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From: Masahiro Yamada <yamada.masahiro@socionext.com>
Date: Sun, 9 Jul 2017 22:29:37 +0900
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Subject: Re: [RFC PATCH] x86: enable dead code and data elimination (LTO)
To: Ingo Molnar <mingo@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        X86 ML <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Nicolas Pitre <nicolas.pitre@linaro.org>,
        Arnd Bergmann <arnd@arndb.de>, Paul Burton <paul.burton@imgtec.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Andrew Morton <akpm@linux-foundation.org>
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Hi.

2017-07-09 18:05 GMT+09:00 Ingo Molnar <mingo@kernel.org>:
>
> * Nicholas Piggin <npiggin@gmail.com> wrote:
>
>> FYI, easiest way to check if you forgot to KEEP a linker table is
>> to look at `readelf -S vmlinux` differences, and to see what is
>> being trimmed, look at nm differences or use --print-gc-sections
>> LD option to see what symbols you're trimming. Linker tables,
>> boot entry, and exception entry tends to require anchoring.
>
> Could you please add a debug build target to display all discarded
> symbols/sections? Something like:
>
>         make lto-check
>
> ... or so?
>
> Thanks,
>
>         Ingo


Actually, LTO activity existed some years ago
(but not pulled in).

http://www.spinics.net/lists/linux-kbuild/msg09242.html


IIUC, this patch enables "dead code elimination",
(or "garbage collection"?),
but I think it is different from what is called LTO.


-- 
Best Regards
Masahiro Yamada