A method of preparing an executable program from a plurality of object code modules, at least one of said object code modules including section data specifying a plurality of functions associated with relocation instructions, at least some of which functions are called in the executable program. The method comprises the steps of assigning an attribute to each function, said attribute being capable of providing an indication of whether the function is reachable, reading the section data and relocation instructions to ascertain if the function is called and setting the attribute to indicate the called status and preparing the executable program to only include functions with an indicated called status of reachable. A linker is provided for preparing the executable program from object code modules containing the relocation instructions. A computer program is provided to control the linker.