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=-11.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 1AE84C433DB for ; Fri, 15 Jan 2021 15:18:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E21A52389B for ; Fri, 15 Jan 2021 15:18:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726030AbhAOPSJ (ORCPT ); Fri, 15 Jan 2021 10:18:09 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:45013 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732208AbhAOPSI (ORCPT ); Fri, 15 Jan 2021 10:18:08 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610723802; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=gk/kn7jsUx99go9pXyOS699OdqvAXfBJlm34KUBZcPw=; b=H5b2n3RznmWlhoL0MgybKOfU2eXp3dRC1VqH581RVWH0wNpkuXdaZ+M87n9oVJBoR1t01z aE+7W6u/4OS1Bkf/F0eLwFltgPTiAmJ2oaiUFHjvtOytxdR4956eLD11MSCOxzQk9I8lFp PPqvqgb2o94fla4Qt7HjCTVVrRNUNXI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-228-e0qZgkjYP_idxDLrqEdSaA-1; Fri, 15 Jan 2021 10:16:40 -0500 X-MC-Unique: e0qZgkjYP_idxDLrqEdSaA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DDD4A1005D44; Fri, 15 Jan 2021 15:16:38 +0000 (UTC) Received: from treble (ovpn-116-102.rdu2.redhat.com [10.10.116.102]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CDF5D19C45; Fri, 15 Jan 2021 15:16:34 +0000 (UTC) Date: Fri, 15 Jan 2021 09:16:32 -0600 From: Josh Poimboeuf To: Mark Brown Cc: linux-kernel@vger.kernel.org, Jiri Kosina , Joe Lawrence , Jonathan Corbet , Miroslav Benes , Petr Mladek , linux-doc@vger.kernel.org, live-patching@vger.kernel.org, Mark Rutland Subject: Re: [PATCH v3] Documentation: livepatch: document reliable stacktrace Message-ID: <20210115151609.lqrl2yuy2zvrcm47@treble> References: <20210115142446.13880-1-broonie@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210115142446.13880-1-broonie@kernel.org> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Fri, Jan 15, 2021 at 02:24:46PM +0000, Mark Brown wrote: > From: Mark Rutland > > Add documentation for reliable stacktrace. This is intended to describe > the semantics and to be an aid for implementing architecture support for > HAVE_RELIABLE_STACKTRACE. > > Unwinding is a subtle area, and architectures vary greatly in both > implementation and the set of concerns that affect them, so I've tried > to avoid making this too specific to any given architecture. I've used > examples from both x86_64 and arm64 to explain corner cases in more > detail, but I've tried to keep the descriptions sufficient for those who > are unfamiliar with the particular architecture. > > I've tried to give rationale for all the recommendations/requirements, > since that makes it easier to spot nearby issues, or when a check > happens to catch a few things at once. I believe what I have written is > sound, but as some of this was reverse-engineered I may have missed > things worth noting. > > I've made a few assumptions about preferred behaviour, notably: > > * If you can reliably unwind through exceptions, you should (as x86_64 > does). > > * It's fine to omit ftrace_return_to_handler and other return > trampolines so long as these are not subject to patching and the > original return address is reported. Most architectures do this for > ftrace_return_handler, but not other return trampolines. > > * For cases where link register unreliability could result in duplicate > entries in the trace or an inverted trace, I've assumed this should be > treated as unreliable. This specific case shouldn't matter to > livepatching, but I assume that that we want a reliable trace to have > the correct order. > > Signed-off-by: Mark Rutland > Cc: Jiri Kosina > Cc: Joe Lawrence > Cc: Jonathan Corbet > Cc: Josh Poimboeuf > Cc: Mark Brown > Cc: Miroslav Benes > Cc: Petr Mladek > Cc: linux-doc@vgert.kernel.org > Cc: live-patching@vger.kernel.org > [Updates following review -- broonie] > Signed-off-by: Mark Brown > --- > > v3: > - Incorporated objtool section from Mark. > - Deleted confusing notes about using annotations. Acked-by: Josh Poimboeuf -- Josh