[galactic] [BUG] When cross compiling to aarch64 from x86_64 host PYTHON_MODULE_EXTENSION is not set #9

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1. clalancette

   assigned

   sloretz

   on Sep 9, 2021
2. AlexisTM commented on Oct 18, 2022

   

   AlexisTM

   on Oct 18, 2022

   Last edited by AlexisTM

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   It seems to be quite a long standing issue ;)

   I have been getting the same issue. The core problem being the suffix is being computed in the host instead of the target python interpreter.

   The logic is close to Pybind11's version:

   https://github.com/pybind/pybind11/blob/914c06fb252b6cc3727d0eedab6736e88a3fcb01/tools/pybind11NewTools.cmake#L110-L116

     execute_process(
       COMMAND
         "${${_Python}_EXECUTABLE}" "-c"
         "import sys, importlib; s = importlib.import_module('distutils.sysconfig' if sys.version_info < (3, 10) else 'sysconfig'); print(s.get_config_var('EXT_SUFFIX') or s.get_config_var('SO'))"
       OUTPUT_VARIABLE _PYTHON_MODULE_EXTENSION
       ERROR_VARIABLE _PYTHON_MODULE_EXTENSION_ERR
       OUTPUT_STRIP_TRAILING_WHITESPACE)

   This could (not in a portable way) be done by using qemu and running the sysroot's version of Python instead, under the rationale you need qemu to create the sysroot. (But some might just have the sysroot built for them)
3. AlexisTM commented on Oct 18, 2022

   

   AlexisTM

   on Oct 18, 2022

   Last edited by AlexisTM

   More actions

   Our quick solution is to fix those variables according to the python command executed on target (or though chroot & qemu in the sysroot)

   python3 -c "import sys, importlib; s = importlib.import_module('distutils.sysconfig' if sys.version_info < (3, 10) else 'sysconfig'); print(s.get_config_var('EXT_SUFFIX') or s.get_config_var('SO'))"
   

   # See: https://github.com/ros2/pybind11_vendor to have pybind11 version, then
   # See: https://github.com/pybind/pybind11/blob/8a4bca8216f94f64d9582997db5e7eaf2e4660b3/tools/pybind11NewTools.cmake#L98-L111
   # Note the point!
   set(PYTHON_MODULE_EXTENSION ".cpython-39-aarch64-linux-gnu.so")
   # python_cmake_module workaround, PYTHON_MODULE_EXTENSION is set to PYTHON_SOABI
   # See: https://github.com/ros2/python_cmake_module/blob/d31a0b13225786e076e537a6f1ba67ba5cb2e620/cmake/Modules/FindPythonExtra.cmake#L159-L197
   # Note the lack of point & .so
   set(PYTHON_SOABI cpython-39-aarch64-linux-gnu)

   Linked to ros2/pybind11_vendor#16