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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT 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 2AE7EC43387 for ; Tue, 18 Dec 2018 02:49:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F14672145D for ; Tue, 18 Dec 2018 02:49:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726474AbeLRCtV (ORCPT ); Mon, 17 Dec 2018 21:49:21 -0500 Received: from mx1.redhat.com ([209.132.183.28]:54984 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726285AbeLRCtV (ORCPT ); Mon, 17 Dec 2018 21:49:21 -0500 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 73F87DD9C0; Tue, 18 Dec 2018 02:49:20 +0000 (UTC) Received: from treble (ovpn-120-179.rdu2.redhat.com [10.10.120.179]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1660351F26; Tue, 18 Dec 2018 02:49:18 +0000 (UTC) Date: Mon, 17 Dec 2018 20:49:16 -0600 From: Josh Poimboeuf To: Andi Kleen Cc: Steven Rostedt , Peter Zijlstra , Arnd Bergmann , Linux Kernel Mailing List , the arch/x86 maintainers , Miroslav Benes Subject: Re: objtool warnings for kernel/trace/trace_selftest_dynamic.o Message-ID: <20181218024916.vmfnyqzouhfxhyvc@treble> References: <20181217173900.ygifx7khwmzn2gv2@treble> <20181217180434.GS25620@tassilo.jf.intel.com> <20181217181638.dfexg6mkmbfyzfli@treble> <20181217192938.GF2218@hirez.programming.kicks-ass.net> <20181217213126.lsqhyszoulel6uq6@treble> <20181217173644.391c2070@gandalf.local.home> <20181218000618.GA25620@tassilo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20181218000618.GA25620@tassilo.jf.intel.com> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Tue, 18 Dec 2018 02:49:20 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 17, 2018 at 04:06:18PM -0800, Andi Kleen wrote: > On Mon, Dec 17, 2018 at 05:36:44PM -0500, Steven Rostedt wrote: > > On Mon, 17 Dec 2018 15:31:26 -0600 > > Josh Poimboeuf wrote: > > > > > On Mon, Dec 17, 2018 at 08:29:38PM +0100, Peter Zijlstra wrote: > > > > On Mon, Dec 17, 2018 at 12:16:38PM -0600, Josh Poimboeuf wrote: > > > > > > > > > > Yes LTO causes the to be treated like static functions. > > > > > > > > > > > > I guess noclone is unlikely to be really needed here because these > > > > > > functions are unlikely to be cloned. > > > > > > > > > > > > So as a workaround it could be removed. > > > > > > > > > > > > But note we have other noclone functions in the tree (like in KVM) > > > > > > which actually need it. > > > > > > > > > > How about we just use the __used attribute then? It seems to have the > > > > > same result of preventing IPA optimizations (without the weird side > > > > > effect of missing frame pointers). > > > > > > > > AFAIK we don't have any in-tree LTO, so it can all go in the bin. > > > > > > > > When/if we get the LTO trainwreck sorted -- which very much includes > > > > getting that memory-order-consume fixed -- we can revisit all that. > > > > > > Ok, then if there are no objections I'll just send a revert of: > > > > > > dd3dad0d716d ("ftrace: Mark function tracer test functions noinline/noclone") Sorry for suggesting this prematurely, my email client stopped syncing and I missed your later replies to Peter about this. > > Should it be reverted, or just remove the noclone, and keep the > > noinline? > > It should not be touched for now, until it is properly debugged. > > IMHO Josh's explanation doesn't make much sense and there > was a lot of handwaving > > And just fixing one case isn't good enough because there are other > noclone functions in the tree. > > It the problem is the plugin the plugin needs to be fixed. > > If the problem is gcc we need a gcc test case and bug, with > some analysis, and then based on that select the proper workaround. The plugin is only used for older versions of GCC. Newer versions have the same functionality builtin with -fsanitize-coverage=trace-pc. So the problem is GCC. We're using a function attribute which at least oneGCC developer doesn't recommend. If you want to keep the LTO support then '__used' seems like a much better choice. -- Josh