Don't expose incomplete frames as frame objects.

Author: markshannon

Include/internal/pycore_frame.h

@@ -210,6 +210,13 @@ PyGenObject *_PyFrame_GetGenerator(_PyInterpreterFrame *frame)
     return (PyGenObject *)(((char *)frame) - offset_in_gen);
 }
 
+
+static inline bool
+_PyFrame_IsIncomplete(_PyInterpreterFrame *frame)
+{
+    return frame->prev_instr < _PyCode_CODE(frame->f_code) + frame->f_code->_co_firsttraceable;
+}
+
 #ifdef __cplusplus
 }
 #endif

Python/frame.c

@@ -68,9 +68,13 @@ take_ownership(PyFrameObject *f, _PyInterpreterFrame *frame)
     f->f_frame = frame;
     frame->owner = FRAME_OWNED_BY_FRAME_OBJECT;
     assert(f->f_back == NULL);
-    if (frame->previous != NULL) {
+    _PyInterpreterFrame *prev = frame->previous;
+    while (prev && _PyFrame_IsIncomplete(prev)) {
+        prev = prev->previous;
+    }
+    if (prev) {
         /* Link PyFrameObjects.f_back and remove link through _PyInterpreterFrame.previous */
-        PyFrameObject *back = _PyFrame_GetFrameObject(frame->previous);
+        PyFrameObject *back = _PyFrame_GetFrameObject(prev);
         if (back == NULL) {
             /* Memory error here. */
             assert(PyErr_ExceptionMatches(PyExc_MemoryError));

Python/sysmodule.c

@@ -1776,9 +1776,17 @@ sys__getframe_impl(PyObject *module, int depth)
         return NULL;
     }
 
-    while (depth > 0 && frame != NULL) {
-        frame = frame->previous;
-        --depth;
+    if (frame != NULL) {
+        while (depth > 0) {
+            frame = frame->previous;
+            if (frame == NULL) {
+                break;
+            }
+            if (_PyFrame_IsIncomplete(frame)) {
+                continue;
+            }
+            --depth;
+        }
     }
     if (frame == NULL) {
         _PyErr_SetString(tstate, PyExc_ValueError,