Annotation of OpenXM_contrib/gc/README.amiga, Revision 1.1
1.1 ! maekawa 1:
! 2: ===========================================================================
! 3: Michel Schinz's notes
! 4: ===========================================================================
! 5: WHO DID WHAT
! 6:
! 7: The original Amiga port was made by Jesper Peterson. I (Michel Schinz)
! 8: modified it slightly to reflect the changes made in the new official
! 9: distributions, and to take advantage of the new SAS/C 6.x features. I also
! 10: created a makefile to compile the "cord" package (see the cord
! 11: subdirectory).
! 12:
! 13: TECHNICAL NOTES
! 14:
! 15: In addition to Jesper's notes, I have the following to say:
! 16:
! 17: - Starting with version 4.3, gctest checks to see if the code segment is
! 18: added to the root set or not, and complains if it is. Previous versions
! 19: of this Amiga port added the code segment to the root set, so I tried to
! 20: fix that. The only problem is that, as far as I know, it is impossible to
! 21: know which segments are code segments and which are data segments (there
! 22: are indeed solutions to this problem, like scanning the program on disk
! 23: or patch the LoadSeg functions, but they are rather complicated). The
! 24: solution I have chosen (see os_dep.c) is to test whether the program
! 25: counter is in the segment we are about to add to the root set, and if it
! 26: is, to skip the segment. The problems are that this solution is rather
! 27: awkward and that it works only for one code segment. This means that if
! 28: your program has more than one code segment, all of them but one will be
! 29: added to the root set. This isn't a big problem in fact, since the
! 30: collector will continue to work correctly, but it may be slower.
! 31:
! 32: Anyway, the code which decides whether to skip a segment or not can be
! 33: removed simply by not defining AMIGA_SKIP_SEG. But notice that if you do
! 34: so, gctest will complain (it will say that "GC_is_visible produced wrong
! 35: failure indication"). However, it may be useful if you happen to have
! 36: pointers stored in a code segment (you really shouldn't).
! 37:
! 38: If anyone has a good solution to the problem of finding, when a program
! 39: is loaded in memory, whether a segment is a code or a data segment,
! 40: please let me know.
! 41:
! 42: PROBLEMS
! 43:
! 44: If you have any problem with this version, please contact me at
! 45: schinz@alphanet.ch (but do *not* send long files, since we pay for
! 46: every mail!).
! 47:
! 48: ===========================================================================
! 49: Jesper Peterson's notes
! 50: ===========================================================================
! 51:
! 52: ADDITIONAL NOTES FOR AMIGA PORT
! 53:
! 54: These notes assume some familiarity with Amiga internals.
! 55:
! 56: WHY I PORTED TO THE AMIGA
! 57:
! 58: The sole reason why I made this port was as a first step in getting
! 59: the Sather(*) language on the Amiga. A port of this language will
! 60: be done as soon as the Sather 1.0 sources are made available to me.
! 61: Given this motivation, the garbage collection (GC) port is rather
! 62: minimal.
! 63:
! 64: (*) For information on Sather read the comp.lang.sather newsgroup.
! 65:
! 66: LIMITATIONS
! 67:
! 68: This port assumes that the startup code linked with target programs
! 69: is that supplied with SAS/C versions 6.0 or later. This allows
! 70: assumptions to be made about where to find the stack base pointer
! 71: and data segments when programs are run from WorkBench, as opposed
! 72: to running from the CLI. The compiler dependent code is all in the
! 73: GC_get_stack_base() and GC_register_data_segments() functions, but
! 74: may spread as I add Amiga specific features.
! 75:
! 76: Given that SAS/C was assumed, the port is set up to be built with
! 77: "smake" using the "SMakefile". Compiler options in "SCoptions" can
! 78: be set with "scopts" program. Both "smake" and "scopts" are part of
! 79: the SAS/C commercial development system.
! 80:
! 81: In keeping with the porting philosophy outlined above, this port
! 82: will not behave well with Amiga specific code. Especially not inter-
! 83: process comms via messages, and setting up public structures like
! 84: Intuition objects or anything else in the system lists. For the
! 85: time being the use of this library is limited to single threaded
! 86: ANSI/POSIX compliant or near-complient code. (ie. Stick to stdio
! 87: for now). Given this limitation there is currently no mechanism for
! 88: allocating "CHIP" or "PUBLIC" memory under the garbage collector.
! 89: I'll add this after giving it considerable thought. The major
! 90: problem is the entire physical address space may have to me scanned,
! 91: since there is no telling who we may have passed memory to.
! 92:
! 93: If you allocate your own stack in client code, you will have to
! 94: assign the pointer plus stack size to GC_stackbottom.
! 95:
! 96: The initial stack size of the target program can be compiled in by
! 97: setting the __stack symbol (see SAS documentaion). It can be over-
! 98: ridden from the CLI by running the AmigaDOS "stack" program, or from
! 99: the WorkBench by setting the stack size in the tool types window.
! 100:
! 101: SAS/C COMPILER OPTIONS (SCoptions)
! 102:
! 103: You may wish to check the "CPU" code option is appropriate for your
! 104: intended target system.
! 105:
! 106: Under no circumstances set the "StackExtend" code option in either
! 107: compiling the library or *ANY* client code.
! 108:
! 109: All benign compiler warnings have been suppressed. These mainly
! 110: involve lack of prototypes in the code, and dead assignments
! 111: detected by the optimizer.
! 112:
! 113: THE GOOD NEWS
! 114:
! 115: The library as it stands is compatible with the GigaMem commercial
! 116: virtual memory software, and probably similar PD software.
! 117:
! 118: The performance of "gctest" on an Amiga 2630 (68030 @ 25Mhz)
! 119: compares favourably with an HP9000 with similar architecture (a 325
! 120: with a 68030 I think).
! 121:
! 122: -----------------------------------------------------------------------
! 123:
! 124: The Amiga port has been brought to you by:
! 125:
! 126: Jesper Peterson.
! 127:
! 128: jep@mtiame.mtia.oz.au (preferred, but 1 week turnaround)
! 129: jep@orca1.vic.design.telecom.au (that's orca<one>, 1 day turnaround)
! 130:
! 131: At least one of these addresses should be around for a while, even
! 132: though I don't work for either of the companies involved.
! 133:
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