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1.1     ! noro        1: Darwin/MacOSX Support - May 20, 2003
        !             2: ====================================
        !             3:
        !             4: Important Usage Notes
        !             5: =====================
        !             6:
        !             7: GC_init() MUST be called before calling any other GC functions. This
        !             8: is necessary to properly register segments in dynamic libraries. This
        !             9: call is required even if you code does not use dynamic libraries as the
        !            10: dyld code handles registering all data segments.
        !            11:
        !            12: The incremental collector is still a bit flaky on darwin. It seems to
        !            13: work reliably with workarounds for a few possible bugs in place however
        !            14: these workaround may not work correctly in all cases. There may also
        !            15: be additional problems that I have not found.
        !            16:
        !            17: Implementation Information
        !            18: ==========================
        !            19: Darwin/MacOSX support is nearly complete. Thread support is reliable on
        !            20: Darwin 6.x (MacOSX 10.2) and there have been reports of success on older
        !            21: Darwin versions (MacOSX 10.1). Shared library support had also been
        !            22: added and the gc can be run from a shared library. There is currently only
        !            23: support for Darwin/PPC although adding x86 support should be trivial.
        !            24:
        !            25: Thread support is implemented in terms of mach thread_suspend and
        !            26: thread_resume calls. These provide a very clean interface to thread
        !            27: suspension. This implementation doesn't rely on pthread_kill so the
        !            28: code works on Darwin < 6.0 (MacOSX 10.1). All the code to stop the
        !            29: world is located in darwin_stop_world.c.
        !            30:
        !            31: The original incremental collector support unfortunatelly no longer works
        !            32: on recent Darwin versions. It also relied on some undocumented kernel
        !            33: structures. Mach, however, does have a very clean interface to exception
        !            34: handing. The current implementation uses Mach's exception handling.
        !            35:
        !            36: Much thanks goes to Andrew Stone, Dietmar Planitzer, Andrew Begel,
        !            37: Jeff Sturm, and Jesse Rosenstock for all their work on the
        !            38: Darwin/OS X port.
        !            39:
        !            40: -Brian Alliet
        !            41: brian@brianweb.net
        !            42:
        !            43:
        !            44: Older Information (Most of this no longer applies to the current code)
        !            45: ======================================================================
        !            46:
        !            47: While the GC should work on MacOS X Server, MacOS X and Darwin, I only tested
        !            48: it on MacOS X Server.
        !            49: I've added a PPC assembly version of GC_push_regs(), thus the setjmp() hack is
        !            50: no longer necessary. Incremental collection is supported via mprotect/signal.
        !            51: The current solution isn't really optimal because the signal handler must decode
        !            52: the faulting PPC machine instruction in order to find the correct heap address.
        !            53: Further, it must poke around in the register state which the kernel saved away
        !            54: in some obscure register state structure before it calls the signal handler -
        !            55: needless to say the layout of this structure is no where documented.
        !            56: Threads and dynamic libraries are not yet supported (adding dynamic library
        !            57: support via the low-level dyld API shouldn't be that hard).
        !            58:
        !            59: The original MacOS X port was brought to you by Andrew Stone.
        !            60:
        !            61:
        !            62: June, 1 2000
        !            63:
        !            64: Dietmar Planitzer
        !            65: dave.pl@ping.at
        !            66:
        !            67: Note from Andrew Begel:
        !            68:
        !            69: One more fix to enable gc.a to link successfully into a shared library for
        !            70: MacOS X. You have to add -fno-common to the CFLAGS in the Makefile. MacOSX
        !            71: disallows common symbols in anything that eventually finds its way into a
        !            72: shared library. (I don't completely understand why, but -fno-common seems to
        !            73: work and doesn't mess up the garbage collector's functionality).
        !            74:
        !            75: Feb 26, 2003
        !            76:
        !            77: Jeff Sturm and Jesse Rosenstock provided a patch that adds thread support.
        !            78: GC_MACOSX_THREADS should be defined in the build and in clients.  Real
        !            79: dynamic library support is still missing, i.e. dynamic library data segments
        !            80: are still not scanned.  Code that stores pointers to the garbage collected
        !            81: heap in statically allocated variables should not reside in a dynamic
        !            82: library.  This still doesn't appear to be 100% reliable.
        !            83:
        !            84: Mar 10, 2003
        !            85: Brian Alliet contributed dynamic library support for MacOSX.  It could also
        !            86: use more testing.