linux-kernel - Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

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Date:   Tue, 29 Nov 2016 18:05:22 +0100
From:   Adam Borowski <kilobyte@...band.pl>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Michal Marek <mmarek@...e.com>,
        Ben Hutchings <ben@...adent.org.uk>,
        Debian kernel maintainers <debian-kernel@...ts.debian.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>, Ingo Molnar <mingo@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/kbuild: enable modversions for symbols exported from
 asm

On Tue, Nov 29, 2016 at 07:27:12AM -0800, Linus Torvalds wrote:
> On Nov 29, 2016 5:51 AM, "Adam Borowski" <kilobyte@...band.pl> wrote:
> > >
> > >  (a) tested
> >
> > By many people.
> 
> No.
> 
> I've tested the build *without* this, and it works fine.

Michal mentioned "why", let's try "where".

I have no idea what setup is required to trigger the problem, but here's a
simple sufficient one:

Current Debian unstable, amd64.
git reset --hard v4.9-rc7
git revert cd3caefb
make defconfig
CONFIG_MODVERSIONS=y
(in my case) CONFIG_BTRFS_FS=y (so I can boot)
enable a module for testing, I used CONFIG_EXT4_FS=m
make bindeb-pkg
dpkg -i linux-image_XXXXX.deb

modprobe ext4
[   63.779490] jbd2: no symbol version for memcpy
[   63.779492] jbd2: Unknown symbol memcpy (err -22)
[   63.779550] jbd2: no symbol version for phys_base
[   63.779551] jbd2: Unknown symbol phys_base (err -22)
[   63.779561] jbd2: no symbol version for memset
[   63.779562] jbd2: Unknown symbol memset (err -22)

Not sure which piece of toolchain matters here, someone said binutils.
In that case, Fedora ships 2.26.1-1.fc25, they were frozen so couldn't
update.  Debian is at 2.27.51.20161127-1, Gentoo at 2.27, same for Arch,
OpenSUSE; Ubuntu at 2.27.51.20161124-1.

Thus, if it's indeed binutils, you'll see the breakage as soon as Fedora
recovers from the freeze.

Meow!
-- 
The bill declaring Jesus as the King of Poland fails to specify whether
the addition is at the top or end of the list of kings.  What should the
historians do?