[U]

1. UIO_READ
2. UIO_SYSSPACE
3. UIO_USERISPACE
4. UIO_USERSPACE
5. UIO_WRITE
6. UNIMP
7. UNINIT_ARRAY_ELEMS
8. UNINIT_PAGES
9. UNLOCKME
10. USERSPACETOP
11. USERSTACK
12. USE_LONGLONG
13. USING_ERR_CODES