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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 7B934C433E2 for ; Wed, 1 Jul 2020 16:03:59 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id D7871206C3 for ; Wed, 1 Jul 2020 16:03:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="ZHXG8ON1" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D7871206C3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-19200-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 1282 invoked by uid 550); 1 Jul 2020 16:03:51 -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 1249 invoked from network); 1 Jul 2020 16:03:50 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593619418; bh=lsVbSj/ss2har/B90Io45Cd2wBUKELeZ+wmjiYF4Efg=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=ZHXG8ON1MQAVd0WWgmGngqjNTqPZiPz9LyxrPLzmg1Y9mxBRyPhX4Zk5/ivtnj4n3 eptU/PsHOZLsOUUXwHFNa+8Zr9742CVsM7nWCzeGKTuFDM4VzgjHe4h0BXahzgELZw AFEbkSo/wshrekgHPJScGghJKuijNH54TSiSEgIg= Date: Wed, 1 Jul 2020 09:03:38 -0700 From: "Paul E. McKenney" To: Peter Zijlstra 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: <20200701160338.GN9247@paulmck-ThinkPad-P72> 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> <20200701150512.GH4817@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200701150512.GH4817@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.4 (2018-02-28) On Wed, Jul 01, 2020 at 05:05:12PM +0200, Peter Zijlstra wrote: > 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'? :-) Turning off all dependency-killing optimizations on all pointers is likely a non-event. Turning off all dependency-killing optimizations on all integers is not the road to happiness. So whatever "need" might be, it would need to be rather earthshaking. ;-) It is probably not -that- hard to convert to pointers, even if they are indexing multiple arrays. > 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. No argument here. But it looks like we are going to have to tell the compiler. Thanx, Paul