— System V Release 4 ABI
To compile support for this ABI into the kernel, place the following line in
your kernel configuration file:
Alternatively, to load the ABI as a module at boot time, place the following
line in loader.conf(5)
module provides limited System V Release 4 ABI
(application binary interface) compatibility for userland applications. The
module provides the following significant facilities:
- An image activator for correctly branded
elf(5) executable images
- Special signal handling for activated images
- SVR4 to native system call translation
- STREAMS network API emulation (via the
streams(4) loadable module, or by means of
in a kernel configuration file)
- Mappings between FreeBSD and
SVR4 ioctl(2) calls, or, where no such mappings exist,
reverse-engineered implementations of the SVR4 calls.
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.
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.
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 brandelf(1)
utility to explicitly brand
the executable, or to set the kern.fallback_elf_brand
variable to define a "default" ABI for
unbranded executables. Value ELFOSABI_SOLARIS represents Solaris;
ELFOSABI_SYSV represents other SysVR4 operating systems. See
branding definitions, and brandelf(1)
for information on
module can be linked into the kernel statically with
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:
if ! kldstat -v | grep -E 'svr4elf' > /dev/null; then
kldload svr4 > /dev/null 2>&1
The kernel will check for the presence of the streams(4)
module, and load it if necessary.
Note that dynamically linked SVR4 executables will require a suitable
environment in /compat/svr4
For information on loading the svr4
kernel loadable module
automatically on system startup, see rc.conf(5)
information applies regardless of whether the svr4
statically linked into the kernel or loaded as a module.
STREAMS emulation is limited but (largely) functional. Assuming the
module is loaded, a STREAMS handle can be
obtained by opening one of the relevant files in /dev
. Internally, the
driver produces a socket descriptor and
“tags” it with additional STREAMS state information before
returning it to the client application. The svr4
uses the additional state information to recognize and manipulate emulated
STREAMS handles when STREAMS-specific ioctl(2)
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.
- minimal SVR4 run-time environment
- mappings between SVR4 syscalls and svr4
System V Release 4 ABI support first appeared in FreeBSD
. The ABI was ported from an equivalent facility present in
written by Christos Zoulas.
Emulation of signal handlers is buggy.
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 streams(4)
mishandling, and interaction between STREAMS and poll(2)
Connection-oriented STREAMS appear to be functional.
Ironically, this SVR4 emulator does not (yet) support SVR4 semaphores or shared
to automatically create the
environment do not exist.
archives containing pre-populated trees can be
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
modules which produce functionality which
contains OS-dependent departures from the behaviour which has been implemented
in this ABI implementation. Alternatively, sysctl(8)
variables could set the “personality” the environment should
present to client applications.