Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752455AbbKJLno (ORCPT ); Tue, 10 Nov 2015 06:43:44 -0500 Received: from mail-pa0-f44.google.com ([209.85.220.44]:35234 "EHLO mail-pa0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752292AbbKJLnm convert rfc822-to-8bit (ORCPT ); Tue, 10 Nov 2015 06:43:42 -0500 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 9.0 \(3094\)) Subject: Re: [V3 PATCH] arm64: remove redundant FRAME_POINTER kconfig option and force to select it From: yalin wang In-Reply-To: <20151110113505.GI21606@e104818-lin.cambridge.arm.com> Date: Tue, 10 Nov 2015 19:43:35 +0800 Cc: Mark Rutland , Yang Shi , linaro-kernel@lists.linaro.org, Will Deacon , LKML , linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 8BIT Message-Id: References: <1447092595-12644-1-git-send-email-yang.shi@linaro.org> <20151110103752.GH21606@e104818-lin.cambridge.arm.com> <49B0431C-4FDA-45CB-82AF-FA010197118D@gmail.com> <20151110113505.GI21606@e104818-lin.cambridge.arm.com> To: Catalin Marinas X-Mailer: Apple Mail (2.3094) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2275 Lines: 60 > On Nov 10, 2015, at 19:35, Catalin Marinas wrote: > > On Tue, Nov 10, 2015 at 07:09:00PM +0800, yalin wang wrote: >>> On Nov 10, 2015, at 18:37, Catalin Marinas wrote: >>> >>> On Mon, Nov 09, 2015 at 10:09:55AM -0800, Yang Shi wrote: >>>> FRAME_POINTER is defined in lib/Kconfig.debug, it is unnecessary to redefine >>>> it in arch/arm64/Kconfig.debug. Actually, the one defined in arm64 directory >>>> is never used. >>> >>> That's not true since the arm64 definition seems to take precedence. >>> >>>> This adds a dependency on DEBUG_KERNEL for building with frame pointers. >>> >>> It doesn't because arm64 selects ARCH_WANT_FRAME_POINTERS. >>> >>>> ARM64 depends on frame pointer to get correct stack backtrace and need >>>> FRAME_POINTER kconfig option enabled all the time. >>>> However, currect implementation makes it could be disabled, so force it >>>> to be selected by ARM64. >>>> >>>> Signed-off-by: Yang Shi >>> >>> Patch applied but I changed the commit log slightly. Thanks. >> i have a question, >> why FRAME_POINTER config must be enabled ? >> and i see ARM arch can disable this config . >> if i don’t need stack trace dump and the software release is for >> final product , don’t need debug stack trace log . >> is it possible to disable it for performance reason ? > > If you don't need any stack trace, perf etc., in theory you can disable > the option. However, the aarch64 gcc compiler always generates it (I'm > not sure whether the AAPCS mandates it). Anyway, the performance impact > is very small since there are more general purpose registers available > in AArch64 already. > i just make a test with -fomit-frame-pointer, seems gcc can generate code without frame pointer, like ARM arch. version: aarch64-linux-gnu-gcc gcc version 4.9.2 20140904 (prerelease) (crosstool-NG linaro-1.13.1-4.9-2014.09 - Linaro GCC 4.9-2014.09) why AARCH64 don’t have frame unwind info just like ARM arch? Thanks -- 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/