gh-152666: Avoid reference counting of code objects

Include/cpython/funcobject.h

@@ -43,6 +43,7 @@ typedef struct {
     PyObject *func_annotations; /* Annotations, a dict or NULL */
     PyObject *func_annotate;    /* Callable to fill the annotations dictionary */
     PyObject *func_typeparams;  /* Tuple of active type variables or NULL */
+    PyObject *func_old_codes;   /* List of past code objects or NULL */
     vectorcallfunc vectorcall;
     /* Version number for use by specializer.
      * Can set to non-zero when we want to specialize.

Include/internal/pycore_interpframe.h

@@ -18,10 +18,9 @@ extern "C" {
     ((int)((IF)->instr_ptr - _PyFrame_GetBytecode((IF))))
 
 static inline PyCodeObject *_PyFrame_GetCode(_PyInterpreterFrame *f) {
-    assert(!PyStackRef_IsNull(f->f_executable));
-    PyObject *executable = PyStackRef_AsPyObjectBorrow(f->f_executable);
-    assert(PyCode_Check(executable));
-    return (PyCodeObject *)executable;
+    assert(f->f_executable != NULL);
+    assert(PyCode_Check(f->f_executable));
+    return (PyCodeObject *)f->f_executable;
 }
 
 // Similar to _PyFrame_GetCode(), but return NULL if the frame is invalid or
@@ -36,15 +35,15 @@ _PyFrame_SafeGetCode(_PyInterpreterFrame *f)
         return NULL;
     }
 
-    if (PyStackRef_IsNull(f->f_executable)) {
+    if (f->f_executable == NULL) {
         return NULL;
     }
     void *ptr;
     memcpy(&ptr, &f->f_executable, sizeof(f->f_executable));
     if (_PyMem_IsPtrFreed(ptr)) {
         return NULL;
     }
-    PyObject *executable = PyStackRef_AsPyObjectBorrow(f->f_executable);
+    PyObject *executable = f->f_executable;
     if (_PyObject_IsFreed(executable)) {
         return NULL;
     }
@@ -132,7 +131,7 @@ _PyFrame_NumSlotsForCodeObject(PyCodeObject *code)
 
 static inline void _PyFrame_Copy(_PyInterpreterFrame *src, _PyInterpreterFrame *dest)
 {
-    dest->f_executable = PyStackRef_MakeHeapSafe(src->f_executable);
+    dest->f_executable = src->f_executable;
     // Don't leave a dangling pointer to the old frame when creating generators
     // and coroutines:
     dest->previous = NULL;
@@ -191,7 +190,7 @@ _PyFrame_Initialize(
 {
     frame->previous = previous;
     frame->f_funcobj = func;
-    frame->f_executable = PyStackRef_FromPyObjectNew(code);
+    frame->f_executable = (PyObject *)code;
     PyFunctionObject *func_obj = (PyFunctionObject *)PyStackRef_AsPyObjectBorrow(func);
     frame->f_builtins = func_obj->func_builtins;
     frame->f_globals = func_obj->func_globals;
@@ -424,7 +423,7 @@ _PyFrame_PushTrampolineUnchecked(PyThreadState *tstate, PyCodeObject *code, int
     assert(tstate->datastack_top < tstate->datastack_limit);
     frame->previous = previous;
     frame->f_funcobj = PyStackRef_None;
-    frame->f_executable = PyStackRef_FromPyObjectNew(code);
+    frame->f_executable = (PyObject *)code;
 #ifdef Py_DEBUG
     frame->f_builtins = NULL;
     frame->f_globals = NULL;

Include/internal/pycore_interpframe_structs.h

@@ -27,7 +27,7 @@ enum _frameowner {
 };
 
 struct _PyInterpreterFrame {
-    _PyStackRef f_executable; /* Deferred or strong reference (code object or None) */
+    PyObject *f_executable; /* Borrowed reference (code object or None) */
     struct _PyInterpreterFrame *previous;
     _PyStackRef f_funcobj; /* Deferred or strong reference. Only valid if not on C stack */
     PyObject *f_globals; /* Borrowed reference. Only valid if not on C stack */

Include/internal/pycore_stackref.h

@@ -770,7 +770,6 @@ PyStackRef_TYPE(_PyStackRef stackref) {
 STACKREF_CHECK_FUNC(Gen)
 STACKREF_CHECK_FUNC(Bool)
 STACKREF_CHECK_FUNC(ExceptionInstance)
-STACKREF_CHECK_FUNC(Code)
 STACKREF_CHECK_FUNC(Function)
 
 static inline bool

Lib/test/test_ctypes/test_functions.py

@@ -9,6 +9,8 @@
 from test.support import import_helper
 _ctypes_test = import_helper.import_module("_ctypes_test")
 from _ctypes import _Pointer,  _SimpleCData
+import gc
+import weakref
 
 
 try:
@@ -463,6 +465,39 @@ def callback(*args):
         callback = proto(callback)
         self.assertRaises(ArgumentError, lambda: callback((1, 2, 3, 4), POINT()))
 
+    def test_reassign_code_while_running(self):
+        freevar1 = None
+        freevar2 = None
+
+        def replacement():
+            freevar1
+            freevar2
+            return "replacement"
+
+        def original():
+            original.__code__ = replacement.__code__
+            return "original"
+
+        self.assertEqual(original(), "original")
+        self.assertEqual(original(), "replacement")
+
+    def test_function_code_object_no_leak(self):
+        def get_code(i):
+            ns = {}
+            exec(f"def f(): return {i}", ns)
+            return ns["f"].__code__
+
+        refs = []
+        def f(): pass
+        for i in range(100):
+            f.__code__ = get_code(i)
+            refs.append(weakref.ref(f.__code__))
+            self.assertEqual(f(), i)
+
+        del f
+        gc.collect()
+        self.assertTrue(all(ref() is None for ref in refs))
+
 
 if __name__ == '__main__':
     unittest.main()

Lib/test/test_sys.py

@@ -1703,7 +1703,7 @@ def func():
         check(x, size('3PiccPPP' + INTERPRETER_FRAME + 'P'))
         # function
         def func(): pass
-        check(func, size('16Pi'))
+        check(func, size('17Pi'))
         class c():
             @staticmethod
             def foo():

Misc/NEWS.d/next/Core_and_Builtins/2026-07-04-17-04-03.gh-issue-152666.Vo5wJv.rst

@@ -0,0 +1,2 @@
+Avoid reference counting of :class:`code` objects when creating and destroying
+frames by having functions retain a list of all past :class:`code` objects.

Modules/_testinternalcapi/interpreter.c

@@ -84,7 +84,7 @@ Test_EvalFrame(PyThreadState *tstate, _PyInterpreterFrame *frame, int throwflag)
     entry.frame.f_globals = (PyObject*)0xaaa3;
     entry.frame.f_builtins = (PyObject*)0xaaa4;
 #endif
-    entry.frame.f_executable = PyStackRef_None;
+    entry.frame.f_executable = NULL;
     entry.frame.instr_ptr = (_Py_CODEUNIT *)_Py_INTERPRETER_TRAMPOLINE_INSTRUCTIONS_PTR + 1;
     entry.frame.stackpointer = entry.stack;
     entry.frame.owner = FRAME_OWNED_BY_INTERPRETER;

Objects/frameobject.c

@@ -1939,7 +1939,7 @@ frame_dealloc(PyObject *op)
 
     /* Kill all local variables including specials, if we own them */
     if (f->f_frame == frame && frame->owner == FRAME_OWNED_BY_FRAME_OBJECT) {
-        PyStackRef_CLEAR(frame->f_executable);
+        frame->f_executable = NULL;
         PyStackRef_CLEAR(frame->f_funcobj);
         Py_CLEAR(frame->f_locals);
         _PyStackRef *locals = _PyFrame_GetLocalsArray(frame);

Objects/funcobject.c

@@ -145,6 +145,7 @@ _PyFunction_FromConstructor(PyFrameConstructor *constr)
     op->func_typeparams = NULL;
     op->vectorcall = _PyFunction_Vectorcall;
     op->func_version = FUNC_VERSION_UNSET;
+    op->func_old_codes = NULL;
     // NOTE: functions created via FrameConstructor do not use deferred
     // reference counting because they are typically not part of cycles
     // nor accessed by multiple threads.
@@ -223,6 +224,7 @@ PyFunction_NewWithQualName(PyObject *code, PyObject *globals, PyObject *qualname
     op->func_typeparams = NULL;
     op->vectorcall = _PyFunction_Vectorcall;
     op->func_version = FUNC_VERSION_UNSET;
+    op->func_old_codes = NULL;
     if (((code_obj->co_flags & CO_NESTED) == 0) ||
         (code_obj->co_flags & CO_METHOD)) {
         // Use deferred reference counting for top-level functions, but not
@@ -686,6 +688,17 @@ func_set_code(PyObject *self, PyObject *value, void *Py_UNUSED(ignored))
 
     handle_func_event(PyFunction_EVENT_MODIFY_CODE, op, value);
     _PyFunction_ClearVersion(op);
+    if (op->func_old_codes == NULL) {
+        op->func_old_codes = PyList_New(0);
+        if (op->func_old_codes == NULL) {
+            return -1;
+        }
+    }
+
+    if (PyList_Append(op->func_old_codes, op->func_code) < 0) {
+        return -1;
+    }
+
     Py_XSETREF(op->func_code, Py_NewRef(value));
     return 0;
 }
@@ -1114,6 +1127,7 @@ func_clear(PyObject *self)
     Py_CLEAR(op->func_annotations);
     Py_CLEAR(op->func_annotate);
     Py_CLEAR(op->func_typeparams);
+    Py_CLEAR(op->func_old_codes);
     // Don't Py_CLEAR(op->func_code), since code is always required
     // to be non-NULL. Similarly, name and qualname shouldn't be NULL.
     // However, name and qualname could be str subclasses, so they
@@ -1169,6 +1183,7 @@ func_traverse(PyObject *self, visitproc visit, void *arg)
     Py_VISIT(f->func_annotate);
     Py_VISIT(f->func_typeparams);
     Py_VISIT(f->func_qualname);
+    Py_VISIT(f->func_old_codes);
     return 0;
 }
 

Objects/genobject.c

@@ -94,9 +94,9 @@ gen_traverse(PyObject *self, visitproc visit, void *arg)
         }
     }
     else {
-        // We still need to visit the code object when the frame is cleared to
+        // We still need to visit the function object when the frame is cleared to
         // ensure that it's kept alive if the reference is deferred.
-        _Py_VISIT_STACKREF(gen->gi_iframe.f_executable);
+        _Py_VISIT_STACKREF(gen->gi_iframe.f_funcobj);
     }
     /* No need to visit cr_origin, because it's just tuples/str/int, so can't
        participate in a reference cycle. */
@@ -231,7 +231,7 @@ gen_dealloc(PyObject *self)
         gen_clear_frame(gen);
     }
     assert(gen->gi_exc_state.exc_value == NULL);
-    PyStackRef_CLEAR(gen->gi_iframe.f_executable);
+    gen->gi_iframe.f_executable = NULL;
     Py_CLEAR(gen->gi_name);
     Py_CLEAR(gen->gi_qualname);
 
@@ -1105,7 +1105,7 @@ make_gen(PyTypeObject *type, PyFunctionObject *func)
     gen->gi_weakreflist = NULL;
     gen->gi_exc_state.exc_value = NULL;
     gen->gi_exc_state.previous_item = NULL;
-    gen->gi_iframe.f_executable = PyStackRef_None;
+    gen->gi_iframe.f_executable = NULL;
     assert(func->func_name != NULL);
     gen->gi_name = Py_NewRef(func->func_name);
     assert(func->func_qualname != NULL);

Python/bytecodes.c

@@ -1870,7 +1870,7 @@ dummy_func(
             /* We don't know which of these is relevant here, so keep them equal */
             assert(INLINE_CACHE_ENTRIES_SEND == INLINE_CACHE_ENTRIES_FOR_ITER);
             #if TIER_ONE && defined(Py_DEBUG)
-            if (!PyStackRef_IsNone(frame->f_executable)) {
+            if (frame->f_executable != NULL) {
                 Py_ssize_t i = frame->instr_ptr - _PyFrame_GetBytecode(frame);
                 assert(i >= 0 && i <= INT_MAX);
                 int opcode = _Py_GetBaseCodeUnit(_PyFrame_GetCode(frame), (int)i).op.code;
@@ -6318,15 +6318,15 @@ dummy_func(
         }
 
         tier2 op(_GUARD_CODE_VERSION__PUSH_FRAME, (version/2 -- )) {
-            PyObject *code = PyStackRef_AsPyObjectBorrow(frame->f_executable);
+            PyObject *code = frame->f_executable;
             assert(PyCode_Check(code));
             if (((PyCodeObject *)code)->co_version != version) {
                 EXIT_IF(true);
             }
         }
 
         tier2 op(_GUARD_CODE_VERSION_YIELD_VALUE, (version/2 -- )) {
-            PyObject *code = PyStackRef_AsPyObjectBorrow(frame->f_executable);
+            PyObject *code = frame->f_executable;
             assert(PyCode_Check(code));
             if (((PyCodeObject *)code)->co_version != version) {
                 frame->instr_ptr += 1 + INLINE_CACHE_ENTRIES_SEND;
@@ -6335,7 +6335,7 @@ dummy_func(
         }
 
         tier2 op(_GUARD_CODE_VERSION_RETURN_VALUE, (version/2 -- )) {
-            PyObject *code = PyStackRef_AsPyObjectBorrow(frame->f_executable);
+            PyObject *code = frame->f_executable;
             assert(PyCode_Check(code));
             if (((PyCodeObject *)code)->co_version != version) {
                 frame->instr_ptr += frame->return_offset;
@@ -6344,7 +6344,7 @@ dummy_func(
         }
 
         tier2 op(_GUARD_CODE_VERSION_RETURN_GENERATOR, (version/2 -- )) {
-            PyObject *code = PyStackRef_AsPyObjectBorrow(frame->f_executable);
+            PyObject *code = frame->f_executable;
             assert(PyCode_Check(code));
             if (((PyCodeObject *)code)->co_version != version) {
                 frame->instr_ptr += frame->return_offset;
@@ -6638,14 +6638,14 @@ dummy_func(
             }
             tracer->prev_state.recorded_count = 0;
             tracer->prev_state.instr = next_instr;
-            PyObject *prev_code = PyStackRef_AsPyObjectBorrow(frame->f_executable);
+            PyObject *prev_code = frame->f_executable;
             if (tracer->prev_state.instr_code != (PyCodeObject *)prev_code) {
                 Py_SETREF(tracer->prev_state.instr_code, (PyCodeObject*)Py_NewRef((prev_code)));
             }
 
             tracer->prev_state.instr_frame = frame;
             tracer->prev_state.instr_oparg = oparg;
-            tracer->prev_state.instr_stacklevel = PyStackRef_IsNone(frame->f_executable) ? 2 : STACK_LEVEL();
+            tracer->prev_state.instr_stacklevel = frame->f_executable == NULL ? 2 : STACK_LEVEL();
             if (_PyOpcode_Caches[_PyOpcode_Deopt[opcode]]
                 // Branch opcodes use the cache for branch history, not
                 // specialization counters.  Don't reset it.

Python/ceval.c

@@ -1272,7 +1272,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
     entry.frame.f_globals = (PyObject*)0xaaa3;
     entry.frame.f_builtins = (PyObject*)0xaaa4;
 #endif
-    entry.frame.f_executable = PyStackRef_None;
+    entry.frame.f_executable = NULL;
     entry.frame.instr_ptr = (_Py_CODEUNIT *)_Py_INTERPRETER_TRAMPOLINE_INSTRUCTIONS + 1;
     entry.frame.stackpointer = entry.stack;
     entry.frame.owner = FRAME_OWNED_BY_INTERPRETER;
@@ -1982,7 +1982,7 @@ clear_thread_frame(PyThreadState *tstate, _PyInterpreterFrame * frame)
         tstate->datastack_top);
     assert(frame->frame_obj == NULL || frame->frame_obj->f_frame == frame);
     _PyFrame_ClearExceptCode(frame);
-    PyStackRef_CLEAR(frame->f_executable);
+    frame->f_executable = NULL;
     _PyThreadState_PopFrame(tstate, frame);
 }
 
@@ -1997,6 +1997,9 @@ clear_gen_frame(PyThreadState *tstate, _PyInterpreterFrame * frame)
     gen->gi_exc_state.previous_item = NULL;
     assert(frame->frame_obj == NULL || frame->frame_obj->f_frame == frame);
     frame->previous = NULL;
+    if (PyGen_Check(gen)) {
+        frame->f_funcobj = PyStackRef_DUP(frame->f_funcobj);
+    }
     _PyFrame_ClearExceptCode(frame);
     _PyErr_ClearExcState(&gen->gi_exc_state);
     // gh-143939: There must not be any escaping calls between setting

Python/ceval.h

@@ -248,7 +248,7 @@ static void
 lltrace_resume_frame(_PyInterpreterFrame *frame)
 {
     PyObject *fobj = PyStackRef_AsPyObjectBorrow(frame->f_funcobj);
-    if (!PyStackRef_CodeCheck(frame->f_executable) ||
+    if (!PyCode_Check(frame->f_executable) ||
         fobj == NULL ||
         !PyFunction_Check(fobj)
     ) {