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From: Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm
Date: Thu, 01 Dec 2016 14:58:17 +0100
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Adam Borowski <kilobyte@angband.pl>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>, Michal Marek <mmarek@suse.com>, Ben Hutchings <ben@decadent.org.uk>, Debian kernel maintainers <debian-kernel@lists.debian.org>, "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>, Ingo Molnar <mingo@kernel.org>, Nicholas Piggin <npiggin@gmail.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>

On Tuesday, November 29, 2016 9:14:46 AM CET Linus Torvalds wrote:
> On Tue, Nov 29, 2016 at 9:10 AM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > So quite frankly, I don't want to make our kernel sources worse due to
> > broken shit tools getting something wrong that we shouldn't even care
> > about.
> 
> And yes, I'm on binutils 2.26 (with no issues), so it could be that
> it's 2.27 that triggers this.
> 
> We could make the pr_warn_once() mention "broken binutils?" so that
> people know why the warning happens.

I've tried to get to the bottom of this, but couldn't find anything
related to the toolchain version. I've tried binutils 2.23, 2.24, 2.26
and 2.27, and also gcc-7.0, gcc-5.4.1 and gcc-4.9.3, but with today's
linux-next, I always get

WARNING: EXPORT symbol "mcount" [arch/x86/entry/built-in.ko] version generation failed, symbol will not be versioned.
WARNING: EXPORT symbol "mcount" [arch/x86/built-in.ko] version generation failed, symbol will not be versioned.
WARNING: EXPORT symbol "cmpxchg8b_emu" [vmlinux] version generation failed, symbol will not be versioned.
WARNING: EXPORT symbol "empty_zero_page" [vmlinux] version generation failed, symbol will not be versioned.
WARNING: EXPORT symbol "mcount" [vmlinux] version generation failed, symbol will not be versioned.
WARNING: EXPORT symbol "cmpxchg8b_emu" [vmlinux] version generation failed, symbol will not be versioned.
WARNING: EXPORT symbol "empty_zero_page" [vmlinux] version generation failed, symbol will not be versioned.
WARNING: EXPORT symbol "mcount" [vmlinux] version generation failed, symbol will not be versioned.

Out of 12 randconfig builds that had CONFIG_MODVERSIONS enabled, all 12
had this problem, though not always with all the symbols.

	Arnd