Python3 Shared Extension Doesn't Link Against Library Dependency
Solution 1:
UPDATE : The problem in this case is the linker optimization option
--as-needed
that is enabled by default, see Missing a library in ldd after using gcc -lAdding
--no-as-needed
fixes this error
For debugging linker errors you can use LD_DEBUG=files,libs /usr/local/ABC/bin/ABC
where ABC
is the executable that throws linker errors at runtime, cf http://www.bnikolic.co.uk/blog/linux-ld-debug.html and libm.so.6: cannot open shared object file: No such file or directory On linux you locate a .so
with i.e. locate libm
(i think you know this)
As the linking is dynamically it is an option to specify the path where your .so
files can be found using the library_dirs
option of disutils.core
that is the -L
or equivalently LD_LIBRARY_PATH
gcc linker option and for reasons of debugging and testing i would use the absolute path (https://docs.python.org/2/distutils/apiref.html)
In your python minimal example the code is then :
#!/usr/bin/env python3import distutils.coreas dc
module = dc.Extension('example',
sources = ['example.c'],
library_dirs = ['/usr/lib/x86_64-linux-gnu/libm.so'],
libraries = ['m'])
dc.setup(name = 'example',
version = '0.1',
ext_modules = [module])
You use the -R
linker flag to specify the rpath
in your gcc invokation, cf Shared library dependencies with distutils and What does the gcc -R parameter do? . In https://www.mpcdf.mpg.de/services/computing/software/libraries/static-and-dynamic-linking-on-linux-systems is a description of the linking process. It is said that LD_LIBRARY_PATH
or equivalently the -L
gcc linker option overrides the rpath and that it should be avoided, however you should give it a try anyway ...
Another possiblity for this behavior could be permission problems, i.e. when you execute example
does it have the permission to access libm
cf https://unix.stackexchange.com/questions/303292/permission-denied-on-some-shared-libraries
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