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 E4F9CC433DB for ; Fri, 19 Mar 2021 18:20:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AF56A61988 for ; Fri, 19 Mar 2021 18:20:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230365AbhCSSTl (ORCPT ); Fri, 19 Mar 2021 14:19:41 -0400 Received: from linux.microsoft.com ([13.77.154.182]:43320 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230223AbhCSSTV (ORCPT ); Fri, 19 Mar 2021 14:19:21 -0400 Received: from [192.168.254.32] (unknown [47.187.194.202]) by linux.microsoft.com (Postfix) with ESMTPSA id 75D3620B26C5; Fri, 19 Mar 2021 11:19:20 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 75D3620B26C5 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1616177961; bh=WDYU6ZhrKgLliZHemxVPNPl+rNx2Em1vUa+9FaS7KBQ=; h=Subject:From:To:Cc:References:Date:In-Reply-To:From; b=C335yTms/oqeyQRT5BCOLOmXEBTyPp/dy1Kktwq2AhGviuNrk727nbSLLC9MVUNR5 3VS2jcZJglSxAanvaUndMgfENdZYEcmBYVaF5X27ME/2eDoPEvcL3AESAEYbHT45g0 ulu4J2TDTm9fjDTa7yHXM+rxFAJEjgxcBHPRAwKg= Subject: Re: [RFC PATCH v2 1/8] arm64: Implement stack trace termination record 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: <5997dfe8d261a3a543667b83c902883c1e4bd270> <20210315165800.5948-1-madvenka@linux.microsoft.com> <20210315165800.5948-2-madvenka@linux.microsoft.com> <20210318150905.GL5469@sirena.org.uk> <8591e34a-c181-f3ff-e691-a6350225e5b4@linux.microsoft.com> <20210319123023.GC5619@sirena.org.uk> <5dbaf34f-b2fc-b9b8-3918-83356f2f752a@linux.microsoft.com> Message-ID: <6e3ac22b-99b8-7d99-59bd-6a2d1158b3c9@linux.microsoft.com> Date: Fri, 19 Mar 2021 13:19:19 -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: <5dbaf34f-b2fc-b9b8-3918-83356f2f752a@linux.microsoft.com> 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 3/19/21 9:29 AM, Madhavan T. Venkataraman wrote: > > > On 3/19/21 7:30 AM, Mark Brown wrote: >> On Thu, Mar 18, 2021 at 03:26:13PM -0500, Madhavan T. Venkataraman wrote: >>> On 3/18/21 10:09 AM, Mark Brown wrote: >> >>>> If we are going to add the extra record there would probably be less >>>> potential for confusion if we pointed it at some sensibly named dummy >>>> function so anything or anyone that does see it on the stack doesn't get >>>> confused by a NULL. >> >>> I agree. I will think about this some more. If no other solution presents >>> itself, I will add the dummy function. >> >> After discussing this with Mark Rutland offlist he convinced me that so >> long as we ensure the kernel doesn't print the NULL record we're >> probably OK here, the effort setting the function pointer up correctly >> in all circumstances (especially when we're not in the normal memory >> map) is probably not worth it for the limited impact it's likely to have >> to see the NULL pointer (probably mainly a person working with some >> external debugger). It should be noted in the changelog though, and/or >> merged in with the relevant change to the unwinder. >> > > OK. I will add a comment as well as note it in the changelog. > > Thanks to both of you. > > Madhavan > I thought about this some more. I think I have a simple solution. I will prepare a patch and send it out. If you and Mark Rutland approve, I will include it in the next version of this RFC. Madhavan