about probe libc

[Huang jw]

Hi all,
       I'm trying to probe memcpy from libc. I have installed
debuginfo for libc(glibc-debuginfo-2.5-42.x86_64.rpm), but when I use
the follow systemtap instruction, it reoprted an error.
Instruction list I used:
sudo stap -e 'probe
process("/lib/libc.so.6").function("memcpy").return{println(probfunc())}'
-c 'ls'

Error information:
"
WARNING: cannot find module /lib/libc-2.5.so debuginfo: No DWARF
information found
semantic error: no match while resolving probe point
process("/lib/libc.so.6").function("memcpy").return"

The os I used is REL5.4, libc version is 2.5.42.
Does any one know why?