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

From Michal Marek <mmarek@suse.com>
Newsgroups linux.kernel, linux.debian.kernel
Subject Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm
Date 2016-11-29 10:20 +0100
Message-ID <sIMJX-6yn-7@gated-at.bofh.it> (permalink)
References <sHt6F-3WZ-15@gated-at.bofh.it> <sIFfs-1lT-7@gated-at.bofh.it> <sIGuR-2c9-1@gated-at.bofh.it>
Organization linux.* mail to news gateway

Cross-posted to 2 groups.

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Dne 29.11.2016 v 03:31 Nicholas Piggin napsal(a):
> On Tue, 29 Nov 2016 01:15:48 +0000
> Ben Hutchings <ben@decadent.org.uk> wrote:
> 
>> [I've had to guess at the cc list for this, because we no longer have
>> mail archives that preserve them.]
> 
> You got it about right.
> 
>> On Fri, 2016-11-25 at 10:01 -0800, Linus Torvalds wrote:
>>> On Thu, Nov 24, 2016 at 4:40 PM, Nicholas Piggin <npiggin@gmail.com> wrote:  
>>>>>
>>>>> Yes, manual "marking" is never going to be a viable solution.  
>>>>
>>>> I guess it really depends on how exactly you want to use it. For distros
>>>> that do stable ABI but rarely may have to break something for security
>>>> reasons, it should work and give exact control.  
>>
>> This is roughly how Debian handles the kernel module ABI during a
>> stable release.
>>
>>> No. Because nobody else will care, so unless it's like a single symbol
>>> or something, it will just be a maintenance nightmare.  
>>
>> I agree with this.  We can explicitly "version" individual symbols
>> anyway by doing something like:
>>
>> -int foo(void);
>> +#define foo foo_2
>> +int foo_2(int);
> 
> Yeah... Benefit being it's very simple and everybody can see exactly
> what it does and knows how it will work.
> 
>>
>>>> What else do people *actually* use it for? Preventing mismatched modules
>>>> when .git version is not attached and release version of the kernel has
>>>> not been bumped. Is that it?  
>>>
>>> It used to be very useful for avoiding loading stale modules and then
>>> wasting days on debugging something that wasn't the case when you had
>>> forgotten to do "make modules_install". Change some subtle internal
>>> ABI issue (add/remove a parameter, whatever) and it would really help.
>>>
>>> These days, for me, LOCALVERSION_AUTO and module signing are what I
>>> personally tend to use.
>>>
>>> The modversions stuff may just be too painful to bother with. Very few
>>> people probably use it, and the ones that do likely don't have any
>>> overriding reason why.  
>> [...]
>>
>> Debian has some strong reasons:

I guess many distros have similar reasons.


>> 1. Changing the release string requires any out-of-tree modules to be
>> upgraded (at least rebuilt) on end-user systems.  So we try to avoid
>> doing that during the lifetime of a stable release, i.e. we don't let
>> the release string change.  Also, the release string is reflected in
>> package names (e.g. linux-image-4.8.0-1-amd64), and introducing new
>> package names requires manual approval by the Debian archive team.
> 
> This is something I've noticed. Would it be better if the module loader
> ignores the kernel version and instead used some internal ABI version
> string to check against? Otherwise (AFAICT) you always have 4.8.0 versions
> despite being 4.8.7 kernel, and you can't upgrade a point release without
> overwriting your old kernel and modules.

The thing is - to maintain an ABI version string, you need some level of
certainty that two given ABIs are really interchangeable. Which means
you need to check whether the symbols _and_ types exposed are unchanged.
Which is a thing that genksyms, the tool behind CONFIG_MODVERSIONS, does
quite well. So yes, you could do a testbuild with CONFIG_MODVERSIONS=y
and a production build with some global ABI string, but what's the point
then.


> It would be nice to get upstream to the point where 4.9 modversions
> works if you just patch out depends BROKEN. That would require reverting
> a few more of Al's arch patches.
> 
> Then in 4.10 we can re-add all those arch patches (which are less
> controversial without the asm-prototypes.h workaround), and implement a
> simple stable ABI version string check, and then in 4.11 we can remove
> modversions.

I'd rather change the kconfig to

depends on BROKEN || <archs that have asm/asm-prototypes.h>

and eventuallly remove the dependency again. PPC has the header already,
so it can be added right away. I do not know why the x86 patch has not
been merged yet.

Michal

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Thread

Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Ben Hutchings <ben@decadent.org.uk> - 2016-11-29 02:20 +0100
  Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-11-29 03:40 +0100
    Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-11-29 10:20 +0100
  Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-29 05:10 +0100
    Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Adam Borowski <kilobyte@angband.pl> - 2016-11-29 14:20 +0100
      Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Ingo Molnar <mingo@kernel.org> - 2016-11-29 14:40 +0100
        Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Adam Borowski <kilobyte@angband.pl> - 2016-11-29 15:30 +0100
      [PATCH] x86/kbuild: enable modversions for symbols exported from asm Adam Borowski <kilobyte@angband.pl> - 2016-11-29 15:00 +0100
        Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-29 16:50 +0100
          Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-11-29 17:20 +0100
            Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-29 17:40 +0100
              Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Ben Hutchings <ben@decadent.org.uk> - 2016-11-29 21:00 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-29 22:00 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-30 20:00 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Ben Hutchings <ben@decadent.org.uk> - 2016-11-30 22:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-01 03:20 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Ben Hutchings <ben@decadent.org.uk> - 2016-12-01 03:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-01 05:00 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-12-01 17:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-12-02 16:00 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-09 05:00 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Ian Campbell <ijc@hellion.org.uk> - 2016-12-09 16:30 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-09 17:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-10 14:00 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-12 05:10 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Ian Campbell <ijc@hellion.org.uk> - 2016-12-12 10:10 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Don Zickus <dzickus@redhat.com> - 2016-12-14 19:20 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Stanislav Kozina <skozina@redhat.com> - 2016-12-13 02:30 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-12-14 00:10 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Dodji Seketeli <dodji@seketeli.org> - 2016-12-14 10:20 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-12-14 10:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-12-14 11:00 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Dodji Seketeli <dodji@seketeli.org> - 2016-12-14 11:00 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-12-14 11:10 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Dodji Seketeli <dodji@seketeli.org> - 2016-12-14 11:20 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-12-14 11:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Dodji Seketeli <dodji@seketeli.org> - 2016-12-14 11:20 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Don Zickus <dzickus@redhat.com> - 2016-12-01 05:50 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-01 05:50 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Don Zickus <dzickus@redhat.com> - 2016-12-01 16:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Don Zickus <dzickus@redhat.com> - 2016-12-01 17:00 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-01 17:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Don Zickus <dzickus@redhat.com> - 2016-12-01 20:10 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Christoph Hellwig <hch@infradead.org> - 2016-12-01 17:10 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-09 05:10 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Stanislav Kozina <skozina@redhat.com> - 2016-12-09 09:20 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-09 09:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Stanislav Kozina <skozina@redhat.com> - 2016-12-09 16:00 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-09 17:20 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-09 17:30 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Stanislav Kozina <skozina@redhat.com> - 2016-12-12 11:10 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-13 08:50 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Hannes Frederic Sowa <hannes@redhat.com> - 2016-12-14 15:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-15 03:30 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Hannes Frederic Sowa <hannes@redhat.com> - 2016-12-15 12:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-15 13:30 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Hannes Frederic Sowa <hannes@redhat.com> - 2016-12-15 14:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-15 15:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Hannes Frederic Sowa <hannes@redhat.com> - 2016-12-15 16:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Stanislav Kozina <skozina@redhat.com> - 2016-12-15 15:00 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Don Zickus <dzickus@redhat.com> - 2016-12-09 17:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Stanislav Kozina <skozina@redhat.com> - 2016-12-01 12:20 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-01 12:30 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Stanislav Kozina <skozina@redhat.com> - 2016-12-01 13:00 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-01 14:00 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Dodji Seketeli <dodji@seketeli.org> - 2016-12-01 16:50 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-12-01 17:40 +0100
          Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Adam Borowski <kilobyte@angband.pl> - 2016-11-29 18:10 +0100
            Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-29 18:30 +0100
              Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-29 18:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Arnd Bergmann <arnd@arndb.de> - 2016-12-01 15:20 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-12-01 17:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-12-01 19:50 +0100
                Re: [RFC, PATCH, v3.9] default exported asm symbols to zero Geert Uytterhoeven <geert@linux-m68k.org> - 2016-12-02 14:00 +0100
                Re: [RFC, PATCH, v3.9] default exported asm symbols to zero Arnd Bergmann <arnd@arndb.de> - 2016-12-02 16:10 +0100
                Re: [RFC, PATCH, v3.9] default exported asm symbols to zero Adam Borowski <kilobyte@angband.pl> - 2016-12-02 16:40 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-12-02 18:30 +0100
                Re: [RFC, PATCH, v3.9] default exported asm symbols to zero Ben Hutchings <ben@decadent.org.uk> - 2016-12-03 05:40 +0100
                Re: [RFC, PATCH, v3.9] default exported asm symbols to zero Arnd Bergmann <arnd@arndb.de> - 2016-12-03 12:10 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Alan Modra <amodra@gmail.com> - 2016-12-04 09:20 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-12-04 22:10 +0100
              Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-11-29 22:50 +0100
        Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Ben Hutchings <ben@decadent.org.uk> - 2016-12-02 03:10 +0100
          Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Adam Borowski <kilobyte@angband.pl> - 2016-12-02 12:30 +0100
            Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Ben Hutchings <ben@decadent.org.uk> - 2016-12-02 16:10 +0100

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