bpo-45711: use exc_value instead of exc_type to determine if exc_info is valid. Add more assertions. (GH-29627)

4 files changed, 91 insertions, 36 deletions

diff --git a/Python/ceval.c b/Python/ceval.c
index 0aec5aa7fb..9beb1a4368 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -1102,7 +1102,7 @@ static void
 _assert_exception_type_is_redundant(PyObject* type, PyObject* val)
 {
     if (type == NULL || type == Py_None) {
-        assert(val == NULL || val == Py_None);
+        assert(val == type);
     }
     else {
         assert(PyExceptionInstance_Check(val));
@@ -3738,7 +3738,9 @@ check_eval_breaker:
 
         TARGET(JUMP_IF_NOT_EXC_MATCH) {
             PyObject *right = POP();
-            PyObject *left = TOP();
+            ASSERT_EXC_TYPE_IS_REDUNDANT(TOP(), SECOND());
+            PyObject *left = SECOND();
+            assert(PyExceptionInstance_Check(left));
             if (check_except_type_valid(tstate, right) < 0) {
                  Py_DECREF(right);
                  goto error;
@@ -4198,7 +4200,13 @@ check_eval_breaker:
             ASSERT_EXC_TYPE_IS_REDUNDANT(type, value);
             _PyErr_StackItem *exc_info = tstate->exc_info;
             SET_THIRD(exc_info->exc_traceback);
-            SET_SECOND(exc_info->exc_value);
+            if (exc_info->exc_value != NULL) {
+                SET_SECOND(exc_info->exc_value);
+            }
+            else {
+                Py_INCREF(Py_None);
+                SET_SECOND(Py_None);
+            }
             if (exc_info->exc_type != NULL) {
                 SET_TOP(exc_info->exc_type);
             }
@@ -5916,7 +5924,9 @@ do_raise(PyThreadState *tstate, PyObject *exc, PyObject *cause)
         type = exc_info->exc_type;
         value = exc_info->exc_value;
         tb = exc_info->exc_traceback;
-        if (Py_IsNone(type) || type == NULL) {
+        assert(((Py_IsNone(value) || value == NULL)) ==
+               ((Py_IsNone(type) || type == NULL)));
+        if (Py_IsNone(value) || value == NULL) {
             _PyErr_SetString(tstate, PyExc_RuntimeError,
                              "No active exception to reraise");
             return 0;
diff --git a/Python/errors.c b/Python/errors.c
index cb3938d208..6e74d19b78 100644
--- a/Python/errors.c
+++ b/Python/errors.c
@@ -79,11 +79,16 @@ _PyErr_StackItem *
 _PyErr_GetTopmostException(PyThreadState *tstate)
 {
     _PyErr_StackItem *exc_info = tstate->exc_info;
-    while ((exc_info->exc_type == NULL || exc_info->exc_type == Py_None) &&
+    assert(exc_info);
+
+    while ((exc_info->exc_value == NULL || exc_info->exc_value == Py_None) &&
            exc_info->previous_item != NULL)
     {
+        assert(exc_info->exc_type == NULL || exc_info->exc_type == Py_None);
         exc_info = exc_info->previous_item;
     }
+    assert(exc_info->previous_item == NULL ||
+           (exc_info->exc_type != NULL && exc_info->exc_type != Py_None));
     return exc_info;
 }
 
@@ -471,10 +476,20 @@ _PyErr_GetExcInfo(PyThreadState *tstate,
                   PyObject **p_type, PyObject **p_value, PyObject **p_traceback)
 {
     _PyErr_StackItem *exc_info = _PyErr_GetTopmostException(tstate);
-    *p_type = exc_info->exc_type;
+
     *p_value = exc_info->exc_value;
     *p_traceback = exc_info->exc_traceback;
 
+    if (*p_value == NULL || *p_value == Py_None) {
+        assert(exc_info->exc_type == NULL || exc_info->exc_type == Py_None);
+        *p_type = Py_None;
+    }
+    else {
+        assert(PyExceptionInstance_Check(*p_value));
+        assert(exc_info->exc_type == PyExceptionInstance_Class(*p_value));
+        *p_type = PyExceptionInstance_Class(*p_value);
+    }
+
     Py_XINCREF(*p_type);
     Py_XINCREF(*p_value);
     Py_XINCREF(*p_traceback);
@@ -507,42 +522,66 @@ PyErr_SetExcInfo(PyObject *p_type, PyObject *p_value, PyObject *p_traceback)
     Py_XDECREF(oldtraceback);
 }
 
+
+PyObject*
+_PyErr_StackItemToExcInfoTuple(_PyErr_StackItem *err_info)
+{
+    PyObject *exc_value = err_info->exc_value;
+    if (exc_value == NULL) {
+        exc_value = Py_None;
+    }
+
+    assert(exc_value == Py_None || PyExceptionInstance_Check(exc_value));
+
+    PyObject *exc_type = PyExceptionInstance_Check(exc_value) ?
+               PyExceptionInstance_Class(exc_value) :
+               Py_None;
+
+    return Py_BuildValue(
+        "(OOO)",
+        exc_type,
+        exc_value,
+        err_info->exc_traceback != NULL ?
+            err_info->exc_traceback : Py_None);
+}
+
+
 /* Like PyErr_Restore(), but if an exception is already set,
    set the context associated with it.
 
    The caller is responsible for ensuring that this call won't create
    any cycles in the exception context chain. */
 void
-_PyErr_ChainExceptions(PyObject *exc, PyObject *val, PyObject *tb)
+_PyErr_ChainExceptions(PyObject *typ, PyObject *val, PyObject *tb)
 {
-    if (exc == NULL)
+    if (typ == NULL)
         return;
 
     PyThreadState *tstate = _PyThreadState_GET();
 
-    if (!PyExceptionClass_Check(exc)) {
+    if (!PyExceptionClass_Check(typ)) {
         _PyErr_Format(tstate, PyExc_SystemError,
                       "_PyErr_ChainExceptions: "
                       "exception %R is not a BaseException subclass",
-                      exc);
+                      typ);
         return;
     }
 
     if (_PyErr_Occurred(tstate)) {
-        PyObject *exc2, *val2, *tb2;
-        _PyErr_Fetch(tstate, &exc2, &val2, &tb2);
-        _PyErr_NormalizeException(tstate, &exc, &val, &tb);
+        PyObject *typ2, *val2, *tb2;
+        _PyErr_Fetch(tstate, &typ2, &val2, &tb2);
+        _PyErr_NormalizeException(tstate, &typ, &val, &tb);
         if (tb != NULL) {
             PyException_SetTraceback(val, tb);
             Py_DECREF(tb);
         }
-        Py_DECREF(exc);
-        _PyErr_NormalizeException(tstate, &exc2, &val2, &tb2);
+        Py_DECREF(typ);
+        _PyErr_NormalizeException(tstate, &typ2, &val2, &tb2);
         PyException_SetContext(val2, val);
-        _PyErr_Restore(tstate, exc2, val2, tb2);
+        _PyErr_Restore(tstate, typ2, val2, tb2);
     }
     else {
-        _PyErr_Restore(tstate, exc, val, tb);
+        _PyErr_Restore(tstate, typ, val, tb);
     }
 }
 
@@ -567,7 +606,11 @@ _PyErr_ChainStackItem(_PyErr_StackItem *exc_info)
     } else {
         exc_info_given = 1;
     }
-    if (exc_info->exc_type == NULL || exc_info->exc_type == Py_None) {
+
+    assert( (exc_info->exc_type == NULL || exc_info->exc_type == Py_None) ==
+            (exc_info->exc_value == NULL || exc_info->exc_value == Py_None) );
+
+    if (exc_info->exc_value == NULL || exc_info->exc_value == Py_None) {
         return;
     }
 
@@ -579,21 +622,32 @@ _PyErr_ChainStackItem(_PyErr_StackItem *exc_info)
         tstate->exc_info = exc_info;
     }
 
-    PyObject *exc, *val, *tb;
-    _PyErr_Fetch(tstate, &exc, &val, &tb);
+    PyObject *typ, *val, *tb;
+    _PyErr_Fetch(tstate, &typ, &val, &tb);
 
-    PyObject *exc2, *val2, *tb2;
-    exc2 = exc_info->exc_type;
+    PyObject *typ2, *val2, *tb2;
+    typ2 = exc_info->exc_type;
     val2 = exc_info->exc_value;
     tb2 = exc_info->exc_traceback;
-    _PyErr_NormalizeException(tstate, &exc2, &val2, &tb2);
+#ifdef Py_DEBUG
+    PyObject *typ2_before = typ2;
+    PyObject *val2_before = val2;
+    PyObject *tb2_before = tb2;
+#endif
+    _PyErr_NormalizeException(tstate, &typ2, &val2, &tb2);
+#ifdef Py_DEBUG
+    /* exc_info should already be normalized */
+    assert(typ2 == typ2_before);
+    assert(val2 == val2_before);
+    assert(tb2 == tb2_before);
+#endif
     if (tb2 != NULL) {
         PyException_SetTraceback(val2, tb2);
     }
 
     /* _PyErr_SetObject sets the context from PyThreadState. */
-    _PyErr_SetObject(tstate, exc, val);
-    Py_DECREF(exc);  // since _PyErr_Occurred was true
+    _PyErr_SetObject(tstate, typ, val);
+    Py_DECREF(typ);  // since _PyErr_Occurred was true
     Py_XDECREF(val);
     Py_XDECREF(tb);
 
diff --git a/Python/pystate.c b/Python/pystate.c
index 56db095d24..ba14c9d8af 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -1341,11 +1341,7 @@ _PyThread_CurrentExceptions(void)
             if (id == NULL) {
                 goto fail;
             }
-            PyObject *exc_info = PyTuple_Pack(
-                3,
-                err_info->exc_type != NULL ? err_info->exc_type : Py_None,
-                err_info->exc_value != NULL ? err_info->exc_value : Py_None,
-                err_info->exc_traceback != NULL ? err_info->exc_traceback : Py_None);
+            PyObject *exc_info = _PyErr_StackItemToExcInfoTuple(err_info);
             if (exc_info == NULL) {
                 Py_DECREF(id);
                 goto fail;
diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index 3e2091e70a..13fae797b2 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -785,12 +785,7 @@ sys_exc_info_impl(PyObject *module)
 /*[clinic end generated code: output=3afd0940cf3a4d30 input=b5c5bf077788a3e5]*/
 {
     _PyErr_StackItem *err_info = _PyErr_GetTopmostException(_PyThreadState_GET());
-    return Py_BuildValue(
-        "(OOO)",
-        err_info->exc_type != NULL ? err_info->exc_type : Py_None,
-        err_info->exc_value != NULL ? err_info->exc_value : Py_None,
-        err_info->exc_traceback != NULL ?
-            err_info->exc_traceback : Py_None);
+    return _PyErr_StackItemToExcInfoTuple(err_info);
 }