bpo-37169: Rewrite _PyObject_IsFreed() unit tests (GH-13888)

Replace two Python function calls with a single one to ensure that no
memory allocation is done between the invalid object is created and
when _PyObject_IsFreed() is called.

Author: vstinner

Lib/test/test_capi.py

@@ -705,28 +705,29 @@ def test_pyobject_malloc_without_gil(self):
         code = 'import _testcapi; _testcapi.pyobject_malloc_without_gil()'
         self.check_malloc_without_gil(code)
 
-    def check_pyobject_is_freed(self, func):
-        code = textwrap.dedent('''
+    def check_pyobject_is_freed(self, func_name):
+        code = textwrap.dedent(f'''
             import gc, os, sys, _testcapi
             # Disable the GC to avoid crash on GC collection
             gc.disable()
-            obj = _testcapi.{func}()
-            error = (_testcapi.pyobject_is_freed(obj) == False)
-            # Exit immediately to avoid a crash while deallocating
-            # the invalid object
-            os._exit(int(error))
+            try:
+                _testcapi.{func_name}()
+                # Exit immediately to avoid a crash while deallocating
+                # the invalid object
+                os._exit(0)
+            except _testcapi.error:
+                os._exit(1)
         ''')
-        code = code.format(func=func)
         assert_python_ok('-c', code, PYTHONMALLOC=self.PYTHONMALLOC)
 
-    def test_pyobject_is_freed_uninitialized(self):
-        self.check_pyobject_is_freed('pyobject_uninitialized')
+    def test_pyobject_uninitialized_is_freed(self):
+        self.check_pyobject_is_freed('check_pyobject_uninitialized_is_freed')
 
-    def test_pyobject_is_freed_forbidden_bytes(self):
-        self.check_pyobject_is_freed('pyobject_forbidden_bytes')
+    def test_pyobject_forbidden_bytes_is_freed(self):
+        self.check_pyobject_is_freed('check_pyobject_forbidden_bytes_is_freed')
 
-    def test_pyobject_is_freed_free(self):
-        self.check_pyobject_is_freed('pyobject_freed')
+    def test_pyobject_freed_is_freed(self):
+        self.check_pyobject_is_freed('check_pyobject_freed_is_freed')
 
 
 class PyMemMallocDebugTests(PyMemDebugTests):

Misc/NEWS.d/next/Tests/2019-06-07-12-23-15.bpo-37169.yfXTFg.rst

@@ -0,0 +1 @@
+Rewrite ``_PyObject_IsFreed()`` unit tests.

Modules/_testcapimodule.c

@@ -4489,15 +4489,17 @@ test_pymem_getallocatorsname(PyObject *self, PyObject *args)
 
 
 static PyObject*
-pyobject_is_freed(PyObject *self, PyObject *op)
+test_pyobject_is_freed(const char *test_name, PyObject *op)
 {
-    int res = _PyObject_IsFreed(op);
-    return PyBool_FromLong(res);
+    if (!_PyObject_IsFreed(op)) {
+        return raiseTestError(test_name, "object is not seen as freed");
+    }
+    Py_RETURN_NONE;
 }
 
 
 static PyObject*
-pyobject_uninitialized(PyObject *self, PyObject *args)
+check_pyobject_uninitialized_is_freed(PyObject *self, PyObject *Py_UNUSED(args))
 {
     PyObject *op = (PyObject *)PyObject_Malloc(sizeof(PyObject));
     if (op == NULL) {
@@ -4506,12 +4508,12 @@ pyobject_uninitialized(PyObject *self, PyObject *args)
     /* Initialize reference count to avoid early crash in ceval or GC */
     Py_REFCNT(op) = 1;
     /* object fields like ob_type are uninitialized! */
-    return op;
+    return test_pyobject_is_freed("check_pyobject_uninitialized_is_freed", op);
 }
 
 
 static PyObject*
-pyobject_forbidden_bytes(PyObject *self, PyObject *args)
+check_pyobject_forbidden_bytes_is_freed(PyObject *self, PyObject *Py_UNUSED(args))
 {
     /* Allocate an incomplete PyObject structure: truncate 'ob_type' field */
     PyObject *op = (PyObject *)PyObject_Malloc(offsetof(PyObject, ob_type));
@@ -4522,12 +4524,12 @@ pyobject_forbidden_bytes(PyObject *self, PyObject *args)
     Py_REFCNT(op) = 1;
     /* ob_type field is after the memory block: part of "forbidden bytes"
        when using debug hooks on memory allocatrs! */
-    return op;
+    return test_pyobject_is_freed("check_pyobject_forbidden_bytes_is_freed", op);
 }
 
 
 static PyObject*
-pyobject_freed(PyObject *self, PyObject *args)
+check_pyobject_freed_is_freed(PyObject *self, PyObject *Py_UNUSED(args))
 {
     PyObject *op = _PyObject_CallNoArg((PyObject *)&PyBaseObject_Type);
     if (op == NULL) {
@@ -4537,7 +4539,7 @@ pyobject_freed(PyObject *self, PyObject *args)
     /* Reset reference count to avoid early crash in ceval or GC */
     Py_REFCNT(op) = 1;
     /* object memory is freed! */
-    return op;
+    return test_pyobject_is_freed("check_pyobject_freed_is_freed", op);
 }
 
 
@@ -5264,10 +5266,9 @@ static PyMethodDef TestMethods[] = {
     {"pymem_api_misuse", pymem_api_misuse, METH_NOARGS},
     {"pymem_malloc_without_gil", pymem_malloc_without_gil, METH_NOARGS},
     {"pymem_getallocatorsname", test_pymem_getallocatorsname, METH_NOARGS},
-    {"pyobject_is_freed", (PyCFunction)(void(*)(void))pyobject_is_freed, METH_O},
-    {"pyobject_uninitialized", pyobject_uninitialized, METH_NOARGS},
-    {"pyobject_forbidden_bytes", pyobject_forbidden_bytes, METH_NOARGS},
-    {"pyobject_freed", pyobject_freed, METH_NOARGS},
+    {"check_pyobject_uninitialized_is_freed", check_pyobject_uninitialized_is_freed, METH_NOARGS},
+    {"check_pyobject_forbidden_bytes_is_freed", check_pyobject_forbidden_bytes_is_freed, METH_NOARGS},
+    {"check_pyobject_freed_is_freed", check_pyobject_freed_is_freed, METH_NOARGS},
     {"pyobject_malloc_without_gil", pyobject_malloc_without_gil, METH_NOARGS},
     {"tracemalloc_track", tracemalloc_track, METH_VARARGS},
     {"tracemalloc_untrack", tracemalloc_untrack, METH_VARARGS},