A segmentation fault is generated in _ctypes.so when calling a function that returns a char pointer on a system 
with 64-bit pointer types.  The attached crash dump is from a Python 2.6.3 built from MacPorts ("port install 
python26 +no_tkinter"), but the same behaviour occurs with the Python 2.6.1 installed by Apple.

To reproduce, build the attached sample program ("testlib.c"):

% gcc -Wall -c testlib.o
% ld -dylib -o testlib.so testlib.o

Then, in Python:

# Common setup for each of the cases below.
>>> from ctypes import *
>>> lib = CDLL('testlib.so')

# Case 1: Integer return value (no crash).
>>> get_value = CFUNCTYPE(c_int)(lib.get_value)
>>> get_value()
12345

# Case 2: Pointer argument value (no crash).
>>> buf = create_string_buffer(256)
>>> copy_message = CFUNCTYPE(None, c_char_p)(lib.copy_message)
>>> copy_message(buf)

# Case 3: Pointer return value (crash).
>>> get_message = CFUNCTYPE(c_char_p)(lib.get_message)
>>> get_message()
Segmentation fault

-- System information:

% uname -a
MacOS 10.6.1
Darwin gorion.local 10.0.0 Darwin Kernel Version 10.0.0: Fri Jul 31 22:47:34 PDT 2009; root:xnu-
1456.1.25~1/RELEASE_I386 i386

% python
Python 2.6.3 (r263:75183, Oct 17 2009, 01:49:30) 
[GCC 4.2.1 (Apple Inc. build 5646) (dot 1)] on darwin

% gcc --version
i686-apple-darwin10-gcc-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5646) (dot 1)