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 214C1C47095 for ; Mon, 7 Jun 2021 18:27:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0C3AC61003 for ; Mon, 7 Jun 2021 18:27:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231214AbhFGS3o (ORCPT ); Mon, 7 Jun 2021 14:29:44 -0400 Received: from gate.crashing.org ([63.228.1.57]:40897 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230514AbhFGS3m (ORCPT ); Mon, 7 Jun 2021 14:29:42 -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 157INap3017668; Mon, 7 Jun 2021 13:23:36 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 157INZNS017666; Mon, 7 Jun 2021 13:23:35 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Mon, 7 Jun 2021 13:23:35 -0500 From: Segher Boessenkool To: "Paul E. McKenney" Cc: Linus Torvalds , Alan Stern , Peter Zijlstra , Will Deacon , Andrea Parri , Boqun Feng , Nick Piggin , David Howells , Jade Alglave , Luc Maranget , Akira Yokosawa , Linux Kernel Mailing List , linux-toolchains@vger.kernel.org, linux-arch Subject: Re: [RFC] LKMM: Add volatile_if() Message-ID: <20210607182335.GI18427@gate.crashing.org> References: <20210606115336.GS18427@gate.crashing.org> <20210606184021.GY18427@gate.crashing.org> <20210606195242.GA18427@gate.crashing.org> <20210606202616.GC18427@gate.crashing.org> <20210606233729.GN4397@paulmck-ThinkPad-P17-Gen-1> <20210607141242.GD18427@gate.crashing.org> <20210607152712.GR4397@paulmck-ThinkPad-P17-Gen-1> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210607152712.GR4397@paulmck-ThinkPad-P17-Gen-1> User-Agent: Mutt/1.4.2.3i Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 07, 2021 at 08:27:12AM -0700, Paul E. McKenney wrote: > > > > > The barrier() thing can work - all we need to do is to simply make it > > > > > impossible for gcc to validly create anything but a conditional > > > > > branch. > > > What would you suggest as a way of instructing the compiler to emit the > > > conditional branch that we are looking for? > > > > You write it in the assembler code. > > > > Yes, it sucks. But it is the only way to get a branch if you really > > want one. Now, you do not really need one here anyway, so there may be > > some other way to satisfy the actual requirements. > > Hmmm... What do you see Peter asking for that is different than what > I am asking for? ;-) I don't know what you are referring to, sorry? I know what you asked for: literally some way to tell the compiler to emit a conditional branch. If that is what you want, the only way to make sure that is what you get is by writing exactly that in assembler. Segher