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docs: GNU symbol visibility option #994

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docs: GNU symbol visibility option #994

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docs: GNU symbol visibility option
aaron-bray Jun 7, 2023
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[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Jun 8, 2023
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16 changes: 16 additions & 0 deletions docs/usage.rst
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Expand Up @@ -572,6 +572,22 @@ If a file is added to the CMake build system by updating one of the ``CMakeLists
will not explicitly reconfigure the project. Instead, the generated build-system will automatically
detect the change and reconfigure the project after :meth:`skbuild.cmaker.CMaker.make` is called.

.. _symbol_visibility:

Controlling exported symbol visibility
--------------------------------------

When using a GNU based compiler on Linux, scikit-build will reduce the binary size by removing all the native exported methods.
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This is part of PythonExtensions, not all of scikit-build, right? Most or all pybind11 and nanobind projects do not use PythonExtensions. Also, FindPythonInterp and FindPythonLibs is being removed (sort-of) from CMake 3.27; users using FindPython won't be affected by this variable either, I believe.

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@jcfr is there another caveot I am missing as to when this would be used?

By default, only the ``PyInit_<moduleName>`` (or ``init<moduleName>``) entry point is exported from the native module.
If you need to preserve native exports in your module, you may set ``SKBUILD_GNU_SKIP_LOCAL_SYMBOL_EXPORT_OVERRIDE`` as a
`CMake option <https://scikit-build.readthedocs.io/en/latest/usage.html#cmake-configure-options>`_
or
`setup.py option <https://scikit-build.readthedocs.io/en/latest/usage.html#scikit-build-options>`_.

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@jcfr jcfr Jun 7, 2023 •
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Suggested change
Note that for Python >= 3.9, setting the option `SKBUILD_GNU_SKIP_LOCAL_SYMBOL_EXPORT_OVERRIDE` to `ON` allow to ...

It would be nice to further improve to provide some historical contest based on the summary available at #703 (comment)

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I added a little more detail as to how this works and on what systems.

Modules built with a GNU based compiler on Linux, can control exports through a `version script <https://ftp.gnu.org/old-gnu/Manuals/ld-2.9.1/html_node/ld_25.html>`_.
For this platform/compiler combination, regardless of the target Python version, scikit-build always creates a version script.
When this option is set to ``OFF``, a version script is created that specifies all local methods to be excluded from export.
When this option is set to ``ON``, a version script is created allowing all local methods to be exported and available in the built module.

Environment variable configuration
----------------------------------
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