load_pop() pops a value if the stack length is >= 0. The test is wrong:
if the length is zero, the stack is empty and stackUnderflow() have to
be called.

Example:

  $ ../../python -c "import cPickle; cPickle.loads('0')"
  Erreur de segmentation

Can you add a test for this?

> Can you add a test for this?

I wasn't sure of the right place to add the test. I tried
Lib/test/pickletester.py, but it doesn't work because UnpicklingError
is not defined there.

Well, here is a new version of my patch with an unit test.

Oops, cpickle_load_pop-2.patch contains an useless variable (picklingError 
= pickle.UnpicklingError). Here is the version 3 of my patch.

This seems to have been introduced in r72930 when the stackUnderflow()
was moved from the top of the function to the bottom.  It used to test
for len > 0.

Question, should cPickle and pickle be raising the same error here? 
UnpicklingError is defined in pickle.py and never used but cPickle.c
uses it frequently.

The patch works correctly on 2.7.

It should be applied on trunk, and backported to other branches, too.

(issue7542 is marked as duplicate of this one)

I moved the test to test.pickletester, so that it can be used for
all 3 tests:
 test_pickle
 test_cpickle
 test_xpickle

(and backported a test which was only on py3k)

Committed in all four branches. Thank you Victor and Florent!

> Committed in all four branches.

trunk: r77352