From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753333AbZAaAgH (ORCPT ); Fri, 30 Jan 2009 19:36:07 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755959AbZAaAfr (ORCPT ); Fri, 30 Jan 2009 19:35:47 -0500 Received: from terminus.zytor.com ([198.137.202.10]:47617 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755634AbZAaAfq (ORCPT ); Fri, 30 Jan 2009 19:35:46 -0500 Message-ID: <49839CC8.7060502@zytor.com> Date: Fri, 30 Jan 2009 16:35:20 -0800 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.19 (X11/20090105) MIME-Version: 1.0 To: Martin Hicks CC: tglx@linutronix.de, mingo@redhat.com, heukelum@mailshack.com, linux-kernel Subject: Re: [PATCH] x86: push old stack address on irqstack for unwinder References: <20090130165053.GE7872@alcatraz.americas.sgi.com> <49838F39.6060603@zytor.com> In-Reply-To: <49838F39.6060603@zytor.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org H. Peter Anvin wrote: > Martin Hicks wrote: >> Hi, >> >> KDB was using this information. Could this be pushed towards 2.6.29 >> please? >> >> This re-adds the old stack pointer to the top of the irqstack to help >> with unwinding. It was removed in commit >> d99015b1abbad743aa049b439c1e1dede6d0fa49 >> as part of the save_args out-of-line work. >> > > This bothers me... why should we add even a single instruction to what > is arguably the single hottest path in the kernel to support an > out-of-tree debugger, especially if kgdb (which is in-tree) doesn't need > it? > > What does kgdb do differently (or is kgdb broken too)? > Thinking about it some more, I think this makes sense under #ifdef CONFIG_FRAME_POINTER ... since if we're not building with frame pointers, this is pretty pointless, and if we are, we're adding these all over the place anyway. Does this work for you? Let me know and I'll get it in if so. -hpa