Experiment: Save native frame pointer in entry frame.

Author: markshannon

Python/ceval.c

@@ -817,6 +817,8 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
     entry_frame.f_globals = (PyObject*)0xaaa3;
     entry_frame.f_builtins = (PyObject*)0xaaa4;
 #endif
+    /* Store C frame pointer -- for debuggers */
+    entry_frame.frame_obj = (PyFrameObject*)__builtin_frame_address(0);
     entry_frame.f_executable = PyStackRef_None;
     entry_frame.instr_ptr = (_Py_CODEUNIT *)_Py_INTERPRETER_TRAMPOLINE_INSTRUCTIONS + 1;
     entry_frame.stackpointer = entry_frame.localsplus;