amiga-clib2/documentation

An ISO 'C' (1994) compliant runtime library for the Amiga
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1. What is this?

This is my attempt to get Samba 2.2.x ported to the Amiga. My first Amiga
port required SAS/C and a number of strange tricks had to be pulled to get
it to support the kind of environment Samba needed. But with the
introduction of Samba 2.2.x many of those tricks did not work any more,
which is why I decided to attack the problem at the root, namely the
runtime library.

Because it was no longer possible to build Samba with SAS/C on the new
Amiga platform, the idea came up to move development to the GNU 'C'
compiler. This turned out to be a challenge due to its somewhat
underdeveloped runtime library and header files. Eventually, I decided to
rewrite that library from scratch.


2. What does it do?

Using "'C' - A reference manual" as a reference I wrote a set of header
files, then proceeded to implement each single function referenced in them.
With few exceptions in the area of wide character support, the result
should be a feature complete implementation of the ISO 'C' (1994) runtime
library.

Because Samba needs a few POSIX-like routines to be supported, the library
functionality is complemented by a set of routines described in "Advanced
programming in the Unix environent". This set is not complete, however. It
will have to grow even further to accomodate for Samba's needs, but this is
a good start. I specifically added hooks for integrating socket I/O at a
later point of time.

This is not a portable implementation of the library in the sense that you
could move it from one 'C' compiler on one operating system to another.
This is an Amiga specific implementation.

The library supports floating point math, which is limited to IEEE single
and double precision or M68881 inline math. There is no support for the
fast floating point (FFP) format or exclusive IEEE single precision. You
either get double precision (IEEE math) or extended precision (M68881
inline math). What it is that you get is determined at compile time. Use
the IEEE_FLOATING_POINT_SUPPORT preprocessor symbol to activate IEEE math
code and the M68881_FLOATING_POINT_SUPPORT symbol for M68881 inline math.

Not unlike SAS/C, you can configure a minimum stack size the program is to
use when it starts up. This is controlled via the '__stack_size' variable
(see "stdlib_main.c").

I added some amiga.lib and debug.lib functionality to the library, but
don't count on it to be complete.


3. What does it not do?

This library is a departure from the typical 'C' runtime environments of
the past which had to run on all AmigaOS releases, down to Kickstart 1.1.
This very library was designed to take advantage of the routines available
since Kickstart 2.04 was introduced and virtually nobody ever put to use.
This helps to cut the code size, and it also helps to keep bugs out of the
library by falling back onto well-tested implementations. However, the
catch is that the code won't run under Kickstart 1.3 and below. But then
these operating system releases have been obsolete for more than a decade,
and you can always go back to a compiler environment which supports them.

Practically all library routines are implemented in a sort of na<6E>ve
fashion. That is, they contain virtually no optimizations whatsoever. This
is particularly apparent in workhorses such as memset() or memmove(). But
then, the issue is easy testability and Amiga platform portability.

There is very little support for amiga.lib functionality. There is
NewList(), HookEntry(), CallHook(), CallHookA(), the DoMethod() family, the
RexxVars family, but that's all. If you need more, you would have to
implement it yourself. Put another way, if you absolutely need
functionality that is only found in amiga.lib, you really shouldn't need in
in the first place.


4. Where does the source code come from?

I originally thought that it might be helpful to piece this library
together from various sources, such as the BSD libc. Turned out that this
code was so 'portable' that it became much more complex than it ought to
be. Also, some side-effects were present which considerably changed the
behaviour of the library. For example, the BSD libc uses bcopy() as an
alias for memcpy(), and unlike memcpy() is documented to, bcopy() supports
overlapping copies.

Eventually, I wrote virtually all the code myself, borrowing algorithmic
ideas from the BSD libc and the Manx Aztec 'C' runtime library. Because I
don't know much about the environment GCC expects, I borrowed code snippets
from libnix, which was written by Matthias Fleischer and Gunther Nikl. This
in particular concerns the integer and floating point math support, the
setjmp/longjmp routines and the startup code. The M68881 inline math code
comes from the <math-68881.h> file written by Matthew Self
(self@bayes.arc.nasa.gov).


5. Limitations and caveats

There is hardly any documentation on the code I wrote. In part this is due
to the fact that the code itself is very simple in design. It should speak
for itself. However, to make a usable runtime library you have to have a
user documentation as in man pages or autodocs. We will eventually have to
have autodocs for this library.

The code is currently plastered with assertions and debug code. It is
therefore much larger than it ought to be and runs much slower than it
ought to be. For example, the malloc() routine will set the contents of the
memory allocated to a 'dirty' bit pattern which is likely to break software
which makes assumptions about its contents. Likewise, the free() routine
will trash the memory to deallocate with a different 'dirty' bit pattern to
turn up reuse of memory after deallocation. All these debugging features
can be disabled by defining the NDEBUG preprocessor symbol at compile time
(see <assert.h>).

The exception handling in the math code is not particularly effective. For
one part this is due to the fact that there is no exception handler
installed by the runtime library when it starts up which could catch and
process the error conditions the CPU or FPU generates. The idea was to
provide for a portable runtime library with little to no assembly language
involved. To make the exception handling complete, such code would be
necessary.

The library currently builds under SAS/C, but because the 'normal' program
startup code is not utilized, the base relative (A4) addressing does not
work. If you are going to test it, use the data=faronly option to compile
the library and the programs.

If you are going to rebuild the library with SAS/C you will need to
reassign INCLUDE: to point to the local 'include' directory or things won't
work.


6. Conventions and design issues

You will have noticed the 330+ files in this directory. This is not the
best way to organize a runtime library, but at least all the bits and
pieces are in plain sight. Each file stands for the one or two routines it
contains. The name indicates what routine(s) that might be. Each file name
is prefixed by the name of the header file in which the corresponding
routine is defined. So, for example, you will find that "unistd_lchown.c"
contains the definition of the lchown() routine, which has its prototype
defined in the <unistd.h> header file.

Internal function and variable names are prefixed with two underscores, as
in '__stdio_init()'.

All routines attempt to do error checking on their parameters. They will
either drop into an assert() or set an errno value and refuse to go any
further. This cuts performance but should help to catch the simple bugs
quite easily (NULL pointers).

Just like any halfway sane Amiga 'C'<27>runtime library, this one performs its
^C checking in the I/O routines. Typically once upon entry and in every
iteration of the loop there might be it will quickly poll the ^C signal and
drop into raise(SIGINT) in case the signal is set. This is just about the
safest method to solve the problem and should be much more robust than the
ixemul approach of 'interrupt anywhere - crash anywhere' using the task
switch/launch hooks to test for signals.

By default all library routines follow the ISO 'C' conventions in that
where implementation defined behaviour is permitted, the AmigaOS rules are
followed. For example, unlink() will by default operate like DeleteFile()
and rename() will return with an error code set if the name of the
file/directory to be renamed would collide with an existing directory
entry. However, your program can set a global variable '__unix_semantics'
which will cause some routines to perform like their Unix counterparts.
This is necessary for Samba to work but not a generally desirable feature.
You have some Unix-like behaviour, but the environment itself is not
completely Unix- or POSIX-compliant. And it shouldn't be. Don't make the
mistake of trying to mold the environment into a POSIX emulation. It
doesn't work; AmigaOS is not Unix.


7. The startup code

There are three program startup files provided. The most simplistic is in
'startup.c' which I use for SAS/C. It just invokes the setup routine which
eventually calls main() and drops straight into exit().

The ncrt0.S file was adapted from the libnix startup code which sets up the
base relative data area, if necessary (the SMALL_DATA preprocessor symbol
must be defined).

The nrcrt0.S file was adapted from libnix startup code, too, and sets up
the base relative data area for programs to be made resident. Note that the
geta4() stub is missing here; it wouldn't work in a resident program
anyway.

The ncrt0.S and nrcrt0.S files are considerably smaller and less complex
than the libnix code they are based on. This is because in this library
design all the more complex tasks are performed in the stdlib_main.c file
rather than in assembly language.


8. Documentation

Well, you're reading it. There isn't anything much yet. You can consult the book
"'C' - A reference manual" and you could look at the Open Group's Single Unix
Specification at <http://www.opengroup.org/onlinepubs/007904975>.


9. Legal status

Because this library is in part based upon free software it would be uncourteous
not to make it free software itself. The BSD license would probably be
appropriate here.

The PowerPC math library is based in part on work by Sun Microsystems:

====================================================
Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.

Developed at SunPro, a Sun Microsystems, Inc. business.
Permission to use, copy, modify, and distribute this
software is freely granted, provided that this notice
is preserved.
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10. Contacting the author

The basic work was done by Olaf Barthel during two weeks in July 2002. You
can reach me at:

   Olaf Barthel
   Gneisenaustr. 43
   D-31275 Lehrte

Or via e-mail:

   olsen@sourcery.han.de