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

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Date:   Thu, 24 Nov 2016 05:40:28 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Adam Borowski <kilobyte@...band.pl>, Michal Marek <mmarek@...e.com>
Cc:     Philip Muller <philm@...jaro.org>, linux-kernel@...r.kernel.org,
        Nicholas Piggin <npiggin@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] x86/kbuild: enable modversions for symbols exported from
 asm


* Adam Borowski <kilobyte@...band.pl> wrote:

> Commit 4efca4ed ("kbuild: modversions for EXPORT_SYMBOL() for asm") adds
> modversion support for symbols exported from asm files. Architectures
> must include C-style declarations for those symbols in asm/asm-prototypes.h
> in order for them to be versioned.
> 
> Add these declarations for x86, and an architecture-independent file that
> can be used for common symbols.
> 
> User impact: kernels may fail to load modules at all when
> CONFIG_MODVERSIONS=y.
> 
> Signed-off-by: Adam Borowski <kilobyte@...band.pl>
> Tested-by: Kalle Valo <kvalo@...eaurora.org>
> Acked-by: Nicholas Piggin <npiggin@...il.com>
> Tested-by: Peter Wu <peter@...ensteyn.nl>
> Tested-by: Oliver Hartkopp <socketcan@...tkopp.net>
> ---
> Changes: corrected Peter Wu's address, added Tested-by: Oliver.
> This is an unsplit version (x86/include/ and include/ together).
> 
>  arch/x86/include/asm/asm-prototypes.h | 12 ++++++++++++
>  include/asm-generic/asm-prototypes.h  |  7 +++++++
>  2 files changed, 19 insertions(+)
>  create mode 100644 arch/x86/include/asm/asm-prototypes.h
>  create mode 100644 include/asm-generic/asm-prototypes.h

Michal, I'm quite unhappy about how the offending commit that broke modversions 
for essentially _everyone_ who does more complex modular builds on x86 ended up 
upstream:

  commit 4efca4ed05cbdfd13ec3e8cb623fb77d6e4ab187
  Author:     Nicholas Piggin <npiggin@...il.com>
  AuthorDate: Tue Nov 1 12:46:19 2016 +1100
  Commit:     Michal Marek <mmarek@...e.com>
  CommitDate: Tue Nov 1 16:20:17 2016 +0100

      kbuild: modversions for EXPORT_SYMBOL() for asm

      Allow architectures to create asm/asm-prototypes.h file that
      provides C prototypes for exported asm functions, which enables
      proper CRC versions to be generated for them.

 scripts/Makefile.build | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 72 insertions(+), 6 deletions(-)

It was applied 4 hours after it was sent in the -rc3 timeframe, and then it went 
upstream in -rc5:

     "Here are some regression fixes for kbuild:
    
       - modversion support for exported asm symbols (Nick Piggin). The
         affected architectures need separate patches adding
         asm-prototypes.h.

... the fine merge log even says that the commit 'needs separate patches'!

It's still totally broken upstream and it didn't fix any regressions AFAICS (or if 
it did then its changelog was very silent on that fact).

Why was such a complex patch applied and why isn't it reverted or fixed upstream?

Thanks,

	Ingo