On Thu, Oct 24, 2019 at 07:47:10PM +0200, Thomas Petazzoni wrote:
kmod's configure.ac uses the -Wl,--no-undefined linker flag to verify at link time that all symbols of shared libraries are available, and that there are no undefined symbols. This make perfect sense for regular shared libraries. However, for Python extensions, which will be dlopen()ed inside the Python interpreter, it makes less sense. Since Python 3.8, there is a change in python-config script and Python's pkg-config file: it no longer links Python extensions with the libpython library. See https://docs.python.org/dev/whatsnew/3.8.html#debug-build-uses-the-same-abi-as-release-build which states: 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 and Cygwin, whose cases are handled by the script); this change is backward incompatible on purpose. (Contributed by Victor Stinner in bpo-36721.) So, when linking the kmod Python extensions, it currently fails with numerous unresolved symbols, that were previously provided by libpython: /home/test/autobuild/run/instance-3/output-1/host/opt/ext-toolchain/bin/../lib/gcc/powerpc64-buildroot-linux-gnu/7.4.0/../../../../powerpc64-buildroot-linux-gnu/bin/ld: libkmod/python/kmod/.libs/list_la-list.o: in function `__Pyx_PyObject_GetAttrStr': list.c:(.text.__Pyx_PyObject_GetAttrStr+0x48): undefined reference to `PyObject_GetAttr' /home/test/autobuild/run/instance-3/output-1/host/opt/ext-toolchain/bin/../lib/gcc/powerpc64-buildroot-linux-gnu/7.4.0/../../../../powerpc64-buildroot-linux-gnu/bin/ld: libkmod/python/kmod/.libs/list_la-list.o: in function `__pyx_tp_dealloc_4kmod_4list_ModListItem': list.c:(.text.__pyx_tp_dealloc_4kmod_4list_ModListItem+0x78): undefined reference to `PyObject_CallFinalizerFromDealloc' /home/test/autobuild/run/instance-3/output-1/host/opt/ext-toolchain/bin/../lib/gcc/powerpc64-buildroot-linux-gnu/7.4.0/../../../../powerpc64-buildroot-linux-gnu/bin/ld: libkmod/python/kmod/.libs/list_la-list.o: in function `__pyx_tp_dealloc_4kmod_4list_ModList': list.c:(.text.__pyx_tp_dealloc_4kmod_4list_ModList+0x30): undefined reference to `PyErr_Fetch' [Complete log at http://autobuild.buildroot.net/results/79a/79a5a0398723e8cfea0d0aa3dec5f7649aee4c63/build-end.log] Linking with libpython is no longer recommended: those symbols should remain unresolved in the Python extensions, as they wil be properly resolved when the Python extension gets loaded into the Python interpreter. Since we want to keep -Wl,--no-undefined globally in kmod, we leave the configure.ac file unchanged, and instead, specifically in the LDFLAGS used to build the Python extensions, we override -Wl,--no-undefined with -Wl,-z,undefs. Ideally, -Wl,--no-undefined is the same as -Wl,-z,defs, and the effect of these options can be canceled on the linker command line by a following -Wl,-z,undefs (see the ld man page for details). Signed-off-by: Thomas Petazzoni <thomas.petazzoni@xxxxxxxxxxx> Cc: Victor Stinner <victor.stinner@xxxxxxxxx>
applied, thanks Lucas De Marchi
--- Makefile.am | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/Makefile.am b/Makefile.am index c5c2f06..8e9c90d 100644 --- a/Makefile.am +++ b/Makefile.am @@ -173,7 +173,7 @@ CPYTHON_MODULE_CFLAGS = \ $(AM_CFLAGS) -DCPYTHON_COMPILING_IN_PYPY=0 \ $(PYTHON_NOWARN) $(PYTHON_CFLAGS) \ -fvisibility=default -CPYTHON_MODULE_LDFLAGS = $(AM_LDFLAGS) -module -avoid-version -shared +CPYTHON_MODULE_LDFLAGS = $(AM_LDFLAGS) -module -avoid-version -shared -Wl,-z,undefs if BUILD_PYTHON pkgpyexec_LTLIBRARIES = \ -- 2.21.0
