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

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Date:   Thu, 1 Dec 2016 12:33:02 +0100
From:   Stanislav Kozina <skozina@...hat.com>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     Don Zickus <dzickus@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ben Hutchings <ben@...adent.org.uk>,
        Michal Marek <mmarek@...e.com>,
        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>
Subject: Re: [PATCH] x86/kbuild: enable modversions for symbols exported from
 asm



On 12/01/2016 12:09 PM, Nicholas Piggin wrote:
> On Thu, 1 Dec 2016 11:48:09 +0100
> Stanislav Kozina <skozina@...hat.com> wrote:
>
>> On 12/01/2016 05:13 AM, Don Zickus wrote:
>>
>> ...
>>
>>> I think GregKH pointed to one such tool, libabigail?  We are working on
>>> others too.
>> I should mention one of the others here:
>> https://github.com/skozina/kabi-dw
>>
>> It's quite comparable to libabigail in the way it works, the main
>> differences are:
>>    - written in pure C
>>    - depends only on elf-utils and flex/yacc
>>    - it's much simpler (4k LOC)
>>    - stores the type information in the text files and compares those
>> instead of directly comparing two sets of DWARF data
> Now this seems much better for distro ABI checking.
>
> The next question is, do they need any kernel support for rare cases
> where they do have to break the ABI of an export? Simple rename of the
> function with a _v2 postfix might be enough. We could retain some per
> symbol versioning in the kernel if needed, but how much would it
> actually help?

The biggest pain point AFAICT is to identify what types (functions, 
structs, enums, ...) should be considered a part of the stable ABI. And 
the problem with modversions is that it pulls in just everything which 
gets (accidentally?) #included in the source file.
The actual ABI maintenance is a different problem, but there are many 
possible approaches, the _v2 suffix being one of them.

Regards,
-Stanislav