Re: Stable library ABI compatibility checking

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 11/02/2021 11:53, Jan Beulich wrote:
> On 11.02.2021 12:30, Andrew Cooper wrote:
>> On 11/02/2021 11:05, Jan Beulich wrote:
>>> On 11.02.2021 02:08, Andrew Cooper wrote:
>>>> Hello,
>>>>
>>>> Last things first, some examples:
>>>>
>>>> http://xenbits.xen.org/people/andrewcoop/abi/libxenevtchn-1.1_to_1.2.html
>>>> http://xenbits.xen.org/people/andrewcoop/abi/libxenforeignmemory-1.3_to_1.4.html
>>>>
>>>> These are an ABI compatibility report between RELEASE-4.14.0 and staging.
>>>>
>>>> They're performed with abi-dumper (takes a shared object and header
>>>> file(s) and write out a text "dump" file which happens to be a perl
>>>> hash) and abi-compliance-checker checker, which takes two dumps and
>>>> produces the HTML reports linked above.  They're both debian tools
>>>> originally, but have found their way across the ecosystem.  They have no
>>>> impact on build time (when invoked correctly).
>>>>
>>>> I'm encouraged to see that the foreignmem analysis has even spotted that
>>>> we deliberately renamed one parameter to clarify its purpose.
>>>>
>>>>
>>>> For the stable libraries, the RELEASE-$X.$Y.0 tag is the formal point
>>>> when accumulated changes in staging become fixed.  What we ought to be
>>>> doing is taking a "dump" of libraries at this point, and publishing
>>>> them, probably on xenbits.
>>>>
>>>> Subsequent builds on all the staging branches should be performing an
>>>> ABI check against the appropriate lib version.  This will let us catch
>>>> breakages in staging (c/s e8af54084586f4) as well as breakages if we
>>>> ever need to backport changes to the libs.
>>>>
>>>> For libraries wrapped by Juergen's tools/libs/ common-makefile changes,
>>>> adding ABI dumping is easy.  The only complicating is needing to build
>>>> everything with "-Og -g", but this is easy to arrange, and frankly ought
>>>> to be the default for debug builds anyway (the current use of -O0 is
>>>> silly and interferes with common distro hardening settings).
>>>>
>>>> What I propose is tweaking the library build to write out
>>>> lib$FOO.so.$X.$Y-$(ARCH).abi.dump files.  A pristine set of these should
>>>> be put somewhere on xenbits, and a task put on the release technicians
>>>> checklist for future releases.
>>>>
>>>> That way, subsequent builds which have these tools available can include
>>>> a call to abi-compliance-checker between the authoritative copy and the
>>>> one from the local build, which will make the report available, and exit
>>>> nonzero on breaking problems.
>>>>
>>>>
>>>> To make the pristine set, I need to retrofit the tooling to 4.14 and
>>>> ideally 4.13.  This is in contravention to our normal policy of not
>>>> backporting features, but I think, being optional build-time-only
>>>> tooling, it is worthy of an exception considering the gains we get
>>>> (specifically - to be able to check for ABI breakages on these branches
>>>> in OSSTest).  Backporting to 4.12 and older is far more invasive, due to
>>>> it being before the library build systems were common'd.
>>>>
>>>>
>>>> Anyway, thoughts?
>>> +1
>>>
>>> Not sure about the backporting effects - tools/libs/ had quite a bit
>>> less content in 4.14 and older, so the coverage would be smaller.
>> tools/libs/ has been the stable libraries, since IanC split them years
>> ago.  The only odd-one-out is libxenstored IIRC, which moved during the
>> 4.15 window.
> As well as ctrl/, guest/, light/, stat/, util/, and vchan/.

Right, but 5 of those don't have stable ABIs.

~Andrew