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=-14.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL autolearn=no 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 15971C4363E for ; Thu, 1 Apr 2021 18:01:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0452A6112F for ; Thu, 1 Apr 2021 18:01:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237231AbhDAR7r (ORCPT ); Thu, 1 Apr 2021 13:59:47 -0400 Received: from linux.microsoft.com ([13.77.154.182]:33150 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235935AbhDARn0 (ORCPT ); Thu, 1 Apr 2021 13:43:26 -0400 Received: from [192.168.254.32] (unknown [47.187.194.202]) by linux.microsoft.com (Postfix) with ESMTPSA id 756E020B5680; Thu, 1 Apr 2021 10:43:26 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 756E020B5680 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1617299007; bh=SXrslQ5h2CELNvXp37RVjh4DI/73D8F1okC67YGXnNE=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=Y4rHwdh5CynAQxFVFMiaX5GOsqqKumJgAktfCoA4eqp/vqaUjt76xJy2kDaEq24Qx b5RwCjL5zXBxgQzfCRx5U28X/gE0Q1oJCf19zlZ8ao/jCvpKsz36fTkaxC+pkuJDAl /CHFdpal5kN6kllSEZCrknTG5uqaVGQAEMYNXBWo= Subject: Re: [RFC PATCH v1 3/4] arm64: Detect FTRACE cases that make the stack trace unreliable To: Mark Brown Cc: mark.rutland@arm.com, jpoimboe@redhat.com, jthierry@redhat.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org References: <77bd5edeea72d44533c769b1e8c0fea7a9d7eb3a> <20210330190955.13707-1-madvenka@linux.microsoft.com> <20210330190955.13707-4-madvenka@linux.microsoft.com> <20210401142759.GJ4758@sirena.org.uk> From: "Madhavan T. Venkataraman" Message-ID: <0bece48b-5fee-2bd1-752e-66d2b89cc5ad@linux.microsoft.com> Date: Thu, 1 Apr 2021 12:43:25 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210401142759.GJ4758@sirena.org.uk> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/1/21 9:27 AM, Mark Brown wrote: > On Tue, Mar 30, 2021 at 02:09:54PM -0500, madvenka@linux.microsoft.com wrote: > >> + * FTRACE trampolines. >> + */ >> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS >> + { (unsigned long) &ftrace_graph_call, 0 }, >> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER >> + { (unsigned long) ftrace_graph_caller, 0 }, >> + { (unsigned long) return_to_handler, 0 }, >> +#endif >> +#endif > > It's weird that we take the address of ftrace_graph_call but not the > other functions - we should be consistent or explain why. It'd probably > also look nicer to not nest the ifdefs, the dependencies in Kconfig will > ensure we only get things when we should. > I have explained it in the comment in the FTRACE trampoline right above ftrace_graph_call(). /* * The only call in the FTRACE trampoline code is above. The above * instruction is patched to call a tracer function. Its return * address is below (ftrace_graph_call). In a stack trace taken from * a tracer function, ftrace_graph_call() will show. The unwinder * checks this for reliable stack trace. Please see the comments * in stacktrace.c. If another call is added in the FTRACE * trampoline code, the special_functions[] array in stacktrace.c * must be updated. */ I also noticed that I have to fix something here. The label ftrace_graph_call is defined like this: #ifdef CONFIG_FUNCTION_GRAPH_TRACER SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller(); nop // If enabled, this will be replaced // "b ftrace_graph_caller" #endif So, it is only defined if CONFIG_FUNCTION_GRAPH_TRACER is defined. I can address this as well as your comment by defining another label whose name is more meaningful to our use: +SYM_INNER_LABEL(ftrace_trampoline, SYM_L_GLOBAL) // checked by the unwinder #ifdef CONFIG_FUNCTION_GRAPH_TRACER SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller(); nop // If enabled, this will be replaced // "b ftrace_graph_caller" #endif Is this acceptable? Thanks. Madhavan