| COMPAT_BSDOS(8) | System Manager's Manual | COMPAT_BSDOS(8) | 
compat_bsdos —
COMPAT_NOMID kernel option includes compatibility
  with
  BSDi 1.x–3.x
  a.out(5) binaries on
  NetBSD/i386 and NetBSD/amd64.
  The option is enabled by default in the GENERIC kernel
  on i386, but needs to be set along with EXEC_AOUT on
  amd64.
Null memory protection must be disabled with the
    sysctl(7) option
    vm.user_va0_disable set to 0
    for the binaries to run successfully.
BSD/OS binaries may be placed under /emul directory to match the location of other non-native executables on NetBSD, but the compatibility environment does not automatically lookup libraries under /emul/bsdos as happens with the shared libraries for NetBSD 1.0–1.5 a.out(5) binaries under /emul/aout.
BSD/386 1.0–1.1 uses static binaries that do not dynamically load libraries at runtime.
BSD/OS 2.0 introduced “static shared libraries” as the default for standard binaries. The shared libraries are compiled from /lib and /usr/lib to a custom format bound to memory loading addresses for each library under /shlib. BSDi libraries under /shlib are not in the standard ar(5) or position-independent shared object formats and cannot be loaded by ldconfig(8) on NetBSD. In order for BSDi executables to access the objects at the hardcoded /shlib path, the user may setup a symbolic link from /shlib to /emul/bsdos/shlib.
BSD/OS 4.0 switched to an ELF binary executable format that does not run under the compatibility layers currently available on NetBSD.
BSD/OS 2.0 was based on
    4.4BSD Lite, but added the new static shared library
    format as the runtime default for executables. The build system included the
    shlicc command with the
    -Bstatic flag that allowed reverting to the standard
    library archive format that remained available under
    /lib and /usr/lib.
NetBSD 1.0 added shared libraries using a standard position-independent shared object format. The previous default relocatable libraries in the traditional ar(5) format remained available.
OpenBSD 2.2–4.7 included a
    different compatibility implementation under the
    COMPAT_BSDOS kernel option.
BSD/OS 3.0 added SPARC support, but the binaries are incorrectly recognized as SunOS executables and fail on NetBSD/sparc and NetBSD/sparc64.
| August 27, 2020 | NetBSD 10.1 |