function probe point

[Mao, Bibo]

Hi,
I view systemtap source code, and by the notation and test, I find that
kretprobe function probe point is based on the entry pc of this
function, but for kprobe function probe point it is based on the
prologue-end of this function. 
I ever objdumped vmlinux, and found that in IA32, EM64T platform kprobe
function probe point is based on prologue-end place, a pointer after the
function's frame has been set up. But in IA64 platform, the function
kprobe point always is entry point plus 1. I do not know why.

Any suggestion is welcome.

Regards
Bibo,mao