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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Py_TRACE_REFS is not compatible with Py_LIMITED_API","articleBody":"# Bug report\n\n### Checklist\n\n- [X] I am confident this is a bug in CPython, not a bug in a third-party project\n- [X] I have searched the [CPython issue tracker](https://github.com/python/cpython/issues?q=is%3Aissue+sort%3Acreated-desc),\nand am confident this bug has not been reported before\n\n\n### CPython versions tested on:\n\nCPython main branch\n\n### Operating systems tested on:\n\nLinux\n\n### Output from running 'python -VV' on the command line:\n\n_No response_\n\n### A clear and concise description of the bug:\n\nTrying to build a C extension targetting the limited C API (defining Py_LIMITED_API) fails if Python is configured with ``./configure --with-trace-refs``. Example with PR #108573:\n\n```\nIn file included from ./Include/Python.h:44,\n                 from ./Modules/_stat.c:16:\n./Include/object.h:62:4: error: #error Py_LIMITED_API is incompatible with Py_TRACE_REFS\n   62 | #  error Py_LIMITED_API is incompatible with Py_TRACE_REFS\n      |    ^~~~~\nmake: *** [Makefile:3194: Modules/_stat.o] Error 1\n```\n\nThe ``#error`` comes from ``Include/object.h``:\n\n```c\n#if defined(Py_LIMITED_API) \u0026\u0026 defined(Py_TRACE_REFS)\n#  error Py_LIMITED_API is incompatible with Py_TRACE_REFS\n#endif\n```\n\nThe problem is that the PyObject ABI is different: Py_TRACE_REFS adds two members to PyObject structure:\n\n```c\n    PyObject *_ob_next;\n    PyObject *_ob_prev;\n```\n\nOne solution to make Py_TRACE_REFS compatible with Py_LIMITED_API would be to **not** add these two members to PyObject, but store the double-linked list outside ``PyObject``. Store it in a different structure, so ``PyObject`` stays ABI compatible.\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-108663\n* gh-108748\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/vstinner","@type":"Person","name":"vstinner"},"datePublished":"2023-08-29T13:33:53.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/108634/cpython/issues/108634"}