It is possible to keep track of every function called when running code, but this involves significant effort in determining which functions are suitable for profiling and in keeping track of the results. To minimize this effort you should specify which functions you want to profile. The profiler checks that these functions have indeed got function definitions and are therefore suitable for profiling. For more information on the types of function that can be profiled, see Profiling pitfalls.
There are two ways of specifying functions that you want to profile: