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 E25A3C433ED for ; Sun, 4 Apr 2021 04:40:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 95A8A6135F for ; Sun, 4 Apr 2021 04:40:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229541AbhDDEk5 (ORCPT ); Sun, 4 Apr 2021 00:40:57 -0400 Received: from linux.microsoft.com ([13.77.154.182]:45828 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229517AbhDDEk5 (ORCPT ); Sun, 4 Apr 2021 00:40:57 -0400 Received: from [192.168.254.32] (unknown [47.187.194.202]) by linux.microsoft.com (Postfix) with ESMTPSA id 8B49220B5680; Sat, 3 Apr 2021 21:40:52 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 8B49220B5680 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1617511253; bh=fCDUNY4RnNwMr8Xnv+6+5QOYhCKjx6Ej87nkMtaPNcI=; h=Subject:From:To:Cc:References:Date:In-Reply-To:From; b=qqKB0cyZSgUYk7HOv+KJkS5rhlZ0iNPmm5LXaVnNmBodZu5B23jedf/4AEo1HXcep ss9uBWRVyijOZ+A0zoJfUBwbrY+F/sGeWA9qkCbhOdNgfns6c10HBlK516049kqCQd wxldRpbrujAk9Ku35HvfkhJYrJj98L8wajD5h2DY= Subject: Re: [RFC PATCH v2 1/1] arm64: Implement stack trace termination record From: "Madhavan T. Venkataraman" To: Josh Poimboeuf Cc: mark.rutland@arm.com, broonie@kernel.org, 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: <659f3d5cc025896ba4c49aea431aa8b1abc2b741> <20210402032404.47239-1-madvenka@linux.microsoft.com> <20210402032404.47239-2-madvenka@linux.microsoft.com> <20210403155948.ubbgtwmlsdyar7yp@treble> <171fef08-17d3-2c2e-dad8-6caf4c0c7f15@linux.microsoft.com> Message-ID: <49790505-f611-b4a2-c804-b779060601a9@linux.microsoft.com> Date: Sat, 3 Apr 2021 23:40:51 -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: <171fef08-17d3-2c2e-dad8-6caf4c0c7f15@linux.microsoft.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On 4/3/21 10:46 PM, Madhavan T. Venkataraman wrote: >> I'm somewhat arm-ignorant, so take the following comments with a grain >> of salt. >> >> >> I don't think changing these to 'bl' is necessary, unless you wanted >> __primary_switched() and __secondary_switched() to show up in the >> stacktrace for some reason? If so, that seems like a separate patch. >> > The problem is with __secondary_switched. If you trace the code back to where > a secondary CPU is started, I don't see any calls anywhere. There are only > branches if I am not mistaken. So, the return address register never gets > set up with a proper address. The stack trace shows some hexadecimal value > instead of a symbol name. > Actually, I take that back. There are calls in that code path. But I did only see some hexadecimal value instead of a proper address in the stack trace. Sorry about that confusion. My reason to convert the branches to calls is this - the value of the return address register at that point is the return PC of the previous branch and link instruction wherever that happens to be. I think that is a little arbitrary. Instead, if I call start_kernel() and secondary_start_kernel(), the return address gets set up to the next instruction which, IMHO, is better. But I am open to other suggestions. Madhavan