PR python/18089

gdb/ChangeLog:

	PR python/18089
	* python/py-prettyprint.c (print_children): Verify result of children
	iterator.  Provide better error message.
	* python/python-internal..h (gdbpy_print_python_errors_p): Declare.
	* python/python.c (gdbpy_print_python_errors_p): New function.

gdb/testsuite/ChangeLog:

	* gdb.python/py-bad-printers.c: New file.
	* gdb.python/py-bad-printers.py: New file.
	* gdb.python/py-bad-printers.exp: New file.

gdb/python/py-prettyprint.c

@@ -554,8 +554,22 @@ print_children (PyObject *printer, const char *hint,
 	  break;
 	}
 
+      if (! PyTuple_Check (item) || PyTuple_Size (item) != 2)
+	{
+	  PyErr_SetString (PyExc_TypeError,
+			   _("Result of children iterator not a tuple"
+			     " of two elements."));
+	  gdbpy_print_stack ();
+	  Py_DECREF (item);
+	  continue;
+	}
       if (! PyArg_ParseTuple (item, "sO", &name, &py_v))
 	{
+	  /* The user won't necessarily get a stack trace here, so provide
+	     more context.  */
+	  if (gdbpy_print_python_errors_p ())
+	    fprintf_unfiltered (gdb_stderr,
+				_("Bad result from children iterator.\n"));
 	  gdbpy_print_stack ();
 	  Py_DECREF (item);
 	  continue;

gdb/python/python-internal.h

@@ -527,6 +527,7 @@ extern const struct language_defn *python_language;
 	}								\
     } while (0)
 
+int gdbpy_print_python_errors_p (void);
 void gdbpy_print_stack (void);
 
 PyObject *python_string_to_unicode (PyObject *obj);

gdb/python/python.c

@@ -1182,6 +1182,14 @@ gdbpy_flush (PyObject *self, PyObject *args, PyObject *kw)
   Py_RETURN_NONE;
 }
 
+/* Return non-zero if print-stack is not "none".  */
+
+int
+gdbpy_print_python_errors_p (void)
+{
+  return gdbpy_should_print_stack != python_excp_none;
+}
+
 /* Print a python exception trace, print just a message, or print
    nothing and clear the python exception, depending on
    gdbpy_should_print_stack.  Only call this if a python exception is