linux-kernel - Re: [PATCH v3 00/30] Add support for Clang LTO

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Message-ID: <CAKwvOd=N5XS+c7X+fM+0aHWoo8j-xZ96Qk1a4n6gvYJZAq1mCQ@mail.gmail.com>
Date:   Fri, 18 Sep 2020 13:53:17 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Sedat Dilek <sedat.dilek@...il.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-pci@...r.kernel.org,
        X86 ML <x86@...nel.org>
Subject: Re: [PATCH v3 00/30] Add support for Clang LTO

On Fri, Sep 18, 2020 at 1:50 PM Sami Tolvanen <samitolvanen@...gle.com> wrote:
>
> On Fri, Sep 18, 2020 at 1:22 PM Sedat Dilek <sedat.dilek@...il.com> wrote:
> >
> > On Fri, Sep 18, 2020 at 10:14 PM 'Sami Tolvanen' via Clang Built Linux
> > <clang-built-linux@...glegroups.com> wrote:
> > >
> > > This patch series adds support for building x86_64 and arm64 kernels
> > > 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 patches 1-5 are not directly related to LTO, but are
> > > needed to compile LTO kernels with ToT Clang, so I'm including them
> > > in the series for your convenience:
> > >
> > >  - Patches 1-3 fix build issues with LLVM and they are already in
> > >    linux-next.
> > >
> > >  - Patch 4 fixes x86 builds with LLVM IAS, but it hasn't yet been
> > >    picked up by maintainers.
> > >
> > >  - Patch 5 is from Masahiro's kbuild tree and makes the LTO linker
> > >    script changes much cleaner.
> > >
> >
> > Hi Sami,
> >
> > might be good to point to your GitHub tree and corresponding
> > release-tag for easy fetching.
>
> Ah, true. You can also pull this series from
>
>   https://github.com/samitolvanen/linux.git lto-v3

Also, I've been using b4 happily for a short while now.
https://people.kernel.org/monsieuricon/introducing-b4-and-patch-attestation

My workflow would be: check lore.kernel.org/lkml/
for the series in question. In this case:
https://lore.kernel.org/lkml/CABCJKueyWvNB2MQw_PCLtZb8F1+sA1QOLJi_5qMKwdFCcwSMGg@mail.gmail.com/T/#t
is the cover letter.  Then in my tree:
$ b4 am https://lore.kernel.org/lkml/CABCJKueyWvNB2MQw_PCLtZb8F1+sA1QOLJi_5qMKwdFCcwSMGg@mail.gmail.com/T/#t
-o - | git am
-- 
Thanks,
~Nick Desaulniers