On Thu, 1 Dec 2016 12:33:02 +0100
Stanislav Kozina [off-list ref] wrote:

On 12/01/2016 12:09 PM, Nicholas Piggin wrote:

quoted

On Thu, 1 Dec 2016 11:48:09 +0100
Stanislav Kozina [off-list ref] wrote:
 

quoted

On 12/01/2016 05:13 AM, Don Zickus wrote:

...
 

quoted

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.

Sure. This is something an automated checker can't solve completely.
Any changes would have to be considered in terms of their impact to
the ABI. It's not just data but also instruction changes involved.

This is policy that should not be mandated by the kernel. Which is
why I'm in favor of using tools like this and just providing mechanism
so distros can implement their own polices.

And 
the problem with modversions is that it pulls in just everything which 
gets (accidentally?) #included in the source file.

I think that's SRCVERSION which is something else. But modversions
has problems too.

The actual ABI maintenance is a different problem, but there are many 
possible approaches, the _v2 suffix being one of them.

Would be good to get a consensus on that too.

Thanks,
Nick