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=unavailable 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 8EFE0C43387 for ; Sat, 12 Jan 2019 09:07:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5BBDF2086C for ; Sat, 12 Jan 2019 09:07:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725857AbfALJHc (ORCPT ); Sat, 12 Jan 2019 04:07:32 -0500 Received: from gate.crashing.org ([63.228.1.57]:59413 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725816AbfALJHb (ORCPT ); Sat, 12 Jan 2019 04:07:31 -0500 Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id x0C8jjRG031682; Sat, 12 Jan 2019 02:45:45 -0600 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id x0C8jfVM031680; Sat, 12 Jan 2019 02:45:41 -0600 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Sat, 12 Jan 2019 02:45:41 -0600 From: Segher Boessenkool To: Balbir Singh Cc: Joe Lawrence , Jiri Kosina , linux-kernel@vger.kernel.org, Torsten Duwe , live-patching@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: ppc64le reliable stack unwinder and scheduled tasks Message-ID: <20190112084541.GK14180@gate.crashing.org> References: <7f468285-b149-37e2-e782-c9e538b997a9@redhat.com> <20190112010914.GB10427@350D> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190112010914.GB10427@350D> User-Agent: Mutt/1.4.2.3i Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Segher