COMPAT_BSDOS(8)

NAME
compat_bsdos - binary compatibility for BSDi releases

DESCRIPTION
The 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.

SEE ALSO
ld.aout_so(1), options(4), a.out(5), elf(5), sysctl(7), compat_netbsd32(8), ldconfig(8)

HISTORY
BSD/386 1.0–1.1 was derived from 4.3BSD Reno code in the Net/2 release.

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.

BUGS
BSD/OS compatibility was broken on NetBSD 5–6.

BSD/OS 3.0 added SPARC support, but the binaries are incorrectly recognized as SunOS executables and fail on NetBSD/sparc and NetBSD/sparc64.