Adding a syscall to specific kernel version

Hi, I am trying to add a new syscall to kernel 3.4. So far I have tried at least four different tutorials from Internet. To my utter frustration, whatever source files they have referred in the tutorials, at least one of those is missing in all the cases. Why isn't there a consistent interface for addition of syscall across kernel version? How will I get to know the method for a specific kernel version officially?