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 42879C43461 for ; Thu, 1 Apr 2021 18:45:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 17BD661002 for ; Thu, 1 Apr 2021 18:45:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236982AbhDASpt (ORCPT ); Thu, 1 Apr 2021 14:45:49 -0400 Received: from linux.microsoft.com ([13.77.154.182]:41004 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239423AbhDASkZ (ORCPT ); Thu, 1 Apr 2021 14:40:25 -0400 Received: from [192.168.254.32] (unknown [47.187.194.202]) by linux.microsoft.com (Postfix) with ESMTPSA id BDFDF20ABC25; Thu, 1 Apr 2021 11:40:24 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com BDFDF20ABC25 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1617302425; bh=SOlvCGNF2qL5Q3qgj9PLqYCmEQf62InHHijTjNlIusI=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=PnrhJu9LCcT59AvJiHeY+krR88BIg5ss+Vm+tOQZcJ+rklhu2M8B38Qvj5bnMgCyT O66WxUU29Ta/gNMB+kWtkN6uCu+FU0EsFnFIlSy4xbDWNI6nMkQK+F3EhHOft3iAmO zx7iV8lXhO2Y5OLAwpQgTmfPaGhtpV7VcF9PFkeg= 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> <0bece48b-5fee-2bd1-752e-66d2b89cc5ad@linux.microsoft.com> <20210401182810.GO4758@sirena.org.uk> From: "Madhavan T. Venkataraman" Message-ID: <2a56fe4b-9929-0d8b-aa49-c2b1c1b82b79@linux.microsoft.com> Date: Thu, 1 Apr 2021 13:40:23 -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: <20210401182810.GO4758@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: live-patching@vger.kernel.org On 4/1/21 1:28 PM, Mark Brown wrote: > On Thu, Apr 01, 2021 at 12:43:25PM -0500, Madhavan T. Venkataraman wrote: > >>>> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS >>>> + { (unsigned long) &ftrace_graph_call, 0 }, >>>> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER >>>> + { (unsigned long) ftrace_graph_caller, 0 }, > >>> 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(). > > Ah, right - it's a result of it being an inner label. I'd suggest > putting a brief note right at that line of code explaining this (eg, > "Inner label, not a function"), it wasn't confusing due to the use of > that symbol but rather due to it being different from everything else > in the list and that's kind of lost in the main comment. > OK, So, I will add a note in the main comment above the list. I will add the comment line you have suggested at the exact line. >> 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 > > I'm not sure we need to bother with that, you'd still need the & I think. I think we need to bother with that. If CONFIG_FUNCTION_GRAPH_TRACER is not on but CONFIG_DYNAMIC_FTRACE_WITH_REGS is, then ftrace_graph_call() will not occur in the stack trace taken from a tracer function. The unwinder still needs to recognize an ftrace frame. I don't want to assume ftrace_common_return which is the label that currently follows the above code. So, we need a different label outside the above ifdef. As for the &, I needed it because ftrace_graph_call is currently defined elsewhere as: extern unsigned long ftrace_graph_call; I did not want to change that. Thanks, Madhavan