=========================================================================== 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, 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.