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=-5.8 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS 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 3546FC433DF for ; Fri, 3 Jul 2020 13:13:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 09BA2208E4 for ; Fri, 3 Jul 2020 13:13:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="ItGZjDRI" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726053AbgGCNNj (ORCPT ); Fri, 3 Jul 2020 09:13:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59686 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725984AbgGCNNj (ORCPT ); Fri, 3 Jul 2020 09:13:39 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F3842C08C5C1; Fri, 3 Jul 2020 06:13:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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=uqsQimSA3ZVIJmzJ+g3hxvE+rQFiKwkEojhvCeRdahw=; b=ItGZjDRIImf27YsAGtOG8yy/um tHTSFrVgQyOISf1u9ovbSydWGKTsYFOu1QdZqaIrPrVC+BQULRRFgfurUr+UHbhbVAjFYXc0yCGNH NRV6Ty0xvDowLbPzhWsEfUHzZqw0FT874nx/34bvhnQsXXmIDYEOYRNqxPNQYH8rAHKE2/8AwTRk8 wHLizFfF5+qhuvmcj3dz1f5NSP8/5ZJsGkhy1O/RcYnmb5zr+RExexvUuyCwYq8Luedw4dSOP2EUv Sin4pSha9/RbjtlWc8OZlJovtZ17d+oq5poGsjxjQDDenUnzl1rkiSj26lYRo48qjQPCyZuX1TsWH IDaagGpA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jrLVT-0003j1-Sa; Fri, 03 Jul 2020 13:13:32 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 71D12301124; Fri, 3 Jul 2020 15:13:30 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 30A0521476E91; Fri, 3 Jul 2020 15:13:30 +0200 (CEST) Date: Fri, 3 Jul 2020 15:13:30 +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: <20200703131330.GX4800@hirez.programming.kicks-ass.net> References: <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> <20200701160338.GN9247@paulmck-ThinkPad-P72> <20200702082040.GB4781@hirez.programming.kicks-ass.net> <20200702175948.GV9247@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200702175948.GV9247@paulmck-ThinkPad-P72> Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org 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: > > > > > But it looks like we are going to have to tell the compiler. > > > > What does the current proposal look like? I can certainly annotate the > > seqcount latch users, but who knows what other code is out there.... > > For pointers, yes, within the Linux kernel it is hopeless, thus the > thought of a -fall-dependent-ptr or some such that makes the compiler > pretend that each and every pointer is marked with the _Dependent_ptr > qualifier. > > New non-Linux-kernel code might want to use his qualifier explicitly, > perhaps something like the following: > > _Dependent_ptr struct foo *p; // Or maybe after the "*"? After, as you've written it, it's a pointer to a '_Dependent struct foo'. > > rcu_read_lock(); > p = rcu_dereference(gp); > // And so on... > > If a function is to take a dependent pointer as a function argument, > then the corresponding parameter need the _Dependent_ptr marking. > Ditto for return values. > > The proposal did not cover integers due to concerns about the number of > optimization passes that would need to be reviewed to make that work. > Nevertheless, using a marked integer would be safer than using an unmarked > one, and if the review can be carried out, why not? Maybe something > like this: > > _Dependent_ptr int idx; > > rcu_read_lock(); > idx = READ_ONCE(gidx); > d = rcuarray[idx]; > rcu_read_unlock(); > do_something_with(d); > > So use of this qualifier is quite reasonable. The above usage might warrant a rename of the qualifier though, since clearly there isn't anything ptr around. > 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; \ 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. And of course, once we're there, can we get explicit support for control dependencies too? :-) :-)