From 55a0a0aac503f5012ff2df7af37107544c757f19 Mon Sep 17 00:00:00 2001
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From: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
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Date: Tue, 22 Oct 2019 09:56:32 +0200
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Subject: [PATCH kmod] Do not check for undefined symbols when building the
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Python modules
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kmod's configure.ac uses the -Wl,--no-undefined linker flag to verify
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at link time that all symbols of shared libraries are available, and
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that there are no undefined symbols.
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This make perfect sense for regular shared libraries. However, for
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Python extensions, which will be dlopen()ed inside the Python
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interpreter, it makes less sense.
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Since Python 3.8, there is a change in python-config script and
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Python's pkg-config file: it no longer links Python extensions with
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the libpython library. See
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https://docs.python.org/dev/whatsnew/3.8.html#debug-build-uses-the-same-abi-as-release-build
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which states:
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On the other hand, pkg-config python3.8 --libs no longer contains
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-lpython3.8. C extensions must not be linked to libpython (except on
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Android and Cygwin, whose cases are handled by the script); this
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change is backward incompatible on purpose. (Contributed by Victor
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Stinner in bpo-36721.)
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So, when linking the kmod Python extensions, it currently fails with
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numerous unresolved symbols, that were previously provided by
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libpython:
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/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':
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list.c:(.text.__Pyx_PyObject_GetAttrStr+0x48): undefined reference to `PyObject_GetAttr'
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/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':
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list.c:(.text.__pyx_tp_dealloc_4kmod_4list_ModListItem+0x78): undefined reference to `PyObject_CallFinalizerFromDealloc'
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/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':
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list.c:(.text.__pyx_tp_dealloc_4kmod_4list_ModList+0x30): undefined reference to `PyErr_Fetch'
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[Complete log at http://autobuild.buildroot.net/results/79a/79a5a0398723e8cfea0d0aa3dec5f7649aee4c63/build-end.log]
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Linking with libpython is no longer recommended: those symbols should
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remain unresolved in the Python extensions, as they wil be properly
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resolved when the Python extension gets loaded into the Python
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interpreter.
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Since we want to keep -Wl,--no-undefined globally in kmod, we leave
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the configure.ac file unchanged, and instead, specifically in the
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LDFLAGS used to build the Python extensions, we override
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-Wl,--no-undefined with -Wl,-z,undefs. Ideally, -Wl,--no-undefined is
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the same as -Wl,-z,defs, and the effect of these options can be
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canceled on the linker command line by a following -Wl,-z,undefs (see
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the ld man page for details).
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Upstream: https://lore.kernel.org/linux-modules/20191024174710.9441-1-thomas.petazzoni@bootlin.com/
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Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
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Cc: Victor Stinner <victor.stinner@gmail.com>
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---
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Makefile.am | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/Makefile.am b/Makefile.am
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index c5c2f06..8e9c90d 100644
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--- a/Makefile.am
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+++ b/Makefile.am
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@@ -173,7 +173,7 @@ CPYTHON_MODULE_CFLAGS = \
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$(AM_CFLAGS) -DCPYTHON_COMPILING_IN_PYPY=0 \
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$(PYTHON_NOWARN) $(PYTHON_CFLAGS) \
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-fvisibility=default
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-CPYTHON_MODULE_LDFLAGS = $(AM_LDFLAGS) -module -avoid-version -shared
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+CPYTHON_MODULE_LDFLAGS = $(AM_LDFLAGS) -module -avoid-version -shared -Wl,-z,undefs
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if BUILD_PYTHON
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pkgpyexec_LTLIBRARIES = \
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--
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2.21.0
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