Re: Stable library ABI compatibility checking

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

Jan