Add ALIGNOF_MAX_ALIGN_T to configure & PC/pyconfig.h

Include/pyport.h

@@ -745,4 +745,10 @@ extern char * _getpty(int *, int, mode_t, int);
 #undef __bool__
 #endif
 
+// Make sure we have alignof(max_align_t)
+// (autoconf report alignment of unknown types to 0)
+#if ALIGNOF_MAX_ALIGN_T <= 0
+#error "ALIGNOF_MAX_ALIGN_T must be positive"
+#endif
+
 #endif /* Py_PYPORT_H */

Modules/_testcapi/heaptype_relative.c

@@ -249,10 +249,28 @@ make_heaptype_with_member(PyObject *module, PyObject *args)
 }
 
 
+static PyObject *
+test_alignof_max_align_t(PyObject *module, PyObject *Py_UNUSED(ignored))
+{
+    // We define ALIGNOF_MAX_ALIGN_T even if the compiler doesn't have
+    // max_afign_t. Double-check that it's correct.
+    assert(ALIGNOF_MAX_ALIGN_T > 0);
+    assert(ALIGNOF_MAX_ALIGN_T >= _Alignof(long long));
+    assert(ALIGNOF_MAX_ALIGN_T >= _Alignof(long double));
+    assert(ALIGNOF_MAX_ALIGN_T >= _Alignof(void*));
+    assert(ALIGNOF_MAX_ALIGN_T >= _Alignof(void (*)(void)));
+
+    // Ensure it's a power of two
+    assert((ALIGNOF_MAX_ALIGN_T & (ALIGNOF_MAX_ALIGN_T - 1)) == 0);
+
+    Py_RETURN_NONE;
+}
+
 static PyMethodDef TestMethods[] = {
     {"make_sized_heaptypes", make_sized_heaptypes, METH_VARARGS},
     {"subclass_var_heaptype", subclass_var_heaptype, METH_VARARGS},
     {"make_heaptype_with_member", make_heaptype_with_member, METH_VARARGS},
+    {"test_alignof_max_align_t", test_alignof_max_align_t, METH_NOARGS},
     {NULL},
 };
 

PC/pyconfig.h

@@ -330,6 +330,7 @@ Py_NO_ENABLE_SHARED to find out.  Also support MS_NO_COREDLL for b/w compat */
 #       define SIZEOF_HKEY 8
 #       define SIZEOF_SIZE_T 8
 #       define ALIGNOF_SIZE_T 8
+#       define ALIGNOF_MAX_ALIGN_T 8
 /* configure.ac defines HAVE_LARGEFILE_SUPPORT iff
    sizeof(off_t) > sizeof(long), and sizeof(long long) >= sizeof(off_t).
    On Win64 the second condition is not true, but if fpos_t replaces off_t
@@ -351,6 +352,7 @@ Py_NO_ENABLE_SHARED to find out.  Also support MS_NO_COREDLL for b/w compat */
 #       else
 #       define SIZEOF_TIME_T 4
 #       endif
+#       define ALIGNOF_MAX_ALIGN_T 4
 #endif
 
 #ifdef _DEBUG

configure.ac

@@ -2914,6 +2914,7 @@ AC_CHECK_SIZEOF(size_t, 4)
 AC_CHECK_ALIGNOF(size_t)
 AC_CHECK_SIZEOF(pid_t, 4)
 AC_CHECK_SIZEOF(uintptr_t)
+AC_CHECK_ALIGNOF(max_align_t)
 
 AC_TYPE_LONG_DOUBLE
 AC_CHECK_SIZEOF(long double, 16)

pyconfig.h.in

@@ -19,6 +19,9 @@
 /* The normal alignment of `long', in bytes. */
 #undef ALIGNOF_LONG
 
+/* The normal alignment of `max_align_t', in bytes. */
+#undef ALIGNOF_MAX_ALIGN_T
+
 /* The normal alignment of `size_t', in bytes. */
 #undef ALIGNOF_SIZE_T