New submission from berthin <berthin...@hotmail.com>:
Hi all, I found one issue related to bitfields and ctypes, and although there is a similar issue already opened (https://bugs.python.org/issue29753), that only covers the case with pragmas. Please, consider the following scenario: >>> from ctypes import * >>> class X(Structure): ... _fields_ = [("a", c_uint8, 8), ("b", c_uint8, 8), ("c", c_uint32, 16)] ... >>> sizeof(X) 5 Which seems to be incorrect, because what natively C does is to generate a 4bytes struct. root@0bc6a647abaa:/target/cpython-fix# cat sample.c #include <stdio.h> #include <stdint.h> struct X { uint8_t a; uint8_t b; uint32_t c:16; } X; int main() { printf("%u\n", sizeof(X)); } root@0bc6a647abaa:/target/cpython-fix# gcc sample.c -o a && ./a 4 Also, if I use different databtypes I get what I expect (a struct of 4 bytes). >>> X = type('X', (Structure,), {'_fields_': [('a', c_uint32, 8), ('b', >>> c_uint32, 8), ('c', c_uint32, 16)]}) >>> sizeof(X) 4 >>> X = type('X', (Structure,), {'_fields_': [('a', c_uint16, 8), ('b', >>> c_uint16, 8), ('c', c_uint16, 16)]}) >>> sizeof(X) 4 >>> X = type('X', (Structure,), {'_fields_': [('a', c_uint8, 8), ('b', c_uint8, >>> 8), ('c', c_uint16, 16)]}) >>> sizeof(X) 4 I tried to debug a little bit, adding some prints before and after calling *PyCField_FromDesc* in *Modules/_ctypes/stgdict.c:L603*.=, if someone wants to look at it, the logs are attached / one log file per each test, using the following gdb init: # before break stgdict.c:601 commands p field_size p bitofs p size p align p *dict continue end # after break stgdict.c:617 commands p field_size p bitofs p size p align p *(CFieldObject*) prop continue end Hope someone could spot the issue, I will also try to investigate it by my own. Best, P.S. For the tests, I worked on top of bpo-29753 (https://github.com/python/cpython/pull/19850) ---------- components: ctypes files: bitfields.zip messages: 377953 nosy: FFY00, berthin priority: normal severity: normal status: open title: Incorrect struct definition with bitfields type: behavior versions: Python 3.10, Python 3.8, Python 3.9 Added file: https://bugs.python.org/file49493/bitfields.zip _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue41932> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
