bpo-45711: remove exc_traceback from _PyErr_StackItem

markshannon · Dec 17, 2021 · Dec 7, 2021 · Dec 7, 2021 · Dec 9, 2021 · Dec 9, 2021
commit 37c7f12e5379c834168f01acefd761141741c912
@@ -56,7 +56,7 @@ typedef struct _err_stackitem {
      * This ensures that the exception state is not impacted by "yields"
      * from an except handler.
      */
-    PyObject *exc_type, *exc_value, *exc_traceback;
+    PyObject *exc_type, *exc_value;
 
     struct _err_stackitem *previous_item;
 

diff --git a/Include/internal/pycore_pyerrors.h b/Include/internal/pycore_pyerrors.h
@@ -24,16 +24,13 @@ static inline PyObject* _PyErr_Occurred(PyThreadState *tstate)
 
 static inline void _PyErr_ClearExcState(_PyErr_StackItem *exc_state)
 {
-    PyObject *t, *v, *tb;
+    PyObject *t, *v;
     t = exc_state->exc_type;
     v = exc_state->exc_value;
-    tb = exc_state->exc_traceback;
     exc_state->exc_type = NULL;
     exc_state->exc_value = NULL;
-    exc_state->exc_traceback = NULL;
     Py_XDECREF(t);
     Py_XDECREF(v);
-    Py_XDECREF(tb);
 }
 
 PyAPI_FUNC(PyObject*) _PyErr_StackItemToExcInfoTuple(

diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
@@ -1340,7 +1340,7 @@ def bar(cls):
             check(bar, size('PP'))
         # generator
         def get_gen(): yield 1
-        check(get_gen(), size('P2PPP4P4c8P2iciP'))
+        check(get_gen(), size('P2PP4P4c8P2iciP'))
         # iterator
         check(iter('abc'), size('lP'))
         # callable-iterator

@@ -812,7 +812,6 @@ FutureObj_traverse(FutureObj *fut, visitproc visit, void *arg)
     _PyErr_StackItem *exc_state = &fut->fut_cancelled_exc_state;
     Py_VISIT(exc_state->exc_type);
     Py_VISIT(exc_state->exc_value);
-    Py_VISIT(exc_state->exc_traceback);
 
     return 0;
 }
@@ -1378,7 +1377,6 @@ _asyncio_Future__make_cancelled_error_impl(FutureObj *self)
     }
     else {
         assert(exc_state->exc_type == NULL);
-        assert(exc_state->exc_traceback == NULL);
     }
 
     return exc;
@@ -2706,13 +2704,13 @@ task_step_impl(TaskObj *task, PyObject *exc)
             PyErr_NormalizeException(&et, &ev, &tb);
             if (tb != NULL) {
                 PyException_SetTraceback(ev, tb);
+                Py_DECREF(tb);
             }
 
             FutureObj *fut = (FutureObj*)task;
             _PyErr_StackItem *exc_state = &fut->fut_cancelled_exc_state;
             exc_state->exc_type = et;
             exc_state->exc_value = ev;
-            exc_state->exc_traceback = tb;
 
             return future_cancel(fut, NULL);
         }

@@ -27,7 +27,6 @@ exc_state_traverse(_PyErr_StackItem *exc_state, visitproc visit, void *arg)
 {
     Py_VISIT(exc_state->exc_type);
     Py_VISIT(exc_state->exc_value);
-    Py_VISIT(exc_state->exc_traceback);
     return 0;
 }
 
@@ -884,7 +883,6 @@ make_gen(PyTypeObject *type, PyFunctionObject *func)
     gen->gi_weakreflist = NULL;
     gen->gi_exc_state.exc_type = NULL;
     gen->gi_exc_state.exc_value = NULL;
-    gen->gi_exc_state.exc_traceback = NULL;
     gen->gi_exc_state.previous_item = NULL;
     if (func->func_name != NULL)
         gen->gi_name = func->func_name;
@@ -973,7 +971,6 @@ gen_new_with_qualname(PyTypeObject *type, PyFrameObject *f,
     gen->gi_weakreflist = NULL;
     gen->gi_exc_state.exc_type = NULL;
     gen->gi_exc_state.exc_value = NULL;
-    gen->gi_exc_state.exc_traceback = NULL;
     gen->gi_exc_state.previous_item = NULL;
     if (name != NULL)
         gen->gi_name = name;

@@ -2728,28 +2728,17 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, InterpreterFrame *frame, int thr
         }
 
         TARGET(POP_EXCEPT) {
-            PyObject *type, *value, *traceback;
+            PyObject *type, *value;
             _PyErr_StackItem *exc_info;
             exc_info = tstate->exc_info;
             type = exc_info->exc_type;
             value = exc_info->exc_value;
-            traceback = exc_info->exc_traceback;
-
             exc_info->exc_type = POP();
             exc_info->exc_value = POP();
 
-            assert(exc_info->exc_value);
-            if (exc_info->exc_value != Py_None) {
-                exc_info->exc_traceback = PyException_GetTraceback(exc_info->exc_value);
-            }
-            else {
-                exc_info->exc_traceback = NULL;
-            }
-
             ASSERT_EXC_TYPE_IS_REDUNDANT(exc_info->exc_type, exc_info->exc_value);
             Py_XDECREF(type);
             Py_XDECREF(value);
-            Py_XDECREF(traceback);
             DISPATCH();
         }
 
@@ -2776,21 +2765,12 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, InterpreterFrame *frame, int thr
             exc_info = tstate->exc_info;
             type = exc_info->exc_type;
             value = exc_info->exc_value;
-            traceback = exc_info->exc_traceback;
             exc_info->exc_type = POP();
             exc_info->exc_value = POP();
 
-            assert(exc_info->exc_value);
-            if (exc_info->exc_value != Py_None) {
-                exc_info->exc_traceback = PyException_GetTraceback(exc_info->exc_value);
-            }
-            else {
-                exc_info->exc_traceback = NULL;
-            }
             ASSERT_EXC_TYPE_IS_REDUNDANT(exc_info->exc_type, exc_info->exc_value);
             Py_XDECREF(type);
             Py_XDECREF(value);
-            Py_XDECREF(traceback);
             goto exception_unwind;
         }
 
@@ -4510,12 +4490,9 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, InterpreterFrame *frame, int thr
         TARGET(PUSH_EXC_INFO) {
             PyObject *type = TOP();
             PyObject *value = SECOND();
-            assert(value && PyExceptionInstance_Check(value));
-            PyObject *tb = PyException_GetTraceback(value);
             ASSERT_EXC_TYPE_IS_REDUNDANT(type, value);
 
             _PyErr_StackItem *exc_info = tstate->exc_info;
-            Py_XDECREF(exc_info->exc_traceback);
             if (exc_info->exc_value != NULL) {
                 SET_SECOND(exc_info->exc_value);
             }
@@ -4530,7 +4507,6 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, InterpreterFrame *frame, int thr
                 Py_INCREF(Py_None);
                 SET_TOP(Py_None);
             }
-            exc_info->exc_traceback = tb;
 
             Py_INCREF(value);
             PUSH(value);

@@ -3292,18 +3292,16 @@ compiler_try_star_finally(struct compiler *c, stmt_ty s)
    []                           POP_BLOCK
    []                           JUMP_FORWARD    L0
 
-   [tb, val, exc]       L1:     <evaluate E1>                   )
-   [tb, val, exc, E1]           JUMP_IF_NOT_EXC_MATCH L2        ) only if E1
-   [tb, val, exc]               POP
-   [tb, val]                    <assign to V1>  (or POP if no V1)
-   [tb]                         POP
+   [exc]                        L1:     <evaluate E1>           )
+   [exc, E1]                    JUMP_IF_NOT_EXC_MATCH L2        ) only if E1
+   [exc]                        <assign to V1>  (or POP if no V1)
    []                           <code for S1>
                                 JUMP_FORWARD    L0
 
-   [tb, val, exc]       L2:     <evaluate E2>
+   [exc]                L2:     <evaluate E2>
    .............................etc.......................
 
-   [tb, val, exc]       Ln+1:   RERAISE     # re-raise exception
+   [exc]                Ln+1:   RERAISE     # re-raise exception
 
    []                   L0:     <next statement>
 

diff --git a/Python/errors.c b/Python/errors.c
@@ -524,27 +524,23 @@ PyErr_GetExcInfo(PyObject **p_type, PyObject **p_value, PyObject **p_traceback)
 void
 PyErr_SetExcInfo(PyObject *type, PyObject *value, PyObject *traceback)
 {
-    PyObject *oldtype, *oldvalue, *oldtraceback;
+    PyObject *oldtype, *oldvalue;
     PyThreadState *tstate = _PyThreadState_GET();
 
     oldtype = tstate->exc_info->exc_type;
     oldvalue = tstate->exc_info->exc_value;
-    oldtraceback = tstate->exc_info->exc_traceback;
 
 
     tstate->exc_info->exc_type = get_exc_type(value);
     Py_XINCREF(tstate->exc_info->exc_type);
     tstate->exc_info->exc_value = value;
-    tstate->exc_info->exc_traceback = get_exc_traceback(value);
-    Py_XINCREF(tstate->exc_info->exc_traceback);
 
     /* These args are no longer used, but we still need to steal a ref */
     Py_XDECREF(type);
     Py_XDECREF(traceback);
 
     Py_XDECREF(oldtype);
     Py_XDECREF(oldvalue);
-    Py_XDECREF(oldtraceback);
 }
 
 

@@ -1030,7 +1030,6 @@ PyThreadState_Clear(PyThreadState *tstate)
 
     Py_CLEAR(tstate->exc_state.exc_type);
     Py_CLEAR(tstate->exc_state.exc_value);
-    Py_CLEAR(tstate->exc_state.exc_traceback);
 
     /* The stack of exception states should contain just this thread. */
     if (verbose && tstate->exc_info != &tstate->exc_state) {