Indeed:

>>> s = b'a' * (2**31)
>>> d = pickle.dumps(s)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
SystemError: error return without exception set

There are two aspects to this:
- (bugfix) raise a proper exception when an object too large for handling by pickle is given
- (feature) improve the pickle protocol to handle objects larger than (2**31-1) elements

The improvement to the pickle protocol should probably be considered along other improvements, because we don't want to create a new protocol too often.

See also issue9614.