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Date: Tue, 1 Dec 2020 13:38:17 -0800
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Kees Cook <keescook@...omium.org>, Will Deacon <will@...nel.org>,
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>,
clang-built-linux <clang-built-linux@...glegroups.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
linux-arch <linux-arch@...r.kernel.org>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>,
Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
PCI <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v7 00/17] Add support for Clang LTO
On Tue, Dec 1, 2020 at 11:51 AM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@...glegroups.com> wrote:
>
> On Tue, Dec 1, 2020 at 9:31 AM Kees Cook <keescook@...omium.org> wrote:
> >
> > 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.
>
> I had some minor stylistic feedback on the Kconfig changes; I'm happy
> for you to land the bulk of the changes and then I follow up with
> patches to the Kconfig after.
These are included in v8, which I just sent out.
Sami
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