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[23.128.96.18]) by mx.google.com with ESMTP id d19si3727926edv.53.2020.06.24.15.05.06; Wed, 24 Jun 2020 15:05:29 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=fail header.i=@infradead.org header.s=casper.20170209 header.b=lvI0AvNC; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390351AbgFXVQF (ORCPT + 99 others); Wed, 24 Jun 2020 17:16:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57274 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390317AbgFXVQF (ORCPT ); Wed, 24 Jun 2020 17:16:05 -0400 Received: from casper.infradead.org (unknown [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EEDC1C061573; Wed, 24 Jun 2020 14:16:04 -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=CYAOBdXXwk5atGG1OkexemEOJEg2uOXvmf8MxtMHkzA=; b=lvI0AvNCOyQRFPEBPSO732MCmS priyMdaeyT9DlHRLc/z9qWhkeCY/G37ozS6HciR55B+xdk3sRO+bn4RdzWVJS4FDFf++roys12UFi 2Xn0aJcu82shXhcuPUJaxr0NiofjiM9cS72P+0UyExr/CWjZItZDE4OZMDMLf4RBiQ+3eGs0RrR20 QerCqnR4yK+D/eqXSR/BaYzSzLfSMZBayOvuxe0uMIgumCmxbS4aKn+HlmJxHDAjxC7KlQlu9/mMK D//TxmU24AKwnTz6mvW3vYpxg3iJ7ar26Kv6tNzbCv4aRAJOYWk+gjYHLWLDLC4v2if3/bM+oS2fR WOLeUYeg==; 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 1joCkB-0004Ne-TF; Wed, 24 Jun 2020 21:15:44 +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 1283B304B6D; Wed, 24 Jun 2020 23:15:41 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 05648203CDC3F; Wed, 24 Jun 2020 23:15:41 +0200 (CEST) Date: Wed, 24 Jun 2020 23:15:40 +0200 From: Peter Zijlstra To: Sami Tolvanen Cc: Masahiro Yamada , Will Deacon , 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: <20200624211540.GS4817@hirez.programming.kicks-ass.net> References: <20200624203200.78870-1-samitolvanen@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200624203200.78870-1-samitolvanen@google.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.