Re: [PATCH v8 00/16] Add support for Clang LTO

Nick Desaulniers
2020-12-03T00:02:15Z

On Tue, Dec 1, 2020 at 1:37 PM Sami Tolvanen <samitolvanen@google.com> 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 arm64 support depends on Will's memory ordering patches
> [1]. I will post x86_64 patches separately after we have fixed the
> remaining objtool warnings [2][3].
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=for-next/lto
> [2] https://lore.kernel.org/lkml/20201120040424.a3wctajzft4ufoiw@treble/
> [3] https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git/log/?h=objtool-vmlinux
>
> You can also pull this series from
>
> https://github.com/samitolvanen/linux.git lto-v8
>
> ---
> Changes in v8:
>
> - Cleaned up the LTO Kconfig options based on suggestions from
> Nick and Kees.

Thanks Sami, for the series:

Tested-by: Nick Desaulniers <ndesaulniers@google.com>

(build and boot tested under emulation with
https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=for-next/lto
additionally rebased on top).

As with v7, if the series changes drastically for v9, please consider
dropping my tested by tag for the individual patches that change and I
will help re-test them.
--
Thanks,
~Nick Desaulniers