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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 6227CC47098 for ; Fri, 4 Jun 2021 15:51:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4701261263 for ; Fri, 4 Jun 2021 15:51:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231283AbhFDPxf (ORCPT ); Fri, 4 Jun 2021 11:53:35 -0400 Received: from gate.crashing.org ([63.228.1.57]:35730 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229809AbhFDPxe (ORCPT ); Fri, 4 Jun 2021 11:53:34 -0400 Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 154FlJPc021199; Fri, 4 Jun 2021 10:47:19 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 154FlIM5021198; Fri, 4 Jun 2021 10:47:18 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Fri, 4 Jun 2021 10:47:18 -0500 From: Segher Boessenkool To: Peter Zijlstra Cc: Will Deacon , Linus Torvalds , paulmck@kernel.org, stern@rowland.harvard.edu, parri.andrea@gmail.com, boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr, akiyks@gmail.com, linux-kernel@vger.kernel.org, linux-toolchains@vger.kernel.org, linux-arch@vger.kernel.org Subject: Re: [RFC] LKMM: Add volatile_if() Message-ID: <20210604154718.GE18427@gate.crashing.org> References: <20210604104359.GE2318@willie-the-truck> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.3i Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 04, 2021 at 01:31:48PM +0200, Peter Zijlstra wrote: > On Fri, Jun 04, 2021 at 11:44:00AM +0100, Will Deacon wrote: > > > +{ > > > + asm_volatile_goto("cbnz %0, %l[l_yes]" > > > + : : "r" (cond) : "cc", "memory" : l_yes); > > > + return 0; > > > +l_yes: > > > + return 1; > > > +} > > > > nit: you don't need the "cc" clobber here. > > Yeah I know, "cc" is implied. It isn't needed at all here. cbnz does not write to the condition register. Neither does it change or access memory, but the "memory" clobber is to force a false dependency. Writing "cc" as well looks a bit confusing, given that. Segher