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=-7.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 5F1FCC433E0 for ; Fri, 3 Jul 2020 14:52:10 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id B20D5206BE for ; Fri, 3 Jul 2020 14:52:09 +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="P08qXOSK" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B20D5206BE 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-19209-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 3607 invoked by uid 550); 3 Jul 2020 14:52:03 -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 3575 invoked from network); 3 Jul 2020 14:52:03 -0000 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= 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> 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) 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