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 D027DC433B4 for ; Thu, 1 Apr 2021 19:47:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8198B610CA for ; Thu, 1 Apr 2021 19:47:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235132AbhDATrO (ORCPT ); Thu, 1 Apr 2021 15:47:14 -0400 Received: from linux.microsoft.com ([13.77.154.182]:49978 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233786AbhDATrN (ORCPT ); Thu, 1 Apr 2021 15:47:13 -0400 Received: from [192.168.254.32] (unknown [47.187.194.202]) by linux.microsoft.com (Postfix) with ESMTPSA id C7C6720B5680; Thu, 1 Apr 2021 12:47:12 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com C7C6720B5680 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1617306433; bh=OWDpaHvm2D0YNKQeRL1yB30M3kQ2iFEviD+jXzZJLw4=; h=Subject:From:To:Cc:References:Date:In-Reply-To:From; b=hFTJ7U55fKBJa5C9uc9lhXSXZj88jm9BczziZFIOsSkr6xWahJtH1OljSGIRXrChG Ns4Ytm0hEXP3U7E58XtVbcl8b4t1Qo/tI3W2sg1NJrjKFgu4cheH6J2xiG00hWGHE9 rvFn/sM5MJA7+E48QTLt2jeiogErJPoyvFe1r7hc= Subject: Re: [RFC PATCH v1 3/4] arm64: Detect FTRACE cases that make the stack trace unreliable From: "Madhavan T. Venkataraman" 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> <2a56fe4b-9929-0d8b-aa49-c2b1c1b82b79@linux.microsoft.com> Message-ID: <9ebc341b-ba5a-db9a-c5e6-17b30d4b1fd4@linux.microsoft.com> Date: Thu, 1 Apr 2021 14:47:11 -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: 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 1:53 PM, Madhavan T. Venkataraman wrote: > > > On 4/1/21 1:40 PM, Madhavan T. Venkataraman wrote: >>>> 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. > > Alternatively, I could just move the SYM_INNER_LABEL(ftrace_graph_call..) to outside the ifdef. > > Madhavan > Or, even better, I could just use ftrace_call+4 because that would be the return address for the tracer function at ftrace_call: SYM_CODE_START(ftrace_common) sub x0, x30, #AARCH64_INSN_SIZE // ip (callsite's BL insn) mov x1, x9 // parent_ip (callsite's LR) ldr_l x2, function_trace_op // op mov x3, sp // regs SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) bl ftrace_stub I think that would be cleaner. And, I don't need the complicated comments for ftrace_graph_call. Is this acceptable? Madhavan