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GeezerVison is showing github.com — gh-146636: Improve ABI/feature selection, add new header for it by encukou · Pull Request #148302 · python/cpython

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encukou commented Apr 9, 2026

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Feature/ABI selection headers (Py_BUILD_CORE, Py_LIMITED_API, Py_GIL_DISABLED) need to be defined early (so they affect all definitions), but after the version (patchlevel.h) and configuration (pyconfig.h).
Put them in their own header to make this more obvious, and easier for contributors to keep them in the proper place.

Add a test that Python headers themselves don't use Py_GIL_DISABLED, since abi3 and abi3t ought to be identical except for the _Py_OPAQUE_PYOBJECT differences.
This is done using the GCC-only poison pragma, which tells the compiler/preprocessor to error if it ever sees the identifier after the pragma.
This needs some rewriting: #if defined(Py_LIMITED_API) && defined(Py_GIL_DISABLED) needs to be split into two lines, as the poisoning doesn't honour short-circuiting.

This should fix gh-148267, but I'm attaching the PR to the abi3t issue, gh-146636, as it continues that effort (GH-148142 specifically).

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encukou added 6 commits

April 9, 2026 13:44


          pythongh-146636: abi3t: Test that Python.h avoids checking Py_GIL_DIS…

1116e1e

…ABLED

Add a test that Python headers themselves don't use
Py_GIL_DISABLED in abi3t: abi3 and abi3t ought to be the
same except the _Py_OPAQUE_PYOBJECT differences.
This is done using the GCC-only poison pragma.


          Move ABI/feature selection macros to their own header


          Update check for <intrin.h>

e1b7500


          Typo

247bd46


          Move Py_BUILD_CORE undefines, and include exports.h directly from Pyt…

…hon.h


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encukou requested a review from vstinner

April 9, 2026 14:35

encukou requested review from a team, AA-Turner, emmatyping and erlend-aasland as code owners

April 9, 2026 14:35

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Apr 9, 2026

bedevere-app Bot mentioned this pull request

Apr 9, 2026

Implement PEP 803 -- abi3t #146636

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Include/pyabi.h Resolved

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Include/pyabi.h

		// whether they need extra synchronization.
		# define Py_GIL_DISABLED
		# endif
		# if defined(_Py_IS_TESTCEXT)

vstinner Apr 9, 2026

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You may move #ifdef __GNUC__ here:

Suggested change

	# if defined(_Py_IS_TESTCEXT)
	# if defined(_Py_IS_TESTCEXT) && defined(__GNUC__)

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encukou Apr 10, 2026

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This subtle style detail is intentional: I'm inviting #elifs for other compilers.

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Include/pyabi.h Resolved

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Include/pyabi.h


		/* The internal C API must not be used with the limited C API: make sure
		* that Py_BUILD_CORE* macros are not defined in this case.
		* But, keep the "original" values, under different names, for "exports.h"

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It's surprising that _PyEXPORTS_CORE and _PyEXPORTS_CORE_MODULE are defined even if Py_LIMITED_API is defined. I tried to undefine Py_BUILD_CORE if Py_LIMITED_API is defined before _PyEXPORTS_CORE code, but I got linker errors on Windows. Examples:

LINK : warning LNK4217: symbol 'PyType_GetFlags' defined in 'typeobject.obj' is imported by '_stat.obj' in fu 
nction '_PyLong_AsMode_t' [C:\victor\python\main\PCbuild\pythoncore.vcxproj]
LINK : warning LNK4217: symbol '_Py_DecRef' defined in 'object.obj' is imported by '_stat.obj' in function '_ 
PyLong_AsMode_t' [C:\victor\python\main\PCbuild\pythoncore.vcxproj]
LINK : warning LNK4286: symbol '_Py_DecRef' defined in 'object.obj' is imported by 'errnomodule.obj' [C:\vict 
or\python\main\PCbuild\pythoncore.vcxproj]
LINK : warning LNK4217: symbol 'PyUnicode_FromStringAndSize' defined in 'unicodeobject.obj' is imported by '_ 
stat.obj' in function 'stat_filemode' [C:\victor\python\main\PCbuild\pythoncore.vcxproj]

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encukou Apr 10, 2026

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Yes; these select whether PyAPI_FUNC sumbols are exported or imported. Anything compiled into the main binary needs to be exported, regardless of the API it uses.

(This is currently done by including "exports.h" in the middle of pyport.h, right before Py_BUILD_CORE is undefined -- which is IMO confusing, as it makes the meaning of Py_BUILD_CORE depend on where you are in the header.)

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          Apply suggestions from code review

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Co-authored-by: Victor Stinner <[email protected]>

encukou mentioned this pull request

Apr 14, 2026

PEP 803: Py_GIL_DISABLED is tested prior to setting, in patchlevel.h #148267

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encukou added the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label

Apr 16, 2026

bedevere-bot commented Apr 16, 2026

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🤖 New build scheduled with the buildbot fleet by @encukou for commit 7c9d920 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F148302%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.

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bedevere-bot removed the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label

Apr 16, 2026

ngoldbaum commented Apr 16, 2026 •

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I ran into an issue similar to gh-148267 while working on CFFI (see https://github.com/python-cffi/cffi/actions/runs/24516133542/job/71660551119?pr=232) and was curious if this PR fixes it. It doesn't. The compiler error I see on this branch is:

In file included from /Users/goldbaum/.pyenv/versions/3.15t-dev-encukoupr/include/python3.15t/Python.h:16:
/Users/goldbaum/.pyenv/versions/3.15t-dev-encukoupr/include/python3.15t/pyabi.h:55:24: error: invalid
      token at start of a preprocessor expression
   55 | #  elif Py_LIMITED_API > Py_TARGET_ABI3T
      |                        ^

I think this is happening because my CFFI branch was using _Py_OPAQUE_PYOBJECT directly and the header doesn't handle someone setting that outside of CPython's headers. Probably unlikely to happen in practice, not sure if it's worth explicitly guarding against so I thought I'd share. On the CFFI side I'll fix this by defining Py_TARGET_ABI3T.

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ngoldbaum commented Apr 16, 2026

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Looking again, maybe it's because CFFI's headers define Py_LIMITED_API but don't set a value:

https://github.com/python-cffi/cffi/blob/5285ae32c9cc1e34b1dd7d50aa6f5294feb4c0d0/src/cffi/_cffi_include.h#L52

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vstinner commented Apr 16, 2026

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buildbot/AMD64 FreeBSD PR
buildbot/AMD64 FreeBSD14 PR
buildbot/s390x Fedora Stable Clang Installed PR
buildbot/s390x Fedora Stable Clang PR
buildbot/x86-64 MacOS Intel NoGIL PR

test_cext.test_build_abi3t() failed. All of these buildbot workers use Clang as the C compiler.

I suppose that the issue can be reproduced with CC=clang CXX=clang++ ./python -m test test_cext -u all -v -m test_build_abi3t.

Example on "buildbot/AMD64 FreeBSD PR":

Building wheels for collected packages: internal__test_abi3t
  Building wheel for internal__test_abi3t (pyproject.toml): started
  Running command Building wheel for internal__test_abi3t (pyproject.toml)
  CC env var: 'cc -pthread'
  CFLAGS env var: <missing>
  CPPFLAGS env var: <missing>
  extra_compile_args: ['-Werror', '-D_Py_IS_TESTCEXT', '-Wcast-qual', '-pedantic-errors', '-Werror=declaration-after-statement', '-DMODULE_NAME=_test_abi3t', '-DPy_TARGET_ABI3T=0x30f00a8']
  running bdist_wheel
  running build
  running build_ext
  building '_test_abi3t' extension
  creating build/temp.freebsd-13.5-RELEASE-p10-amd64-cpython-315-pydebug
  cc -pthread -fno-strict-overflow -Wsign-compare -g -Og -Wall -fPIC -I/buildbot/buildarea/pull_request.ware-freebsd/build/build/test_python_81305æ/tempcwd/env/include -I/buildbot/buildarea/pull_request.ware-freebsd/build/Include -I/buildbot/buildarea/pull_request.ware-freebsd/build -c extension.c -o build/temp.freebsd-13.5-RELEASE-p10-amd64-cpython-315-pydebug/extension.o -Werror -D_Py_IS_TESTCEXT -Wcast-qual -pedantic-errors -Werror=declaration-after-statement -DMODULE_NAME=_test_abi3t -DPy_TARGET_ABI3T=0x30f00a8
  In file included from extension.c:13:
  In file included from /buildbot/buildarea/pull_request.ware-freebsd/build/Include/Python.h:79:
  /buildbot/buildarea/pull_request.ware-freebsd/build/Include/object.h:126:16: error: attempt to use a poisoned identifier
    126 | #elif !defined(Py_GIL_DISABLED)
        |                ^
  In file included from extension.c:13:
  In file included from /buildbot/buildarea/pull_request.ware-freebsd/build/Include/Python.h:80:
  /buildbot/buildarea/pull_request.ware-freebsd/build/Include/refcount.h:342:15: error: attempt to use a poisoned identifier
    342 | #elif defined(Py_GIL_DISABLED) && defined(Py_REF_DEBUG)
        |               ^
  In file included from extension.c:13:
  In file included from /buildbot/buildarea/pull_request.ware-freebsd/build/Include/Python.h:128:
  /buildbot/buildarea/pull_request.ware-freebsd/build/Include/modsupport.h:117:15: error: attempt to use a poisoned identifier
    117 | #elif defined(Py_GIL_DISABLED)
        |               ^
  3 errors generated.
  error: command '/usr/local/libexec/ccache/cc' failed with exit code 1
  error: subprocess-exited-with-error

I can reproduce the issue on Fedora with Clang on this short program:

#define Py_TARGET_ABI3T 0x30f00a8
#pragma GCC poison Py_GIL_DISABLED

#ifdef Py_TARGET_ABI3T
#  define _Py_OPAQUE_PYOBJECT
#endif

int main()
{
#ifdef _Py_OPAQUE_PYOBJECT
    // All good
    return 0;
#elif defined(Py_GIL_DISABLED)
    // Not good
    return 1;
#endif
    return 0;
}

Clang output:

x.c:13:15: error: attempt to use a poisoned identifier
   13 | #elif defined(Py_GIL_DISABLED)
      |               ^
1 error generated.

The workaround is to write:

#ifdef _Py_OPAQUE_PYOBJECT
    // All good
    return 0;
#else
#  if defined(Py_GIL_DISABLED)
    // Not good
    return 1;
#  endif
#endif

ARM Raspbian PR

test.test_io.test_fileio failed: waiting for #148648 fix.

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vstinner commented Apr 16, 2026

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Looking again, maybe it's because CFFI's headers define Py_LIMITED_API but don't set a value:
https://github.com/python-cffi/cffi/blob/5285ae32c9cc1e34b1dd7d50aa6f5294feb4c0d0/src/cffi/_cffi_include.h#L52

Oh, maybe we can set the Py_LIMITED_API macro value to 3 if the macro is empty or if its value is smaller than 3, with a warning:

#if Py_LIMITED_API+0 < 3
#  warning "Py_LIMITED_API macro value must be at least 3"
#  undef Py_LIMITED_API
#  define Py_LIMITED_API 3
#endif

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ngoldbaum commented Apr 16, 2026 •

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@mgorny and I were also looking at the stable-abi-testing repo and got into a situation where "weird" things happen if you define Py_TARGET_ABI3T but don't define Py_LIMITED_API. IMO it'd be more helpful if Python's headers could trigger a build error if you don't explicitly set Py_LIMITED_API when Py_TARGET_ABI3T is set.

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encukou added 4 commits

April 17, 2026 15:22


          Merge in the main branch

38950b8


          Don't poison on clang

c477a14


          Error out if _Py_OPAQUE_PYOBJECT is defined by user

05e7c90


          Require version in Py_LIMITED_API & Py_TARGET_ABI3T

72b1637

encukou added the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label

Apr 21, 2026

bedevere-bot commented Apr 21, 2026

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🤖 New build scheduled with the buildbot fleet by @encukou for commit 72b1637 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F148302%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.

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encukou commented Apr 22, 2026

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RHEL8 changes are unrelated. (I'll remove them from the 🔨 test-with-buildbots set, but probably not before beta.)

I'm planning to merge this PR soon, and base Windows changes & further tests on it.

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encukou merged commit ab41a34 into python:main

Apr 23, 2026

117 of 124 checks passed

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bedevere-app Bot removed the awaiting core review label

Apr 23, 2026

encukou deleted the abi3t-pygildisabled branch

April 23, 2026 09:52

ljfp pushed a commit to ljfp/cpython that referenced this pull request

Apr 25, 2026


          pythongh-146636: Improve ABI/feature selection, add new header for it (…

8abf101

…pythonGH-148302)

Improve ABI/feature selection, add new header for it.

Add a test that Python headers themselves don't use
Py_GIL_DISABLED in abi3t: abi3 and abi3t ought to be the
same except the _Py_OPAQUE_PYOBJECT differences.
This is done using the GCC-only poison pragma.

Co-authored-by: Victor Stinner <[email protected]>

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