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From: Lucas De Marchi <>
To: Thomas Petazzoni <>
Cc:, Victor Stinner <>
Subject: Re: [PATCH kmod] Do not check for undefined symbols when building the Python modules
Date: Fri, 25 Oct 2019 15:07:22 -0700
Message-ID: <> (raw)
In-Reply-To: <>

On Thu, Oct 24, 2019 at 07:47:10PM +0200, Thomas Petazzoni wrote:
>kmod's 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
>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
>/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]
>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
>Since we want to keep -Wl,--no-undefined globally in kmod, we leave
>the 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 <>
>Cc: Victor Stinner <>

applied, thanks

Lucas De Marchi

> | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>diff --git a/ b/
>index c5c2f06..8e9c90d 100644
>--- a/
>+++ b/
>@@ -173,7 +173,7 @@ CPYTHON_MODULE_CFLAGS = \
> 	-fvisibility=default
>-CPYTHON_MODULE_LDFLAGS = $(AM_LDFLAGS) -module -avoid-version -shared
>+CPYTHON_MODULE_LDFLAGS = $(AM_LDFLAGS) -module -avoid-version -shared -Wl,-z,undefs
> pkgpyexec_LTLIBRARIES = \

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Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-24 17:47 Thomas Petazzoni
2019-10-25 22:07 ` Lucas De Marchi [this message]

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