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README

README for ixemul.library and ixnet.library version 48.0


IMPORTANT
=========

Always read the NEWS file for information about new features! The NEWS file
is part of the ixemul source archive.

Also look at the ix.h header: ixemul-specific functions are documented in that
header.

Starting with ixemul.library version 42.0 the ssystem() function is no longer
supported. The only two applications use this function are (to my knowledge)
gcc and man. You should either upgrade to the latest gcc (2.7.2 or higher)
or replace gcc by gccv (which is part of older gcc distributions). You can
find a new 'man' version in Geek Gadgets.

Starting with ixemul.library version 43.1 various networking functions have
been moved to libc.a. See the NEWS file for details. It only concerns
certain somewhat specialized functions, so 'normal' clients and daemons
shouldn't be affected.

This library is part of Geek Gadgets.  For more information see
ftp.ninemoons.com, /pub/geekgadgets.



INTRODUCTION
============

Originally created in 1991 or 1992 by Markus Wild, the ixemul.library has
become the driving force behind the Geek Gadgets project.

Essentially it is a BSD Unix kernel running under the Amiga OS.  The
code for handling Unix signals is taken almost verbatim from the BSD kernel
sources, for example.  Multitasking and file I/O is, of course, passed on
to the Amiga OS.  Because the library resembles BSD Unix so closely, it has
made it possible to port almost all Unix programs.

However, because of the conformance to BSD, the library is not too
conservative with resources or overly concerned with Amiga standards.  For
example, command line expansion uses Unix semantics and doesn't use
ReadArgs().  The purpose of ixemul.library is to emulate Unix as well as is
technically possible.  So given a choice between Amiga behavior or Unix
behavior, the last one is chosen.



HISTORY
=======

As I mentioned, the library was originally created by Markus Wild.  It
allowed him to port Unix programs, most notably gcc and a Unix shell
(pdksh), which in turn gave him the opportunity to start porting NetBSD
Unix.  At some point he stopped working on ixemul.library and continued
with the real thing, NetBSD.

Although Markus made some snapshots of his library available on Internet,
he was about the only one who could actually compile it.  The snapshots
where never complete and didn't use a standard Make tool.

Rafael W. Luebbert managed around June 1994 to actually compile the
library using bits and pieces from four different source releases.  Even
then he had to write some missing code and had to debug a lot before he got
it working.  Luebbert released versions 40.1 through 40.4.  Since this was
the only version available that could actually be compiled, Fred Fish
switched to version 40.4 for his FreshFish CDROM series.

Leonard Norrgard also started working on 40.4, fixing a variety of
problems.  So for a time there were two versions of the library, both
derived from 40.4.  Around March 1995 I began contributing my own fixes for
the library to Fred, including a fix for a horrible memory trashing bug
which substantially improved the stability of the library.  Starting with
version 42.0 I became the new maintainer of the library.  I merged
Leonard's version of the library into 42.0, the whole source distribution
was cleaned up and reorganized and many bugs were fixed.  Also new
functionality was added such as timezone support.

Thanks to Jeff Shepherd the support for network functions has been totally
reorganized for version 43.0.  A new ixnet.library was introduced that
contains all the network handling.  This new library supports both AS225
and AmiTCP.  Furthermore, there is no longer any need to maintain two
versions of an Internet client or daemon as ixnet.library will do the
multiplexing for you.  The program itself is completely shielded from the
actual networking package in use.  Also, should a new networking package
appear for the Amiga, then it is relatively easy to add support for that
package to ixnet.library.  All existing programs will automatically be able
to work with the new package too.

Version 43.0 also introduced support for automatic stack extension
(provided you compiled your program with the -mstackextend flag).  This
support was done by Matthias Fleischer.

Last, but not least, I've added the ptrace() function, which was essential
for porting the GNU debugger, GDB.  So it is now possible to use a decent
debugger with gcc (and with the GNU C++, fortran and ADA compilers).

Version 43.1 was a bug-fix release, which further improved stability.

Version 44.0 made the library much more (Net)BSD compatible, making it even
easier to port Unix programs. Also many bugs were fixed.

Version 45.0 fixed a few bugs, improved stack extension (see the new ixstack
utility) and further improved Ctrl-C handling by adding 'sessions', something
that was needed for the Geek Gadgets X port.

Version 45.1 was a bug-fix release, and also improved uid/gid handling.

Version 46.0 adds shared memory (shm*) and basic p.OS support.

Version 46.1 renames the __os variable to ix_os.

Version 47.0 completes the p.OS support and adds Unix semaphore and message
support. Also fixes several bugs.

Version 47.1 fixes a minor but very irritating bug in the ixstack utility.

Version 47.2 is a bug-fix release.

Version 47.3 is a bug-fix release.

Version 48.0 is a bug-fix release and removes the p.OS support. p.OS didn't
become a success, so ixemul no longer supports it.


USAGE
=====

The Aminet distribution of ixemul consists of several archives:  one for
each flavor (CPU/FPU combination) of the library, one for the timezone
support, an archive for documentation, an archive for various utilities and
an SDK archive, containing headers, libraries and C-objects that provide
the startup code.  There is also an ixemul source archive.  If you don't
mind recompiling everything, and if you have a decent Geek Gadgets
environment, then all you have to do is retrieve this archive, as all the
other archives are generated from this source distribution.

Besides the library itself, there are also some utilities and other
goodies.  First of all, there is a special trace version of the library.
Together with the ixtrace tool it allows you to see which library functions
are called by the program you want to debug.  If you compile the library
yourself you will also get, as part of the compile process, a debug version
of the library.  If you get an Enforcer hit in the library, and if you have
SegTracker installed, then you can track down in which source and at which
line the hit took place using the gccfindhit tool (available from Aminet
and Geek Gadgets) that is similar to the FindHit tool which is part of the
Enforcer package.  I've used this with great success in the past.

Various settings that influence the behavior of the library can be set
using the ixprefs utility.  A small tool ixrun allowing you to run AmigaOS
scripts from within the Unix shell is also provided.  An ixemul-specific
pipe-handler allows you to set up a pipe between an AmigaOS utility and an
Unix program.  A pipe between two Unix programs is handled by the
ixemul.library itself, but since AmigaOS programs are not under the
control of the library, this handler is used instead.

A recent addition is the ixstack tool, which can list and set the minimum
stack size an ixemul program needs.  It can also show the actual stack
usage of ixemul programs if you start it with '-s'.

Finally, the tools zic (for manipulating the timezone databases) and
ixtimezone are also part of ixemul.  The ixtimezone tool can be used to
automatically adjust the Amiga time based on the currently selected
timezone.  The best way to use this tool is to install the timezone
databases (in etc:zoneinfo), set the TZ environment variable correctly (in
my case "Europe/Amsterdam"), add the line "ixtimezone -patch-resource
>nil:" to your user-startup and set the Amiga clock to Greenwich Mean Time
(or Universal Time, as it is now called).  Now you will never have to worry
about things like Daylight Saving Time as each time ixtimezone is called,
this tool checks the current timezone and will patch the Amiga clock to the
right time.  This tool is also very useful if you also run NetBSD or Linux,
as these OSes expect that the internal Amiga clock adheres to GMT.

I advise that you set the ixemul "Network support" to the correct method
using the ixprefs program. It will improve performance somewhat if ixemul
doesn't have to guess which network library is available, if any.



MEMORY REQUIREMENTS
===================

The library itself needs about 200 Kb, but if you want to do some useful
work, such as compiling programs, I advise at least 4 Mb.  More importantly
is the stack size:  set it to at least 50 Kb. If you have problems with
certain programs try to increase the stack size.

The reason for these large stacks is that the Unix operating system
automatically extends the stack if it is too small. Therefore some Unix
programs aren't exactly conservative with their stack space.

We can do the same on AmigaOS, however, by compiling programs with the
-mstackextend flag. Or you can set the minimum stack size of a program
using the ixstack tool. If the current stack is too small, the program will
automatically extend the stack on startup.



PROGRAMMING WITH IXEMUL
=======================

There is really very little to do.  If you have a decent Geek Gadgets setup
with the necessary compilers and tools, and if you have installed the
ixemul SDK, then you are ready to go.  There is no need to do anything
special, the communication between your program and ixemul.library is
handled by the startup code (the *crt0.o files in the /gg/lib directory)
and the standard C library (libc.a, also in /gg/lib) which are
automatically linked with your program.  Note that ixemul.library together
with the compile tools also provides profiling support (compile and link
with -pg), and base-relative and resident support (compile with -fbaserel
or -resident).  Compile and link with -g to add debug information so that
you can debug your program with gdb.

If you start gdb with the -enforcer option, then the program you are
debugging will automatically stop and drop into the debugger as soon as an
Enforcer hit occurs.  This is obviously very useful.

The startup code will automatically expand the command-line for you (e.g.
'echo *' will expand to 'echo <filenames in current directory>'). If you
want to disable this in your program, then you should add the line:

	int ix_expand_cmd_line = 0;

to your source. This global variable will tell the system not to expand the
command-line.

Code like you would on a Unix system, so DON'T USE any information
private to the library!



PORTING UNIX PROGRAMS
=====================

Most programs compile out-of-the-box.  There are a few exceptions to this
rule.  First of all, programs like linkers and the like that have to be
able to read or write the standard Amiga hunk format obviously need a lot
of work.

Secondly, there is no virtual memory support, and therefore no real fork()
function.  In most cases the fork() function is only used to spawn a new
program, and in such cases it is possible to replace fork() by vfork(),
which is a light-weight fork() replacement that was originally created for
Unix to reduce the overhead a real fork() introduced.

A vfork() doesn't create a copy of itself as fork() does, but uses the
parent's code and data.  Since the child will quickly call execve() to
spawn another program, this sharing of the code and data is no problem and
saves a lot of time.

There is one restriction, however: since the child process is running on
the stack of the parent until an exit() or execve() call the child must be
careful not to clobber the parent's stack. So this will fail:

      main()
      {
        switch (vfork())
        {
          case -1:      // Error
          case 0:       // Child
            return 0;	// Return from main()

          default:      // Parent
            wait(0);
            break;
        }
        
        return 0;
      }

It fails because the child just returns, and this return will clobber the
stack for when the parent returns. But this is correct:

      main()
      {
        switch (vfork())
        {
          case -1:              // Error
          case 0:               // Child
            exit(0);            // Exit
            break;

          default:              // Parent
            wait(0);
            break;
        }
        
        return 0;
      }

Here the child calls exit or execve and therefor leaves the underlying
stack intact for the parent. This restriction can cause very hard to find
bugs (I know, I spent quite a few hours researching this problem).

In some cases, such as a Unix shell (pdksh for example), you really want to
be able to port a program that uses a fork() that cannot be replaced with
vfork().  There is a way to do this, although it is a lot of work.  First
of all, the program has to be compiled with -resident.  Now you replace the
fork() by a ix_vfork() call, and in the child code you call vfork_setup_child()
(new for 44.0!  Replaces the ix_resident()/ix_get_vars2() pair) to copy the
original data hunk to a new location.  Next you have to copy all the
parent's data structures to the child.  In other words, you have to copy
the complete state of the parent process to the child process.  This can be
a lot of work.  Finally, you call vfork_resume() which unblocks the parent
so that you now have two processes running separately from each other.

It is important to realize that you should never exit() from the parent
before all vfork()'ed children have died.  Since exiting from the parent
causes the parents code and data segments to be deallocated, the child
would find itself without code space to run on, and would probably cause a
severe machine crash!

So always call at least `wait(0)' before returning from the parent.

For an example of how this works, see jobs.c from the pdksh source
distribution.  It's a kind of poor-man's fork().

The third case I've come across that couldn't easily be ported were
programs that dump their state to a new file.  Emacs does this, as does GNU
Common Lisp.  The idea is that such a program will read lots of packages,
and then dump itself to a new file.  That new file can in turn be executed,
and you will no longer have to load all those packages.  All this assumes
that each time you load a program, all the code and data ends up at the same
memory addresses as before.  Something that is true for Unix, but not for
the Amiga due to the lack of virtual memory.

However, if someone wants to do a port of such a program, please contact me
as I have developed a technique to implement this.  At least, I've made
this work with a small test program.  I've tried to use it with GNU Common
Lisp, but time constraints prevented me from developing this further.

The last problematic category I've seen is GNU Emacs.  This program assumes
that all the data it allocates will always end up in a continuous memory
block, and that the upper 8 bits of each memory address are always the
same.  The Amiga, however, can have multiple memory blocks positioned at
various places in memory.  While there is a GNU Emacs port, this port does
assume this limitation and if you have an Amiga with many memory blocks (as
I had) GNU Emacs may easily crash.  No easy solution exists.



AMIGA PROGRAMMING & IXEMUL
==========================

If you use Amiga specific resources like Windows and Screens from
Intuition, make sure to add an atexit() handler to close those resources,
if the user should decide to interrupt your program.  Before the program is
left, the chain of registered atexit-handlers is called in exit().  So
PLEASE NEVER EVER call _exit() if you have registered any custom atexit()
handlers.  It is a bad habit anyway, but normally you may call _exit()
without resource lossage (stdio won't flush its buffers, but that's about
all).

Ixemul provides a new unique Amiga specific signal called SIGMSG.  If you
set up a handler for this signal, then the default mapping from
SIGBREAKB_CTRL_C into SIGINT will no longer occur, and your handler is
called with the following arguments:

  signal_handler(SIGMSG, new_exec_signal_mask)

In this case, you have to deal with Exec signals yourself, so don't forget
to clear those signals that you want to receive notification about again
later.  Thus if you'd want to handle SIGBREAKB_CTRL_C yourself, don't
forget to

  SetSignal(0, SIGBREAKF_CTRL_C)

at the end of the handler, or you'll never get notification about that
signal again.

Most of the original BSD signals are implemented.  SIGSTOP is currently not
implemented, although it would be relatively easy to add.  The mechanisms
are already in place.



HANDLING OF UID/GID IN IXEMUL.LIBRARY
=====================================

The following information was provided by Norbert Pueschel:

Here is a list of functions that are concerned with uid/gid management
and access to user/group information:

a) uid/gid management:
   get(e)uid, set((r)e)uid, get(e)gid, set((r)e)gid, (init|set|get)groups

b) access to user/group informations:
   set(pass|group)ent, (set|get|end)pwent, get(pw|gr)nam, getpwuid, getgrgid,
   (_)getlogin, setlogin

c) other functions:
   setsid, crypt


Ixemul.library has several options how to implement these functions:

1) When MultiUser is installed, ixemul.library will use it to implement the
   functions named above.

2) When MultiUser is _not_ installed, ixemul.library will use its own
   uid/gid handling: uids and gids will be inherited by child processes
   and files and directories created by ixemul using programs will have
   the current user and group set as long as the filesystem supports that.
   However, for file accesses only the setting of the flags for the file
   owner is used (as for any other AmigaOS program).

Processes that are not started by other ixemul using programs use
environment variables to determine their (e)uid and (e)gid:

They will first check the variables LOGNAME and USER for a valid user
name. If they find this user in the passwd file, they will set up (e)uid
and (e)gid respectively. Then the environment variables UID, EUID, GID and
EGID will be queried, and, if present, their values will be used.

If none of the above variables is found, the process will be owned by
nobody/nogroup (uid/gid -2).


Ixemul.library has three different methods to get user/group
informations:

a) If networking software (AmiTCP or Inet) is installed, it will use their
   user/group databases.

b) If no networking is available, it will try to read the files etc:passwd
   and etc:group.

c) If both a) and b) fails, it will use a builtin user/group database.
   This database only knows the nobody/nogroup (uid/gid -2), root/wheel
   (uid/gid 0) and a user/group combination described by the environment
   variables LOGNAME or USER, GROUP, UID and GID.

                      Hans Verkuil (hans@wyst.hobby.nl, July 14, 1998)

(Parts of this README are from the original README by Markus Wild).