a) hope this is not something you expect to be on -list, if so - my apologies! Getting this message (here using c99 as compiler name, but same issue with xlc as compiler name) c99 -qarch=pwr4 -qbitfields=signed -DNDEBUG -O -I. -IInclude -I./Include -I/data/prj/aixtools/python/python-2.7.11.2/Include -I/data/prj/aixtools/python/python-2.7.11.2 -c /data/prj/aixtools/python/python-2.7.11.2/Modules/_ctypes/_ctypes_test.c -o build/temp.aix-5.3-2.7/data/prj/aixtools/python/python-2.7.11.2/Modules/_ctypes/_ctypes_test.o "/data/prj/aixtools/python/python-2.7.11.2/Modules/_ctypes/_ctypes_test.c", line 387.5: 1506-009 (S) Bit field M must be of type signed int, unsigned int or int. "/data/prj/aixtools/python/python-2.7.11.2/Modules/_ctypes/_ctypes_test.c", line 387.5: 1506-009 (S) Bit field N must be of type signed int, unsigned int or int. "/data/prj/aixtools/python/python-2.7.11.2/Modules/_ctypes/_ctypes_test.c", line 387.5: 1506-009 (S) Bit field O must be of type signed int, unsigned int or int. "/data/prj/aixtools/python/python-2.7.11.2/Modules/_ctypes/_ctypes_test.c", line 387.5: 1506-009 (S) Bit field P must be of type signed int, unsigned int or int. "/data/prj/aixtools/python/python-2.7.11.2/Modules/_ctypes/_ctypes_test.c", line 387.5: 1506-009 (S) Bit field Q must be of type signed int, unsigned int or int. "/data/prj/aixtools/python/python-2.7.11.2/Modules/_ctypes/_ctypes_test.c", line 387.5: 1506-009 (S) Bit field R must be of type signed int, unsigned int or int. "/data/prj/aixtools/python/python-2.7.11.2/Modules/_ctypes/_ctypes_test.c", line 387.5: 1506-009 (S) Bit field S must be of type signed int, unsigned int or int. for: struct BITS { int A: 1, B:2, C:3, D:4, E: 5, F: 6, G: 7, H: 8, I: 9; short M: 1, N: 2, O: 3, P: 4, Q: 5, R: 6, S: 7; }; in short xlC v11 does not like short (xlC v7 might have accepted it, but "32-bit machines were common then". I am guessing that 16-bit is not well liked on 64-bit hw now. reference for xlC v7, where short was (apparently) still accepted: http://www.serc.iisc.ernet.in/facilities/ComputingFacilities/systems/cluster... I am taking this is from xlC v7 documentation from the URL, not because I know it personally. So - my question: if "short" is unacceptable for POWER, or maybe only xlC (not tried with gcc) - how terrible is this, and is it possible to adjust the test so - the test is accurate? I am going to modify the test code so it is struct BITS { signed int A: 1, B:2, C:3, D:4, E: 5, F: 6, G: 7, H: 8, I: 9; unsigned int M: 1, N: 2, O: 3, P: 4, Q: 5, R: 6, S: 7; }; And see what happens - BUT - what does this have for impact on python - assuming that "short" bitfields are not supported? p.s. not submitting this a bug (now) as it may just be that "you" consider it a bug in xlC to not support (signed) short bit fields. p.p.s. Note: xlc, by default, considers bitfields to be unsigned. I was trying to force them to signed with -qbitfields=signed - and I still got messages. So, going back to defaults.