Limited access to parameter value and return value

[tylergu]

Due to the structure of emitted baseTramp structure, we can only access the parameter values in the pre-instrumentation function; we can only access the return value of the call in the post-instrumentation function.

In the former case, it is possible to pass the parameter information from pre-instrumentation function to the post-instrumentation function. In the later case, it is impossible to get return value in the pre-instrumentation function since the function is not actually called yet.