New submission from Kyle Altendorf: I am cross compiling Python 3.5.2 for use on a 32-bit ARM processor with Linux. I use socket.CAN_EFF_FLAG and noticed that it is negative on the target despite being positive on my host (64-bit Intel Linux).
Host: altendky@tp:~$ uname -a Linux tp 4.4.0-31-generic #50-Ubuntu SMP Wed Jul 13 00:07:12 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux altendky@tp:~$ python3 --version Python 3.5.2 altendky@tp:~$ python3 -c 'import socket; print(socket.CAN_EFF_FLAG)' 2147483648 ^^ Is expected Target: root@rosi ~$ uname -a Linux rosi 3.0.101-rt130-opusa3-2.1.0-2 #1 PREEMPT Tue Apr 12 13:49:26 CEST 2016 armv6l GNU/Linux root@rosi ~$ /opt/epc/bin/python3 --version Python 3.5.2 root@rosi ~$ /opt/epc/bin/python3 -c 'import socket; print(socket.CAN_EFF_FLAG)' -2147483648 ^^ Is not expected to be negative Only CAN_EFF_FLAG reference in my source used to cross build Python: Modules/socketmodule.c: PyModule_AddIntMacro(m, CAN_EFF_FLAG); Definition in cross compiler include: altendky@tp:/opt/freescale/usr/local/gcc-4.6.2-glibc-2.13-linaro-multilib-2011.12/fsl-linaro-toolchain/arm-fsl-linux-gnueabi/multi-libs/default/usr/include$ grep -r CAN_EFF_FLAG linux/can.h:#define CAN_EFF_FLAG 0x80000000U /* EFF/SFF is set in the MSB */ For reference, here it is on the host system (looks the same to me): altendky@tp:/usr/include$ grep -r CAN_EFF_FLAG linux/can.h:#define CAN_EFF_FLAG 0x80000000U /* EFF/SFF is set in the MSB */ But perhaps this `long` type for the value is the issue? If signed and only 4-bytes as is the case on my target then this will misinterpret the 0x80000000U literal resulting in the above observed -2147483648. PyModule_AddIntConstant(PyObject *m, const char *name, long value) On my target system, printf("%d", sizeof(long)) yields 4. For now I just work around it in my application by reassigning it to be it's absolute value. socket.CAN_EFF_FLAG = abs(socket.CAN_EFF_FLAG) ---------- messages: 277036 nosy: altendky priority: normal severity: normal status: open title: PyModule_AddIntConstant() wraps >=2^32 values when long is 4 bytes type: behavior versions: Python 3.5 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue28215> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com