Sharing a common library between C/C++ s-functions?

I have a single common library that I would like to share between multiple C/C++ s-function (not multiple instances of the same s-function). The shared library contains a global data object.

What is the correct way to mex this on Linux?

mex sfun1.cpp mylib.cpp
mex sfun2.cpp mylib.cpp

Successfully builds but each s-function has its own instance of the global data object. If I do:

mex mylib.cpp
mex sfun1.cpp
mex sfun2.cpp

Each of the s-functions can not find the symbols from mylib.cpp