linux-kernel - Re: [PATCH 00/22] add support for Clang LTO

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Message-ID: <20200712184041.GA1838@Ryzen-9-3900X.localdomain>
Date:   Sun, 12 Jul 2020 11:40:41 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Sedat Dilek <sedat.dilek@...il.com>
Cc:     Paul Menzel <pmenzel@...gen.mpg.de>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Will Deacon <will@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        kernel-hardening@...ts.openwall.com, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH 00/22] add support for Clang LTO

On Sun, Jul 12, 2020 at 10:59:17AM +0200, Sedat Dilek wrote:
> On Sat, Jul 11, 2020 at 6:32 PM Paul Menzel <pmenzel@...gen.mpg.de> wrote:
> >
> > Dear Sami,
> >
> >
> > Am 24.06.20 um 22:31 schrieb Sami Tolvanen:
> > > 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's
> > > Pixel devices have shipped with LTO+CFI kernels 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 first objtool patch in the series is already in linux-next,
> > > but as it's needed with LTO, I'm including it also here to make testing
> > > easier.
> >
> > […]
> >
> > Thank you very much for sending these changes.
> >
> > Do you have a branch, where your current work can be pulled from? Your
> > branch on GitHub [1] seems 15 months old.
> >
> 
> Agreed it's easier to git-pull.
> I have seen [1] - not sure if this is the latest version.
> Alternatively, you can check patchwork LKML by searching for $submitter.
> ( You can open patch 01/22 and download the whole patch-series by
> following the link "series", see [3]. )
> 
> - Sedat -
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git/log/?h=lto
> [2] https://lore.kernel.org/patchwork/project/lkml/list/?series=&submitter=19676
> [3] https://lore.kernel.org/patchwork/series/450026/mbox/
> 

Sami tagged this series on his GitHub:

https://github.com/samitolvanen/linux/releases/tag/lto-v1

git pull https://github.com/samitolvanen/linux lto-v1

Otherwise, he is updating the clang-cfi branch that includes both the
LTO and CFI patchsets. You can pull that and just turn on
CONFIG_LTO_CLANG.

Lastly, for the future, I would recommend grabbing b4 to easily apply
patches (specifically full series) from lore.kernel.org.

https://git.kernel.org/pub/scm/utils/b4/b4.git/
https://git.kernel.org/pub/scm/utils/b4/b4.git/tree/README.rst

You could grab this series and apply it easily by either downloading the
mbox file and following the instructions it gives for applying the mbox
file:

$ b4 am 20200624203200.78870-1-samitolvanen@...gle.com

or I prefer piping so that I don't have to clean up later:

$ b4 am -o - 20200624203200.78870-1-samitolvanen@...gle.com | git am

Cheers,
Nathan