Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756175AbbGTQxA (ORCPT ); Mon, 20 Jul 2015 12:53:00 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:38837 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752884AbbGTQw7 (ORCPT ); Mon, 20 Jul 2015 12:52:59 -0400 Date: Mon, 20 Jul 2015 18:52:32 +0200 From: Peter Zijlstra To: Josh Poimboeuf 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: <20150720165232.GD19282@twins.programming.kicks-ass.net> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150720163646.GA28075@treble.redhat.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1385 Lines: 30 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? > 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? 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. -- 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/