bpo-46913: Fix test_faulthandler.test_read_null() on UBSan (GH31672)

Disable undefined behavior sanitizer (UBSan) on
faulthandler._read_null().

Author: vstinner

Modules/faulthandler.c

@@ -32,6 +32,23 @@
 
 #define PUTS(fd, str) _Py_write_noraise(fd, str, strlen(str))
 
+
+// clang uses __attribute__((no_sanitize("undefined")))
+// GCC 4.9+ uses __attribute__((no_sanitize_undefined))
+#if defined(__has_feature)  // Clang
+#  if __has_feature(undefined_behavior_sanitizer)
+#    define _Py_NO_SANITIZE_UNDEFINED __attribute__((no_sanitize("undefined")))
+#  endif
+#endif
+#if defined(__GNUC__) \
+    && ((__GNUC__ >= 5) || (__GNUC__ == 4) && (__GNUC_MINOR__ >= 9))
+#  define _Py_NO_SANITIZE_UNDEFINED __attribute__((no_sanitize_undefined))
+#endif
+#ifndef _Py_NO_SANITIZE_UNDEFINED
+#  define _Py_NO_SANITIZE_UNDEFINED
+#endif
+
+
 #ifdef HAVE_SIGACTION
 typedef struct sigaction _Py_sighandler_t;
 #else
@@ -1013,7 +1030,7 @@ faulthandler_suppress_crash_report(void)
 #endif
 }
 
-static PyObject *
+static PyObject* _Py_NO_SANITIZE_UNDEFINED
 faulthandler_read_null(PyObject *self, PyObject *args)
 {
     volatile int *x;
@@ -1102,21 +1119,6 @@ faulthandler_fatal_error_c_thread(PyObject *self, PyObject *args)
     Py_RETURN_NONE;
 }
 
-// clang uses __attribute__((no_sanitize("undefined")))
-// GCC 4.9+ uses __attribute__((no_sanitize_undefined))
-#if defined(__has_feature)  // Clang
-#  if __has_feature(undefined_behavior_sanitizer)
-#    define _Py_NO_SANITIZE_UNDEFINED __attribute__((no_sanitize("undefined")))
-#  endif
-#endif
-#if defined(__GNUC__) \
-    && ((__GNUC__ >= 5) || (__GNUC__ == 4) && (__GNUC_MINOR__ >= 9))
-#  define _Py_NO_SANITIZE_UNDEFINED __attribute__((no_sanitize_undefined))
-#endif
-#ifndef _Py_NO_SANITIZE_UNDEFINED
-#  define _Py_NO_SANITIZE_UNDEFINED
-#endif
-
 static PyObject* _Py_NO_SANITIZE_UNDEFINED
 faulthandler_sigfpe(PyObject *self, PyObject *args)
 {