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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 06340C433E0 for ; Wed, 20 May 2020 09:50:38 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id AF4252070A for ; Wed, 20 May 2020 09:50:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="bAzl3WUw"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="ebH3UqRe" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AF4252070A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject: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=tcc90tnJ8a6ufHlwK7O0+xZQr8uKQYBP0PCRKd63NuQ=; b=bAzl3WUw7+ehBi xeo9zMw/8dE36XXdCmRMJkeqYiE9tTDdy0+h5Qb//2lzXFYK0I2gxVCzeGIbWgB7IWX/QSZw/Cpxt UhqbvxFlCexqlEpRPv4GsMqhNAQtPlRmU2gjlPVV3pmZTwS5gsRgO8Elizmrf1GSIcnR+JZmTPs12 J+I79mslCwQ0HnjJ4aDdZSubz/RQNq3+1HF1psRKRhps4oQBp+oPZOgJdqAARK1uMQiKL8C715kbU eDyDvlxXViE6Bvjz3BLYsfiaJ5MJA99DLKpBkP/22Emo2FmPUZin+52jeBY1PYYWCdF41Mbed+RIJ b2D5kWfNBYYNob+ELMnA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jbLMz-0006du-Dl; Wed, 20 May 2020 09:50:37 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jbLMw-0006dM-VV for linux-arm-kernel@lists.infradead.org; Wed, 20 May 2020 09:50:36 +0000 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9C3932070A; Wed, 20 May 2020 09:50:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589968232; bh=53rt/NhFNDY+d2dbfI/806WF/r8+V8zlLTSpUE7ZGk0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ebH3UqRe/uBa1CpuRjBTW1cuS+4Otc+WaT0u3l+J6rnl1zp/cwbwP+mD/xlGtLS6E YRt/6TXOTggME78RdlzpeUK8FbKOxWiGjwzUY9y/LSGJ1xn3IQkuFdajsQ0TMrMpPE O3+foJt3ruV3Gpa7nfz/dnoeXxFkumR5KtXBVS54= Date: Wed, 20 May 2020 10:50:28 +0100 From: Will Deacon To: Dave Martin Subject: Re: [PATCH v2 2/2] arm64: vdso: Fix CFI directives in sigreturn trampoline Message-ID: <20200520095027.GE24293@willie-the-truck> References: <20200519162821.16857-1-will@kernel.org> <20200519162821.16857-3-will@kernel.org> <20200520094212.GK5031@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200520094212.GK5031@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200520_025035_039445_110AA660 X-CRM114-Status: GOOD ( 16.47 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Tamas Zsoldos , Mark Brown , kernel-team@android.com, linux-arm-kernel@lists.infradead.org, Daniel Kiss Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, May 20, 2020 at 10:42:13AM +0100, Dave Martin wrote: > On Tue, May 19, 2020 at 05:28:21PM +0100, Will Deacon wrote: > > @@ -14,7 +18,34 @@ > > > > .text > > > > - nop > > +/* Ensure that the mysterious NOP can be associated with a function. */ > > + .cfi_startproc > > + > > +/* > > + * .cfi_signal_frame causes the corresponding Frame Description Entry in the > > + * .eh_frame section to be annotated as a signal frame. This allows DWARF > > + * unwinders (e.g. libstdc++) to implement _Unwind_GetIPInfo(), which permits > > + * unwinding out of the signal trampoline without the need for the mysterious > > + * NOP. > > + */ > > + .cfi_signal_frame > > + > > +/* > > + * Tell the unwinder where to locate the frame record linking back to the > > + * interrupted context. > > + */ > > + .cfi_def_cfa x29, 0 > > + .cfi_offset x29, 0 * 8 > > + .cfi_offset x29, 1 * 8 > > We should also give rationale for why we don't describe how to recover > other regs here. At a signal, every reg is potentially live with data > essential to the backtrace, so custom unwind entries further up the > stack may unwind badly after trying to unwind out of the signal handler. Hmm, I'm not sure I get what you're asking for. We can't recover the other registers even if we tried, can we? I think the only way to get a reliable backtrace here is not to clobber the framepointer. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel