From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757404AbbKFQZk (ORCPT ); Fri, 6 Nov 2015 11:25:40 -0500 Received: from foss.arm.com ([217.140.101.70]:42917 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751615AbbKFQZh (ORCPT ); Fri, 6 Nov 2015 11:25:37 -0500 Date: Fri, 6 Nov 2015 16:25:38 +0000 From: Will Deacon To: Catalin Marinas Cc: Mark Rutland , Yang Shi , linaro-kernel@lists.linaro.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] arm64: remove redundant FRAME_POINTER kconfig option Message-ID: <20151106162538.GU6087@arm.com> References: <1446658671-16238-1-git-send-email-yang.shi@linaro.org> <20151106123008.GK6087@arm.com> <20151106125002.GA8116@leverpostej> <20151106162109.GZ7637@e104818-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151106162109.GZ7637@e104818-lin.cambridge.arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 06, 2015 at 04:21:09PM +0000, Catalin Marinas wrote: > On Fri, Nov 06, 2015 at 12:50:02PM +0000, Mark Rutland wrote: > > On Fri, Nov 06, 2015 at 12:30:09PM +0000, Will Deacon wrote: > > > On Wed, Nov 04, 2015 at 09:37:51AM -0800, Yang Shi wrote: > > > > FRAME_POINTER is defined in lib/Kconfig.debug, it is unnecessary to redefine > > > > it in arch/arm64/Kconfig.debug. > > > > > > It might be worth noting that this adds a dependency on DEBUG_KERNEL > > > for building with frame pointers. I'm ok with that (it appears to be > > > enabled in defconfig and follows the vast majority of other archs) but > > > it is a change in behaviour. > > > > > > With that: > > > > > > Acked-by: Will Deacon > > > > The code in arch/arm64/kernel/stacktrace.c assumes we have frame > > pointers regardless of FRAME_POINTER. Depending on what the compiler > > decides to use x29 for, we could get some weird fake unwinding and/or > > dodgy memory accesses. > > > > I think we should first audit the uses of frame pointers to ensure that > > they are guarded for !FRAME_POINTER. > > Or we just select FRAME_POINTER in the ARM64 Kconfig entry. Yang, did you see any benefit disabling frame pointers, or was this patch purely based on you spotting a duplicate Kconfig entry? Will