Stackless issue #249: Mitigate usage of PEP 523 frame evaluation API

Stackless does not support custom frame evaluation functions defined by
PEP 523. If an extension module sets a custom frame evaluation function,
Stackless now terminates to prevent undefined behavior.

(cherry picked from commit d57b317)

Author: Anselm Kruis

Python/ceval.c

@@ -4071,6 +4071,16 @@ PyEval_EvalFrameEx_slp(PyFrameObject *f, int throwflag, PyObject *retval)
 {
     PyThreadState *tstate = PyThreadState_GET();
 
+    /* Check, if an extension module has changed tstate->interp->eval_frame.
+     * PEP 523 defines this function pointer as an API to customise the frame
+     * evaluation. Stackless can not support this API. In order to prevent
+     * undefined behavior, we terminate the interpreter.
+     */
+    if (tstate->interp->eval_frame != _PyEval_EvalFrameDefault)
+        Py_FatalError("An extension module has set a custom frame evaluation function (see PEP 523).\n"
+                      "Stackless Python does not support the frame evaluation API defined by PEP 523.\n"
+                      "The programm now terminates to prevent undefined behavior.\n");
+
     /* Start of code, similar to non stackless
      * PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
      */

Stackless/changelog.txt

@@ -9,6 +9,11 @@ What's New in Stackless 3.X.X?
 
 *Release date: 20XX-XX-XX*
 
+- https://github.com/stackless-dev/stackless/issues/249
+  Stackless does not support custom frame evaluation functions defined by
+  PEP 523. If an extension module sets a custom frame evaluation function,
+  Stackless now terminates to prevent undefined behavior.
+
 - https://github.com/stackless-dev/stackless/issues/248
   Documentation update: Mention, that module "stackless" must be imported, to
   enable the extended pickling capabilities.