[issue41916] cxx pthread check is not overrideable

[Dustin Spicuzza]

Dustin Spicuzza  added the comment:

FWIW, I've been using the patch in my PR and it seems to work.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue41916] cxx pthread check is not overrideable

[Dustin Spicuzza]

Change by Dustin Spicuzza :


--
keywords: +patch
pull_requests: +21530
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/22525

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue41916] cxx pthread check is not overrideable

[Dustin Spicuzza]

New submission from Dustin Spicuzza :

I'm cross-compiling python to ARM, following instructions from the crossenv 
project @ 
https://crossenv.readthedocs.io/en/latest/quickstart.html#build-or-obtain-host-python

I was getting pthread related errors when using cross-built extension modules. 
I realized the issue was that distutils wasn't passing -pthread to gcc.

On my native python (Fedora 32 Python 3.8):

>>> import pprint, distutils.sysconfig
>>> pprint.pprint({i: distutils.sysconfig.get_config_vars(i)[0] for i in ('CC', 
>>> 'CXX', 'LDSHARED')})
{'CC': 'gcc -pthread',
 'CXX': 'g++ -pthread',
 'LDSHARED': 'gcc -pthread -shared -Wl,-z,relro -Wl,--as-needed  -Wl,-z,now  '
 '-g  -Wl,-z,relro -Wl,--as-needed  -Wl,-z,now  -g'}

In my cross-compiled python environment:

>>> import pprint, distutils.sysconfig
>>> pprint.pprint({i: distutils.sysconfig.get_config_vars(i)[0] for i in ('CC', 
>>> 'CXX', 'LDSHARED')})
{'CC': 'arm-frc2020-linux-gnueabi-gcc',
 'CXX': 'arm-frc2020-linux-gnueabi-c++',
 'LDSHARED': 'arm-frc2020-linux-gnueabi-gcc -shared'}

As you can see, no -pthread flag. I went digging in the configure script and 
found this comment in configure.ac:2110:

# Some compilers won't report that they do not support -pthread,
# so we need to run a program to see whether it really made the
# function available.

... well, that doesn't work when cross-compiling. I looked at some other 
variables set to override things for cross compiling, and tried adding 
"ac_cv_pthread_is_default=no ac_cv_pthread=yes ac_cv_cxx_thread=yes" to my 
cross-compile ./configure, and it's closer:

>>> import pprint, distutils.sysconfig
>>> pprint.pprint({i: distutils.sysconfig.get_config_vars(i)[0] for i in ('CC', 
>>> 'CXX', 'LDSHARED')})
{'CC': 'arm-frc2020-linux-gnueabi-gcc -pthread',
 'CXX': 'arm-frc2020-linux-gnueabi-c++',
 'LDSHARED': 'arm-frc2020-linux-gnueabi-gcc -pthread -shared'}

Closer, but not there yet! It appears that the $ac_cv_cxx_thread is not 
externally settable (unlike ac_cv_pthread), which I guess is because it's not 
wrapped in a AC_CACHE_VAL macro?

It seems that the right fix would be for someone to use AC_CACHE_VAL to allow 
$ac_cv_cxx_thread to be set externally? I'm happy to cargo cult some code from 
other parts of configure.ac and make a PR for it, but it's not immediately 
clear (a) what bad side effects this could cause and (b) what the best 
mechanism to use to regenerate configure et al is?

--
components: Cross-Build
messages: 377858
nosy: Alex.Willmer, virtuald
priority: normal
severity: normal
status: open
title: cxx pthread check is not overrideable
versions: Python 3.8

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com