The arguments to entry probes are the same as the arguments to the corresponding operating system kernel function. These arguments may be accessed in a typed fashion by using the args array. These arguments may be accessed as int64_t's by using the arg0 .. argn variables.
While a given function only has a single point of entry, it may have many different points where it returns to its caller. You are usually interested in either the value that a function returned or the fact that the function returned at all rather than the specific return path taken. FBT therefore collects a function's multiple return sites into a single return probe. If the exact return path is of interest, you can examine the return probe args value, which indicates the offset (in bytes) of the returning instruction in the function text.
If the function has a return value, the return value is stored in args. If a function does not have a return value, args is not defined.