Why dbx had permission error?

I'm trying to get disassembly output of the function KJBRRCRES, but even I run the dbx as oracle user, "permission denied" happened:

sh-3.00$ dbx $ORACLE_HOME/bin/oracle
For information about new features see `help changes'
To remove this message, put `dbxenv suppress_startup_message 7.6' in your .dbxrc
Reading oracle
dbx: warning: setuid program exec()ed. Reattaching
dbx: Reattach failed -- Permission denied
dbx: program could not begin execution
dbx: warning: process initialization failed
(dbx)
(dbx) d                                                                      
(dbx) dis  kjbrrcres /1000
dbx: warning: unknown language, 'c' assumed
0x0000000101a96ce0:     <bad address 0x101a96ce0>
0x0000000101a96ce4:     <bad address 0x101a96ce4>