iBCS Emulation for Linux The Intel Binary Compatibility Specification, or iBCS, specifies the interfaces between application programs and the surrounding operating system environment for i386 based systems. There are however several flavours of iBCS in use - SVR4, SVR3 plus several vendor specific extensions to SVR3 which are slightly different and incompatible. The iBCS emulator for Linux supports all flavours known so far. SUPPORTED CPU ARCHITECTURES * Intel 386/486/Pentium and compatibles * Sparc SUPPORTED BINARY FORMATS * A.OUT (using standard Linux loader unless using BSD support) * ELF (using standard Linux loader) * COFF * XOUT SUPPORTED OS EMULATIONS * Sparc Solaris * i386 BSD (386BSD, FreeBSD, NetBSD, BSDI/386) - very alpha, very old. * SVR4 (Interactive, Unixware, USL, Dell etc.) * SVR3 generic * SCO (SVR3 with extensions for symlinks and long filenames) * SCO OpenServer 5 * Wyse V/386 (SVR3 with extensions for symlinks) * Xenix V/386 (386 small model binaries only) * Xenix 286 Unrecognised binaries will default to the Linux personality for ELF or the SVR3 personality for COFF binaries. COFF binaries which have had their .comment section completely removed will default to the SCO personality. If there are non-standard extensions which require handling a new personality may need creating in the emulator. SUPPORTED SUBSYSTEM EMULATIONS * SYSV IPC * /dev/socksys socket interface as used by the Lachman STREAMS based networking implementation. * BSD and Wyse V/386 system call socket interface. * /dev/spx STREAMS device (limited server support). * XTI/TLI transports for TCP, UDP and related protocols - client only (outgoing connections). Accepting connections untested. LIMITATIONS Unix variants with non-standard extensions which are not SVr4, SCO or Wyse will not be recognised and may fail unexpectedly. A new personality may need to be built. The recognition of COFF binaries is dependent on comment strings embedded in the binary at compile time. If these strings are missing or not as expected the binary will not be recognised correctly and may fail unexpectedly. It is also possible that binaries from other systems may be misrecognised although given the strings used this should be unlikely. Some Xenix functions are unimplemented, in particular Xenix semaphores. SVr4 local connections are made using the same named pipes that linux uses. SVr4 networking should be working if you use the libnsl.so and libsocket.so shared libraries that come with the libc_s package. There is little STREAMS support. Programs that rely on STREAMS features and functionality may not work. Programs, applications or packages which require modules or device drivers to be linked in to the kernel will not work. Linux is *not* based on SYSV code and does not have SYSV internals. The driver would need rewriting for use under Linux. MAILING LIST The mail list for this project is located at linux-ibcs2@vger.rutgers.edu. To subscribe send mail to majordomo@vger.rutgers.edu with the text "subscribe linux-ibcs2" in the body. This mailing list is also carried on sme news servers as linux.ibcs2. INSTALLATION 1. Extract the archive (you have already done this of course). It doesn't matter where you put this source. You will need the "insmod" program from the modutils archive to load the compiled emulator module (available on all major Linux archive sites). 2. There may be optional patches - check the options in the Makefile and the patches in the Patches directory. If you are using a non-current 2.1 kernel you should upgrade it. The 2.1 series is a development kernel and liable to frequent changes. The kernel supported by iBCS is always the current "stable" kernel release however it may work with one or more contemporary development releases and may require a development release in order to support some functionality. # patch -d /usr/src/linux -p1 < Patches/3. Link or copy one of the architecture specific configurations (CONFIG.i386, CONFIG.sparc etc.) to CONFIG and edit it to make any changes you wish. # cp CONFIG.i386 CONFIG # vi CONFIG 4. Do a 'make' in the ibcs directory. A 'make install' will then install the iBCS module in /usr/lib/modules/iBCS and the x286emul Xenix 286 emulation overlay in /usr/lib/x286emul. The Xenix 286 overlay will only compile if you have an ELF development system and have installed the a.out compiler support. If you have a pre-ELF development system comment out the BINTYPE definition at the beginning of x286emul/Makefile. If you are unable to compile x286emul don't worry. It is *only* required if you need to run Xenix 286 programs. 5. The interfaces to some subsystems occur at the device layer and thus you need to create some device files in order to use them. A 'make install' will create them automatically replacing any that you had from a previous version of iBCS (which may be different from what the current iBCS requires). You can recreate devices at any time by doing a 'make devices' in the top level ibcs directory or by running the MAKEDEV.ibcs script in /dev/. 6. Load the iBCS emulator using "modprobe iBCS". If it fails to load the most likely explanations are that you either got the CONFIG wrong or you compiled against a different kernel from the one you are running. If iBCS loads successfully and you are running kerneld you can "rmmod iBCS" again - kerneld will load it as needed. 7. Run the SVr4, SCO or other x86 programs. Pay attention to the COMPAT file, the HINTS file and any patches that may be in PROD.Patches. Just because they are commercial doesn't make them perfect :-(. UTILITIES The emulator has the ability to trace the events which it processes. The program to enable the tracing function is contained in the Tools directory. To make the trace utility, go to the Tools directory and do a make. Run 'trace' with no arguments to get a list of capabilities. Full tracing is enabled using 'trace all'. This is extremely verbose - you probably want to kill syslogd and use 'tail -f' to dump /proc/kmsg directly to a file as quickly as possible if you enable this. If you have no intention of ever using the trace facilities (and will never complain that something doesn't work) you can remove the IBCS_TRACE option and recompile the emulator without the tracing facilities. This makes the emulator about a third smaller but ensures that there is no way for you to find out if program failures are directly due to faults in the emulator. LIBRARIES Many programs require shared libraries. You can use the shared libraries from an existing non-Linux system under Linux, but it is your responsibility to check whether your license allows you to do this whether directly or using NFS. A shared libc is being developed by Eric Youngdale and can be compiled both as ELF (for SVR4) and COFF (for SVR3/SCO). Replacements for the SVR3/SCO libnsl_s and protlib_s are under development by Mike Jagdis. All the available replacement shared libraries should be available from the same place you got the iBCS module. The replacement shared libraries are not perfect but largely usable. The SVr4 X11 libraries are not part of this package, but precompiled libraries for X11 can be obtained from the binary sites for XFree86. No shared library replacements for COFF X libraries are currently available. There are quite a few variations so many programs simply don't use them. It is theoretically possible to recreate the necessary jump tables and compile the relevant version of the X libraries. (The X code is public anyway of course...) BUG HUNTING If you find a program which produces warnings about unsupported syscalls or ioctls please look at available header files and/or man pages and try and identify what should be happening. If we know what the program expects to happen we can emulate it. If you find a program which runs but crashes at some point then try and reproduce the problem. Once you can crash it at will you can generate a trace of the relevant section. Run the program and bring it to a point a little before it crashes then enable tracing in the emulator and dump the trace to a file by running (on a different VT or xterm): # killall syslogd syslogk klogd # dmesg -c > /dev/null # tail -f /proc/kmsg > /tmp/log & # .../ibcs/Tools/trace all Then do whatever it is that causes the crash, disable the emulator tracing and kill the tail: # .../ibcs/Tools/trace off # killall tail and examine the log. If the program is trying to access a device that doesn't exist and whose intended behaviour is not readily apparent (not all devices are devices, take a look at /dev/socksys which implements the socket system calls behind ioctls) you may wish to use the devtrace module. Firstly, if you aren't using a recent (1.1.45+?) kernel you will need to edit the file devtrace.c and define a fixed major number. Build the module using 'make devtrace' and load it with insmod. If you left the major number as zero look up the allocated number in /proc/devices then create whatever device nodes your program is trying to access. The devtrace module simply writes kernel syslog messages for all operations performed on it and pretends that everything succeeds. This will cause your program to die horribly but should leave you with enough information to find out what was expected of the real device. If you can fix the problem do so and post the fix to the IBCS2 mailing list, otherwise post the *relevant* details you have - parts of the log file, ioctl details, syscall details etc. Remember, it's better to post too little initially and then post further details when asked than it is to post too much and annoy people who may be able to help! LIMITATIONS Until and unless the COFF X library is implemented, COFF X windows applications probably will not work on this system. However statically linked binaries will work. WordPerfect ship a statically linked version of their SCO port which is known to work with Linux+iBCS. For SVr4, you can obtain the X11 shared libraries from the binary distribution sites of XFree86. REFERENCES The Intel Binary Compatibility Specification, version 2 is described in the "McGraw Hill book". Intel Binary Compatibility Specification McGraw-Hill, Inc. 1221 Avenue of the Americas New York, NY 10020 ISBN 0-07-031219-2 The McGraw Hill order desk can be reached on 1-800-722-4726 or 1-614-755-4151. Vendor specific extensions were determined through a combination of header files, man pages, manuals and the behaviour of existing programs. To the best of my knowledge no developer of the iBCS emulator has ever had access to controlled Unix source - never mind used it as a reference. To be honest it probably wouldn't have helped...