On Tue, Dec 1, 2020 at 1:37 PM Sami Tolvanen [off-list ref] 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/ (local)
[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 <redacted>

(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

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