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gh-82909: Update PC/pyconfig.h to allow disabling pragma based auto-linking (GH-19740)

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Define Py_NO_LINK_LIB to build extension disabling pragma based auto-linking. This is relevant when using build-system generator (e.g CMake) where the linking is explicitly handled
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Jean-Christophe Fillion-Robin 2025-03-11 00:40:17 +07:00 • committed by GitHub
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commit c3487c941d
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4 changed files with 56 additions and 14 deletions
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56
Doc/extending/windows.rst
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@ -96,6 +96,13 @@ gives you access to spam's names, but does not create a separate copy. On Unix,
linking with a library is more like ``from spam import *``; it does create a
separate copy.
.. c:macro:: Py_NO_LINK_LIB
Turn off the implicit, ``#pragma``-based linkage with the Python
library, performed inside CPython header files.
.. versionadded:: 3.14
.. _win-dlls:
@ -108,21 +115,46 @@ Using DLLs in Practice
Windows Python is built in Microsoft Visual C++; using other compilers may or
may not work. The rest of this section is MSVC++ specific.
When creating DLLs in Windows, you must pass :file:`pythonXY.lib` to the linker.
To build two DLLs, spam and ni (which uses C functions found in spam), you could
use these commands::
When creating DLLs in Windows, you can use the CPython library in two ways:
cl /LD /I/python/include spam.c ../libs/pythonXY.lib
cl /LD /I/python/include ni.c spam.lib ../libs/pythonXY.lib
1. By default, inclusion of :file:`PC/pyconfig.h` directly or via
:file:`Python.h` triggers an implicit, configure-aware link with the
library. The header file chooses :file:`pythonXY_d.lib` for Debug,
:file:`pythonXY.lib` for Release, and :file:`pythonX.lib` for Release with
the `Limited API <stable-application-binary-interface>`_ enabled.
The first command created three files: :file:`spam.obj`, :file:`spam.dll` and
:file:`spam.lib`. :file:`Spam.dll` does not contain any Python functions (such
as :c:func:`PyArg_ParseTuple`), but it does know how to find the Python code
thanks to :file:`pythonXY.lib`.
To build two DLLs, spam and ni (which uses C functions found in spam), you
could use these commands::
The second command created :file:`ni.dll` (and :file:`.obj` and :file:`.lib`),
which knows how to find the necessary functions from spam, and also from the
Python executable.
cl /LD /I/python/include spam.c
cl /LD /I/python/include ni.c spam.lib
The first command created three files: :file:`spam.obj`, :file:`spam.dll`
and :file:`spam.lib`. :file:`Spam.dll` does not contain any Python
functions (such as :c:func:`PyArg_ParseTuple`), but it does know how to find
the Python code thanks to the implicitly linked :file:`pythonXY.lib`.
The second command created :file:`ni.dll` (and :file:`.obj` and
:file:`.lib`), which knows how to find the necessary functions from spam,
and also from the Python executable.
2. Manually by defining :c:macro:`Py_NO_LINK_LIB` macro before including
:file:`Python.h`. You must pass :file:`pythonXY.lib` to the linker.
To build two DLLs, spam and ni (which uses C functions found in spam), you
could use these commands::
cl /LD /DPy_NO_LINK_LIB /I/python/include spam.c ../libs/pythonXY.lib
cl /LD /DPy_NO_LINK_LIB /I/python/include ni.c spam.lib ../libs/pythonXY.lib
The first command created three files: :file:`spam.obj`, :file:`spam.dll`
and :file:`spam.lib`. :file:`Spam.dll` does not contain any Python
functions (such as :c:func:`PyArg_ParseTuple`), but it does know how to find
the Python code thanks to :file:`pythonXY.lib`.
The second command created :file:`ni.dll` (and :file:`.obj` and
:file:`.lib`), which knows how to find the necessary functions from spam,
and also from the Python executable.
Not every identifier is exported to the lookup table. If you want any other
modules (including Python) to be able to see your identifiers, you have to say

4
Doc/whatsnew/3.14.rst
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@ -1415,6 +1415,10 @@ Build changes
* GNU Autoconf 2.72 is now required to generate :file:`configure`.
(Contributed by Erlend Aasland in :gh:`115765`.)
* ``#pragma``-based linking with ``python3*.lib`` can now be switched off
with :c:expr:`Py_NO_LINK_LIB`. (Contributed by Jean-Christophe
Fillion-Robin in :gh:`82909`.)
.. _whatsnew314-pep761:
PEP 761: Discontinuation of PGP signatures

2
Misc/NEWS.d/next/Build/2023-04-02-14-20-29.gh-issue-82909.LGcZJy.rst Normal file
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@ -0,0 +1,2 @@
``#pragma``-based linking with ``python3*.lib`` can now be switched off with
:c:expr:`Py_NO_LINK_LIB`. Patch by Jean-Christophe Fillion-Robin.

8
PC/pyconfig.h.in
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@ -311,9 +311,13 @@ Py_NO_ENABLE_SHARED to find out. Also support MS_NO_COREDLL for b/w compat */
#ifdef MS_COREDLL
# if !defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_BUILTIN)
/* not building the core - must be an ext */
# if defined(_MSC_VER)
# if defined(_MSC_VER) && !defined(Py_NO_LINK_LIB)
/* So MSVC users need not specify the .lib
file in their Makefile */
/* Define Py_NO_LINK_LIB to build extension disabling pragma
based auto-linking.
This is relevant when using build-system generator (e.g CMake) where
the linking is explicitly handled */
# if defined(Py_GIL_DISABLED)
# if defined(_DEBUG)
# pragma comment(lib,"python314t_d.lib")
@ -331,7 +335,7 @@ Py_NO_ENABLE_SHARED to find out. Also support MS_NO_COREDLL for b/w compat */
# pragma comment(lib,"python314.lib")
# endif /* _DEBUG */
# endif /* Py_GIL_DISABLED */
# endif /* _MSC_VER */
# endif /* _MSC_VER && !Py_NO_LINK_LIB */
# endif /* Py_BUILD_CORE */
#endif /* MS_COREDLL */