From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757482Ab1GDNW3 (ORCPT ); Mon, 4 Jul 2011 09:22:29 -0400 Received: from mail-vx0-f174.google.com ([209.85.220.174]:33826 "EHLO mail-vx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756267Ab1GDNW2 (ORCPT ); Mon, 4 Jul 2011 09:22:28 -0400 Date: Mon, 4 Jul 2011 15:22:23 +0200 From: Frederic Weisbecker To: Jan Beulich Cc: Peter Zijlstra , Ingo Molnar , Thomas Gleixner , Arnaldo Carvalho de Melo , LKML , "H. Peter Anvin" Subject: Re: [PATCH 5/6] x86: Remove useless unwinder backlink from irq regs saving Message-ID: <20110704132158.GA5551@somewhere> References: <1309624184-9790-1-git-send-email-fweisbec@gmail.com> <1309624184-9790-6-git-send-email-fweisbec@gmail.com> <4E1187E4020000780004BF2C@nat28.tlf.novell.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4E1187E4020000780004BF2C@nat28.tlf.novell.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 04, 2011 at 08:29:08AM +0100, Jan Beulich wrote: > >>> On 02.07.11 at 18:29, Frederic Weisbecker wrote: > > The unwinder backlink in interrupt entry is very useless. > > It's actually not part of the stack frame chain and thus is > > never used. > > I very much doubt this - see dump_trace()'s comment in its IRQ-stack > related code portion (and the corresponding use of irq_stack_end[-1]). > > Jan Good point. I misunderstood that. But then I believe I accidentally fixed it back in "x86: Don't use frame pointer to save old stack on irq entry" by pushing %rsi instead in the new stack. It contains the backlink to the old stack. If we keep the macro as-is, I'll add a comment to explain further what is involved there.