Date: Tue, 1 Dec 2020 09:31:00 -0800 From: Kees Cook <keescook@...omium.org> To: Will Deacon <will@...nel.org> Cc: Sami Tolvanen <samitolvanen@...gle.com>, Masahiro Yamada <masahiroy@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, Josh Poimboeuf <jpoimboe@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Paul E. McKenney" <paulmck@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, clang-built-linux@...glegroups.com, kernel-hardening@...ts.openwall.com, linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org Subject: Re: [PATCH v7 00/17] Add support for Clang LTO 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 , and drops x86_64 while we work > > on fixing the remaining objtool warnings . > > 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
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