svr4 (4)

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Copyright (c) 2000 Mark Newton
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(The comments found at the beginning of the groff file "man4/svr4.4freebsd".)

NAME

svr4 - System V Release 4 ABI support

SYNOPSIS

To compile support for this ABI into the kernel, place the following line in your kernel configuration file:

options COMPAT_SVR4

Alternatively, to load the ABI as a module at boot time, place the following line in loader.conf5:

svr4_load="YES"

DESCRIPTION

The 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

  device streams

  in a kernel configuration file)
• Mappings between Fx 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.

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.

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 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 brandelf(1) for information on branding executables.

The module can be linked into the kernel statically with the 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:

if ! kldstat -v | grep -E 'svr4elf' > /dev/null; then
        kldload svr4 > /dev/null 2>&1
fi

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 kernel loadable module automatically on system startup, see rc.conf5. This information applies regardless of whether the module is statically linked into the kernel or loaded as a module.

STREAMS emulation is limited but (largely) functional. Assuming the streams(4) module is loaded, a STREAMS handle can be obtained by opening one of the relevant files in /dev or /compat/svr4/dev Internally, the streams(4) driver produces a socket descriptor and ``tags'' it with additional STREAMS state information before returning it to the client application. The environment uses the additional state information to recognize and manipulate emulated STREAMS handles when STREAMS-specific ioctl(2) calls are executed.

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.

FILES

/compat/svr4

minimal SVR4 run-time environment

/sys/compat/svr4/syscalls.master

mappings between SVR4 syscalls and module entrypoints.

SEE ALSO

brandelf(1), streams(4), elf(5)

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.

BUGS

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) module is 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 memory.

ports(7) to automatically create the /compat/svr4 environment do not exist. tar(1) archives containing pre-populated trees can be obtained from people.FreeBSD.org/~newton/freebsd-svr4

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 kld(4) 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.