From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 51AF2C10F13 for ; Sun, 14 Apr 2019 15:37:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0EEEA20896 for ; Sun, 14 Apr 2019 15:37:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b="xeuhtCSf" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726355AbfDNPhV (ORCPT ); Sun, 14 Apr 2019 11:37:21 -0400 Received: from pandora.armlinux.org.uk ([78.32.30.218]:60092 "EHLO pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726055AbfDNPhV (ORCPT ); Sun, 14 Apr 2019 11:37:21 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=aHU8pYkD4d9ZDBsmRbagbI5VZOamvJFLd3K+l+zwu8c=; b=xeuhtCSfZyvyYmIZVWVAFMY3Y VqP8QfN5DINn+b4xfYBQ3HxGfwpe69iT0DHnlxNlqHj1iAOxXkic4l19gvgBh8Nw82krs5MYXx48l 0h74GzoXG4B/4SdiiyUd1tFTwrZIEVgvRUPdX9Z+vTjOZgtxAiwOEUtYjaV13uGGLOHd1mxeMEkzP wOn3MbKeVr/nvwmILfJy0dZCZogakJM8UwIdwLuG4wN08Te3JPMLhMujfPvjZZjn3xfKgQo8h9RL+ +wc+Ba4WyI8Hryv5Eb48qrgtN3j+b0lE1Jify5eBqlcx9o5DRSkkj/F2etDpwC3UmPmbIW0wMhncw evZv29hKQ==; Received: from shell.armlinux.org.uk ([2002:4e20:1eda:1:5054:ff:fe00:4ec]:37762) by pandora.armlinux.org.uk with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1hFhBs-0007pn-0J; Sun, 14 Apr 2019 16:37:08 +0100 Received: from linux by shell.armlinux.org.uk with local (Exim 4.89) (envelope-from ) id 1hFhBo-0006jZ-S7; Sun, 14 Apr 2019 16:37:04 +0100 Date: Sun, 14 Apr 2019 16:37:04 +0100 From: Russell King - ARM Linux admin To: Masami Hiramatsu Cc: Steven Rostedt , Stefan Agner , Arnd Bergmann , Masahiro Yamada , linux-arm-kernel@lists.infradead.org, naresh.kamboju@linaro.org, linux-kernel@vger.kernel.org Subject: Re: Kconfig dependency issue on function-graph tracer and frame pointer on arm Message-ID: <20190414153704.7xlyluams3rl2mvo@shell.armlinux.org.uk> References: <20190414194705.2e10802aca2df36c8f27f349@kernel.org> <20190414133458.zxdekgx6qwd562qa@shell.armlinux.org.uk> <20190414235238.e860b1ce234752eff2b8c61c@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190414235238.e860b1ce234752eff2b8c61c@kernel.org> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Apr 14, 2019 at 11:52:38PM +0900, Masami Hiramatsu wrote: > On Sun, 14 Apr 2019 14:34:58 +0100 > Russell King - ARM Linux admin wrote: > > > On Sun, Apr 14, 2019 at 07:47:05PM +0900, Masami Hiramatsu wrote: > > > Hello, > > > > > > Recently, Naresh reported that the function-graph tracer on the latest > > > kernel crashes on arm. I could reproduce it and bisected. I finally found > > > the commit f9b58e8c7d03 ("ARM: 8800/1: use choice for kernel unwinders") > > > was the first bad commit. > > > > I don't think that littering the rest of the kernel Kconfig with ARM > > specific stuff is really a viable solution to this. > > > > If we examine the current situation, we have: > > > > - THUMB2_KERNEL selecting ARM_UNWIND when enabled. > > - UNWINDER_FRAME_POINTER disabled if THUMB2_KERNEL is enabled, provided > > we're not using Clang. This leaves UNWINDER_ARM as the only choice, > > which also selects ARM_UNWIND. > > - The default choice is dependent on the settings of AEABI and > > FUNCTION_GRAPH_TRACER. > > - HAVE_FUNCTION_GRAPH_TRACER is disabled if THUMB2_KERNEL is enabled. > > > > which seems to be _way_ too messy. > > > > Looking back before this commit, the function graph tracer never had a > > strong dependence on frame pointers being enabled in the kernel, but it > > seems the code relies upon them (see ftrace_return_to_handler() in > > kernel/trace/ and return_to_handler in arch/arm/kernel/entry-frace.S). > > There is also the __ftrace_graph_caller macro which seems to rely on it. > > Yes, so I think similar bug is hiding in other LTS kernels. It should > have a dependency to FRAME_POINTER on arm. > > > Since Clang does not support frame pointers, we shouldn't even offer > > the function graph tracer for Clang compilers, so let's do that with > > the first hunk of the patch below. > > > > The subsequent hunks remove the defaulting of the choice according to > > the function graph tracer - this is not a "hint" where the user can > > still choose either option irrespective of the state of the function > > graph tracer. They should only be able to select the frame pointer > > option in that case. > > Agreed. Using default for making dependency is wrong. > > > > > Another way forward would be for someone to put the work in to making > > the function graph tracer work without frame pointers. > > Yes, we eventually need that. But for fixing current released kernel > (this bug is in v5.0 series), I think Kconfig fix is needed. > > > > > So, how about this: > > > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > > index 850b4805e2d1..9aed25a6019b 100644 > > --- a/arch/arm/Kconfig > > +++ b/arch/arm/Kconfig > > @@ -73,7 +73,7 @@ config ARM > > select HAVE_EFFICIENT_UNALIGNED_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7) && MMU > > select HAVE_EXIT_THREAD > > select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL > > - select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL > > + select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL && !CC_IS_CLANG > > select HAVE_FUNCTION_TRACER if !XIP_KERNEL > > select HAVE_GCC_PLUGINS > > select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7) > > diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug > > index 6d6e0330930b..e388af4594a6 100644 > > --- a/arch/arm/Kconfig.debug > > +++ b/arch/arm/Kconfig.debug > > @@ -47,8 +47,8 @@ config DEBUG_WX > > > > choice > > prompt "Choose kernel unwinder" > > - default UNWINDER_ARM if AEABI && !FUNCTION_GRAPH_TRACER > > - default UNWINDER_FRAME_POINTER if !AEABI || FUNCTION_GRAPH_TRACER > > + default UNWINDER_ARM if AEABI > > + default UNWINDER_FRAME_POINTER if !AEABI > > If UNWINDER_ARM depends on ARM EABI, would we really need this "if !AEABI"? > (I doubt we need these default...) > > > help > > This determines which method will be used for unwinding kernel stack > > traces for panics, oopses, bugs, warnings, perf, /proc//stack, > > @@ -65,7 +65,7 @@ config UNWINDER_FRAME_POINTER > > > > config UNWINDER_ARM > > bool "ARM EABI stack unwinder" > > - depends on AEABI > > + depends on AEABI && !FUNCTION_GRAPH_TRACER > > Hmm, AFAIK, FUNCTION_GRAPH_TRACER only depends on FRAME_POINTER, but not > UNWINDER_FRAME_POINTER. So can user still choose UNWINDER_ARM even if > FUNCTION_GRAPH_TRACER=y ? (Of course that may not be a meaningful option) The UNWINDER_* options do not control anything except whether FRAME_POINTER is enabled or not. FRAME_POINTER controls not only whether we build with frame pointers, but also how we unwind. If both ARM_UNWIND and FRAME_POINTER are set, the kernel will fail to link due to a multiple definition of unwind_frame(). The UNWINDER_* symbols were added in the commit you referenced merely to select which of ARM_UNWIND or FRAME_POINTER are enabled. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up