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 01EC058232; Thu, 21 Mar 2024 14:56:48 +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=1711033011; cv=none; b=TfAkEV1j6ibjsFDXzBGPlb5iKxHRs3quc6BHK/P5guMTbFjA4vjGrxXzHTEPzZqNEp5Yj1lQGOWZGxi6YvqciqSQ32AA8R+v84XcMmUoHqHptou02YTXWd7o0Lxz1KPoqCrN5yo0reoBGiU1YFFvFy/hD8p9+iu67Lfr+2iadY4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711033011; c=relaxed/simple; bh=IYptOw1JdLSVTAap2b6UQcuFR8coEdbT6avF0DWiV0U=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=MYlyzsmyh2xShHL9kYccrwpkHGXuI4QH7RxQRnXPJfOBMePCspgB52jRkM0wDDstg342eWLh/APJCJOqMJ/0+8rBFDls0YgALroHyBQWfMl/uLODfgJgpx2ovC5YNwdQU/UB/SbQewHUGgU+jX+OKgN5JYuq9v493WhfhdnY8i8= 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=R9Q7yXVV; 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="R9Q7yXVV" 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=OLw2lU9lpBwjLUSQ/UpfVBslsUspZQKPHPTl4U7tJ60=; b=R9Q7yXVVqgdbeoUTqOfF1D1JUY aVv2jE88tkz8pMKojqD8CZqYgL9NubNF9nWhDccFAIkkV+5AJgfAM1EALCONOzStkFp1CSsMZQbpS IG5l3HeC2csOb9vAD64Ahpjih6SmyKwg3HLHGr6WiStHqNxDoTqA90taj0TBS9XOBjeQiewIjwZfM 3lbNvC82x5qmvxcdFY1EGZ+zdq/ldoh0GIKmTyB2QMViG3lk1lSkqMaBnqW54Lc2t6vFGMImVmiuN +4j6EcjYrvSqHnpkc8ESZ8VCbxohMyaNsOvoXPkEMtyxab20/i4TuP8zdyPkNTVb8vQSweRG8kAjT XWDfLbRA==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:35816) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1rnJq4-0007fb-2f; Thu, 21 Mar 2024 14:56:16 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1rnJpx-0003jQ-8t; Thu, 21 Mar 2024 14:56:09 +0000 Date: Thu, 21 Mar 2024 14:56:09 +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: <84a57ca8-8963-ca24-8bd1-ddc5c33bf4da@huawei.com> <0fd55e156195440bb1d815dd8300894b@AcuMS.aculab.com> <9d6057b110034c04b6b590522c8c69cc@AcuMS.aculab.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: <9d6057b110034c04b6b590522c8c69cc@AcuMS.aculab.com> Sender: Russell King (Oracle) On Thu, Mar 21, 2024 at 02:37:28PM +0000, David Laight wrote: > From: Russell King > > Sent: 21 March 2024 13:08 > > > > On Thu, Mar 21, 2024 at 12:57:07PM +0000, David Laight wrote: > > > From: Russell King > > > > Sent: 21 March 2024 12:23 > > > ... > > > > > 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. > > > > > > Actually you can get there with a function that has a lot of args. > > > So you can have: > > > if (...) { > > > push x > > > bl func > > > add %sp, #8 > > > } > > > code; > > > which is fine. > > > > No you can't.... and that isn't even Arm code. Arm doesn't use %sp. > > Moreover, that "bl" will stomp over the link register, meaning this > > function can not return. > > With 9+ arguments they spill to see https://godbolt.org/z/Yj3ovd8bY > > Where the compiler generates: > f9: > cmp w0, 0 > ble .L2 > sub sp, sp, #32 > mov w7, w0 > mov w6, w0 > mov w5, w0 > mov w4, w0 > mov w3, w0 > stp x29, x30, [sp, 16] > add x29, sp, 16 > mov w2, w0 > mov w1, w0 > str w0, [sp] > bl f > .L2: > ret Don't show me Arm64 assembly when we're discussing Arm32. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!