Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934159AbaLBT5F (ORCPT ); Tue, 2 Dec 2014 14:57:05 -0500 Received: from www.linutronix.de ([62.245.132.108]:49757 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933377AbaLBT5D (ORCPT ); Tue, 2 Dec 2014 14:57:03 -0500 Date: Tue, 2 Dec 2014 20:56:52 +0100 (CET) From: Thomas Gleixner To: Andy Lutomirski cc: "Berthier, Emmanuel" , "H. Peter Anvin" , X86 ML , "Jarzmik, Robert" , LKML Subject: Re: [PATCH v2] [LBR] Dump LBRs on Exception In-Reply-To: Message-ID: References: <65CD3FC07F3BF942ABE211646D72D770356EACA5@IRSMSX110.ger.corp.intel.com> <1417099205-13309-1-git-send-email-emmanuel.berthier@intel.com> <65CD3FC07F3BF942ABE211646D72D770356EB2B2@IRSMSX110.ger.corp.intel.com> <65CD3FC07F3BF942ABE211646D72D770356EC658@IRSMSX110.ger.corp.intel.com> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2 Dec 2014, Andy Lutomirski wrote: > TBH, I'm wondering whether this is actually a good idea. It might be > more valuable and less scary to try to make this work for BUG instead. > To get the most impact, it might be worth allocating a new exception > vector for BUG and using 'int 0xwhatever', and the prologue to that > could read out all the MSRs without any branches. BUG is pretty uninteresting. We usually know how we got there. Now where LBR might be useful is if you have stack corruption and branch into nirvana or access random crap via a few hoops. There the LBR data might help, because the corrupted stack does not tell anything. So yes, this is a corner case debugging scenario, but given the complexity of coordination with perf and the possible intrusiveness in the low level entry path, we really need to see a few real world examples where this helps, aside of the constructed case. Thanks, tglx -- 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/