From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753990Ab1AFRYJ (ORCPT ); Thu, 6 Jan 2011 12:24:09 -0500 Received: from mail-fx0-f46.google.com ([209.85.161.46]:34096 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753626Ab1AFRYH (ORCPT ); Thu, 6 Jan 2011 12:24:07 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=Soc8Fc4QXEpEEpb6mRiHrE546zej3/xMeRQz2Tdm9NtM+MhAAxciQvMkuQ8YdacB3R y220BYG10JRxakAbhNx1RKHAuADmBS24SHj3aZ7hAOW63HfQmcG0q/ohnqhYthzi8UC8 mMmYWkSJuSv1/PFNxpyRXXtSIdkL/X+C/9R00= Date: Thu, 6 Jan 2011 18:24:02 +0100 From: Frederic Weisbecker To: Jan Beulich Cc: "H. Peter Anvin" , Ingo Molnar , Stephane Eranian , Thomas Gleixner , Arnaldo Carvalho de Melo , Soeren Sandmann Pedersen , LKML Subject: Re: [RFC PATCH 1/2] x86: Fix rbp saving in pt_regs on irq entry Message-ID: <20110106172355.GE2308@nowhere> References: <1294325513-14276-1-git-send-email-fweisbec@gmail.com> <1294325513-14276-2-git-send-email-fweisbec@gmail.com> <4D25EB4B020000780002ABF7@vpn.id2.novell.com> <20110106154536.GA2308@nowhere> <4D25F79F020000780002AC20@vpn.id2.novell.com> <20110106162236.GB2308@nowhere> <4D25FE5B020000780002AC50@vpn.id2.novell.com> <20110106165452.GC2308@nowhere> <4D2602DE020000780002ACA3@vpn.id2.novell.com> <20110106171231.GD2308@nowhere> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110106171231.GD2308@nowhere> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 06, 2011 at 06:12:33PM +0100, Frederic Weisbecker wrote: > On Thu, Jan 06, 2011 at 04:58:54PM +0000, Jan Beulich wrote: > > >>> On 06.01.11 at 17:54, Frederic Weisbecker wrote: > > > On Thu, Jan 06, 2011 at 04:39:39PM +0000, Jan Beulich wrote: > > >> >>> On 06.01.11 at 17:22, Frederic Weisbecker wrote: > > >> > On Thu, Jan 06, 2011 at 04:10:55PM +0000, Jan Beulich wrote: > > >> >> >>> On 06.01.11 at 16:45, Frederic Weisbecker wrote: > > >> >> > Before we had: > > >> >> > > > >> >> > > > >> >> > leaveq > > >> >> > > > >> >> > CFI_RESTORE rbp > > >> >> > CFI_DEF_CFA_REGISTER rsp > > >> >> > CFI_ADJUST_CFA_OFFSET -8 > > >> >> > > > >> >> > So CFI_RESTORE means rbp has now the value of the base frame of > > >> >> > the calling frame (the base frame pointer of the interrupted proc) ? > > >> >> > > >> >> No - all it means is that %rbp now has its original (caller or > > >> >> interrupted procedure) value again (i.e. an unwinder should not > > >> >> try to read it from the stack [or other previously recorded > > >> >> location] anymore). > > >> >> > > >> >> > And what follows means that rsp-8 points to the return address? > > >> >> > > >> >> No - .cfi_def_cfa_register says which register serves as the frame > > >> >> pointer, and .cfi_adjust_cfa_offset says to adjust the offset from > > >> >> the frame pointer to the top [or bottom] of frame. At any time > > >> >> > > >> >> CFA = cfa_register + cfa_offset > > >> >> > > >> >> with CFA being what all locations on the stack are expressed > > >> >> relative to. > > >> > > > >> > Ok. > > >> > > > >> > So here rsp points to pt_regs::r11 > > >> > > > >> > I don't understand why locations relative to the stack must be > > >> > expressed here by taking rsp - 8 as a base. > > >> > > >> Nothing says rsp-8. The annotations merely say to set the base > > >> register to rsp and to *adjust* the offset by -8 (after all, that's > > >> what the leaveq instruction does). > > > > > > Ah! So CFA acts like a virtual frame base pointer right? > > > > Correct. > > Ah great. I was starting to prepare for the case you come to stab me :) > > So what do you think about that: > > leaveq > > CFI_RESTORE rbp > CFI_DEF_CFA_REGISTER rsp > CFI_ADJUST_CFA_OFFSET -8 > > /* we did not save rbx, restore only from ARGOFFSET */ > addq $8, %rsp > CFI_ADJUST_CFA_OFFSET -16 Or if CFI_ADJUST_CFA_OFFSET is already relative to its previous value, it should be CFI_ADJUST_CFA_OFFSET -8