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.
diff --git a/Doc/distutils/apiref.rst b/Doc/distutils/apiref.rst
index cbeedab..2601d30 100644
--- a/Doc/distutils/apiref.rst
+++ b/Doc/distutils/apiref.rst
@@ -290,7 +290,7 @@
.. versionchanged:: 3.8
On Unix, C extensions are no longer linked to libpython except on
- Android.
+ Android and Cygwin.
.. class:: Distribution
diff --git a/Doc/whatsnew/3.8.rst b/Doc/whatsnew/3.8.rst
index b91f7bc..b5d70b5 100644
--- a/Doc/whatsnew/3.8.rst
+++ b/Doc/whatsnew/3.8.rst
@@ -138,7 +138,8 @@
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 @@
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 @@
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`,
diff --git a/Lib/distutils/command/build_ext.py b/Lib/distutils/command/build_ext.py
index c3b9602..2d7cdf0 100644
--- a/Lib/distutils/command/build_ext.py
+++ b/Lib/distutils/command/build_ext.py
@@ -714,20 +714,32 @@
# don't extend ext.libraries, it may be shared with other
# extensions, it is a reference to the original list
return ext.libraries + [pythonlib]
- # 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 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).
+ # 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)):
- ldversion = get_config_var('LDVERSION')
- return ext.libraries + ['python' + ldversion]
+ # 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]
return ext.libraries
diff --git a/Misc/NEWS.d/3.8.0a4.rst b/Misc/NEWS.d/3.8.0a4.rst
index b92e60a..80e01d9 100644
--- a/Misc/NEWS.d/3.8.0a4.rst
+++ b/Misc/NEWS.d/3.8.0a4.rst
@@ -1052,7 +1052,8 @@
.. 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.
diff --git a/configure b/configure
index 9f2007f..c76eb7a 100755
--- a/configure
+++ b/configure
@@ -15129,9 +15129,9 @@
{ $as_echo "$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}${ABIFLAGS}"
diff --git a/configure.ac b/configure.ac
index 0baf0d6..99d99ae 100644
--- a/configure.ac
+++ b/configure.ac
@@ -4620,9 +4620,9 @@
LDVERSION='$(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}"