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=-4.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_PASS 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 97B8FC43387 for ; Sun, 13 Jan 2019 15:41:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1E9AF20675 for ; Sun, 13 Jan 2019 15:41:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=agner.ch header.i=@agner.ch header.b="lyJwjnJa" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726649AbfAMPl5 (ORCPT ); Sun, 13 Jan 2019 10:41:57 -0500 Received: from mail.kmu-office.ch ([178.209.48.109]:54652 "EHLO mail.kmu-office.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726543AbfAMPl4 (ORCPT ); Sun, 13 Jan 2019 10:41:56 -0500 Received: from webmail.kmu-office.ch (unknown [IPv6:2a02:418:6a02::a3]) by mail.kmu-office.ch (Postfix) with ESMTPSA id 0543B5C24F2; Sun, 13 Jan 2019 16:41:54 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=agner.ch; s=dkim; t=1547394114; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=whId9VZUnwaqxuqa4KlUIdkBQryPsOBB/uh+zXCwGk4=; b=lyJwjnJa2J/3QCxmW/d/gOHvcb5Tlwf3FQ5Ty+HeMGPFbysyuqOl/gpW7OjPx1gd9rRSC0 QB3YgEsWwVaVPAhPjhyV039gLGj+NivIKYAwbh9mnn8/R+g9pgqjT7eQBXi3WmXqYiObqT WsjWz71QAi+eWJ8P99hUMA2U5iUKFKM= MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Date: Sun, 13 Jan 2019 16:41:52 +0100 From: Stefan Agner To: Jeremy Fertic Cc: Arnd Bergmann , Russell King , rostedt@goodmis.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: ARM: config issue with ftrace function graph tracer In-Reply-To: <20190112010139.GA5288@r2700x.localdomain> References: <20190112010139.GA5288@r2700x.localdomain> Message-ID: X-Sender: stefan@agner.ch User-Agent: Roundcube Webmail/1.3.7 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 12.01.2019 02:01, Jeremy Fertic wrote: > I'm having a problem with the ftrace function graph tracer on a 32 bit arm > board (orangepi pc). A bisect points to the following commit: > > f9b58e8c7d03 ("ARM: 8800/1: use choice for kernel unwinders") > > Before this commit, if I use sunxi_defconfig and then menuconfig to enable > FTRACE and FUNCTION_TRACER then the function graph tracer works. With this > commit, and as of v5.0-rc1, doing the same as above results in a broken > function graph tracer and often an oops as well. The commit introduces a > choice group and it looks like it should default to UNWINDER_FRAME_POINTER > if FUNCTION_GRAPH_TRACER is enabled. FUNCTION_GRAPH_TRACER is enabled by > default when I enable FUNCTION_TRACER but this has no effect on the choice. > The choice always defaults to the other option which is UNWINDER_ARM. If I > manually choose UNWINDER_FRAME_POINTER then the function graph tracer works > fine. The default selection is there, but this is made at "make sunxi_defconfig" time. At this point FUNCTION_GRAPH_TRACER is not enabled, hence Kconfig uses UNWIDER_ARM. However, when enabling the FUNCTION_GRAPH_TRACER Kconfig will _not_ reconsider and switch enable UNWINDER_FRAME_POINTER. Before that commit, when enabling FUNCTION_GRAPH_TRACER, we simply also enabled FRAME_POINTER... I guess we need to make sure that FUNCTION_GRAPH_TRACER depends on the UNWINDER_FRAME_POINTER choice. There is already a similar dependency with THUMB2_KERNEL. We can cleanup that dependency since UNWINDER_FRAME_POINTER already depends on !THUMB2_KERNEL. diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 664e918e2624..a2ac65a8b2cc 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -69,7 +69,7 @@ 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 UNWINDER_FRAME_POINTER select HAVE_FUNCTION_TRACER if !XIP_KERNEL select HAVE_GCC_PLUGINS select HAVE_GENERIC_DMA_COHERENT diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug index 6d6e0330930b..8341649fa71d 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 help This determines which method will be used for unwinding kernel stack traces for panics, oopses, bugs, warnings, perf, /proc//stack, > > Any idea why the default behaviour has changed? The rational is stated in the commit message, the main reason was to disallow UNWINDER_FRAME_POINTER in case Clang is used (since Clang does not create the expected function prologue). The choice also aligns with how unwinders are selected on x86. -- Stefan