[c0l0]

FWIW (and iirc), with programs using recent-ish glibc, you will never see a call to open() in the wild unless the program takes special care to bypass the implicit libc wrapper. glibc will transparently convert these calls to openat() under its own hood. I do notice that this probably doesn't do you any good on FreeBSD, though :)

[markjdb]

This is mostly true on FreeBSD as well. The real problem is that capability mode also disallows openat(AT_FDCWD) - there has to be an explicit directory descriptor.