FreeBSD has mapping at zero address feature turned off since 8.0-RC2:

  http://security.freebsd.org/advisories/FreeBSD-EN-09:05.null.asc

This is required to read EDID data via classical VBE interface (to avoid
"mmap /dev/mem: Invalid argument" message from libx86).  To temporarily
disable this protection, issue the following command:

  # sysctl security.bsd.map_at_zero=1

To return to secure state:

  # sysctl security.bsd.map_at_zero=0