GH-125868: Fix STORE_ATTR_WITH_HINT specialization

Lib/dis.py

@@ -778,8 +778,10 @@ def _get_instructions_bytes(code, linestarts=None, line_offset=0, co_positions=N
 
         if caches:
             cache_info = []
+            cache_offset = offset
             for name, size in _cache_format[opname[deop]].items():
-                data = code[offset + 2: offset + 2 + 2 * size]
+                data = code[cache_offset + 2: cache_offset + 2 + 2 * size]
+                cache_offset += size * 2
                 cache_info.append((name, size, data))
         else:
             cache_info = None

Lib/test/test_opcache.py

@@ -1155,6 +1155,50 @@ class D(dict): pass
             {'a':1, 'b':2}
         )
 
+    def test_125868(self):
+
+        def make_special_dict():
+            """Create a dictionary an object with a this table:
+            index | key | value
+            ----- | --- | -----
+              0   | 'b' | 'value'
+              1   | 'b' | NULL
+            """
+            class A:
+                pass
+            a = A()
+            a.a = 1
+            a.b = 2
+            d = a.__dict__.copy()
+            del d['a']
+            del d['b']
+            d['b'] = "value"
+            return d
+
+        class NoInlineAorB:
+            pass
+        for i in range(ord('c'), ord('z')):
+            setattr(NoInlineAorB(), chr(i), i)
+
+        c = NoInlineAorB()
+        c.a = 0
+        c.b = 1
+        self.assertFalse(_testinternalcapi.has_inline_values(c))
+
+        def f(o, n):
+            for i in range(n):
+                o.b = i
+        # Prime f to store to dict slot 1
+        f(c, 100)
+
+        test_obj = NoInlineAorB()
+        test_obj.__dict__ = make_special_dict()
+        self.assertEqual(test_obj.b, "value")
+
+        #This should set x.b = 0
+        f(test_obj, 1)
+        self.assertEqual(test_obj.b, 0)
+
 
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Core_and_Builtins/2024-10-23-14-05-47.gh-issue-125868.uLfXYB.rst

@@ -0,0 +1,3 @@
+It was possible in 3.14.0a1 only for attribute lookup to give the wrong
+value. This was due to an incorrect specialization in very specific
+circumstances. This is fixed in 3.14.0a2.

Python/bytecodes.c

@@ -2303,17 +2303,16 @@ dummy_func(
             assert(PyDict_CheckExact((PyObject *)dict));
             PyObject *name = GETITEM(FRAME_CO_NAMES, oparg);
             DEOPT_IF(hint >= (size_t)dict->ma_keys->dk_nentries);
-            PyObject *old_value;
             DEOPT_IF(!DK_IS_UNICODE(dict->ma_keys));
             PyDictUnicodeEntry *ep = DK_UNICODE_ENTRIES(dict->ma_keys) + hint;
             DEOPT_IF(ep->me_key != name);
+            PyObject *old_value = ep->me_value;
+            DEOPT_IF(old_value == NULL);
             /* Ensure dict is GC tracked if it needs to be */
             if (!_PyObject_GC_IS_TRACKED(dict) && _PyObject_GC_MAY_BE_TRACKED(PyStackRef_AsPyObjectBorrow(value))) {
                 _PyObject_GC_TRACK(dict);
             }
-            old_value = ep->me_value;
-            PyDict_WatchEvent event = old_value == NULL ? PyDict_EVENT_ADDED : PyDict_EVENT_MODIFIED;
-            _PyDict_NotifyEvent(tstate->interp, event, dict, name, PyStackRef_AsPyObjectBorrow(value));
+            _PyDict_NotifyEvent(tstate->interp, PyDict_EVENT_MODIFIED, dict, name, PyStackRef_AsPyObjectBorrow(value));
             ep->me_value = PyStackRef_AsPyObjectSteal(value);
             // old_value should be DECREFed after GC track checking is done, if not, it could raise a segmentation fault,
             // when dict only holds the strong reference to value in ep->me_value.