enum { PER_LINUX = 0x0000, PER_LINUX_32BIT = 0x0000 | ADDR_LIMIT_32BIT, PER_LINUX_FDPIC = 0x0000 | FDPIC_FUNCPTRS, PER_SVR4 = 0x0001 | STICKY_TIMEOUTS | MMAP_PAGE_ZERO, [...] So this is a combination of a personality ID and flag bits. And the only difference between PER_LINUX and PER_LINUX_32BIT is one of those flag bits. Nicolas