In order to access parameters or return values from system calls, the function must be prototyped. This implementation detail is somewhat unique to Vue amongst the dynamic trace tools on the market. These prototypes can be collected in a common include file. (Note: ProbeVue cannot parse all the complexities of a common .h file. These must be converted/simplified and usually have a .i extension in this format.) It has been suggested that a common include file be created and auto-included for each provider requiring one (uft excluded of course).

In this example we are interested in the return value from fork(). It has three possible values: -1 on error, 0 if we are the child, and >0 (the PID of the child) if we are the parent.

Note the read() prototype in the data type / context slide. It mentions some usage notes on what data type is specified when prototyping and the impact on actual data types Vue uses.