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Date:   Tue, 1 Dec 2020 09:31:00 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Will Deacon <will@kernel.org>
Cc:     Sami Tolvanen <samitolvanen@google.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        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>
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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