From: Sedat Dilek <sedat.dilek@gmail.com>
To: Nicolas Pitre <nico@fluxnic.net>
Cc: Arnd Bergmann <arnd@kernel.org>,
Masahiro Yamada <masahiroy@kernel.org>,
Nicholas Piggin <npiggin@gmail.com>,
Fangrui Song <maskray@google.com>,
Ard Biesheuvel <ardb@kernel.org>,
Andrew Scull <ascull@google.com>,
Mark Brown <broonie@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
clang-built-linux <clang-built-linux@googlegroups.com>,
David Brazdil <dbrazdil@google.com>,
Geert Uytterhoeven <geert+renesas@glider.be>,
Ionela Voinescu <ionela.voinescu@arm.com>,
Kees Cook <keescook@chromium.org>,
Kristina Martsenko <kristina.martsenko@arm.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Marc Zyngier <maz@kernel.org>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Will Deacon <will@kernel.org>
Subject: Re: [PATCH] [RFC] arm64: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION
Date: Wed, 10 Mar 2021 22:57:23 +0100 [thread overview]
Message-ID: <CA+icZUW8SqpTuANz7brtR+QSxKn+UnYOVve-C+TOMh9RqdQh+w@mail.gmail.com> (raw)
In-Reply-To: <ros2o1p7-r65q-n4p-3o38-oo36rr58q041@syhkavp.arg>
On Wed, Mar 10, 2021 at 10:47 PM Nicolas Pitre <nico@fluxnic.net> wrote:
...
> > With CONFIG_TRIM_UNUSED_KSYMS=y I see a 3x-loops of building .version
> > and folowing steps - got no answer if this is intended.
>
> Yes it is intended. I explained it here:
>
> https://lkml.org/lkml/2021/3/9/1099
>
Ah, cool.
Thanks for that link.
> With CONFIG_TRIM_UNUSED_KSYMS some EXPORT_SYMBOL() are removed, which
> allows for optimizing away the corresponding code, which in turn opens
> the possibility for more EXPORT_SYMBOL() to be removed, etc. The process
> eventually converge to a stable build. Normally only 2 passes are needed
> to converge, but LTO opens the possibilities for extra passes.
>
> > Means longer build-time.
>
> Oh, absolutely. LTO (at least when I played with it) is slow. Add the
> multi-pass from CONFIG_TRIM_UNUSED_KSYMS on top of that and your kernel
> build becomes agonizingly slow. This is not something you want when
> doing kernel development.
>
Thanks for the feedback.
> > I did not follow this anymore as both Kconfigs with Clang-LTO consume
> > more build-time and the resulting vmlinux is some MiB bigger than with
> > Clang-CFI.
>
> That's rather strange. At least with gcc LTO I always obtained smaller
> kernels.
>
I cannot say much to GCC-LTO - I never used it.
If you are interested in Clang-CFI (see [1]) - which requires
Clang-LTO enabled and LLVM/Clang >= 12.
Some hours ago version 12.0.0-rc3 was released, see [2].
- Sedat -
[1] https://github.com/samitolvanen/linux/commits/clang-cfi
[2] https://github.com/ClangBuiltLinux/linux/issues/1259
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next prev parent reply other threads:[~2021-03-10 22:00 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-25 11:20 [PATCH] [RFC] arm64: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION Arnd Bergmann
2021-02-25 20:16 ` Kees Cook
2021-02-26 0:36 ` Sedat Dilek
2021-02-26 8:14 ` Arnd Bergmann
2021-02-26 9:05 ` Sedat Dilek
2021-02-26 9:51 ` Arnd Bergmann
2021-02-26 10:02 ` Sedat Dilek
2021-02-26 21:13 ` Fangrui Song
2021-02-27 9:49 ` Arnd Bergmann
2021-03-01 1:11 ` Nicholas Piggin
2021-03-10 20:49 ` Masahiro Yamada
2021-03-10 21:08 ` Arnd Bergmann
2021-03-10 21:24 ` Sedat Dilek
2021-03-10 21:47 ` Nicolas Pitre
2021-03-10 21:57 ` Sedat Dilek [this message]
2021-03-10 22:02 ` Nick Desaulniers
2021-03-10 22:08 ` Nicolas Pitre
2021-03-10 22:29 ` Fangrui Song
2021-03-10 21:45 ` Rasmus Villemoes
2021-03-10 21:19 ` Nicolas Pitre
2021-03-10 22:42 ` Fangrui Song
2021-03-17 14:37 ` Catalin Marinas
2021-03-17 16:18 ` Catalin Marinas
2021-03-18 8:41 ` Arnd Bergmann
2021-03-19 12:25 ` Catalin Marinas
2021-03-19 14:01 ` Arnd Bergmann
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