linux-kernel - Re: [RFC PATCH] x86: enable dead code and data elimination (LTO)

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Message-ID: <20170709090551.bm2c55ctt3togim7@gmail.com>
Date:   Sun, 9 Jul 2017 11:05:51 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     linux-arch@...r.kernel.org, linux-kbuild@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Paul Burton <paul.burton@...tec.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH] x86: enable dead code and data elimination (LTO)


* Nicholas Piggin <npiggin@...il.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