Move initialization of frame->previous to init_frame.

Use self.assertEquals instead of assert.
python · kumaraditya303 · Dec 23, 2022 · Dec 12, 2022 · Dec 12, 2022 · Dec 12, 2022
commit d6797833bcb0fb6195de0fb23b4c2643122af69f
diff --git a/Include/internal/pycore_frame.h b/Include/internal/pycore_frame.h
@@ -109,10 +109,10 @@ _PyFrame_InitializeSpecials(
     frame->f_locals = locals;
     frame->stacktop = code->co_nlocalsplus;
     frame->frame_obj = NULL;
-    frame->previous = NULL;
     frame->prev_instr = _PyCode_CODE(code) - 1;
     frame->yield_offset = 0;
     frame->owner = FRAME_OWNED_BY_THREAD;
+    // frame->previous: initialized when frame is linked into the frame stack
 }
 
 /* Gets the pointer to the locals array

diff --git a/Lib/test/test_ctypes/test_python_api.py b/Lib/test/test_ctypes/test_python_api.py
@@ -109,7 +109,7 @@ def dummy():
         )
 
         # The following line should not cause a segmentation fault.
-        assert frame.f_back is None
+        self.assertEqual(frame.f_back, None)
 
 
 if __name__ == "__main__":

diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-12-12-01-05-16.gh-issue-99110.1JqtIg.rst b/Misc/NEWS.d/next/Core and Builtins/2022-12-12-01-05-16.gh-issue-99110.1JqtIg.rst
@@ -1 +1,2 @@
-Initialize frame->previous in _PyFrame_InitializeSpecials.
+Initialize frame->previous in frameobject.c to fix a segmentation fault when
+accessing frames created by ctypes.
@@ -1013,6 +1013,7 @@ init_frame(_PyInterpreterFrame *frame, PyFunctionObject *func, PyObject *locals)
     PyCodeObject *code = (PyCodeObject *)func->func_code;
     _PyFrame_InitializeSpecials(frame, (PyFunctionObject*)Py_NewRef(func),
                                 Py_XNewRef(locals), code);
+    frame->previous = NULL;
     for (Py_ssize_t i = 0; i < code->co_nlocalsplus; i++) {
         frame->localsplus[i] = NULL;
     }