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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 52154C54E68 for ; Thu, 21 Mar 2024 12:23:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=m1Nu0tAOGYx9U050L+ipK0T97gG6BmwYfPCFz7sBYEc=; b=nGAoOP7tdyijdx 9eQLz2tA2FoVdWkl4mNo/IxAx8hUd3YDY7Edk2GK2CrpyoMGKx/13lgTFFMNsjaJ5K7RZcDPT6HCI A551aEEz3qb6cwTpnsBdD+I3NJGbrvwbkvmGOkUB5zNuOHlYNjnXzxJbevp4ZhdRuqLRvnxTGg434 f8gKQFCBh1+ICK/ywoEVswCnYEbOHte34UKgyVydsh0rxWvHLYU5X+L7dvgMwFiZazqDWBCCu0uqk AqQDSfzhJ3iAR/ePMcHARydayPC6aP43NBm41Z6u8K4cBF7oWfoM3TH7Uva4t1rpSgWa8yBF9k+9a YfLz+NFjjp7Nhukz8wVA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1rnHSM-00000002xJn-3bWq; Thu, 21 Mar 2024 12:23:38 +0000 Received: from pandora.armlinux.org.uk ([2001:4d48:ad52:32c8:5054:ff:fe00:142]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1rnHSK-00000002xIZ-1kvR for linux-arm-kernel@lists.infradead.org; Thu, 21 Mar 2024 12:23:38 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=bv5iaIHPCtllbUdTBibdobMZ0uFxV6D8XvDh1qKAPRc=; b=Lkj3c18YRRBepAzzJc64myDSZ6 vTbXteiIViBqHGeU6E9lDwpYqA0nDPgbUdpNDKiKND3D3T7kC05v3NOAPvITBZ8sQH/gZ/oYjHuR0 Jr9QRYKBkKGYOSs1J56y0aTRsIsA7gFEzzc4ioVpgPvb96lA+eVHPF27AqqLR96jTwaTeYsmli5DK 6lHemPYIN4ZXJrAQ8ki1duGAs00GxSlSMT5x5tqU7qxB7/sU9bKdNQuB3hXCxVSDzBg5CdCm9aXGM t7xvvUgoUj6DAWZuSdv/CrgjYFfm8lenv+szEn2gueWVKhEgXbVFPfutWDZd7VNTtqWD43wt/75rk 5W9R5S2w==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:55568) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1rnHRo-0007XB-0R; Thu, 21 Mar 2024 12:23:04 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1rnHRi-0003dh-TB; Thu, 21 Mar 2024 12:22:58 +0000 Date: Thu, 21 Mar 2024 12:22:58 +0000 From: "Russell King (Oracle)" To: David Laight Cc: Ard Biesheuvel , 'Jiangfeng Xiao' , "arnd@arndb.de" , "keescook@chromium.org" , "haibo.li@mediatek.com" , "angelogioacchino.delregno@collabora.com" , "amergnat@baylibre.com" , "akpm@linux-foundation.org" , "dave.hansen@linux.intel.com" , "douzhaolei@huawei.com" , "gustavoars@kernel.org" , "jpoimboe@kernel.org" , "kepler.chenxin@huawei.com" , "kirill.shutemov@linux.intel.com" , "linux-hardening@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "linux-arm-kernel@lists.infradead.org" , "nixiaoming@huawei.com" , "peterz@infradead.org" , "wangbing6@huawei.com" , "wangfangpeng1@huawei.com" , "jannh@google.com" , "willy@infradead.org" Subject: Re: [PATCH v2] ARM: unwind: improve unwinders for noreturn case Message-ID: References: <1709516385-7778-1-git-send-email-xiaojiangfeng@huawei.com> <1710906278-23851-1-git-send-email-xiaojiangfeng@huawei.com> <84a57ca8-8963-ca24-8bd1-ddc5c33bf4da@huawei.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240321_052336_481547_D7DB876D X-CRM114-Status: GOOD ( 19.61 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Mar 21, 2024 at 12:07:51PM +0000, David Laight wrote: > From: Russell King > > Sent: 21 March 2024 11:24 > > > > On Thu, Mar 21, 2024 at 10:22:30AM +0000, David Laight wrote: > > > How aggressively does the compiler optimise 'noreturn' functions? > > > > I've seen cases where the compiler emits a BL instruction as the very > > last thing in the function, and nothing after it. > > I've also seen the compiler defer generating a stack frame until > after an initial conditional. .. which is why we pass -mno-sched-prolog to GCC. > That might mean you can get the BL in the middle of a function > but where the following instruction is for the 'no stack frame' > side of the branch. > That is very likely to break any stack offset calculations. No it can't. At any one point in the function, the stack has to be in a well defined state, so that access to local variables can work, and also the stack can be correctly unwound. If there exists a point in the function body which can be reached where the stack could be in two different states, then the stack can't be restored to the parent context. > > This is where the problem lies - because the link register value > > created by the BL instruction will point to the instruction after the > > BL which will _not_ part of the function that invoked the BL. That > > will probably cause issues for the ELF unwinder, which means this > > issue probably goes beyond _just_ printing the function name. > > Isn't this already in the unwinder? > A BL itself isn't going to fault with PC = next-instruction. You are missing the fact that the PC can be the saved LR, and thus can very well be the next instruction. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last! _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel