Work around lack of alignof & max_align_t

encukou · encukou · commit 291731b60fcf · 2023-04-19T14:49:11.000+02:00
diff --git a/Modules/_testcapi/heaptype_relative.c b/Modules/_testcapi/heaptype_relative.c
@@ -262,7 +262,13 @@ _PyTestCapi_Init_HeaptypeRelative(PyObject *m) {
         return -1;
     }
 
+#ifdef __alignof_is_defined
+    // C11
     PyModule_AddIntConstant(m, "alignof_max_align_t", alignof(max_align_t));
+#else
+    // if alignof and max_align_t is unavailable, skip the alignment tests
+    PyModule_AddIntConstant(m, "alignof_max_align_t", 1);
+#endif
 
     return 0;
 }
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
@@ -3553,10 +3553,22 @@ static const PySlot_Offset pyslot_offsets[] = {
 /* Align up to the nearest multiple of alignof(max_align_t)
  * (like _Py_ALIGN_UP, but for a size rather than pointer)
  */
+#if __alignof_is_defined
+    // C11
+    #define MAX_ALIGN alignof(max_align_t)
+#else
+    // workaround for MSVC
+    typedef union {
+        intmax_t x;
+        long double y;
+        void *z;
+        void (*f)();
+    } _max_align_t_wannabe;
+    #define MAX_ALIGN _Alignof(_max_align_t_wannabe)
+#endif
 static Py_ssize_t
 _align_up(Py_ssize_t size) {
-    const Py_ssize_t alignment = alignof(max_align_t);
-    return (size + alignment - 1) & ~(alignment - 1);
+    return (size + MAX_ALIGN - 1) & ~(MAX_ALIGN - 1);
 }
 
 /* Given a PyType_FromMetaclass `bases` argument (NULL, type, or tuple of

Original file line number	Diff line number	Diff line change
`@@ -262,7 +262,13 @@ _PyTestCapi_Init_HeaptypeRelative(PyObject *m) {`
`262`	`262`	`return -1;`
`263`	`263`	`}`
`264`	`264`
	`265`	`+#ifdef __alignof_is_defined`
	`266`	`+ // C11`
`265`	`267`	`PyModule_AddIntConstant(m, "alignof_max_align_t", alignof(max_align_t));`
	`268`	`+#else`
	`269`	`+ // if alignof and max_align_t is unavailable, skip the alignment tests`
	`270`	`+ PyModule_AddIntConstant(m, "alignof_max_align_t", 1);`
	`271`	`+#endif`
`266`	`272`
`267`	`273`	`return 0;`
`268`	`274`	`}`