From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [78.32.30.218]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 83A4B58228; Thu, 21 Mar 2024 11:24:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=78.32.30.218 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711020278; cv=none; b=DqdoqsmPZX8AEG55T29y3qqsU/yNyr6TNBUjOKDLbp/S87LGp7OQI3DytqW/3Z7zgOG1/IymVdS2eMzpiErvOXFZT2Njxfkh5yONZzVLehPx2mnZ5ny7NbOMjUm8iLkBURpD6neluPfpjiw3Z4CKre+4Ixh4Uts1f2SN5X6tAA4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711020278; c=relaxed/simple; bh=2xmJIUpAnX0WoR/2adOWV/CSntMFENrOlMHHKXNqdjQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=fED/qPVSN663kh3X01UD4mHGXbN1+s2GuOFYFw1oC09Azgh2t34Ri9IHvKZL0N2is1gi5CY+HsUCkU98AJnVKAbMaP4da3oTul/Qm3sfWMI79DDR7gCHmp0SYCkzNSwr0U/dLrvzneUmg3cLX+6EXuZ2Zzcr1H6LK8qOiAOySLA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=armlinux.org.uk; spf=none smtp.mailfrom=armlinux.org.uk; dkim=pass (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b=W99tkOqB; arc=none smtp.client-ip=78.32.30.218 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=armlinux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=armlinux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b="W99tkOqB" 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=/68CR4f0azvzcAmAfC291AOl4wS99r8FrcRejyLq6xM=; b=W99tkOqBejY893YpC1mtzh9mSp gSa43/zdRcQpaebucrIyVrHxRsSIDRvVgZnItXAPDixGHUB5u4//H27eDTOTj5newSQixHC6+jynm r5qETHV1Ogr4iSiXWxS3zADgqkER/fq/MSBqvSy/GOvGWWlzeV+SY1pG5MjPt9mOY5lligJmN3UIf yDp2jMybyFbaLB866k7EJlMFVUhcd0byz9JSyy+ds6mo4HUA1IBkeXoaAVNobNqzOepGc56fHbhct zKUDDEkpK0iAbRYRuCslUcOC/6KBZycr2Okkdz1t+aI3TOKfG5SePHOuDK5s5Tw7nf21CYpdbDkyk AQVn5l7g==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:46498) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1rnGWd-0007UH-2y; Thu, 21 Mar 2024 11:24:01 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1rnGWW-0003bL-0S; Thu, 21 Mar 2024 11:23:52 +0000 Date: Thu, 21 Mar 2024 11:23:51 +0000 From: "Russell King (Oracle)" To: David Laight , Ard Biesheuvel Cc: '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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: Russell King (Oracle) 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. 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. I have vague memories that Ard has been involved in the unwinder, maybe he could comment on this problem? Maybe we need the unwinder itself to do the correction? I also wonder whether we should only do the correction if we detect that we're pointing at the first instruction of a function, and the previous instruction in the text segment was a BL. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!