Abstract: In one embodiment, an indirect branch is detected in computer program code. The indirect branch calls one of a plurality of functions using a first register. In response, the computer program code is augmented to store an identifier of the indirect branch call in a second register, and the code for each of the plurality of functions is augmented to: determine whether an identifier for the function matches the identifier stored in the second register and render the first register unusable if the identifier for the function does not match the identifier stored in the second register.