gh-137210: Add a struct, slot & function for checking an extension's ABI by encukou · Pull Request #137212 · python/cpython

encukou · 2025-07-29T16:21:09Z

See the issue.

Issue: Add a struct, slot & function for checking an extension's ABI #137210

📚 Documentation preview 📚: https://cpython-previews--137212.org.readthedocs.build/

Doc/c-api/stable.rst

zooba · 2025-07-29T18:48:50Z

Doc/c-api/stable.rst

+      (except if :c:macro:`Py_LIMITED_API` is ``3``; use
+      :c:expr:`Py_PACK_VERSION(3, 2)` in that case).


Seems easier for us to just check this on our side than to expect users to get it right?

And isn't the legacy value 1 rather than 3?

Well, users should use PyABIInfo_DEFAULT_ABI_VERSION or PyABIInfo_VAR -- those are our side too.
I prefer the data to be simpler, but if you want, we can keep the exception in.

The legacy value is 3. (Not that it matters that much; it's always compared to a Python version.)

zooba · 2025-07-29T18:50:58Z

Doc/c-api/stable.rst

+            Specifies ABI specific to a particular build of CPython.
+            Internal use only.
+
+      Free-threading compatibility -- one of:


We're still planning to get rid of these options once FT is merged, right? Maybe we ought to use abiflags here (i.e. a string) instead, for future extensibility? This isn't going to be checked anywhere that it needs to be bitflags.

How would you encode being compatible with both GIL and FT?

IMO, we can remove them when there are no GIL-only extensions around any more. That would be a lot of time after FT is the only option.

Include/modsupport.h

zooba · 2025-07-29T18:52:45Z

Include/modsupport.h

 #endif /* New in 3.5 */

+/* ABI info & checking (new in 3.15) */
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= _Py_PACK_VERSION(3, 15)


What are all of these warnings about? Does _Py_PACK_VERSION do something funky?

No idea. I'll need to check on a Windows box.

I wasn't able to figure it out. Something seems to be compiling modsupport.h outside of Python.h -- that is, without pymacro.h being included first: I get an error if I add this before the line:

#ifndef Py_PYMACRO_H #error this should not happen #endif

The error is currently quite impenetrable to me:

ResourceCompile: C:\Program Files (x86)\Windows Kits\10\bin\10.0.26100.0\x86\rc.exe /D "ORIGINAL_FILENAME=\\\"python315_d.dll\\\"" /D FIELD3=100 /D _DEBUG /l"0x0409" /IC:\Users\encukou\dev\cpython\PC /IC:\Users\encu kou\dev\cpython\Include /IC:\Users\encukou\dev\cpython\PCbuild\obj\315amd64_Debug\pythoncore\ /nologo /fo"C:\Users\encukou\dev\cpython\PCbuild\obj\315amd64_Debug\pythoncore\python_nt.res" ..\PC\pyth on_nt.rc 3>C:\Users\encukou\dev\cpython\Include\modsupport.h(98): error RC2188: C:\Users\encukou\dev\cpython\PCbuild\obj\315amd64_Debug\pythoncore\RCa08340(52) : fatal error RC1116: RC terminating after preproce ssor errors [C:\Users\encukou\dev\cpython\PCbuild\pythoncore.vcxproj] 3>Done Building Project "C:\Users\encukou\dev\cpython\PCbuild\pythoncore.vcxproj" (Build target(s)) -- FAILED.

Ah, it's being referenced from PC\python_ver_rc.h, which runs under the resource compiler rather than the C compiler. It's pretty much entirely compatible, but occasionally has some obscure/subtle differences.

I think it's just bypassing a lot of unnecessary includes here, assuming that modsupport.h stands alone. If that's not true, then the header needs updating and whatever constant it's referencing will have to move elsewhere.

I switched this PR to use 0x030f0000; I plan to switch to _Py_PACK_VERSION(3, 15) in a follow-up PR.

Co-authored-by: Steve Dower <[email protected]>

…ion's ABI (pythonGH-137212) Co-authored-by: Steve Dower <[email protected]>

ZeroIntensity · 2025-11-11T15:25:46Z

Include/modsupport.h

+#define PyABIInfo_FREETHREADED  0x0004
+#define PyABIInfo_INTERNAL      0x0008
+
+#define PyABIInfo_FREETHREADING_AGNOSTIC (PyABIInfo_GIL|PyABIInfo_FREETHREADED)


Is there any reason this wasn't documented?

Thanks, good catch! This should probably not have been added right now :/
But it should be added for PEP 803 or PEP 809.
Can we put this on hold until the rest of #141004 is done? Flipping the stable ABI status on and off and on again is somewhat disruptive, even in the alpha period.

Sounds good, I'll just mark it as tracked by either PEP.

This is a downstream workaround "implementing" python#137212 - the mechanism for the check exists in Python 3.15+, where it needs to be added to the standard library modules. In Fedora, we need it also in previous Python versions, as we experience segmentation fault when importing stdlib modules after update while Python is running. _tkinter, _tracemalloc and readline are not calling PyModuleDef_Init, which is modified with this patch, hence they need a direct call to the check function.

This is a downstream workaround "implementing" python#137212 - the mechanism for the check exists in Python 3.15+, where it needs to be added to the standard library modules. In Fedora, we need it also in previous Python versions, as we experience segmentation fault when importing stdlib modules after update while Python is running. _tkinter, _tracemalloc and readline are not calling PyModuleDef_Init, which is modified with this patch, hence they need a direct call to the check function. Co-Authored-By: Karolina Surma <[email protected]>

This is a downstream workaround "implementing" python#137212 - the mechanism for the check exists in Python 3.15+, where it needs to be added to the standard library modules. In Fedora, we need it also in previous Python versions, as we experience segmentation fault when importing stdlib modules after update while Python is running. _curses, _tkinter, _tracemalloc and readline are not calling PyModuleDef_Init, which is modified with this patch, hence they need a direct call to the check function. Co-Authored-By: Karolina Surma <[email protected]>

…thon This is a downstream workaround "implementing" python#137212 - the mechanism for the check exists in Python 3.15+, where it needs to be added to the standard library modules. In Fedora, we need it also in previous Python versions, as we experience segmentation fault when importing stdlib modules after update while Python is running. _curses, _tkinter, _tracemalloc and readline are not calling PyModuleDef_Init, which is modified with this patch, hence they need a direct call to the check function. Co-Authored-By: Karolina Surma <[email protected]>

…thon This is a downstream workaround "implementing" python#137212 - the mechanism for the check exists in Python 3.15+, where it needs to be added to the standard library modules. In Fedora, we need it also in previous Python versions, as we experience segmentation fault when importing stdlib modules after update while Python is running. _tkinter, _tracemalloc and readline are not calling PyModuleDef_Init, which is modified with this patch, hence they need a direct call to the check function. Co-Authored-By: Karolina Surma <[email protected]>

…thon This is a downstream workaround "implementing" python#137212 - the mechanism for the check exists in Python 3.15+, where it needs to be added to the standard library modules. In Fedora, we need it also in previous Python versions, as we experience segmentation fault when importing stdlib modules after update while Python is running. _curses, _tkinter, _tracemalloc and readline are not calling PyModuleDef_Init, which is modified with this patch, hence they need a direct call to the check function. Co-Authored-By: Karolina Surma <[email protected]>

…thon This is a downstream workaround "implementing" python#137212 - the mechanism for the check exists in Python 3.15+, where it needs to be added to the standard library modules. In Fedora, we need it also in previous Python versions, as we experience segmentation fault when importing stdlib modules after update while Python is running. _tkinter, _tracemalloc and readline are not calling PyModuleDef_Init, which is modified with this patch, hence they need a direct call to the check function. Co-Authored-By: Karolina Surma <[email protected]>

…fferent Python This is a downstream workaround "implementing" python#137212 - the mechanism for the check exists in Python 3.15+, where it needs to be added to the standard library modules. In Fedora, we need it also in previous Python versions, as we experience segmentation fault when importing stdlib modules after update while Python is running. _curses, _tkinter, _tracemalloc and readline are not calling PyModuleDef_Init, which is modified with this patch, hence they need a direct call to the check function. Co-Authored-By: Karolina Surma <[email protected]>

…fferent Python This is a downstream workaround "implementing" python#137212 - the mechanism for the check exists in Python 3.15+, where it needs to be added to the standard library modules. In Fedora, we need it also in previous Python versions, as we experience segmentation fault when importing stdlib modules after update while Python is running. _tkinter, _tracemalloc and readline are not calling PyModuleDef_Init, which is modified with this patch, hence they need a direct call to the check function. Co-Authored-By: Karolina Surma <[email protected]>

…fferent Python version This is a downstream workaround "implementing" python#137212 - the mechanism for the check exists in Python 3.15+, where it needs to be added to the standard library modules. In Fedora, we need it also in previous Python versions, as we experience segmentation fault when importing stdlib modules after update while Python is running. _tkinter, _tracemalloc and readline are not calling PyModuleDef_Init, which is modified with this patch, hence they need a direct call to the check function. Co-Authored-By: Karolina Surma <[email protected]>

…fferent Python version This is a downstream workaround "implementing" python#137212 - the mechanism for the check exists in Python 3.15+, where it needs to be added to the standard library modules. In Fedora, we need it also in previous Python versions, as we experience segmentation fault when importing stdlib modules after update while Python is running. _curses, _tkinter, _tracemalloc and readline are not calling PyModuleDef_Init, which is modified with this patch, hence they need a direct call to the check function. Co-Authored-By: Karolina Surma <[email protected]>

…fferent Python version This is a downstream workaround "implementing" python#137212 - the mechanism for the check exists in Python 3.15+, where it needs to be added to the standard library modules. In Fedora, we need it also in previous Python versions, as we experience segmentation fault when importing stdlib modules after update while Python is running. _tkinter, _tracemalloc and readline are not calling PyModuleDef_Init, which is modified with this patch, hence they need a direct call to the check function. Co-Authored-By: Karolina Surma <[email protected]>

encukou added 9 commits July 29, 2025 17:13

Add _PyUnicodeWriter_FormatV

894ef3d

Add capi test file for modsupport

72349ba

Add PyABIInfo

3b6aa96

Add _Py_INTERNAL_ABI_SLOT (to _datetime for now)

c015606

Add docs

c5740af

Add to limited API manifest

da293e3

Un-document PyABIInfo_FREETHREADING_AGNOSTIC for now

44df416

Blurb & What's New

feb428d

Fix docs

aa1eb4a

encukou requested review from a team, abalkin, corona10, ericsnowcurrently, erlend-aasland and pganssle as code owners July 29, 2025 16:21

bedevere-app bot added the awaiting core review label Jul 29, 2025

bedevere-app bot mentioned this pull request Jul 29, 2025

Add a struct, slot & function for checking an extension's ABI #137210

Closed

Remove duplicated test

b628d7d

encukou mentioned this pull request Jul 29, 2025

Add a struct, slot & function for checking an extension's ABI capi-workgroup/decisions#72

Closed

zooba reviewed Jul 29, 2025

View reviewed changes

encukou and others added 4 commits July 30, 2025 09:37

Apply suggestions from code review

4800a5d

Co-authored-by: Steve Dower <[email protected]>

Casts to avoid data loss warnings

4c9e918

Use hex literal for 3.15

1b18761

Merge in the main branch

814ac60

encukou requested a review from AA-Turner as a code owner August 7, 2025 11:52

encukou added 4 commits August 26, 2025 11:21

Merge in the main branch

f6f5b1d

Add example of intended usage before the API documentation

2644080

Restore changelog / comments for PYTHON_API_VERSION

cb0309f

Merge branch 'main' into abiinfo-slot

7492e16

encukou merged commit 0c74fc8 into python:main Sep 5, 2025
45 checks passed

bedevere-app bot removed the awaiting core review label Sep 5, 2025

encukou deleted the abiinfo-slot branch September 5, 2025 14:23

encukou mentioned this pull request Sep 9, 2025

Segfault when updating from 3.13.0 to 3.13.1 while Python is running #128341

Open

lkollar pushed a commit to lkollar/cpython that referenced this pull request Sep 9, 2025

pythongh-137210: Add a struct, slot & function for checking an extens…

8ac4c6e

…ion's ABI (pythonGH-137212) Co-authored-by: Steve Dower <[email protected]>

ZeroIntensity reviewed Nov 11, 2025

View reviewed changes

		(except if :c:macro:`Py_LIMITED_API` is ``3``; use
		:c:expr:`Py_PACK_VERSION(3, 2)` in that case).

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encukou commented Jul 29, 2025 • edited by github-actions bot Loading Uh oh! There was an error while loading. Please reload this page.

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encukou commented Jul 29, 2025 •

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