linux-kernel - Re: [PATCH v2 00/28] Add support for Clang LTO

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Message-ID: <CAK7LNARfoNg1wFi8oGar3bhzUXtNRMyuz0ksSh2hhzG_PdAMVg@mail.gmail.com>
Date:   Fri, 11 Sep 2020 03:07:49 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     ian.bearman@...rosoft.com,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: Re: [PATCH v2 00/28] Add support for Clang LTO

On Fri, Sep 11, 2020 at 2:46 AM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@...glegroups.com> wrote:
>
> Hey Ian,
> It was nice to meet you at Linux plumbers.  You might want to take a
> look at this series.  It implements builds of the Linux kernel with
> LTO.  It would be good to get eyes on it and help review it from folks
> working on this from the GCC angle.  The series has some configs that
> split where Clang specific changes need to be made; it might be of
> interest to think about what would the similar changes be needed for
> GCC.  Also, congrats on your LWN article!
> https://lwn.net/Articles/830300/


FYI.

Some people may remember GCC LTO was posted in 2014
(and rejected by Linus).

https://lore.kernel.org/linux-kbuild/20140407201919.GA15838@sepie.suse.cz/


In my understanding, GCC LTO does not work for relocatable objects
because GNU linker is agnostic about LTO.

GCC LTO was implemented in the final link stage (i.e. vmlinux)
by using $(CC) as a linker driver.


On the other hand, Clang LTO, in this series implementation,
works in the pre-mospost stage (i.e. vmlinux.o).




--
Best Regards
Masahiro Yamada