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

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Message-ID: <CA+icZUWyqb8jdzTAophvBKuX3e2NvG7vQPnMW+SRW5v0PmU7TA@mail.gmail.com>
Date: Tue, 14 Jul 2020 11:44:10 +0200
From: Sedat Dilek <sedat.dilek@...il.com>
To: Nathan Chancellor <natechancellor@...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 8:40 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> 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
>

It is always a pleasure to read your replies and enrich my know-how
beyond Linux-kernel hacking :-).

Thanks for the tip with "b4" tool.
Might add this to our ClangBuiltLinux wiki "Command line tips and tricks"?

- Sedat -

[1] https://github.com/ClangBuiltLinux/linux/wiki/Command-line-tips-and-tricks
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