The use of the serporid structure with several embedded unions to split up the specific NFS request/response structures is quite a hack. It breaks on 64-bit targets due to the presence of pointer members which affect the overall alignment.
The license details can be viewed if you mount with a -v option: # mount -i nfs -o "-v" 1.2.3.4:/mnt /mnt
RTEMS Git commit 251c94d3d3d27e0039f01b718e5c2eb06f39fdf7.