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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 61CC8C10F11 for ; Wed, 10 Apr 2019 07:20:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2B2E22070D for ; Wed, 10 Apr 2019 07:20:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728952AbfDJHUg (ORCPT ); Wed, 10 Apr 2019 03:20:36 -0400 Received: from foss.arm.com ([217.140.101.70]:48846 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728787AbfDJHUf (ORCPT ); Wed, 10 Apr 2019 03:20:35 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 15131A78; Wed, 10 Apr 2019 00:20:35 -0700 (PDT) Received: from [10.1.197.45] (e112298-lin.cambridge.arm.com [10.1.197.45]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9A5AC3F68F; Wed, 10 Apr 2019 00:20:33 -0700 (PDT) Subject: Re: [PATCH 0/6] objtool: Add support for Arm64 To: Josh Poimboeuf , Ard Biesheuvel Cc: Raphael Gault , Linux Kernel Mailing List , linux-arm-kernel , Peter Zijlstra , Catalin Marinas , Will Deacon References: <20190409135243.12424-1-raphael.gault@arm.com> <20190410033732.ibtpnd36655afpfj@treble> From: Julien Thierry Message-ID: Date: Wed, 10 Apr 2019 08:20:31 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20190410033732.ibtpnd36655afpfj@treble> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/04/2019 04:37, Josh Poimboeuf wrote: > On Tue, Apr 09, 2019 at 10:43:18AM -0700, Ard Biesheuvel wrote: >> On Tue, 9 Apr 2019 at 06:53, Raphael Gault wrote: >>> >>> Hi, >>> >>> As of now, objtool only supports the x86_64 architecture but the >>> groundwork has already been done in order to add support for other >>> architecture without too much effort. >>> >>> This series of patches adds support for the arm64 architecture >>> based on the Armv8.5 Architecture Reference Manual. >>> >> >> I think it makes sense to clarify *why* we want this on arm64. Also, >> we should identify things that objtool does today that maybe we don't >> want on arm64, rather than buy into all of it by default. > > Agreed, the "why" should at least be in the cover letter. From my > perspective, the "why" includes: > > - Live patching - objtool stack validation is the foundation for a > reliable unwinder > Yes, as I understand Live patching is a work in progress for arm64. Having objtool to provide more guarantees would be nice. > - ORC unwinder - benefits include presumed improved overall performance > from disabling frame pointers, and the ability to unwind across > interrupts and exceptions > I'm unsure this will be part of the plan. I believe so far arm64 code heavily relies on the presence of frame pointers. It's also part of the Aarch64 Procedure Call Standard. But who knows. > - PeterZ's new uaccess validation? > Yes, we've reverted twice our implementation of user_access_begin/end() on arm64 because of the issue of potentially calling sleeping functions. Once we have the base of objtool work, this would be one of the next work items. Thanks, -- Julien Thierry