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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id j143sm400818pfd.20.2020.12.01.09.31.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Dec 2020 09:31:01 -0800 (PST) Date: Tue, 1 Dec 2020 09:31:00 -0800 From: Kees Cook To: Will Deacon Cc: Sami Tolvanen , Masahiro Yamada , Steven Rostedt , Josh Poimboeuf , Peter Zijlstra , Greg Kroah-Hartman , "Paul E. McKenney" , 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 Subject: Re: [PATCH v7 00/17] Add support for Clang LTO Message-ID: <202012010929.3788AF5@keescook> References: <20201118220731.925424-1-samitolvanen@google.com> <20201130120130.GF24563@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201130120130.GF24563@willie-the-truck> Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Mon, Nov 30, 2020 at 12:01:31PM +0000, Will Deacon wrote: > Hi Sami, > > On Wed, Nov 18, 2020 at 02:07:14PM -0800, Sami Tolvanen wrote: > > This patch series adds support for building the kernel 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 has shipped millions of Pixel devices > > running three major kernel versions with LTO+CFI 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 v7 brings back arm64 support as Will has now staged the > > prerequisite memory ordering patches [1], and drops x86_64 while we work > > on fixing the remaining objtool warnings [2]. > > Sounds like you're going to post a v8, but that's the plan for merging > that? The arm64 parts look pretty good to me now. I haven't seen Masahiro comment on this in a while, so given the review history and its use (for years now) in Android, I will carry v8 (assuming all is fine with it) it in -next unless there are objections. -- Kees Cook