Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759998Ab2BJT15 (ORCPT ); Fri, 10 Feb 2012 14:27:57 -0500 Received: from mx1.redhat.com ([209.132.183.28]:17879 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759027Ab2BJT14 (ORCPT ); Fri, 10 Feb 2012 14:27:56 -0500 Date: Fri, 10 Feb 2012 17:27:14 -0200 From: Arnaldo Carvalho de Melo To: Linus Torvalds Cc: Peter Zijlstra , Jiri Olsa , 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 Subject: Re: [RFC 0/5] kernel: backtrace unwind support Message-ID: <20120210192714.GE4998@infradead.org> References: <1328873119-21553-1-git-send-email-jolsa@redhat.com> <1328895795.25989.29.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Url: http://acmel.wordpress.com User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2074 Lines: 44 Em Fri, Feb 10, 2012 at 10:59:51AM -0800, Linus Torvalds escreveu: > 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. "Vote for --fno-omit-frame-pointer! One register is a cheap price to pay for not going insane!" /me goes back to non political things. - Arnaldo -- 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/