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=-6.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 B5D78C43381 for ; Fri, 8 Mar 2019 21:56:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7C3C120643 for ; Fri, 8 Mar 2019 21:56:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726626AbfCHV4K (ORCPT ); Fri, 8 Mar 2019 16:56:10 -0500 Received: from mx1.redhat.com ([209.132.183.28]:47522 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726267AbfCHV4J (ORCPT ); Fri, 8 Mar 2019 16:56:09 -0500 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 8E6D0C01EE87; Fri, 8 Mar 2019 21:56:09 +0000 (UTC) Received: from treble (ovpn-123-151.rdu2.redhat.com [10.10.123.151]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B68F617CE9; Fri, 8 Mar 2019 21:56:04 +0000 (UTC) Date: Fri, 8 Mar 2019 15:56:02 -0600 From: Josh Poimboeuf To: Peter Zijlstra Cc: torvalds@linux-foundation.org, tglx@linutronix.de, hpa@zytor.com, julien.thierry@arm.com, will.deacon@arm.com, luto@amacapital.net, mingo@kernel.org, catalin.marinas@arm.com, james.morse@arm.com, valentin.schneider@arm.com, brgerst@gmail.com, luto@kernel.org, bp@alien8.de, dvlasenk@redhat.com, linux-kernel@vger.kernel.org, dvyukov@google.com, rostedt@goodmis.org Subject: Re: [PATCH 20/20] objtool: Add Direction Flag validation Message-ID: <20190308215602.txm4bv2eg2tyubuj@treble> References: <20190307114511.870090179@infradead.org> <20190307115200.878625203@infradead.org> <20190308211603.fpjbd5avcuoox6xf@treble> <20190308213343.GE2482@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190308213343.GE2482@worktop.programming.kicks-ass.net> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Fri, 08 Mar 2019 21:56:09 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 08, 2019 at 10:33:43PM +0100, Peter Zijlstra wrote: > On Fri, Mar 08, 2019 at 03:16:03PM -0600, Josh Poimboeuf wrote: > > On Thu, Mar 07, 2019 at 12:45:31PM +0100, Peter Zijlstra wrote: > > > Having DF escape is BAD(tm). > > > > > > Suggested-by: Linus Torvalds > > > Signed-off-by: Peter Zijlstra (Intel) > > > > Can you elaborate on why (in the patch description)? Did this actually > > find any occurrences? > > Nope, didn't find anything. Also, all DF users are in asm so I didn't > really expect any. Having it escape would probably result in fairly > instant wreckage though. > > DF=1 results in things like rep mov going _backwards_. Ok, I wonder if we really need to add this then. -- Josh