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

[Stanislav Kozina]

On 12/01/2016 12:09 PM, Nicholas Piggin wrote:
> On Thu, 1 Dec 2016 11:48:09 +0100
> Stanislav Kozina <skozina@xxxxxxxxxx> 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