Stackless issue python#168: make Stackless compatible with old Cython modules

Add another test case for a pathological situation.

Author: Anselm Kruis

Python/ceval.c

@@ -4052,7 +4052,9 @@ _PyEval_EvalFrameDefault(PyFrameObject *f, int throwflag)
             /* and (&(f->f_code))[-1] looks like a valid code object */
             (&(f->f_code))[-1] && PyCode_Check((&(f->f_code))[-1]) &&
             /* and there are arguments */
-            (&(f->f_code))[-1]->co_argcount > 0)
+            (&(f->f_code))[-1]->co_argcount > 0 &&
+            /* the last argument is NULL */
+            f->f_localsplus[(&(f->f_code))[-1]->co_argcount - 1] == NULL)
         {
             PyCodeObject * code = (&(f->f_code))[-1];
             memmove(f->f_localsplus, f->f_localsplus-1, code->co_argcount * sizeof(f->f_localsplus[0]));

Stackless/module/stacklessmodule.c

@@ -1131,9 +1131,10 @@ by Stackless Python.\n\
 The function creates a frame from code, globals and args and executes the frame.");
 
 static PyObject* test_PyEval_EvalFrameEx(PyObject *self, PyObject *args, PyObject *kwds) {
-    static char *kwlist[] = {"code", "globals", "args", "alloca", "throw", "oldcython", NULL};
+    static char *kwlist[] = {"code", "globals", "args", "alloca", "throw", "oldcython",
+                             "code2", NULL};
     PyThreadState *tstate = PyThreadState_GET();
-    PyCodeObject *co;
+    PyCodeObject *co, *code2 = NULL;
     PyObject *globals, *co_args = NULL;
     Py_ssize_t alloca_size = 0;
     PyObject *exc = NULL;
@@ -1143,9 +1144,9 @@ static PyObject* test_PyEval_EvalFrameEx(PyObject *self, PyObject *args, PyObjec
     void *p;
     Py_ssize_t na;
 
-    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O!O!|O!nOO!:test_PyEval_EvalFrameEx", kwlist,
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O!O!|O!nOO!O!:test_PyEval_EvalFrameEx", kwlist,
             &PyCode_Type, &co, &PyDict_Type, &globals, &PyTuple_Type, &co_args, &alloca_size,
-            &exc, &PyBool_Type, &oldcython))
+            &exc, &PyBool_Type, &oldcython, &PyCode_Type, &code2))
         return NULL;
     if (exc && !PyExceptionInstance_Check(exc)) {
         PyErr_SetString(PyExc_TypeError, "exc must be an exception instance");
@@ -1198,6 +1199,10 @@ static PyObject* test_PyEval_EvalFrameEx(PyObject *self, PyObject *args, PyObjec
     if (exc) {
         PyErr_SetObject(PyExceptionInstance_Class(exc), exc);
     }
+    if (code2) {
+        Py_INCREF(code2);
+        Py_SETREF(f->f_code, code2);
+    }
     result = PyEval_EvalFrameEx(f, exc != NULL);
     /* result = Py_None; Py_INCREF(Py_None); */
 exit:

Stackless/unittests/test_capi.py

@@ -31,7 +31,8 @@
 import unittest
 
 from support import test_main  # @UnusedImport
-from support import StacklessTestCase, withThreads, require_one_thread
+from support import (StacklessTestCase, withThreads, require_one_thread,
+                     testcase_leaks_references)
 
 if withThreads:
     try:
@@ -165,7 +166,7 @@ def test_oldcython_frame(self):
         # A test for Stackless issue #168
         self.assertEqual(self.call_PyEval_EvalFrameEx(47110816, oldcython=True), 47110816)
 
-    def test_oldcython_frame_code_is_1st_arg(self):
+    def test_oldcython_frame_code_is_1st_arg_good(self):
         # A pathological test for Stackless issue #168
         def f(code):
             return code
@@ -175,13 +176,30 @@ def f2(code):
 
         self.assertIs(stackless.test_PyEval_EvalFrameEx(f.__code__, f.__globals__, (f.__code__,), oldcython=False), f.__code__)
         self.assertIs(stackless.test_PyEval_EvalFrameEx(f.__code__, f.__globals__, (f2.__code__,), oldcython=True), f2.__code__)
+
+    @testcase_leaks_references("f->f_code get overwritten without Py_DECREF")
+    def test_oldcython_frame_code_is_1st_arg_bad(self):
+        # A pathological test for Stackless issue #168
+        def f(code):
+            return code
+
         # we can't fix this particular case:
         #  - running code object is its 1st arg and
         #  - oldcython=True,
         # because a fix would result in a segmentation fault, if the number of
         # arguments is to low (test case test_0_args)
         self.assertRaises(UnboundLocalError, stackless.test_PyEval_EvalFrameEx, f.__code__, f.__globals__, (f.__code__,), oldcython=True)
 
+    def test_other_code_object(self):
+        # A pathological test for Stackless issue #168
+        def f(arg):
+            return arg
+
+        def f2(arg):
+            return arg
+
+        self.assertIs(stackless.test_PyEval_EvalFrameEx(f.__code__, f.__globals__, (f2,), code2=f2.__code__), f2)
+
 
 if __name__ == "__main__":
     if not sys.argv[1:]: