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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 67D02C433DF for ; Thu, 25 Jun 2020 08:27:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3A0082081A for ; Thu, 25 Jun 2020 08:27:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593073637; bh=GncOVRnsRbmrObVuGed/d33M2KDkzxTcEILATAJbLBA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=VmIxukOXt/BUrjB0iWNBjP3sWQ2QMmLOn8lbvuZdI7S+Wg514mO7KiwZ6TRrMPgZ1 RMOZsygcGvHpMBEKVUzmcTmVm7KDIIY/8a3zhFQ/e+3gX0TIVo342kPz9ZJ8rEfAEB 5XkPp6Gd9zRoff8xQN1+kBsK8gc+8iFhmhHHhxTg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390631AbgFYI1N (ORCPT ); Thu, 25 Jun 2020 04:27:13 -0400 Received: from mail.kernel.org ([198.145.29.99]:41500 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389747AbgFYI1M (ORCPT ); Thu, 25 Jun 2020 04:27:12 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (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 AC6FB207E8; Thu, 25 Jun 2020 08:27:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593073632; bh=GncOVRnsRbmrObVuGed/d33M2KDkzxTcEILATAJbLBA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KLWf/lD9VcylMACtq8p1wJiRL0bWr2kYSku0VKCkfSWkCAqHKhXHxHOSwvWTS7j3l w9u9NiMdpF5uccefpWlPwAM4Q9i0V+Qe7aZAsJdNvHebMPPRWYp9leOEenbVEgwE27 4Y8WoUS9Iu/d8VHbgPuJp11WLopn88ZGoDVDvOts= Date: Thu, 25 Jun 2020 09:27:06 +0100 From: Will Deacon To: Sami Tolvanen Cc: Peter Zijlstra , Masahiro Yamada , Greg Kroah-Hartman , "Paul E. McKenney" , Kees Cook , Nick Desaulniers , clang-built-linux@googlegroups.com, kernel-hardening@lists.openwall.com, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH 00/22] add support for Clang LTO Message-ID: <20200625082706.GA7584@willie-the-truck> References: <20200624203200.78870-1-samitolvanen@google.com> <20200624211540.GS4817@hirez.programming.kicks-ass.net> <20200624213014.GB26253@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200624213014.GB26253@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Wed, Jun 24, 2020 at 02:30:14PM -0700, Sami Tolvanen wrote: > On Wed, Jun 24, 2020 at 11:15:40PM +0200, Peter Zijlstra wrote: > > On Wed, Jun 24, 2020 at 01:31:38PM -0700, Sami Tolvanen wrote: > > > This patch series adds support for building x86_64 and arm64 kernels > > > with Clang's Link Time Optimization (LTO). > > > > > > In addition to performance, the primary motivation for LTO is to allow > > > Clang's Control-Flow Integrity (CFI) to be used in the kernel. Google's > > > Pixel devices have shipped with LTO+CFI kernels since 2018. > > > > > > Most of the patches are build system changes for handling LLVM bitcode, > > > which Clang produces with LTO instead of ELF object files, postponing > > > ELF processing until a later stage, and ensuring initcall ordering. > > > > > > Note that first objtool patch in the series is already in linux-next, > > > but as it's needed with LTO, I'm including it also here to make testing > > > easier. > > > > I'm very sad that yet again, memory ordering isn't addressed. LTO vastly > > increases the range of the optimizer to wreck things. > > I believe Will has some thoughts about this, and patches, but I'll let > him talk about it. Thanks for reminding me! I will get patches out ASAP (I've been avoiding the rebase from hell, but this is the motivation I need). Will