From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:40012 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S936390AbdKPRsh (ORCPT ); Thu, 16 Nov 2017 12:48:37 -0500 Received: from pps.filterd (m0098413.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id vAGHj8U9135998 for ; Thu, 16 Nov 2017 12:48:37 -0500 Received: from e13.ny.us.ibm.com (e13.ny.us.ibm.com [129.33.205.203]) by mx0b-001b2d01.pphosted.com with ESMTP id 2e9ec13mpc-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Thu, 16 Nov 2017 12:48:36 -0500 Received: from localhost by e13.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 16 Nov 2017 12:48:35 -0500 Date: Thu, 16 Nov 2017 09:48:30 -0800 From: "Paul E. McKenney" Subject: Re: [PATCH v2 18/18] arm64: select ARCH_SUPPORTS_LTO_CLANG Reply-To: paulmck@linux.vnet.ibm.com References: <20171115213428.22559-1-samitolvanen@google.com> <20171115213428.22559-19-samitolvanen@google.com> <20171116115810.GH9361@arm.com> <20171116161731.GA94341@samitolvanen.mtv.corp.google.com> <20171116163054.kcsdsomr7u2mqql2@hirez.programming.kicks-ass.net> <20171116165922.llrojrvomuihabrt@hirez.programming.kicks-ass.net> <20171116173417.nqsh5dpu65uj7b5s@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171116173417.nqsh5dpu65uj7b5s@hirez.programming.kicks-ass.net> Message-Id: <20171116174830.GX3624@linux.vnet.ibm.com> Sender: linux-kbuild-owner@vger.kernel.org List-ID: To: Peter Zijlstra Cc: Nick Desaulniers , Sami Tolvanen , Will Deacon , Alex Matveev , Andi Kleen , Ard Biesheuvel , Greg Hackmann , Kees Cook , linux-arm-kernel@lists.infradead.org, Linux Kbuild mailing list , LKML , Mark Rutland , Masahiro Yamada , Maxim Kuvyrkov , Michal Marek , Yury Norov , Matthias Kaehlcke On Thu, Nov 16, 2017 at 06:34:17PM +0100, Peter Zijlstra wrote: > On Thu, Nov 16, 2017 at 09:16:49AM -0800, Nick Desaulniers wrote: > > On Thu, Nov 16, 2017 at 8:59 AM, Peter Zijlstra wrote: > > > On Thu, Nov 16, 2017 at 08:50:41AM -0800, Nick Desaulniers wrote: > > >> On Thu, Nov 16, 2017 at 8:30 AM, Peter Zijlstra wrote: > > >> > > >> > Ideally we'd get the toolchain people to commit to supporting the kernel > > >> > memory model along side the C11 one. That would help a ton. > > >> > > >> Does anyone from the kernel side participate in the C standardization process? > > > > > > Yes, Paul McKenney and Will Deacon. Doesn't mean these two can still be > > > reconciled though. From what I understand C11 (and onwards) are > > > incompatible with the kernel model on a number of subtle points. > > > > It would be good to have these incompatibilities written down, then > > for the sake of argument, they can be cited both for discussions on > > LKML and in the C standardization process. For example, a running > > list in Documentation/ or something would make it so that anyone could > > understand and cite current issues with the latest C standard. > > Will should be able to produce this list; I know he's done before, I > just can't find it -- my Google-foo isn't strong today. Here you go: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0124r4.html > > I don't understand why we'd block patches for enabling experimental > > features. We've been running this patch-set on actual devices for > > months and would love to provide them to the community for further > > testing. If bugs are found, then there's more evidence to bring to > > the C standards committee. Otherwise we're shutting down feature > > development for the sake of potential bugs in a C standard we're not > > even using. > > So the problem is that its very very hard (and painful) to find these > bugs. Getting the tools people to comment on these specific > optimizations would really help lots. It would be good to get something similar to LKMM into KTSAN, for example. There would probably be a few differences due to efficiency concerns, but closer is better than less close. ;-) Thanx, Paul