Issue #18408: Add a new PyFrame_FastToLocalsWithError() function to handle

exceptions when merging fast locals into f_locals of a frame.
PyEval_GetLocals() now raises an exception and return NULL on failure.

Author: vstinner

Include/frameobject.h

@@ -78,6 +78,8 @@ PyAPI_FUNC(PyObject **) PyFrame_ExtendStack(PyFrameObject *, int, int);
 /* Conversions between "fast locals" and locals in dictionary */
 
 PyAPI_FUNC(void) PyFrame_LocalsToFast(PyFrameObject *, int);
+
+PyAPI_FUNC(int) PyFrame_FastToLocalsWithError(PyFrameObject *f);
 PyAPI_FUNC(void) PyFrame_FastToLocals(PyFrameObject *);
 
 PyAPI_FUNC(int) PyFrame_ClearFreeList(void);

Misc/NEWS

@@ -10,6 +10,10 @@ Projected release date: 2013-11-24
 Core and Builtins
 -----------------
 
+- Issue #18408: Add a new PyFrame_FastToLocalsWithError() function to handle
+  exceptions when merging fast locals into f_locals of a frame.
+  PyEval_GetLocals() now raises an exception and return NULL on failure.
+
 - Issue #19369: Optimized the usage of __length_hint__().
 
 - Issue #18603: Ensure that PyOS_mystricmp and PyOS_mystrnicmp are in the

Objects/frameobject.c

@@ -21,7 +21,8 @@ static PyMemberDef frame_memberlist[] = {
 static PyObject *
 frame_getlocals(PyFrameObject *f, void *closure)
 {
-    PyFrame_FastToLocals(f);
+    if (PyFrame_FastToLocalsWithError(f) < 0)
+        return NULL;
     Py_INCREF(f->f_locals);
     return f->f_locals;
 }
@@ -772,12 +773,9 @@ PyFrame_BlockPop(PyFrameObject *f)
    If deref is true, then the values being copied are cell variables
    and the value is extracted from the cell variable before being put
    in dict.
-
-   Exceptions raised while modifying the dict are silently ignored,
-   because there is no good way to report them.
  */
 
-static void
+static int
 map_to_dict(PyObject *map, Py_ssize_t nmap, PyObject *dict, PyObject **values,
             int deref)
 {
@@ -794,14 +792,19 @@ map_to_dict(PyObject *map, Py_ssize_t nmap, PyObject *dict, PyObject **values,
             value = PyCell_GET(value);
         }
         if (value == NULL) {
-            if (PyObject_DelItem(dict, key) != 0)
-                PyErr_Clear();
+            if (PyObject_DelItem(dict, key) != 0) {
+                if (PyErr_ExceptionMatches(PyExc_KeyError))
+                    PyErr_Clear();
+                else
+                    return -1;
+            }
         }
         else {
             if (PyObject_SetItem(dict, key, value) != 0)
-                PyErr_Clear();
+                return -1;
         }
     }
+    return 0;
 }
 
 /* Copy values from the "locals" dict into the fast locals.
@@ -858,42 +861,49 @@ dict_to_map(PyObject *map, Py_ssize_t nmap, PyObject *dict, PyObject **values,
     }
 }
 
-void
-PyFrame_FastToLocals(PyFrameObject *f)
+int
+PyFrame_FastToLocalsWithError(PyFrameObject *f)
 {
     /* Merge fast locals into f->f_locals */
     PyObject *locals, *map;
     PyObject **fast;
-    PyObject *error_type, *error_value, *error_traceback;
     PyCodeObject *co;
     Py_ssize_t j;
     Py_ssize_t ncells, nfreevars;
-    if (f == NULL)
-        return;
+
+    if (f == NULL) {
+        PyErr_BadInternalCall();
+        return -1;
+    }
     locals = f->f_locals;
     if (locals == NULL) {
         locals = f->f_locals = PyDict_New();
-        if (locals == NULL) {
-            PyErr_Clear(); /* Can't report it :-( */
-            return;
-        }
+        if (locals == NULL)
+            return -1;
     }
     co = f->f_code;
     map = co->co_varnames;
-    if (!PyTuple_Check(map))
-        return;
-    PyErr_Fetch(&error_type, &error_value, &error_traceback);
+    if (!PyTuple_Check(map)) {
+        PyErr_Format(PyExc_SystemError,
+                     "co_varnames must be a tuple, not %s",
+                     Py_TYPE(map)->tp_name);
+        return -1;
+    }
     fast = f->f_localsplus;
     j = PyTuple_GET_SIZE(map);
     if (j > co->co_nlocals)
         j = co->co_nlocals;
-    if (co->co_nlocals)
-        map_to_dict(map, j, locals, fast, 0);
+    if (co->co_nlocals) {
+        if (map_to_dict(map, j, locals, fast, 0) < 0)
+            return -1;
+    }
     ncells = PyTuple_GET_SIZE(co->co_cellvars);
     nfreevars = PyTuple_GET_SIZE(co->co_freevars);
     if (ncells || nfreevars) {
-        map_to_dict(co->co_cellvars, ncells,
-                    locals, fast + co->co_nlocals, 1);
+        if (map_to_dict(co->co_cellvars, ncells,
+                        locals, fast + co->co_nlocals, 1))
+            return -1;
+
         /* If the namespace is unoptimized, then one of the
            following cases applies:
            1. It does not contain free variables, because it
@@ -903,11 +913,24 @@ PyFrame_FastToLocals(PyFrameObject *f)
            into the locals dict used by the class.
         */
         if (co->co_flags & CO_OPTIMIZED) {
-            map_to_dict(co->co_freevars, nfreevars,
-                        locals, fast + co->co_nlocals + ncells, 1);
+            if (map_to_dict(co->co_freevars, nfreevars,
+                            locals, fast + co->co_nlocals + ncells, 1) < 0)
+                return -1;
         }
     }
-    PyErr_Restore(error_type, error_value, error_traceback);
+    return 0;
+}
+
+void
+PyFrame_FastToLocals(PyFrameObject *f)
+{
+    int res;
+
+    assert(!PyErr_Occurred());
+
+    res = PyFrame_FastToLocalsWithError(f);
+    if (res < 0)
+        PyErr_Clear();
 }
 
 void

Objects/object.c

@@ -1407,12 +1407,11 @@ static PyObject *
 _dir_locals(void)
 {
     PyObject *names;
-    PyObject *locals = PyEval_GetLocals();
+    PyObject *locals;
 
-    if (locals == NULL) {
-        PyErr_SetString(PyExc_SystemError, "frame does not exist");
+    locals = PyEval_GetLocals();
+    if (locals == NULL)
         return NULL;
-    }
 
     names = PyMapping_Keys(locals);
     if (!names)

Python/bltinmodule.c

@@ -755,8 +755,11 @@ builtin_eval(PyObject *self, PyObject *args)
     }
     if (globals == Py_None) {
         globals = PyEval_GetGlobals();
-        if (locals == Py_None)
+        if (locals == Py_None) {
             locals = PyEval_GetLocals();
+            if (locals == NULL)
+                return NULL;
+        }
     }
     else if (locals == Py_None)
         locals = globals;
@@ -820,6 +823,8 @@ builtin_exec(PyObject *self, PyObject *args)
         globals = PyEval_GetGlobals();
         if (locals == Py_None) {
             locals = PyEval_GetLocals();
+            if (locals == NULL)
+                return NULL;
         }
         if (!globals || !locals) {
             PyErr_SetString(PyExc_SystemError,
@@ -1926,13 +1931,9 @@ builtin_vars(PyObject *self, PyObject *args)
         return NULL;
     if (v == NULL) {
         d = PyEval_GetLocals();
-        if (d == NULL) {
-            if (!PyErr_Occurred())
-                PyErr_SetString(PyExc_SystemError,
-                                "vars(): no locals!?");
-        }
-        else
-            Py_INCREF(d);
+        if (d == NULL)
+            return NULL;
+        Py_INCREF(d);
     }
     else {
         _Py_IDENTIFIER(__dict__);

Python/ceval.c

@@ -2472,7 +2472,9 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
         TARGET(IMPORT_STAR) {
             PyObject *from = POP(), *locals;
             int err;
-            PyFrame_FastToLocals(f);
+            if (PyFrame_FastToLocalsWithError(f) < 0)
+                goto error;
+
             locals = f->f_locals;
             if (locals == NULL) {
                 PyErr_SetString(PyExc_SystemError,
@@ -4005,9 +4007,15 @@ PyObject *
 PyEval_GetLocals(void)
 {
     PyFrameObject *current_frame = PyEval_GetFrame();
-    if (current_frame == NULL)
+    if (current_frame == NULL) {
+        PyErr_SetString(PyExc_SystemError, "frame does not exist");
         return NULL;
-    PyFrame_FastToLocals(current_frame);
+    }
+
+    if (PyFrame_FastToLocalsWithError(current_frame) < 0)
+        return NULL;
+
+    assert(current_frame->f_locals != NULL);
     return current_frame->f_locals;
 }
 
@@ -4017,8 +4025,9 @@ PyEval_GetGlobals(void)
     PyFrameObject *current_frame = PyEval_GetFrame();
     if (current_frame == NULL)
         return NULL;
-    else
-        return current_frame->f_globals;
+
+    assert(current_frame->f_globals != NULL);
+    return current_frame->f_globals;
 }
 
 PyFrameObject *

Python/sysmodule.c

@@ -332,12 +332,16 @@ static PyObject *
 call_trampoline(PyThreadState *tstate, PyObject* callback,
                 PyFrameObject *frame, int what, PyObject *arg)
 {
-    PyObject *args = PyTuple_New(3);
+    PyObject *args;
     PyObject *whatstr;
     PyObject *result;
 
+    args = PyTuple_New(3);
     if (args == NULL)
         return NULL;
+    if (PyFrame_FastToLocalsWithError(frame) < 0)
+        return NULL;
+
     Py_INCREF(frame);
     whatstr = whatstrings[what];
     Py_INCREF(whatstr);
@@ -349,7 +353,6 @@ call_trampoline(PyThreadState *tstate, PyObject* callback,
     PyTuple_SET_ITEM(args, 2, arg);
 
     /* call the Python-level function */
-    PyFrame_FastToLocals(frame);
     result = PyEval_CallObject(callback, args);
     PyFrame_LocalsToFast(frame, 1);
     if (result == NULL)