STINNER Victor <vstin...@redhat.com> added the comment:
PyGC_Head structure size depends on the Python version, sizes of 64-bit: * 2.7: 32 bytes * 3.6, 3.7: 24 bytes * 3.8 (master): 16 bytes bpo-36618 "clang expects memory aligned on 16 bytes, but pymalloc aligns to 8 bytes" should be even worse on 3.7: 24 is not aligned on 16. I don't understand why nobody saw this alignment issue previously. Maybe clang only became stricer about 16 bytes alignment recently? 2.7: typedef union _gc_head { struct { union _gc_head *gc_next; union _gc_head *gc_prev; Py_ssize_t gc_refs; } gc; double dummy; /* Force at least 8-byte alignment. */ char dummy_padding[sizeof(union _gc_head_old)]; } PyGC_Head; 3.7: typedef union _gc_head { struct { union _gc_head *gc_next; union _gc_head *gc_prev; Py_ssize_t gc_refs; } gc; double dummy; /* force worst-case alignment */ } PyGC_Head; 3.8: typedef struct { // Pointer to next object in the list. // 0 means the object is not tracked uintptr_t _gc_next; // Pointer to previous object in the list. // Lowest two bits are used for flags documented later. uintptr_t _gc_prev; } PyGC_Head; In 3.8, the union used to ensure alignment on a C double is gone. ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue27987> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com