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,URIBL_BLOCKED,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 88A15C433E6 for ; Thu, 18 Mar 2021 20:26:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4342C64F2B for ; Thu, 18 Mar 2021 20:26:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233013AbhCRU0Z (ORCPT ); Thu, 18 Mar 2021 16:26:25 -0400 Received: from linux.microsoft.com ([13.77.154.182]:46208 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233020AbhCRU0P (ORCPT ); Thu, 18 Mar 2021 16:26:15 -0400 Received: from [192.168.254.32] (unknown [47.187.194.202]) by linux.microsoft.com (Postfix) with ESMTPSA id 07B2C209C385; Thu, 18 Mar 2021 13:26:13 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 07B2C209C385 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1616099174; bh=SErigyigsB0CpeFt4XrJIuybAQdBkzUzy9hIoufBLVI=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=ZrFg9y5qLvRUHYY1YNzQUvIM046vnG2grx/rbBeb1HEIh+Km+1V1A8PJjCyRTtwwm +kcZcaQeEx4bR4vMvgv4uf4VePkcFT44JZvSs7O+HvmhY5aPe+HaKvw6BaNYC0j/oP Dg3myggTvd9jAj8y4mi+wAdCj/vOjmb0qmH1QIIQ= Subject: Re: [RFC PATCH v2 1/8] arm64: Implement stack trace termination record 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> From: "Madhavan T. Venkataraman" Message-ID: <8591e34a-c181-f3ff-e691-a6350225e5b4@linux.microsoft.com> Date: Thu, 18 Mar 2021 15:26:13 -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: <20210318150905.GL5469@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 3/18/21 10:09 AM, Mark Brown wrote: > On Mon, Mar 15, 2021 at 11:57:53AM -0500, madvenka@linux.microsoft.com wrote: > >> In summary, task pt_regs->stackframe is where a successful stack trace ends. > >> .if \el == 0 >> - mov x29, xzr >> + stp xzr, xzr, [sp, #S_STACKFRAME] >> .else >> stp x29, x22, [sp, #S_STACKFRAME] >> - add x29, sp, #S_STACKFRAME >> .endif >> + add x29, sp, #S_STACKFRAME > > For both user and kernel threads this patch (at least by itself) results > in an additional record being reported in stack traces with a NULL > function pointer since it keeps the existing record where it is and adds > this new fixed record below it. This is addressed for the kernel later > in the series, by "arm64: Terminate the stack trace at TASK_FRAME and > EL0_FRAME", but will still be visible to other unwinders such as > debuggers. I'm not sure that this *matters* but it might and should at > least be called out more explicitly. > > 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. Madhavan > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >