function parameter access in kretprobe handler

[Mao, Bibo]

Hi, 
	I remembered that previously I saw some scripts where function
parameter is accessed in return probe function. But I think that
currently systemtap has not this capability. 
	Because return probe handler happens when function returns and
causes one trap, sometimes function parameter is passed by register, for
example in IA32 the first parameter is passed by EAX register, and EAX
register can be changed during execution of this function. So when
return probe handler happens, if it accesses the first parameter by EAX
register, it will be wrong value.
	I do not know what is wrong with my thought.

Regards
Bibo,mao