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cxx pthread check is not overrideable #86082

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cxx pthread check is not overrideable#86082
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3.8 (EOL)end of lifebuildThe build process and cross-build

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@virtuald
virtuald
mannequin
opened on Oct 3, 2020
BPO 41916
Nosy @moreati, @virtuald
PRs
  • bpo-41916: allow cross-compiled python to have -pthread set for CXX #22525
    		•

    Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    assignee = None
closed_at = None
created_at = <Date 2020-10-03.07:20:28.934>
labels = ['build', '3.8']
title = 'cxx pthread check is not overrideable'
updated_at = <Date 2020-10-25.19:38:59.827>
user = 'https://github.com/virtuald'

    bugs.python.org fields:

    activity = <Date 2020-10-25.19:38:59.827>
actor = 'virtuald'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Cross-Build']
creation = <Date 2020-10-03.07:20:28.934>
creator = 'virtuald'
dependencies = []
files = []
hgrepos = []
issue_num = 41916
keywords = ['patch']
message_count = 2.0
messages = ['377858', '379602']
nosy_count = 2.0
nosy_names = ['Alex.Willmer', 'virtuald']
pr_nums = ['22525']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue41916'
versions = ['Python 3.8']

    Activity

    1. virtuald commented on Oct 3, 2020

      @virtuald
      virtualdmannequin
      on Oct 3, 2020
      MannequinAuthor

      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?

    2. virtuald
      added
      3.8 (EOL)end of life
      buildThe build process and cross-build
      on Oct 3, 2020

    3. virtuald commented on Oct 25, 2020

      @virtuald
      virtualdmannequin
      on Oct 25, 2020
      MannequinAuthor

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

    4. ezio-melotti
      transferred this issue fromon Apr 10, 2022
    5. gpshead
      added a commit that references this issue on Jan 5, 2023

      gh-86082: bpo-41916: allow cross-compiled python to have -pthread set…

      cc87487

    6. gpshead commented on Jan 5, 2023

      @gpshead
      gpshead
      on Jan 5, 2023
      Member

      thanks!

    7. gpshead
      closed this as completedon Jan 5, 2023
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