A method for generating a profile of a target program executed by a target data processing apparatus comprises performing at least one profile updating operation. Each profile updating operation includes identifying based on at least one waypoint marker indicating an outcome of a corresponding waypoint instruction of a target program, a next block of instructions executed by the target data processing apparatus during execution of the target program; determining whether a target entry for the next block of instructions is present in a profile cache; when the target entry is present updating the profile of the target program according to zero, one or more profile updating actions specified by the target entry. When the target entry is absent, any profile updating actions can be determined based on an instruction-by-instruction representation of the target program. This approach helps to speed up instruction-based summaries from program flow trace.