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=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 3CC06C43612 for ; Thu, 17 Jan 2019 14:54:32 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 8E6CE20652 for ; Thu, 17 Jan 2019 14:54:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8E6CE20652 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 43gRtW6Jw2zDqwm for ; Fri, 18 Jan 2019 01:54:27 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=permerror (mailfrom) smtp.mailfrom=kernel.crashing.org (client-ip=63.228.1.57; helo=gate.crashing.org; envelope-from=segher@kernel.crashing.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 43gRrg3GNgzDqvN for ; Fri, 18 Jan 2019 01:52:51 +1100 (AEDT) Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id x0HEqabh031907; Thu, 17 Jan 2019 08:52:36 -0600 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id x0HEqYcN031906; Thu, 17 Jan 2019 08:52:34 -0600 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Thu, 17 Jan 2019 08:52:33 -0600 From: Segher Boessenkool To: Balbir Singh Subject: Re: ppc64le reliable stack unwinder and scheduled tasks Message-ID: <20190117145233.GQ14180@gate.crashing.org> References: <7f468285-b149-37e2-e782-c9e538b997a9@redhat.com> <20190112010914.GB10427@350D> <20190112084541.GK14180@gate.crashing.org> <20190113123356.GA26056@350D> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190113123356.GA26056@350D> User-Agent: Mutt/1.4.2.3i X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Joe Lawrence , Jiri Kosina , linux-kernel@vger.kernel.org, Torsten Duwe , live-patching@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Sun, Jan 13, 2019 at 11:33:56PM +1100, Balbir Singh wrote: > On Sat, Jan 12, 2019 at 02:45:41AM -0600, Segher Boessenkool wrote: > > On Sat, Jan 12, 2019 at 12:09:14PM +1100, Balbir Singh wrote: > > > Could you please define interesting frame on top a bit more? Usually > > > the topmost return address is in LR > > > > There is no reliable way (other than DWARF unwind info) to find out where > > the value of LR at function entry currently lives (if anywhere). It may or > > may not be still available in LR, it may or may not be saved to the return > > stack slot. It can also live in some GPR, or in some other stack slot. > > > > (The same is true for all other registers). > > > > The only thing the ABI guarantees you is that you can find all stack frames > > via the back chain. If you want more you can use some heuristics and do > > some heroics (like GDB does), but this is not fully reliable. Using DWARF > > unwind info is, but that requires big tables. > > > > Thanks, so are you suggesting that a reliable stack is not possible on > ppc64le? Even with the restricted scope of the kernel? It depends on what you mean with "reliable stack unwinder". You can unwind the stack reliably on Power, but you want more, you want to know where some state local to functions is kept on the stack. Segher