[Python-Dev] Stable ABI

[Brett Cannon]

I know Kushal set up ABI testing for Fedora and has brought up taking the
work he did for that and bringing it over to CPython, but I also know he is
offline for personal reasons ATM and won't be able to to reply for a little
while.

On Mon, 4 Jun 2018 at 08:06 Eric Snow <ericsnowcurrently at gmail.com> wrote:

> I've pointed out in bpo-21142 the similar script I added last year to
> track C globals:
>
>   https://github.com/python/cpython/tree/master/Tools/c-globals
>
> -eric
>
> On Mon, Jun 4, 2018 at 1:17 AM, Ronald Oussoren <ronaldoussoren at mac.com>
> wrote:
> >
> >
> > On 4 Jun 2018, at 08:35, Ronald Oussoren <ronaldoussoren at mac.com> wrote:
> >
> >
> >
> > On 3 Jun 2018, at 17:04, Eric V. Smith <eric at trueblade.com> wrote:
> >
> > On 6/3/2018 10:55 AM, Christian Tismer wrote:
> >
> > On 03.06.18 13:18, Ronald Oussoren wrote:
> >
> >
> >
> > On 3 Jun 2018, at 12:03, Christian Tismer <tismer at stackless.com> wrote:
> >
> > ...
> >
> >
> > I have written a script that scans all relevant header files
> > and analyses all sections which are reachable in the limited API
> > context.
> > All macros that don't begin with an underscore which contain
> > a "->tp_" string are the locations which will break.
> >
> > I found exactly 7 locations where this is the case.
> >
> > My PR will contain the 7 fixes plus the analysis script
> > to go into tools. Preparind that in the evening.
> >
> >
> > Having tests would still be nice to detect changes to the stable ABI when
> > they are made.
> >
> > Writing those tests is quite some work though, especially if those at
> least
> > smoke test the limited ABI by compiling snippets the use all symbols that
> > should be exposed by the limited ABI. Writing those tests should be
> fairly
> > simple for someone that knows how to write C extensions, but is some
> work.
> >
> > Writing a tests that complain when the headers expose symbols that
> shouldn’t
> > be exposed is harder, due to the need to parse headers (either by hacking
> > something together using regular expressions, or by using tools like
> gccxml
> > or clang’s C API).
> >
> > What do you mean?
> > My script does that with all "tp_*" type fields.
> > What else would you want to check?
> >
> >
> > I think Ronald is saying we're trying to answer a few questions:
> >
> > 1. Did we accidentally drop anything from the stable ABI?
> >
> > 2. Did we add anything to the stable ABI that we didn't mean to?
> >
> > 3. (and one of mine): Does the stable ABI already contain things that we
> > don't expect it to?
> >
> >
> > That’s correct.  There have been instances of the second item over the
> year,
> > and not all of them have been caught before releases.  What doesn’t help
> for
> > all of these is that the stable ABI documentation says that every
> documented
> > symbol is part of the stable ABI unless there’s explicit documentation to
> > the contrary. This makes researching if functions are intended to be
> part of
> > the stable ABI harder.
> >
> > And also:
> >
> > 4. Does the stable ABI actually work?
> >
> > Christian’s script finds cases where exposed names don’t actually work
> when
> > you try to use them.
> >
> >
> > To reply to myself, the gist below is a very crude version of what I was
> > trying to suggest:
> >
> >
> https://gist.github.com/ronaldoussoren/fe4f80351a7ee72c245025df7b2ef1ed#file-gistfile1-txt
> >
> > The gist is far from usable, but shows some tests that check that
> symbols in
> > the stable ABI can be used, and tests that everything exported in the
> stable
> > ABI is actually tested.
> >
> > Again, the code in the gist is a crude hack and I have currently no
> plans to
> > turn this into something that could be added to the testsuite.
> >
> > Ronald
> >
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> >
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> >
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