an executable program is prepared from a plurality of object code modules , at least one of the object code modules including section data specifying a plurality of code sequences each associated with relocation instructions identifying condition parameters . only one of the code sequences is selected for inclusion in the executable program , determined by whether the condition for that parameter is satisfied . a linker for preparing the executable program includes a stack , a relocation module for reading the relocations , carrying out the relocation operations and selecting code sequences for inclusion in the executable program in dependence on values taken from the stack , a section data module for holding section data which is subject to the relocation operations , and a program forming module for preparing executable programs . also disclosed is a method of assembling an object code module such that the assembled object code module includes the conditional code sequences .