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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Build Failure in posixmodule.c with Clang, ThreadSanitizer, and free-threaded build enabled","articleBody":"**Description:**\n\nA build failure occurs in `Modules/posixmodule.c` when compiling CPython from the `main` branch using Clang with ThreadSanitizer and the `--disable-gil` flag.\n\nThe compilation fails with two distinct types of errors:\n1.  The compiler reports that the `statx` struct has no member named `stx_atomic_write_unit_max_opt`. This error originates from the `MM` macro expansion within the `pystatx_result_members` definition.\n2.  Subsequently, multiple errors are reported for an invalid application of `sizeof` to an incomplete type `PyMemberDef[]`. This happens when the `Py_ARRAY_LENGTH` macro is used on `pystatx_result_members`, indicating that the array's definition was not completed due to the initial error.\n\nThis suggests that the feature detection or conditional compilation logic for the `stx_atomic_write_unit_max_opt` member is not functioning correctly under this specific build configuration.\n\n**Steps to Reproduce:**\n1.  Check out the `main` branch of cpython.\n2.  Configure the build with the following command:\n    ```sh\n    CC=clang CXX=clang++ ./configure --with-thread-sanitizer --with-pydebug --disable-gil\n    ```\n3.  Run the build:\n    ```sh\n    make\n    ```\n\n**Expected Behavior:**\nThe build process should complete successfully.\n\n**Actual Behavior:**\nThe build fails with the following errors logged from `Modules/posixmodule.c`:\n\n```\n../Modules/posixmodule.c:3369:5: error: no member named 'stx_atomic_write_unit_max_opt' in 'statx'\n3369 |     MM(stx_atomic_write_unit_max_opt, Py_T_UINT, atomic_write_unit_max_opt,\n|     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n3370 |         \"maximum optimized size for direct I/O with torn-write protection\"),\n|         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n./Modules/posixmodule.c:3325:20: note: expanded from macro 'MM'\n3325 |     M(#attr, type, offsetof(Py_statx_result, stx.stx_##member), doc)\n|     ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n/usr/lib/llvm-20/lib/clang/20/include/__stddef_offsetof.h:16:24: note: expanded from macro 'offsetof'\n16 | #define offsetof(t, d) __builtin_offsetof(t, d)\n|                        ^\n./Modules/posixmodule.c:3323:18: note: expanded from macro 'M'\n3323 |     {attr, type, offset, Py_READONLY, PyDoc_STR(doc)}\n|                  ^~~~~~\n./Modules/posixmodule.c:3427:28: error: invalid application of 'sizeof' to an incomplete type 'PyMemberDef[]' (aka 'struct PyMemberDef[]')\n3427 |     for (size_t i = 0; i \u003c Py_ARRAY_LENGTH(pystatx_result_members) - 1; ++i) {\n|                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n./Include/pymacro.h:190:12: note: expanded from macro 'Py_ARRAY_LENGTH'\n190 |     (sizeof(array) / sizeof((array)[0]))\n|            ^~~~~~~\n./Modules/posixmodule.c:3447:9: error: invalid application of 'sizeof' to an incomplete type 'PyMemberDef[]' (aka 'struct PyMemberDef[]')\n3447 |     if (Py_ARRAY_LENGTH(pystatx_result_members) \u003e 1\n|         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n./Include/pymacro.h:190:12: note: expanded from macro 'Py_ARRAY_LENGTH'\n190 |     (sizeof(array) / sizeof((array)[0]))\n|            ^~~~~~~\n```\n\n**Environment:**\n*   **Compiler:** Clang\n*   **Configuration Flags:** `--with-thread-sanitizer --with-pydebug --disable-gil`","author":{"url":"https://github.com/ashm-dev","@type":"Person","name":"ashm-dev"},"datePublished":"2025-10-15T14:06:11.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/140159/cpython/issues/140159"}