getuid, getgid, geteuid, getegid \- get user and group identity
returns the real user ID of the current process,
The real user ID identifies the person who is logged in,
in contradistinction to the effective user ID, which
determines his access permission at the moment.
It is thus useful to programs which operate using
the `set user ID' mode, to find out who invoked them.
returns the real group ID,
(real user ID in r0, effective user ID in r1)
(real group ID in r0, effective group ID in r1)