source: trunk/gcc/boehm-gc/doc/README.amiga@ 3801

===========================================================================
            Kjetil S. Matheussen's notes (28-11-2000)
===========================================================================
Compiles under SAS/C again. Should allso still compile under other
amiga compilers without big changes. I haven't checked if it still
works under gcc, because I don't have gcc for amiga. But I have
updated 'Makefile', and hope it compiles fine.


WHATS NEW:

1.
   Made a pretty big effort in preventing GCs allocating-functions from returning
   chip-mem.

   The lower part of the new file AmigaOS.c does this in various ways, mainly by
   wrapping GC_malloc, GC_malloc_atomic, GC_malloc_uncollectable,
   GC_malloc_atomic_uncollectable, GC_malloc_stubborn, GC_malloc_ignore_off_page
   and GC_malloc_atomic_ignore_off_page. GC_realloc is allso wrapped, but
   doesn't do the same effort in preventing to return chip-mem.
   Other allocating-functions (f.ex. GC_*_typed_) can probably be
   used without any problems, but beware that the warn hook will not be called.
   In case of problems, don't define GC_AMIGA_FASTALLOC.

   Programs using more time actually using the memory allocated
   (instead of just allocate and free rapidly) have
   the most to earn on this, but even gctest now normally runs twice
   as fast and uses less memory, on my poor 8MB machine.

   The changes have only effect when there is no more
   fast-mem left. But with the way GC works, it
   could happen quite often. Beware that an atexit handler had to be added,
   so using the abort() function will make a big memory-loss.
   If you absolutely must call abort() instead of exit(), try calling
   the GC_amiga_free_all_mem function before abort().

   New amiga-spesific compilation flags:

   GC_AMIGA_FASTALLOC - By NOT defining this option, GC will work like before,
                        it will not try to force fast-mem out of the OS, and
                        it will use normal calloc for allocation, and the rest
                        of the following flags will have no effect.

   GC_AMIGA_ONLYFAST - Makes GC never to return chip-mem. GC_AMIGA_RETRY have
                       no effect if this flag is set.

   GC_AMIGA_GC - If gc returns NULL, do a GC_gcollect, and try again. This
                 usually is a success with the standard GC configuration. 
                 It is allso the most important flag to set to prevent
                 GC from returning chip-mem. Beware that it slows down a lot
                 when a program is rapidly allocating/deallocating when
                 theres either very little fast-memory left or verly little
                 chip-memory left. Its not a very common situation, but gctest
                 sometimes (very rare) use many minutes because of this.

   GC_AMIGA_RETRY - If gc succeed allocating memory, but it is chip-mem,
                    try again and see if it is fast-mem. Most of the time,
                    it will actually return fast-mem for the second try.
                    I have set max number of retries to 9 or size/5000. You
                    can change this if you like. (see GC_amiga_rec_alloc())

   GC_AMIGA_PRINTSTATS - Gather some statistics during the execution of a
                         program, and prints out the info when the atexit-handler
                         is called.

   My reccomendation is to set all this flags, except GC_AMIGA_PRINTSTATS and
   GC_AMIGA_ONLYFAST.

   If your program demands high response-time, you should
   not define GC_AMIGA_GC, and possible allso define GC_AMIGA_ONLYFAST.
   GC_AMIGA_RETRY does not seem to slow down much.

   Allso, when compiling up programs, and GC_AMIGA_FASTALLOC was not defined when
   compilling gc, you can define GC_AMIGA_MAKINGLIB to avoid having these allocation-
   functions wrapped. (see gc.h)

   Note that GC_realloc must not be called before any of
   the other above mentioned allocating-functions have been called. (shouldn't be
   any programs doing so either, I hope).

   Another note. The allocation-function is wrapped when defining
   GC_AMIGA_FASTALLOC by letting the function go thru the new
   GC_amiga_allocwrapper_do function-pointer (see gc.h). Means that
   sending function-pointers, such as GC_malloc, GC_malloc_atomic, etc.,
   for later to be called like f.ex this, (*GC_malloc_functionpointer)(size),
   will not wrap the function. This is normally not a big problem, unless
   all allocation function is called like this, which will cause the
   atexit un-allocating function never to be called. Then you either
   have to manually add the atexit handler, or call the allocation-
   functions function-pointer functions like this;
   (*GC_amiga_allocwrapper_do)(size,GC_malloc_functionpointer).
   There are probably better ways this problem could be handled, unfortunately,
   I didn't find any without rewriting or replacing a lot of the GC-code, which
   I really didn't want to. (Making new GC_malloc_* functions, and just
   define f.ex GC_malloc as GC_amiga_malloc should allso work).


   New amiga-spesific function:

     void GC_amiga_set_toany(void (*func)(void));

   'func' is a function that will be called right before gc has to change
   allocation-method from MEMF_FAST to MEMF_ANY. Ie. when it is likely
   it will return chip-mem.


2. A few small compiler-spesific additions to make it compile with SAS/C again.

3. Updated and rewritten the smakefile, so that it works again and that
   the "unnecesarry" 'SCOPTIONS' files could be removed. Allso included
   the cord-smakefile stuff in the main smakefile, so that the cord smakefile
   could be removed too. By writing smake -f Smakefile.smk, both gc.lib and
   cord.lib will be made.



STILL MISSING:

Programs can not be started from workbench, at least not for SAS/C. (Martin
Tauchmanns note about that it now works with workbench is definitely wrong
when concerning SAS/C). I guess it works if you use the old "#if 0'ed"-code,
but I haven't tested it. I think the reason for MT to replace the
"#if 0'ed"-code was only because it was a bit to SAS/C-spesific. But I
don't know. An iconx-script solves this problem anyway.


BEWARE!

-To run gctest, set the stack to around 200000 bytes first.
-SAS/C-spesific: cord will crash if you compile gc.lib with
 either parm=reg or parm=both. (missing legal prototypes for
 function-pointers someplace is the reason I guess.).


tested with software: Radium, http://www.stud.ifi.uio.no/~ksvalast/radium/

tested with hardware: MC68060


-ksvalast@ifi.uio.no


===========================================================================
                           Martin Tauchmann's notes             (1-Apr-99)
===========================================================================

Works now, also with the GNU-C compiler V2.7.2.1. <ftp://ftp.unina.it/pub/amiga/geekgadgets/amiga/m68k/snapshots/971125/amiga-bin/>
Modify the `Makefile`
CC=cc $(ABI_FLAG)
to
CC=gcc $(ABI_FLAG)

TECHNICAL NOTES

- `GC_get_stack_base()`, `GC_register_data_segments()` works now with every
   C compiler; also Workbench.

- Removed AMIGA_SKIP_SEG, but the Code-Segment must not be scanned by GC.


PROBLEMS
- When the Linker, does`t merge all Code-Segments to an single one. LD of GCC
  do it always.

- With ixemul.library V47.3, when an GC program launched from another program
  (example: `Make` or `if_mach M68K AMIGA gctest`), `GC_register_data_segments()`
  found the Segment-List of the caller program.
  Can be fixed, if the run-time initialization code (for C programs, usually *crt0*)
  support `__data` and `__bss`.

- PowerPC Amiga currently not supported.

- Dynamic libraries (dyn_load.c) not supported.


TESTED WITH SOFTWARE

`Optimized Oberon 2 C` (oo2c) <http://cognac.informatik.uni-kl.de/download/index.html>


TESTED WITH HARDWARE

MC68030


CONTACT

Please, contact me at <martintauchmann@bigfoot.com>, when you change the
Amiga port. <http://martintauchmann.home.pages.de>
 
===========================================================================
                           Michel Schinz's notes
===========================================================================
WHO DID WHAT

The original Amiga port was made by Jesper Peterson. I (Michel Schinz)
modified it slightly to reflect the changes made in the new official
distributions, and to take advantage of the new SAS/C 6.x features. I also
created a makefile to compile the "cord" package (see the cord
subdirectory).

TECHNICAL NOTES

In addition to Jesper's notes, I have the following to say:

- Starting with version 4.3, gctest checks to see if the code segment is
  added to the root set or not, and complains if it is. Previous versions
  of this Amiga port added the code segment to the root set, so I tried to
  fix that. The only problem is that, as far as I know, it is impossible to
  know which segments are code segments and which are data segments (there
  are indeed solutions to this problem, like scanning the program on disk
  or patch the LoadSeg functions, but they are rather complicated). The
  solution I have chosen (see os_dep.c) is to test whether the program
  counter is in the segment we are about to add to the root set, and if it
  is, to skip the segment. The problems are that this solution is rather
  awkward and that it works only for one code segment. This means that if
  your program has more than one code segment, all of them but one will be
  added to the root set. This isn't a big problem in fact, since the
  collector will continue to work correctly, but it may be slower.

  Anyway, the code which decides whether to skip a segment or not can be
  removed simply by not defining AMIGA_SKIP_SEG. But notice that if you do
  so, gctest will complain (it will say that "GC_is_visible produced wrong
  failure indication"). However, it may be useful if you happen to have
  pointers stored in a code segment (you really shouldn't).

  If anyone has a good solution to the problem of finding, when a program
  is loaded in memory, whether a segment is a code or a data segment,
  please let me know.

PROBLEMS

If you have any problem with this version, please contact me at
schinz@alphanet.ch (but do *not* send long files, since we pay for
every mail!).

===========================================================================
                          Jesper Peterson's notes
===========================================================================

ADDITIONAL NOTES FOR AMIGA PORT

These notes assume some familiarity with Amiga internals.

WHY I PORTED TO THE AMIGA

The sole reason why I made this port was as a first step in getting
the Sather(*) language on the Amiga. A port of this language will
be done as soon as the Sather 1.0 sources are made available to me.
Given this motivation, the garbage collection (GC) port is rather
minimal.

(*) For information on Sather read the comp.lang.sather newsgroup.

LIMITATIONS

This port assumes that the startup code linked with target programs
is that supplied with SAS/C versions 6.0 or later. This allows
assumptions to be made about where to find the stack base pointer
and data segments when programs are run from WorkBench, as opposed
to running from the CLI. The compiler dependent code is all in the
GC_get_stack_base() and GC_register_data_segments() functions, but
may spread as I add Amiga specific features.

Given that SAS/C was assumed, the port is set up to be built with
"smake" using the "SMakefile". Compiler options in "SCoptions" can
be set with "scopts" program. Both "smake" and "scopts" are part of
the SAS/C commercial development system.

In keeping with the porting philosophy outlined above, this port
will not behave well with Amiga specific code. Especially not inter-
process comms via messages, and setting up public structures like
Intuition objects or anything else in the system lists. For the
time being the use of this library is limited to single threaded
ANSI/POSIX  compliant or near-complient code. (ie. Stick to stdio
for now). Given this limitation there is currently no mechanism for
allocating "CHIP" or "PUBLIC" memory under the garbage collector.
I'll add this after giving it considerable thought. The major
problem is the entire physical address space may have to me scanned,
since there is no telling who we may have passed memory to.

If you allocate your own stack in client code, you will have to
assign the pointer plus stack size to GC_stackbottom.

The initial stack size of the target program can be compiled in by
setting the __stack symbol (see SAS documentaion). It can be over-
ridden from the CLI by running the AmigaDOS "stack" program, or from
the WorkBench by setting the stack size in the tool types window.

SAS/C COMPILER OPTIONS (SCoptions)

You may wish to check the "CPU" code option is appropriate for your
intended target system.

Under no circumstances set the "StackExtend" code option in either
compiling the library or *ANY* client code.

All benign compiler warnings have been suppressed. These mainly
involve lack of prototypes in the code, and dead assignments
detected by the optimizer.

THE GOOD NEWS

The library as it stands is compatible with the GigaMem commercial
virtual memory software, and probably similar PD software.

The performance of "gctest" on an Amiga 2630 (68030 @ 25Mhz)
compares favourably with an HP9000 with similar architecture (a 325
with a 68030 I think).

-----------------------------------------------------------------------

The Amiga port has been brought to you by:

Jesper Peterson.

jep@mtiame.mtia.oz.au           (preferred, but 1 week turnaround)
jep@orca1.vic.design.telecom.au (that's orca<one>, 1 day turnaround)

At least one of these addresses should be around for a while, even
though I don't work for either of the companies involved.