Dynamic loading of C functions

I've written a function in C, compiled it and trying to use the same function in one of my postgres functions like this:

CREATE FUNCTION add_one(integer) RETURNS integer
     AS '/usr/include/pgsql/server/test_func, 'add_one'
     LANGUAGE C STRICT

test_func is the name of my object file and add_one is the name of
the function i want to call from test_func.c  C file.

I get the follwing error
ERROR:  could not access file "/usr/include/pgsql/server/test_func": No such file or directory

/usr/include/pgsql/server/ is exactly the path where test_func object file resides.
Don't know why isn't postgres able to find it there.

Any kind of help would be appreciated.

~Jas