Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756584AbbGTRTN (ORCPT ); Mon, 20 Jul 2015 13:19:13 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60488 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756530AbbGTRTM (ORCPT ); Mon, 20 Jul 2015 13:19:12 -0400 Date: Mon, 20 Jul 2015 12:19:10 -0500 From: Josh Poimboeuf To: Peter Zijlstra Cc: Andy Lutomirski , Ingo Molnar , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Michal Marek , Andy Lutomirski , Borislav Petkov , Linus Torvalds , Andi Kleen , Pedro Alves , X86 ML , live-patching@vger.kernel.org, "linux-kernel@vger.kernel.org" Subject: Re: [RFC PATCH 13/21] x86/asm/crypto: Fix frame pointer usage in aesni-intel_asm.S Message-ID: <20150720171910.GB28075@treble.redhat.com> References: <2ea0f0602978178eafd012e52b8bdb83cfb159d5.1437150175.git.jpoimboe@redhat.com> <20150717194307.GA26757@gmail.com> <20150717203746.GB12761@treble.redhat.com> <20150718025116.GB13059@gmail.com> <20150718035623.GA22664@treble.redhat.com> <20150720163646.GA28075@treble.redhat.com> <20150720165232.GD19282@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20150720165232.GD19282@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1665 Lines: 44 On Mon, Jul 20, 2015 at 06:52:32PM +0200, Peter Zijlstra wrote: > On Mon, Jul 20, 2015 at 11:36:46AM -0500, Josh Poimboeuf wrote: > > If a function doesn't call any other functions, then it won't ever show > > up in a stack trace unless: > > > > a) the function itself walks the stack, in which case the frame pointer > > isn't necessary; or > > > > b) The function gets hit by an interrupt/exception, in which case frame > > pointers can't be 100% relied upon anyway. > > In case the interrupt happens whilst setting up the frame, right? Right. > > I've noticed that gcc *does* seem to create stack frames for leaf > > functions. But it's inconsistent, because the early exit path of some > > functions will skip the stack frame creation and go straight to the > > return. > > > > We could probably get a good performance boost with the > > -momit-leaf-frame-pointer flag. Though it would make stack traces less > > reliable when a leaf function gets interrupted. > > So the information we'd loose in that case would be the location in the > calling function, right? Right. > Which isn't a problem, if the current function (as obtained > through RIP) is only ever called once. However if there's multiple call > sites this might be a wee bit confusing. Agreed, though the stack dump code always prints '?' for any kernel address it finds on the stack. So there would still be a good clue. -- Josh -- 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/