[C API] Prepare PyTypeObject structure for a stable ABI: avoid accessing members in the public API

[vstinner]

BPO	40170
Nosy	@rhettinger, @ronaldoussoren, @vstinner, @corona10, @miss-islington, @shihai1991, @erlend-aasland
PRs	bpo-40170: Remove PyIndex_Check() macro #19375 bpo-40170: Convert PyObject_CheckBuffer() macro to a function #19376 bpo-40170: PyObject_GET_WEAKREFS_LISTPTR() becomes a function #19377 bpo-40170: PyType_HasFeature() no longer acccess directly tp_flags #19378 bpo-40170: PyObject_NEW() becomes an alias to PyObject_New() #19379 bpo-40170: Add _PyIndex_Check() internal function #19426 bpo-40170: Remove PyIndex_Check() macro #19428 bpo-40170: Convert PyObject_IS_GC() macro to a function #19464 bpo-40170: Add _PyObject_CheckBuffer() internal function #19541 Revert "bpo-40170: PyType_HasFeature() now always calls PyType_GetFlags() (GH-19378)" #21390 [3.9] Revert "bpo-40170: PyType_HasFeature() now always calls PyType_GetFlags() (GH-19378)" (GH-21390) #21391 bpo-40170: Use inline _PyType_HasFeature() function #22375 bpo-40170: Add PyType_SetBase() function #23153 bpo-40170: Hide implementation detail of Py_TRASHCAN_BEGIN macro #23235 bpo-40170: Fix PyType_Ready() refleak on static type #23236 bpo-40170: Convert PyDescr_IsData macro to C function #24535 bpo-40170: Convert PyIter_Check macro to a function #24548 bpo-40170: Always define PyExceptionClass_Name as a function #24553 bpo-40170: Move 3 NEWS entries to the C API section #24555 bpo-40170: Update What's New in Python 3.9 #29470 [3.10] bpo-40170: Update What's New in Python 3.9 (GH-29470) #29471 [3.9] bpo-40170: Update What's New in Python 3.9 (GH-29470) #29472 bpo-40170: PyType_SUPPORTS_WEAKREFS() becomes a regular function #30938 bpo-40170: Remove _Py_GetAllocatedBlocks() function #30940 bpo-40170: Remove PyHeapType_GET_MEMBERS() macro #30942 bpo-40170: Move _Py_GetAllocatedBlocks() to pycore_pymem.h #30943

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = <Date 2022-01-28.14:25:55.330>
created_at = <Date 2020-04-03.11:57:03.054>
labels = ['expert-C-API', '3.10']
title = '[C API] Prepare PyTypeObject structure for a stable ABI: avoid accessing members in the public API'
updated_at = <Date 2022-01-28.14:25:55.330>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2022-01-28.14:25:55.330>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2022-01-28.14:25:55.330>
closer = 'vstinner'
components = ['C API']
creation = <Date 2020-04-03.11:57:03.054>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 40170
keywords = ['patch']
message_count = 59.0
messages = ['365689', '365795', '365848', '365850', '365852', '365862', '365863', '365873', '365956', '365960', '365961', '365962', '365964', '365966', '366152', '366155', '366417', '366474', '366494', '366521', '366522', '366529', '372050', '372054', '372056', '373293', '373295', '373298', '373338', '373346', '377372', '380757', '381775', '385176', '387057', '387059', '387092', '387113', '387115', '387129', '387131', '387133', '387140', '387142', '387146', '387177', '405956', '405964', '405966', '411816', '411817', '411818', '411819', '411822', '411824', '411919', '411939', '411998', '411999']
nosy_count = 7.0
nosy_names = ['rhettinger', 'ronaldoussoren', 'vstinner', 'corona10', 'miss-islington', 'shihai1991', 'erlendaasland']
pr_nums = ['19375', '19376', '19377', '19378', '19379', '19426', '19428', '19464', '19541', '21390', '21391', '22375', '23153', '23235', '23236', '24535', '24548', '24553', '24555', '29470', '29471', '29472', '30938', '30940', '30942', '30943']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue40170'
versions = ['Python 3.10']

[vstinner]

Leaking the PyTypeObject structure in the C API indirectly causes ABI issue (especially for statically allocated types), cause practical issues when old fields are removed and new fields are added (ex: tp_vectorcall addition and tp_print removal caused a lot of troubles with C code generated by Cython: see bpo-37250), prevents us to add feature and experiment optimization.

I don't expect that we will be able to make PyTypeObject opaque soon. The purpose of this issue is to track the work done towards this goal.

I propose to slowly prepare the Python code base, the C API and third party code (especially Cython) to make PyTypeObject structure opaque.

We have to identify most common code patterns which access directly PyTypeObject fields, provide helper functions, and ease the migration to solutions which don't access directly PyTypeObject.

See also bpo-39573: "Make PyObject an opaque structure in the limited C API" and bpo-39947 "Make the PyThreadState structure opaque (move it to the internal C API)".

Longer rationale about making structures of the C API opaque:

• https://pythoncapi.readthedocs.io/
• https://pythoncapi.readthedocs.io/bad_api.html
• https://pythoncapi.readthedocs.io/optimization_ideas.html

--

Multiple practical issues are preventing us to make PyTypeObject opaque right now.

(*) Many C extension modules are still using statically allocated types: there is an on-going effort in bpo-40077 to convert C extension modules one by one to PyType_FromSpec().

(*) Py_TYPE(obj)->tp_name is commonly accessed to format an error message. Example:

 PyErr_Format(PyExc_TypeError, "exec() globals must be a dict, not %.100s",
 Py_TYPE(globals)->tp_name);

I worked on bpo-34595 and started a discussion on python-dev to propose to add a new %T formatter to PyUnicode_FromFormatV() and so indirectly to PyUnicode_FromFormat() and PyErr_Format():
https://mail.python.org/archives/list/python-dev@python.org/thread/HKYUMTVHNBVB5LJNRMZ7TPUQKGKAERCJ/#3UAMHYG6UF4MPLXBZORHO4JVKUBRUZ53

Sadly, we failed to reach a consensus and I gave up on this idea. We should reconsider this idea.

We need to agree on how types should be formatted:

• just the name without any dot "type_name",
• qualified name "something.type_name",
• fully qualified name "module.something.type_name"

There is also the question of breaking applications which rely on the current exact error message. And the question of removing legacy "%.100s" which was used before Python was able to allocate a buffer large enough to arbitrary string length. When an error is formatted in pure Python, names are never truncated.

(*) Call the function of the parent type when a method is overriden in a subclass. Example with PyTypeObject.tp_free called in a deallocator:

static void
abc_data_dealloc(_abc_data *self)
{
 PyTypeObject *tp = Py_TYPE(self);
 ...
 tp->tp_free(self);
 Py_DECREF(tp);
}

() The PEP-384 provides the most generic PyType_GetSlot() but it's not convenient to use: need to handle error (NULL), need to cast the void into the expected type (error prone cast), etc.

We should slowly add more and more helper functions for most common use cases. We can try to convert a few C extension modules of the Python stdlib to see which use cases are the most common.

Hopefully, many use cases are already abstracted by widely used functions like PyNumber_Add(), PySequence_Size(), etc.

(*) Likely other issues that I forgot.

[vstinner]

Macros and static inline functions of the public C API which access directly PyTypeObject fields. There may be more.

#define _PyObject_SIZE(typeobj) ( (typeobj)->tp_basicsize )

static inline vectorcallfunc
PyVectorcall_Function(PyObject *callable)
{
...
tp = Py_TYPE(callable);
offset = tp->tp_vectorcall_offset;
...
}

#define PyObject_CheckBuffer(obj) \
 ((Py_TYPE(obj)->tp_as_buffer != NULL) && \
 (Py_TYPE(obj)->tp_as_buffer->bf_getbuffer != NULL))

#define PyIndex_Check(obj) \
 (Py_TYPE(obj)->tp_as_number != NULL && \
 Py_TYPE(obj)->tp_as_number->nb_index != NULL)

#define PyObject_GET_WEAKREFS_LISTPTR(o) \
 ((PyObject **) (((char *) (o)) + Py_TYPE(o)->tp_weaklistoffset))

static inline int
PyType_HasFeature(PyTypeObject *type, unsigned long feature){
#ifdef Py_LIMITED_API
 return ((PyType_GetFlags(type) & feature) != 0);
#else
 return ((type->tp_flags & feature) != 0);
#endif
}

#define _PyObject_SIZE(typeobj) ( (typeobj)->tp_basicsize )

[vstinner]

New changeset 38aefc5 by Victor Stinner in branch 'master':
bpo-40170: PyObject_GET_WEAKREFS_LISTPTR() becomes a function (GH-19377)
38aefc5

[aixtools]

Just manually verified that PR19377, when compiled against xlc - crashes during make:

rm -f libpython3.9d.a
ar rcs libpython3.9d.a [Modules/getbuildinfo.o](https://github.com/python/cpython/blob/main/Modules/getbuildinfo.o) [Parser/acceler.o](https://github.com/python/cpython/blob/main/Parser/acceler.o) [Parser/grammar1.o](https://github.com/python/cpython/blob/main/Parser/grammar1.o) [Parser/listnode.o](https://github.com/python/cpython/blob/main/Parser/listnode.o) [Parser/node.o](https://github.com/python/cpython/blob/main/Parser/node.o) [Parser/parser.o](https://github.com/python/cpython/blob/main/Parser/parser.o) [Parser/token.o](https://github.com/python/cpython/blob/main/Parser/token.o) [Parser/myreadline.o](https://github.com/python/cpython/blob/main/Parser/myreadline.o) [Parser/parsetok.o](https://github.com/python/cpython/blob/main/Parser/parsetok.o) [Parser/tokenizer.o](https://github.com/python/cpython/blob/main/Parser/tokenizer.o) [Objects/abstract.o](https://github.com/python/cpython/blob/main/Objects/abstract.o) [Objects/accu.o](https://github.com/python/cpython/blob/main/Objects/accu.o) [Objects/boolobject.o](https://github.com/python/cpython/blob/main/Objects/boolobject.o) [Objects/bytes_methods.o](https://github.com/python/cpython/blob/main/Objects/bytes_methods.o) [Objects/bytearrayobject.o](https://github.com/python/cpython/blob/main/Objects/bytearrayobject.o) [Objects/bytesobject.o](https://github.com/python/cpython/blob/main/Objects/bytesobject.o) [Objects/call.o](https://github.com/python/cpython/blob/main/Objects/call.o) [Objects/capsule.o](https://github.com/python/cpython/blob/main/Objects/capsule.o) [Objects/cellobject.o](https://github.com/python/cpython/blob/main/Objects/cellobject.o) [Objects/classobject.o](https://github.com/python/cpython/blob/main/Objects/classobject.o) [Objects/codeobject.o](https://github.com/python/cpython/blob/main/Objects/codeobject.o) [Objects/complexobject.o](https://github.com/python/cpython/blob/main/Objects/complexobject.o) [Objects/descrobject.o](https://github.com/python/cpython/blob/main/Objects/descrobject.o) [Objects/enumobject.o](https://github.com/python/cpython/blob/main/Objects/enumobject.o) [Objects/exceptions.o](https://github.com/python/cpython/blob/main/Objects/exceptions.o) [Objects/genobject.o](https://github.com/python/cpython/blob/main/Objects/genobject.o) [Objects/fileobject.o](https://github.com/python/cpython/blob/main/Objects/fileobject.o) [Objects/floatobject.o](https://github.com/python/cpython/blob/main/Objects/floatobject.o) [Objects/frameobject.o](https://github.com/python/cpython/blob/main/Objects/frameobject.o) [Objects/funcobject.o](https://github.com/python/cpython/blob/main/Objects/funcobject.o) [Objects/interpreteridobject.o](https://github.com/python/cpython/blob/main/Objects/interpreteridobject.o) [Objects/iterobject.o](https://github.com/python/cpython/blob/main/Objects/iterobject.o) [Objects/listobject.o](https://github.com/python/cpython/blob/main/Objects/listobject.o) [Objects/longobject.o](https://github.com/python/cpython/blob/main/Objects/longobject.o) [Objects/dictobject.o](https://github.com/python/cpython/blob/main/Objects/dictobject.o) [Objects/odictobject.o](https://github.com/python/cpython/blob/main/Objects/odictobject.o) [Objects/memoryobject.o](https://github.com/python/cpython/blob/main/Objects/memoryobject.o) [Objects/methodobject.o](https://github.com/python/cpython/blob/main/Objects/methodobject.o) [Objects/moduleobject.o](https://github.com/python/cpython/blob/main/Objects/moduleobject.o) [Objects/namespaceobject.o](https://github.com/python/cpython/blob/main/Objects/namespaceobject.o) [Objects/object.o](https://github.com/python/cpython/blob/main/Objects/object.o) [Objects/obmalloc.o](https://github.com/python/cpython/blob/main/Objects/obmalloc.o) [Objects/picklebufobject.o](https://github.com/python/cpython/blob/main/Objects/picklebufobject.o) [Objects/rangeobject.o](https://github.com/python/cpython/blob/main/Objects/rangeobject.o) [Objects/setobject.o](https://github.com/python/cpython/blob/main/Objects/setobject.o) [Objects/sliceobject.o](https://github.com/python/cpython/blob/main/Objects/sliceobject.o) [Objects/structseq.o](https://github.com/python/cpython/blob/main/Objects/structseq.o) [Objects/tupleobject.o](https://github.com/python/cpython/blob/main/Objects/tupleobject.o) [Objects/typeobject.o](https://github.com/python/cpython/blob/main/Objects/typeobject.o) [Objects/unicodeobject.o](https://github.com/python/cpython/blob/main/Objects/unicodeobject.o) [Objects/unicodectype.o](https://github.com/python/cpython/blob/main/Objects/unicodectype.o) [Objects/weakrefobject.o](https://github.com/python/cpython/blob/main/Objects/weakrefobject.o) [Python/_warnings.o](https://github.com/python/cpython/blob/main/Python/_warnings.o) [Python/Python-ast.o](https://github.com/python/cpython/blob/main/Python/Python-ast.o) [Python/asdl.o](https://github.com/python/cpython/blob/main/Python/asdl.o) [Python/ast.o](https://github.com/python/cpython/blob/main/Python/ast.o) [Python/ast_opt.o](https://github.com/python/cpython/blob/main/Python/ast_opt.o) [Python/ast_unparse.o](https://github.com/python/cpython/blob/main/Python/ast_unparse.o) [Python/bltinmodule.o](https://github.com/python/cpython/blob/main/Python/bltinmodule.o) [Python/ceval.o](https://github.com/python/cpython/blob/main/Python/ceval.o) [Python/codecs.o](https://github.com/python/cpython/blob/main/Python/codecs.o) [Python/compile.o](https://github.com/python/cpython/blob/main/Python/compile.o) [Python/context.o](https://github.com/python/cpython/blob/main/Python/context.o) [Python/dynamic_annotations.o](https://github.com/python/cpython/blob/main/Python/dynamic_annotations.o) [Python/errors.o](https://github.com/python/cpython/blob/main/Python/errors.o) [Python/frozenmain.o](https://github.com/python/cpython/blob/main/Python/frozenmain.o) [Python/future.o](https://github.com/python/cpython/blob/main/Python/future.o) [Python/getargs.o](https://github.com/python/cpython/blob/main/Python/getargs.o) [Python/getcompiler.o](https://github.com/python/cpython/blob/main/Python/getcompiler.o) [Python/getcopyright.o](https://github.com/python/cpython/blob/main/Python/getcopyright.o) [Python/getplatform.o](https://github.com/python/cpython/blob/main/Python/getplatform.o) [Python/getversion.o](https://github.com/python/cpython/blob/main/Python/getversion.o) [Python/graminit.o](https://github.com/python/cpython/blob/main/Python/graminit.o) [Python/hamt.o](https://github.com/python/cpython/blob/main/Python/hamt.o) [Python/import.o](https://github.com/python/cpython/blob/main/Python/import.o) [Python/importdl.o](https://github.com/python/cpython/blob/main/Python/importdl.o) [Python/initconfig.o](https://github.com/python/cpython/blob/main/Python/initconfig.o) [Python/marshal.o](https://github.com/python/cpython/blob/main/Python/marshal.o) [Python/modsupport.o](https://github.com/python/cpython/blob/main/Python/modsupport.o) [Python/mysnprintf.o](https://github.com/python/cpython/blob/main/Python/mysnprintf.o) [Python/mystrtoul.o](https://github.com/python/cpython/blob/main/Python/mystrtoul.o) [Python/pathconfig.o](https://github.com/python/cpython/blob/main/Python/pathconfig.o) [Python/peephole.o](https://github.com/python/cpython/blob/main/Python/peephole.o) [Python/preconfig.o](https://github.com/python/cpython/blob/main/Python/preconfig.o) [Python/pyarena.o](https://github.com/python/cpython/blob/main/Python/pyarena.o) [Python/pyctype.o](https://github.com/python/cpython/blob/main/Python/pyctype.o) [Python/pyfpe.o](https://github.com/python/cpython/blob/main/Python/pyfpe.o) [Python/pyhash.o](https://github.com/python/cpython/blob/main/Python/pyhash.o) [Python/pylifecycle.o](https://github.com/python/cpython/blob/main/Python/pylifecycle.o) [Python/pymath.o](https://github.com/python/cpython/blob/main/Python/pymath.o) [Python/pystate.o](https://github.com/python/cpython/blob/main/Python/pystate.o) [Python/pythonrun.o](https://github.com/python/cpython/blob/main/Python/pythonrun.o) [Python/pytime.o](https://github.com/python/cpython/blob/main/Python/pytime.o) [Python/bootstrap_hash.o](https://github.com/python/cpython/blob/main/Python/bootstrap_hash.o) [Python/structmember.o](https://github.com/python/cpython/blob/main/Python/structmember.o) [Python/symtable.o](https://github.com/python/cpython/blob/main/Python/symtable.o) [Python/sysmodule.o](https://github.com/python/cpython/blob/main/Python/sysmodule.o) [Python/thread.o](https://github.com/python/cpython/blob/main/Python/thread.o) [Python/traceback.o](https://github.com/python/cpython/blob/main/Python/traceback.o) [Python/getopt.o](https://github.com/python/cpython/blob/main/Python/getopt.o) [Python/pystrcmp.o](https://github.com/python/cpython/blob/main/Python/pystrcmp.o) [Python/pystrtod.o](https://github.com/python/cpython/blob/main/Python/pystrtod.o) [Python/pystrhex.o](https://github.com/python/cpython/blob/main/Python/pystrhex.o) [Python/dtoa.o](https://github.com/python/cpython/blob/main/Python/dtoa.o) [Python/formatter_unicode.o](https://github.com/python/cpython/blob/main/Python/formatter_unicode.o) [Python/fileutils.o](https://github.com/python/cpython/blob/main/Python/fileutils.o) [Python/dynload_shlib.o](https://github.com/python/cpython/blob/main/Python/dynload_shlib.o) [Modules/config.o](https://github.com/python/cpython/blob/main/Modules/config.o) [Modules/getpath.o](https://github.com/python/cpython/blob/main/Modules/getpath.o) [Modules/main.o](https://github.com/python/cpython/blob/main/Modules/main.o) [Modules/gcmodule.o](https://github.com/python/cpython/blob/main/Modules/gcmodule.o) [Modules/posixmodule.o](https://github.com/python/cpython/blob/main/Modules/posixmodule.o) [Modules/errnomodule.o](https://github.com/python/cpython/blob/main/Modules/errnomodule.o) [Modules/pwdmodule.o](https://github.com/python/cpython/blob/main/Modules/pwdmodule.o) [Modules/_sre.o](https://github.com/python/cpython/blob/main/Modules/_sre.o) [Modules/_codecsmodule.o](https://github.com/python/cpython/blob/main/Modules/_codecsmodule.o) [Modules/_weakref.o](https://github.com/python/cpython/blob/main/Modules/_weakref.o) [Modules/_functoolsmodule.o](https://github.com/python/cpython/blob/main/Modules/_functoolsmodule.o) [Modules/_operator.o](https://github.com/python/cpython/blob/main/Modules/_operator.o) [Modules/_collectionsmodule.o](https://github.com/python/cpython/blob/main/Modules/_collectionsmodule.o) [Modules/_abc.o](https://github.com/python/cpython/blob/main/Modules/_abc.o) [Modules/itertoolsmodule.o](https://github.com/python/cpython/blob/main/Modules/itertoolsmodule.o) [Modules/atexitmodule.o](https://github.com/python/cpython/blob/main/Modules/atexitmodule.o) [Modules/signalmodule.o](https://github.com/python/cpython/blob/main/Modules/signalmodule.o) [Modules/_stat.o](https://github.com/python/cpython/blob/main/Modules/_stat.o) [Modules/timemodule.o](https://github.com/python/cpython/blob/main/Modules/timemodule.o) [Modules/_threadmodule.o](https://github.com/python/cpython/blob/main/Modules/_threadmodule.o) [Modules/_localemodule.o](https://github.com/python/cpython/blob/main/Modules/_localemodule.o) [Modules/_iomodule.o](https://github.com/python/cpython/blob/main/Modules/_iomodule.o) [Modules/iobase.o](https://github.com/python/cpython/blob/main/Modules/iobase.o) [Modules/fileio.o](https://github.com/python/cpython/blob/main/Modules/fileio.o) [Modules/bytesio.o](https://github.com/python/cpython/blob/main/Modules/bytesio.o) [Modules/bufferedio.o](https://github.com/python/cpython/blob/main/Modules/bufferedio.o) [Modules/textio.o](https://github.com/python/cpython/blob/main/Modules/textio.o) [Modules/stringio.o](https://github.com/python/cpython/blob/main/Modules/stringio.o) [Modules/faulthandler.o](https://github.com/python/cpython/blob/main/Modules/faulthandler.o) [Modules/_tracemalloc.o](https://github.com/python/cpython/blob/main/Modules/_tracemalloc.o) [Modules/hashtable.o](https://github.com/python/cpython/blob/main/Modules/hashtable.o) [Modules/symtablemodule.o](https://github.com/python/cpython/blob/main/Modules/symtablemodule.o) [Modules/xxsubtype.o](https://github.com/python/cpython/blob/main/Modules/xxsubtype.o) [Python/frozen.o](https://github.com/python/cpython/blob/main/Python/frozen.o)
./Modules/makexp_aix [Modules/python.exp](https://github.com/python/cpython/blob/main/Modules/python.exp) . libpython3.9d.a; xlc_r -Wl,-bE:Modules/python.exp -lld -o python [Programs/python.o](https://github.com/python/cpython/blob/main/Programs/python.o) libpython3.9d.a -lintl -ldl -lm -lm 
 ./python -E -S -m sysconfig --generate-posix-vars ; if test $? -ne 0 ; then echo "generate-posix-vars failed" ; rm -f ./pybuilddir.txt ; exit 1 ; fi

Objects/genobject.c:127: _PyObject_GC_TRACK: Assertion "!(((PyGC_Head *)(op)-1)->_gc_next != 0)" failed: object already tracked by the garbage collector
Enable tracemalloc to get the memory block allocation traceback
object address : 30084150
object refcount : 0
object type : 20013aa8
object type name: generator
object repr : <refcnt 0 at 30084150>
Fatal Python error: _PyObject_AssertFailed: _PyObject_AssertFailed
Python runtime state: core initialized
Current thread 0x00000001 (most recent call first):
File "<frozen importlib._bootstrap_external>", line 1593 in _setup
File "<frozen importlib._bootstrap_external>", line 1634 in _install
File "<frozen importlib._bootstrap>", line 1189 in _install_external_importers
/bin/sh: 24117648 IOT/Abort trap(coredump)
make: 1254-004 The error code from the last command is 134.
Stop.

FYI: about two hours ago I verified that xlc and 08050e9 : bpo-40147: Fix a compiler warning on Windows in Python/compile.c (GH-19389)

all was green.

[aixtools]

Just checked - seems to be SPECIFIC to xlc-v16 as neither xlv-v11 nor xlc-v13 have any issues building.

[vstinner]

Py_TRASHCAN_BEGIN() access directly PyTypeObject.tp_dealloc:

#define Py_TRASHCAN_BEGIN(op, dealloc) \
 Py_TRASHCAN_BEGIN_CONDITION(op, \
 Py_TYPE(op)->tp_dealloc == (destructor)(dealloc))

It should use PyType_GetSlot() or a new getter function (to read PyTypeObject.tp_dealloc) should be added.

[vstinner]

It should use PyType_GetSlot()

Oh. It seems like currently, PyType_GetSlot() can only be used on a heap allocated types :-( The function starts with:

 if (!PyType_HasFeature(type, Py_TPFLAGS_HEAPTYPE) || slot < 0){
 PyErr_BadInternalCall();
 return NULL;
 }

[vstinner]

Just checked - seems to be SPECIFIC to xlc-v16 as neither xlv-v11 nor xlc-v13 have any issues building.

That sounds like an AIX specific issue. Please open a separated issue.

[vstinner]

New changeset 9205520 by Victor Stinner in branch 'master':
bpo-40170: PyObject_NEW() becomes an alias to PyObject_New() (GH-19379)
9205520

[vstinner]

New changeset ef5c615 by Victor Stinner in branch 'master':
bpo-40170: Convert PyObject_CheckBuffer() macro to a function (GH-19376)
ef5c615

[vstinner]

New changeset 45ec5b9 by Victor Stinner in branch 'master':
bpo-40170: PyType_HasFeature() now always calls PyType_GetFlags() (GH-19378)
45ec5b9