Bug 800187

Description of problem:
I've been writing an experimental static analysis tool to detect bugs commonly occurring within C Python extension modules:
  https://fedorahosted.org/gcc-python-plugin/
  http://gcc-python-plugin.readthedocs.org/en/latest/cpychecker.html
  http://fedoraproject.org/wiki/Features/StaticAnalysisOfPythonRefcounts

I ran the latest version of the tool (in git master; post 0.9) on
python-yenc-0.3-10.fc17.src.rpm, and it reports various errors.

You can see a list of errors here, triaged into categories (from most significant to least significant):
http://fedorapeople.org/~dmalcolm/gcc-python-plugin/2012-03-05/python-yenc-0.3-10.fc17/

I've manually reviewed the issues reported by the tool.

Within the category "Unclassified errors" the 1 issue reported is difficult to read (the line numbering seems to be out of sync; the wrong lines are being highlighted), but I think it's complaining about this line:
     172                 encoded++;
which I *think* is a genuine bug: where does "encoded" get initialized?

Within the category "Segfaults within error-handling paths" the 2 issues reported appear to be genuine crashers under low-memory conditions, where the call to PyString_FromStringAndSize could fail, returning NULL:
    Py_output_string = PyString_FromStringAndSize(output_buffer, output_len);
    retval = Py_BuildValue("(S,i,i)", Py_output_string, ...
    ... 
    Py_DECREF(Py_output_string);  << segfault

It may be easier to instead to use the "s#" format code to Py_BuildValue so that it builds the intermediate string object:
    retval = Py_BuildValue("(s#,i,i)", output_buffer, output_len, ....)
and it correctly performs the necessary error-handling.
(see http://docs.python.org/c-api/arg.html#Py_BuildValue for more information).

There may of course be other bugs in my checker tool.

Hope this is helpful; let me know if you need help reading the logs that the tool generates - I know that it could use some improvement.

Version-Release number of selected component (if applicable):
python-yenc-0.3-10.fc17
gcc-python-plugin post-0.9 git 11462291a66c8db693c8884cb84b795bb5988ffb running the checker in an *f16* chroot