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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 57898C433DF for ; Wed, 1 Jul 2020 15:05:39 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id B06A620760 for ; Wed, 1 Jul 2020 15:05:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="i74sl3ZO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B06A620760 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-19199-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 7532 invoked by uid 550); 1 Jul 2020 15:05:31 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 7497 invoked from network); 1 Jul 2020 15:05:30 -0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=yjUbAZQQ9f4rcShW5GkixqYv9x2nD42GGzyjdsiFm50=; b=i74sl3ZOPr1xqJIhkMJglGWOkB U8dqkz+3Y5fKVBDLcgGRCYbTPQFBGPgHtaCMun69vkwL/Ry/Z+4Jsl8Mf+SEd1g2rFtmyvmpbWIYZ K0Ycyjqzo60JLazLm+uQfh7KsY8FqjTzInhLzUzA/uu1WwZ1uS4jmIhsjRK2swdHfjsLC2mBUqXmb tjLVkf7OGf4kz+DTg9+2SwJMjK14kVHRsmKF/8JUPsny87vwFakQlM7eTrs35Vus1k5vP28RmJNHc Yyq+PGlJEHTv7w05Krc9LSs+q+qVge1miTYAIcksAas9z16JswYUyikbLlMyiWZjWWnmMZFBaj5Bf 7m/rqxmg==; Date: Wed, 1 Jul 2020 17:05:12 +0200 From: Peter Zijlstra To: "Paul E. McKenney" Cc: Marco Elver , Nick Desaulniers , Sami Tolvanen , Masahiro Yamada , Will Deacon , Greg Kroah-Hartman , Kees Cook , clang-built-linux , Kernel Hardening , linux-arch , Linux ARM , Linux Kbuild mailing list , LKML , linux-pci@vger.kernel.org, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" Subject: Re: [PATCH 00/22] add support for Clang LTO Message-ID: <20200701150512.GH4817@hirez.programming.kicks-ass.net> References: <20200625080313.GY4817@hirez.programming.kicks-ass.net> <20200625082433.GC117543@hirez.programming.kicks-ass.net> <20200625085745.GD117543@hirez.programming.kicks-ass.net> <20200630191931.GA884155@elver.google.com> <20200630201243.GD4817@hirez.programming.kicks-ass.net> <20200630203016.GI9247@paulmck-ThinkPad-P72> <20200701114027.GO4800@hirez.programming.kicks-ass.net> <20200701140654.GL9247@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200701140654.GL9247@paulmck-ThinkPad-P72> On Wed, Jul 01, 2020 at 07:06:54AM -0700, Paul E. McKenney wrote: > The current state in the C++ committee is that marking variables > carrying dependencies is the way forward. This is of course not what > the Linux kernel community does, but it should not be hard to have a > -fall-variables-dependent or some such that causes all variables to be > treated as if they were marked. Though I was hoping for only pointers. > Are they -sure- that they -absolutely- need to carry dependencies > through integers??? What's 'need'? :-) I'm thinking __ktime_get_fast_ns() is better off with a dependent load than it is with an extra smp_rmb(). Yes we can stick an smp_rmb() in there, but I don't like it. Like I wrote earlier, if I wanted a control dependency, I'd have written one.