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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 22836C433E0 for ; Mon, 6 Jul 2020 16:28:03 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E38AF20702 for ; Mon, 6 Jul 2020 16:28:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="TwBe+8Y1"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="NWnqF8yN" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E38AF20702 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:Reply-To:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=G+ckTx6RQR8HiK5nKSt38gINjH25txTo6vWUwu14lGM=; b=TwBe+8Y1YP1mcFmV0PVtTS07vC 7EWiPYp4sDv2qA0Wu2zVVLrndG1OOAi9CZ7/mW02yTyJblI+6hP6+kYyPTVHnmsT2P726lb5FP5Me 5xCaZ/o/oZdUgbYn+WabVRW1XDHPuNPmCkeFblLD6/3nCgw00T185k51hPs1sKZ5qCt5B/W6d7dIJ 5nixAA4TKJZFz90TTMW/Q5pYiJvMprN6DAT+cb9B96Kq1HlRVpaDR7IhAbDhzHOyVtWAT2HYNbM7N WuS5DxUrDu+X3cZQofWp3mrL/iHprLSFDg8YyAvbgngIKpGCyH9fu1bEpPWVz9MKMnJYZqLt3lWMG C0uubpGg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jsTwz-0008Kt-Id; Mon, 06 Jul 2020 16:26:37 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jsTwx-0008Jd-KZ for linux-arm-kernel@lists.infradead.org; Mon, 06 Jul 2020 16:26:36 +0000 Received: from paulmck-ThinkPad-P72.home (50-39-111-31.bvtn.or.frontiernet.net [50.39.111.31]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C63D220702; Mon, 6 Jul 2020 16:26:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1594052793; bh=ELC0Qf8GBOcW7d74k7xE/syM0cqkEfG1ZwnEhNH0Xwc=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=NWnqF8yNh1kmeojBtU/hvJnKQi+pZfEw8tRN6xyWsQTMlbnwqrlnw5lTOXvjlFbT7 B5rw2d8haDBAV5oFbA0B0HdNl5tN/Er570PuYfYx1NWaxj3XhsCuq3jsWx3nC14oRK 3IoGxJUeXAP3v3i6Usrl18oSx/B8BE0q7l0vU15Q= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id B23463521502; Mon, 6 Jul 2020 09:26:33 -0700 (PDT) Date: Mon, 6 Jul 2020 09:26:33 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Subject: Re: [PATCH 00/22] add support for Clang LTO Message-ID: <20200706162633.GA13288@paulmck-ThinkPad-P72> References: <20200630203016.GI9247@paulmck-ThinkPad-P72> <20200701114027.GO4800@hirez.programming.kicks-ass.net> <20200701140654.GL9247@paulmck-ThinkPad-P72> <20200701150512.GH4817@hirez.programming.kicks-ass.net> <20200701160338.GN9247@paulmck-ThinkPad-P72> <20200702082040.GB4781@hirez.programming.kicks-ass.net> <20200702175948.GV9247@paulmck-ThinkPad-P72> <20200703131330.GX4800@hirez.programming.kicks-ass.net> <20200703144228.GF9247@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200703144228.GF9247@paulmck-ThinkPad-P72> User-Agent: Mutt/1.9.4 (2018-02-28) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200706_122635_803576_C2C7F0BA X-CRM114-Status: GOOD ( 17.39 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: paulmck@kernel.org Cc: linux-arch , Marco Elver , "maintainer:X86 ARCHITECTURE \(32-BIT AND 64-BIT\)" , Kees Cook , Kernel Hardening , Greg Kroah-Hartman , Masahiro Yamada , Linux Kbuild mailing list , Nick Desaulniers , LKML , clang-built-linux , Sami Tolvanen , linux-pci@vger.kernel.org, Will Deacon , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Jul 03, 2020 at 07:42:28AM -0700, Paul E. McKenney wrote: > On Fri, Jul 03, 2020 at 03:13:30PM +0200, Peter Zijlstra wrote: > > On Thu, Jul 02, 2020 at 10:59:48AM -0700, Paul E. McKenney wrote: > > > On Thu, Jul 02, 2020 at 10:20:40AM +0200, Peter Zijlstra wrote: > > > > On Wed, Jul 01, 2020 at 09:03:38AM -0700, Paul E. McKenney wrote: [ . . . ] > > Also, if C goes and specifies load dependencies, in any form, is then > > not the corrolary that they need to specify control dependencies? How > > else can they exclude the transformation. > > By requiring that any temporaries generated from variables that are > marked _Dependent_ptr also be marked _Dependent_ptr. This is of course > one divergence of _Dependent_ptr from the volatile keyword. > > > And of course, once we're there, can we get explicit support for control > > dependencies too? :-) :-) > > Keep talking like this and I am going to make sure that you attend a > standards committee meeting. If need be, by arranging for you to be > physically dragged there. ;-) > > More seriously, for control dependencies, the variable that would need > to be marked would be the program counter, which might require some > additional syntax. And perhaps more constructively, we do need to prioritize address and data dependencies over control dependencies. For one thing, there are a lot more address/data dependencies in existing code than there are control dependencies, and (sadly, perhaps more importantly) there are a lot more people who are convinced that address/data dependencies are important. For another (admittedly more theoretical) thing, the OOTA scenarios stemming from control dependencies are a lot less annoying than those from address/data dependencies. And address/data dependencies are as far as I know vulnerable to things like conditional-move instructions that can cause problems for control dependencies. Nevertheless, yes, control dependencies also need attention. Thanx, Paul _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel