.\" $NetBSD: compat_bsdos.8,v 1.7 2020/09/02 23:38:11 uwe Exp $
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Dan Plassche.
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.Dd August 27, 2020
.Dt COMPAT_BSDOS 8
.Os
.Sh NAME
.Nm compat_bsdos
.Nd binary compatibility for BSDi releases
.Sh DESCRIPTION
The
.Dv COMPAT_NOMID
kernel option includes compatibility with
.Tn BSDi Ns No \ 1. Ns Em \^x Ns \|\(en\|3. Ns Em \^x
.Xr a.out 5
binaries on
.Nx Ns Tn /i386
and
.Nx Ns Tn /amd64 .
The option is enabled by default in the
.Li GENERIC
kernel on i386,
but needs to be set along with
.Dv EXEC_AOUT
on amd64.
.Pp
Null memory protection must be disabled with the
.Xr sysctl 7
option
.Va vm.user_va0_disable
set to
.Li 0
for the binaries to run successfully.
.Pp
.Bsx
binaries may be placed under
.Pa /emul
directory to match the location of other
non-native executables
on
.Nx ,
but the compatibility environment
does not automatically lookup libraries
under
.Pa /emul/bsdos
as happens with the shared
libraries
for
.Nx 1.0\|\(en\|1.5
.Xr a.out 5
binaries under
.Pa /emul/aout .
.Pp
.Tn BSD/386 Ns No \ 1.0\|\(en\|1.1
uses static binaries that do not
dynamically load libraries at runtime.
.Pp
.Bsx 2.0
introduced
.Dq "static shared libraries"
as the default for standard binaries.
The shared libraries are compiled from
.Pa /lib
and
.Pa /usr/lib
to a custom format bound to memory
loading addresses for each library
under
.Pa /shlib .
BSDi libraries
under
.Pa /shlib
are not in the standard
.Xr ar 5
or position-independent shared object
formats and cannot be loaded by
.Xr ldconfig 8
on
.Nx .
In order for BSDi executables to
access the objects at the
hardcoded
.Pa /shlib
path,
the user may setup a
symbolic link from
.Pa /shlib
to
.Pa /emul/bsdos/shlib .
.\" or run a shell under a
.\" .Ic chroot
.\" with the command
.\" .Ic chroot "/emul/bsdos /bin/sh" .
.\" One could rebuild the BSDi userland
.\" from source using
.\" .Pa /emul/bsdos/lib
.\" and
.\" .Pa /emul/bsdos/usr/lib .
.\" Then adding
.\" .Pa /emul/bsdos/lib
.\" and
.\" .Pa /emul/bsdos/usr/lib
.\" to
.\" .Pa /etc/ld.so.conf
.\" and running
.\" .Ic ldconfig
.\" to regenerate
.\" .Pa /var/run/ld.so.hints
.\" for a new hybrid setup.
.Pp
.Bsx 4.0
switched to an ELF binary executable format
that does not run under the
compatibility layers currently available on
.Nx .
.Sh SEE ALSO
.Xr ld.aout_so 1 ,
.Xr options 4 ,
.Xr a.out 5 ,
.Xr elf 5 ,
.Xr sysctl 7 ,
.Xr compat_netbsd32 8 ,
.Xr ldconfig 8
.Sh HISTORY
.Tn BSD/386 Ns No \ 1.0\|\(en\|1.1
was derived from
.Bx 4.3 Tn Reno
code in the
.Tn Net/2
release.
.Pp
.Bsx 2.0
was based on
.Bx 4.4 Tn Lite ,
but added the new static shared library
format as the runtime default for executables.
The build system included the
.Li shlicc
command with the
.Fl Bstatic
flag that allowed reverting to the standard
library archive format that remained available
under
.Pa /lib
and
.Pa /usr/lib .
.Pp
.Nx 1.0
added shared libraries using a standard
position-independent shared object
format.
The previous default relocatable libraries
in the traditional
.Xr ar 5
format remained available.
.Pp
.Ox 2.2\|\(en\|4.7
included a different compatibility implementation
under the
.Dv COMPAT_BSDOS
kernel option.
.Sh BUGS
.Bsx
compatibility was broken on
.Nx 5\|\(en\|6 .
.Pp
.Bsx 3.0
added
.Tn SPARC
support, but the binaries are incorrectly recognized as
.Tn SunOS
executables and fail on
.Nx Ns Tn /sparc
and
.Nx Ns Tn /sparc64 .