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=-7.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 171FEC433DF for ; Fri, 3 Jul 2020 14:51:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EBBDC20899 for ; Fri, 3 Jul 2020 14:51:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593787916; bh=OfQ9QrrhTEkwVc9D/6kQ4OLMbBVifUwGjpIqyu/to+g=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=gI4wlW014RlqP+3JUZWqXYzBV3JfhulOZjoiIeOEDGSkIHcrrIZKySFGRPJ+C6KBn CYdAp0MjGtVKin2zX9/FzuXRYeSV/Lq9Bm5BWfvwKtTUl9D6I0TCy38ogXlqojErDw Uj7FqymHNqmsfRZRcsix47MPoMersmrlaf1DkvGU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726258AbgGCOvw (ORCPT ); Fri, 3 Jul 2020 10:51:52 -0400 Received: from mail.kernel.org ([198.145.29.99]:55518 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726098AbgGCOvw (ORCPT ); Fri, 3 Jul 2020 10:51:52 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (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 61D192088E; Fri, 3 Jul 2020 14:51:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593787911; bh=OfQ9QrrhTEkwVc9D/6kQ4OLMbBVifUwGjpIqyu/to+g=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=P08qXOSK/SsmY8VAxSWxJZlh9y2mElMtAZzYp/JpETdbeuKyxfeNiEOPVeAjMtgmm cVQ6zWd/th8wPaVLaFElx/6ZkEKB/7VSwS0fonaGWl2nOftDG+g5Bf9ZqxlWOJSJrJ eDszUhoHxsOqHSNzzZyn6clVtx/aI8MGpxWzyq84= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 4C40135206C0; Fri, 3 Jul 2020 07:51:51 -0700 (PDT) Date: Fri, 3 Jul 2020 07:51:51 -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: <20200703145151.GG9247@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org 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> <20200703132523.GM117543@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200703132523.GM117543@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Fri, Jul 03, 2020 at 03:25:23PM +0200, Peter Zijlstra wrote: > On Fri, Jul 03, 2020 at 03:13:30PM +0200, Peter Zijlstra wrote: > > > The prototype for GCC is here: https://github.com/AKG001/gcc/ > > > > Thanks! Those test cases are somewhat over qualified though: > > > > static volatile _Atomic (TYPE) * _Dependent_ptr a; \ > > One question though; since its a qualifier, and we've recently spend a > whole lot of effort to strip qualifiers in say READ_ONCE(), how does, > and how do we want, this qualifier to behave. Dereferencing a _Dependent_ptr pointer gives you something that is not _Dependent_ptr, unless the declaration was like this: _Dependent_ptr _Atomic (TYPE) * _Dependent_ptr a; And if I recall correctly, the current state is that assigning a _Dependent_ptr variable to a non-_Dependent_ptr variable strips this marking (though the thought was to be able to ask for a warning). So, yes, it would be nice to be able to explicitly strip the _Dependent_ptr, perhaps the kill_dependency() macro, which is already in the C standard. > C++ has very convenient means of manipulating qualifiers, so it's not > much of a problem there, but for C it is, as we've found, really quite > cumbersome. Even with _Generic() we can't manipulate individual > qualifiers afaict. Fair point, and in C++ this is a templated class, at least in the same sense that std::atomic<> is a templated class. But in this case, would kill_dependency do what you want? Thanx, Paul