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

1 files changed, 75 insertions, 21 deletions

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);