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bpo-21536: On Cygwin, C extensions must be linked with libpython (GH-13549) 

It is also possible to link against a library or executable with a
statically linked libpython, but not both with the same DLL.  In fact
building a statically linked python is currently broken on Cygwin
for other (related) reasons.

The same problem applies to other POSIX-like layers over Windows
(MinGW, MSYS) but Python's build system does not seem to attempt
to support those platforms at the moment.
This commit is contained in:
E. M. Bray 2019-05-24 17:33:47 +02:00 committed by Victor Stinner
parent 438a12dd9d
commit c994c8fc19
6 changed files with 40 additions and 26 deletions
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2
Doc/distutils/apiref.rst
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@ -290,7 +290,7 @@ the full reference.
.. versionchanged:: 3.8
On Unix, C extensions are no longer linked to libpython except on
Android.
Android and Cygwin.
.. class:: Distribution

17
Doc/whatsnew/3.8.rst
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@ -138,7 +138,8 @@ environment variable, can be set using the new ``./configure --with-trace-refs``
build option.
(Contributed by Victor Stinner in :issue:`36465`.)
On Unix, C extensions are no longer linked to libpython except on Android.
On Unix, C extensions are no longer linked to libpython except on Android
and Cygwin.
It is now possible
for a statically linked Python to load a C extension built using a shared
library Python.
@ -163,8 +164,8 @@ previous command fails (replace ``X.Y`` with the Python version).
On the other hand, ``pkg-config python3.8 --libs`` no longer contains
``-lpython3.8``. C extensions must not be linked to libpython (except on
Android, case handled by the script); this change is backward incompatible on
purpose.
Android and Cygwin, whose cases are handled by the script);
this change is backward incompatible on purpose.
(Contributed by Victor Stinner in :issue:`36721`.)
f-strings now support = for quick and easy debugging
@ -1061,12 +1062,12 @@ Changes in the C API
instead.
(Contributed by Victor Stinner in :issue:`36728`.)
* On Unix, C extensions are no longer linked to libpython except on
Android. When Python is embedded, ``libpython`` must not be loaded with
* On Unix, C extensions are no longer linked to libpython except on Android
and Cygwin. When Python is embedded, ``libpython`` must not be loaded with
``RTLD_LOCAL``, but ``RTLD_GLOBAL`` instead. Previously, using
``RTLD_LOCAL``, it was already not possible to load C extensions which were
not linked to ``libpython``, like C extensions of the standard library built
by the ``*shared*`` section of ``Modules/Setup``.
``RTLD_LOCAL``, it was already not possible to load C extensions which
were not linked to ``libpython``, like C extensions of the standard
library built by the ``*shared*`` section of ``Modules/Setup``.
* Use of ``#`` variants of formats in parsing or building value (e.g.
:c:func:`PyArg_ParseTuple`, :c:func:`Py_BuildValue`, :c:func:`PyObject_CallFunction`,

24
Lib/distutils/command/build_ext.py
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@ -714,19 +714,31 @@ class build_ext(Command):
# don't extend ext.libraries, it may be shared with other
# extensions, it is a reference to the original list
return ext.libraries + [pythonlib]
else:
# On Android only the main executable and LD_PRELOADs are considered
# to be RTLD_GLOBAL, all the dependencies of the main executable
# remain RTLD_LOCAL and so the shared libraries must be linked with
# libpython when python is built with a shared python library (issue
# bpo-21536).
else:
# On Cygwin (and if required, other POSIX-like platforms based on
# Windows like MinGW) it is simply necessary that all symbols in
# shared libraries are resolved at link time.
from distutils.sysconfig import get_config_var
link_libpython = False
if get_config_var('Py_ENABLE_SHARED'):
# Either a native build on an Android device or the
# cross-compilation of Python.
if (hasattr(sys, 'getandroidapilevel') or
('_PYTHON_HOST_PLATFORM' in os.environ and
get_config_var('ANDROID_API_LEVEL') != 0)):
# A native build on an Android device or on Cygwin
if hasattr(sys, 'getandroidapilevel'):
link_libpython = True
elif sys.platform == 'cygwin':
link_libpython = True
elif '_PYTHON_HOST_PLATFORM' in os.environ:
# We are cross-compiling for one of the relevant platforms
if get_config_var('ANDROID_API_LEVEL') != 0:
link_libpython = True
elif get_config_var('MACHDEP') == 'cygwin':
link_libpython = True
if link_libpython:
ldversion = get_config_var('LDVERSION')
return ext.libraries + ['python' + ldversion]

3
Misc/NEWS.d/3.8.0a4.rst
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@ -1052,7 +1052,8 @@ Remove the stale scriptsinstall Makefile target.
.. nonce: ACQkiC
.. section: Build
On Unix, C extensions are no longer linked to libpython except on Android.
On Unix, C extensions are no longer linked to libpython except on Android
and Cygwin.
It is now possible for a statically linked Python to load a C extension
built using a shared library Python.

4
configure vendored
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@ -15129,9 +15129,9 @@ LDVERSION='$(VERSION)$(ABIFLAGS)'
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $LDVERSION" >&5
$as_echo "$LDVERSION" >&6; }
# On Android the shared libraries must be linked with libpython.
# On Android and Cygwin the shared libraries must be linked with libpython.
if test -z "$ANDROID_API_LEVEL"; then
if test -z "$ANDROID_API_LEVEL" -o "$MACHDEP" != "cygwin"; then
LIBPYTHON=''
else
LIBPYTHON="-lpython${VERSION}${ABIFLAGS}"

4
configure.ac
View File

@ -4620,9 +4620,9 @@ AC_MSG_CHECKING(LDVERSION)
LDVERSION='$(VERSION)$(ABIFLAGS)'
AC_MSG_RESULT($LDVERSION)
# On Android the shared libraries must be linked with libpython.
# On Android and Cygwin the shared libraries must be linked with libpython.
AC_SUBST(LIBPYTHON)
if test -z "$ANDROID_API_LEVEL"; then
if test -z "$ANDROID_API_LEVEL" -o "$MACHDEP" != "cygwin"; then
LIBPYTHON=''
else
LIBPYTHON="-lpython${VERSION}${ABIFLAGS}"