On Alpha, instead of a pair of getgid() and
getegid() system calls, a single
getxgid() system call is provided, which returns a pair
of real and effective GIDs. The glibc getgid() and
getegid() wrapper functions transparently deal with
this. See syscall(2) for details regarding register
mapping.
The original Linux getgid() and
getegid() system calls supported only 16-bit group IDs.
Subsequently, Linux 2.4 added getgid32() and
getegid32(), supporting 32-bit IDs. The glibc
getgid() and getegid() wrapper
functions transparently deal with the variations across kernel
versions.