[issue29753] Ctypes Packing Bitfields Incorrectly - Linux
Marc Le Roy <mleroy...@gmail.com> added the comment: No solution found to solve this issue ? The anomaly is not a cross platform inconsistency, it is an inconsistency between the behaviours of GCC and ctypes, both under Linux or Cygwin, when defining packed structures : [Marc@I7-860 ~/dev/python/ctypes-bitfields-bug] make test ./bitfield_test1 sizeof(BF32) = 12 ; Memory dump of BF32 = 0x sizeof(BF64) = 12 ; Memory dump of BF64 = 0x python3 bitfield_test1.py sizeof(BF32) = 16 ; Memory dump of BF32 = 0xff00ff00ff00ff00 sizeof(BF64) = 16 ; Memory dump of BF64 = 0x -- Added file: https://bugs.python.org/file47511/ctypes-bitfields-bug.tar.gz ___ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue29753> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue29753] Ctypes Packing Bitfields Incorrectly - Linux
Change by Marc Le Roy <mleroy...@gmail.com>: -- nosy: +mleroy003 ___ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue29753> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue31987] Ctypes Packing Bitfields Incorrectly - GCC both Linux and Cygwin
New submission from Marc Le Roy <mleroy...@gmail.com>:
The structure :
typedef struct __attribute__ ((packed)) {
unsigned int F0:24;
unsigned int F3:24;
unsigned int F6:24;
unsigned int F9:24;
} StructF_T;
is mapped as expected by GCC under both Linux and Cygwin.
As expected, the memory layout seen by the C program is :
0x11223344
Using this definition :
class StructF(ctypes.BigEndianStructure):
_pack_ = 1
_fields_ = [
('F0', ctypes.c_uint, 24),
('F3', ctypes.c_uint, 24),
('F6', ctypes.c_uint, 24),
('F9', ctypes.c_uint, 24),
]
The memory layout seen from Python is not consistent :
0x1100220033004400
It seems that the pack option is ignored by ctypes in such a case.
I found the same problem using both ctypes.BigEndianStructure and
ctypes.LittleEndianStructure
--
components: ctypes
messages: 305914
nosy: mleroy003
priority: normal
severity: normal
status: open
title: Ctypes Packing Bitfields Incorrectly - GCC both Linux and Cygwin
versions: Python 3.6
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