrect unwinding information - and never ever follows a bad pointer, I'll reconsider. In the absence of that, just follow the damn chain on the stack *without* the "smarts" of an inevitably buggy piece of crap. Linus -- 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/