How do I compile with shared libraries for my MEX files on Linux?

I'm trying to compile a CPP script, "foo.cpp", that relies on a shared library, "libfoolibrary.so", into a MEX file on Linux. However, even though it compiles successfully, it fails at runtime, giving me the following error message:

>> mex -DLIN -DUNIX -DNDEBUG -D_USRDLL -O foo.cpp -output foo_mex -lfoolibrary -L./
Building LIN64 MEX function...
Building with 'g++'.
MEX completed successfully.
MEX function compilation completed successfully

>> foo_mex
Running the MEX function... Invalid MEX-file '/home/MATLAB/foo_mex.mexa64': libfoolibrary.so: cannot open shared object file: No such file or directory

This doesn't happen when I try to do this on Windows. Am I doing something wrong?

Answer 1

[MathWorks Support Team]

The issue is that even though you have told the "g++" command that it is looking for a shared library called "libfoolibrary.so" in the current directory when compiling, the GNU linker itself doesn't know where to look for dependencies at runtime.

 

Passing the options "-Wl,-rpath,\$ORIGIN" to the "LDFLAGS" flag would add the current directory ("$ORIGIN") to the dynamic library search path. So, at runtime, the dynamic loader would look for dependencies in the current directory (or any directory specified with "-rpath"). On computers running Windows, the current directory is added by default, so this would not be necessary.

Dependencies are searched for by the GNU linker in the following order:

    1. Directories in "rpath"

    2. Directories in "LD_LIBRARY_PATH"

    3. System directories 

For more information about the GNU linker and its many options, you can look at its "man" page:

https://manpages.org/ld

In your case, the following command should allow your MEX file to compile and run successfully, assuming that your SO file is in the same directory as your CPP file:

mex -DLIN64 -DUNIX -DNDEBUG -D_USRDLL -O xfft_v9_1_bitacc_mex.cpp ...
       -output xfft_v9_1_bitacc_mex -lIp_xfft_v9_1_bitacc_cmodel -L./ 'LDFLAGS=$LDFLAGS -Wl,-rpath,\$ORIGIN'