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.\" $FreeBSD: release/9.1.0/share/man/man4/man4.i386/svr4.4 177293 2008-03-17 08:17:04Z brueffer $
.\"
.Dd March 17, 2008
.Dt SVR4 4 i386
.Os
.Sh NAME
.Nm svr4
.Nd System V Release 4 ABI support
.Sh SYNOPSIS
To compile support for this ABI into the kernel,
place the following line in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "options COMPAT_SVR4"
.Ed
.Pp
Alternatively, to load the ABI as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
svr4_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
module provides limited
System V Release 4 ABI (application binary interface) compatibility
for userland applications.
The module provides the following significant facilities:
.Bl -bullet
.It
An image activator
for correctly branded
.Xr elf 5
executable images
.It
Special signal handling for activated images
.It
SVR4 to native system call translation
.It
STREAMS network API emulation (via the
.Xr streams 4
loadable module, or by means of
.Dl device streams
in a kernel configuration file)
.It
Mappings between
.Fx
and SVR4
.Xr ioctl 2
calls, or, where no such mappings exist, reverse-engineered implementations
of the SVR4 calls.
.El
.Pp
It is important to note that the SVR4 ABI support
it not provided through an emulator.
Rather, a true (albeit limited) "clean room" reverse-engineered ABI
implementation is provided.
.Sh LIMITATIONS
Because the provided ABI has been developed in ignorance of actual SVR4
source code, there are bound to be unforeseen interactions between SVR4
client applications and the emulated ABI which cause applications to
malfunction.
.Pp
Additionally, some SVR4 operating systems do not adhere to the SVR4
ELF standard.
In particular, Solaris does not set the ELF interpreter field in the
ELF header to a value which would allow the kernel to correctly
identify a client executable as an SVR4 application.
Thus, in certain instances it is necessary to use the
.Xr brandelf 1
utility to explicitly brand the executable, or to set the
kern.fallback_elf_brand
.Xr sysctl 8
variable to define a "default" ABI for unbranded executables.
Value ELFOSABI_SOLARIS represents Solaris; ELFOSABI_SYSV represents other
SysVR4 operating systems.
See
.In sys/elf_common.h
for ELFOSABI branding definitions, and
.Xr brandelf 1
for information on branding executables.
.Pp
The
.Nm
module can be linked into the kernel statically with the
.Dv COMPAT_SVR4
kernel configuration option
or loaded as required.
The following command will load the module
if it is neither linked into the kernel
nor already loaded as a module:
.Bd -literal -offset indent
if ! kldstat -v | grep -E 'svr4elf' > /dev/null; then
	kldload svr4 > /dev/null 2>&1
fi
.Ed
.Pp
The kernel
will check for the presence of the
.Xr streams 4
module, and load it if necessary.
.Pp
Note that dynamically linked SVR4 executables
will require a suitable environment in
.Pa /compat/svr4 .
.Pp
For information on loading the
.Nm
kernel loadable module automatically on system startup,
see
.Xr rc.conf 5 .
This information applies
regardless of whether the
.Nm
module is statically linked into the kernel
or loaded as a module.
.Pp
STREAMS emulation is limited but (largely) functional.
Assuming the
.Xr streams 4
module is loaded, a STREAMS handle can be obtained by opening one of the
relevant files in
.Pa /dev
or
.Pa /compat/svr4/dev .
Internally, the
.Xr streams 4
driver produces a socket descriptor and
.Dq tags
it with additional STREAMS
state information before returning it to the client application.
The
.Nm
environment uses the additional state information to recognize and
manipulate emulated STREAMS handles when STREAMS-specific
.Xr ioctl 2
calls are executed.
.Pp
The subset of STREAMS functionality which is provided is small, probably
little more than what is required to enable programs on the Solaris CD
sets to run.
.Sh FILES
.Bl -tag -width /sys/compat/svr4/syscalls.master -compact
.It Pa /compat/svr4
minimal SVR4 run-time environment
.It Pa /sys/compat/svr4/syscalls.master
mappings between SVR4 syscalls and
.Nm
module entrypoints.
.El
.Sh SEE ALSO
.Xr brandelf 1 ,
.Xr streams 4 ,
.Xr elf 5
.Sh HISTORY
System V Release 4 ABI support first appeared in
.Fx 4.0 .
The ABI was ported from an equivalent facility present in
.Nx 1.3
written by Christos Zoulas.
.Sh BUGS
Emulation of signal handlers is buggy.
.Pp
Emulated connectionless STREAMS fail to receive data from the network in
some circumstances (but succeed in others -- probably due to particular
ways of initializing them which the
.Xr streams 4
module is mishandling, and interaction between STREAMS and
.Xr poll 2 ) .
Connection-oriented STREAMS appear to be functional.
.Pp
Ironically, this SVR4 emulator does not (yet) support SVR4 semaphores or
shared memory.
.Pp
.Xr ports 7
to automatically create the
.Pa /compat/svr4
environment do not exist.
.Xr tar 1
archives containing pre-populated trees can be obtained from
.Pa http://people.FreeBSD.org/~newton/freebsd-svr4/ .
.Pp
Extensive testing has only really been carried out with Solaris 2.x binaries,
with anecdotal reports of limited success coming from testers with
early-revision SCO media.
In theory, the basic SVR4 ABI should be constant
across the set of vendors who produce SVR4 operating systems, but in
practice that is probably not the case.
If necessary, future work can
either implement additional
.Xr kld 4
modules which produce functionality which contains OS-dependent
departures from the behaviour which has been implemented in this
ABI implementation.
Alternatively,
.Xr sysctl 8
variables could set the
.Dq personality
the environment should present to
client applications.