Fix a possible segfault from recursing too deep to get the repr of a list.

Closes issue #1096.

Lib/test/list_tests.py

@@ -46,6 +46,11 @@ class CommonTest(seq_tests.CommonTest):
         self.assertEqual(str(a2), "[0, 1, 2, [...], 3]")
         self.assertEqual(repr(a2), "[0, 1, 2, [...], 3]")
 
+        l0 = []
+        for i in xrange(sys.getrecursionlimit() + 100):
+            l0 = [l0]
+        self.assertRaises(RuntimeError, repr, l0)
+
     def test_print(self):
         d = self.type2test(xrange(200))
         d.append(d)

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python 2.6 alpha 1?
 Core and builtins
 -----------------
 
+- Issue #1096: Prevent a segfault from getting the repr of a very deeply nested
+  list by using the recursion counter.
+
 - Issue #1202533: Fix infinite recursion calls triggered by calls to
   PyObject_Call() never calling back out to Python code to trigger recursion
   depth updates/checks.  Required the creation of a static RuntimeError

Objects/listobject.c

@@ -324,7 +324,10 @@ list_repr(PyListObject *v)
 	   so must refetch the list size on each iteration. */
 	for (i = 0; i < Py_Size(v); ++i) {
 		int status;
+		if (Py_EnterRecursiveCall(" while getting the repr of a list"))
+			goto Done;
 		s = PyObject_Repr(v->ob_item[i]);
+		Py_LeaveRecursiveCall();
 		if (s == NULL)
 			goto Done;
 		status = PyList_Append(pieces, s);