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

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Message-ID: <b1cfc44e-e1ee-0fdd-59a3-2b5e96933d20@stressinduktion.org>
Date:   Fri, 2 Dec 2016 15:36:42 +0100
From:   Hannes Frederic Sowa <hannes@...essinduktion.org>
To:     Michal Marek <mmarek@...e.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Ben Hutchings <ben@...adent.org.uk>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Adam Borowski <kilobyte@...band.pl>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        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>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dodji Seketeli <dodji@...eteli.org>
Subject: Re: [PATCH] x86/kbuild: enable modversions for symbols exported from
 asm

On 01.12.2016 17:12, Michal Marek wrote:
> On 2016-12-01 04:39, Nicholas Piggin wrote:
>> On Thu, 01 Dec 2016 02:35:54 +0000
>> Ben Hutchings <ben@...adent.org.uk> wrote:
>>> As I understand it, genksyms incorporates the definitions of a
>>> function's parameter and return types - not just their names - and all
>>> the types they refer to, recursively.  So a structure size change
>>> should change the version of all functions where the function and its
>>> caller pass that structure between them, however indirectly.  It finds
>>> such indirect ABI breakage for me fairly regularly, though of course I
>>> don't know that it finds everything.
>>
>> It is only the type name.
>>
>> Not only that but even if you did extend it further to structure type
>> arrangement then you still have to deal with other structures followed
>> via pointers. Or (rarer but not unheard of):
>>
>> - changes to structures without changes of the types of their members
>> - changes to arguments without changes of their type
> 
> This is already covered by genksyms. Try make V=1 with
> CONFIG_MODVERSIONS=y and add the -D option to one of the genksyms
> command. I wanted to paste the expanded signature for
> register_filesystem() as an example, but vger would probably drop the
> mail for being too big :).

It is easier to just use e.g. `make net/core/dev.symtypes` and look at
the generated file.

Bye,
Hannes