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+This is a rough history of garbage collector bugs and versions.
+
+This has been maintained with varying diligence over the years.
+
+I made an attempt to include recent contributors here.  I apologize for any
+omissions.
+
+-------------------------
+
+  Version 1.3 and immediately preceding versions contained spurious
+assembly language assignments to TMP_SP.  Only the assignment in the PC/RT
+code is necessary.  On other machines, with certain compiler options,
+the assignments can lead to an unsaved register being overwritten.
+Known to cause problems under SunOS 3.5 WITHOUT the -O option.  (With
+-O the compiler recognizes it as dead code.  It probably shouldn't,
+but that's another story.)
+
+  Version 1.4 and earlier versions used compile time determined values
+for the stack base.  This no longer works on Sun 3s, since Sun 3/80s use
+a different stack base.  We now use a straightforward heuristic on all
+machines on which it is known to work (incl. Sun 3s) and compile-time
+determined values for the rest.  There should really be library calls
+to determine such values.
+
+  Version 1.5 and earlier did not ensure 8 byte alignment for objects
+allocated on a sparc based machine.
+
+  Version 1.8 added ULTRIX support in gc_private.h.
+  
+  Version 1.9 fixed a major bug in gc_realloc.
+  
+  Version 2.0 introduced a consistent naming convention for collector
+routines and added support for registering dynamic library data segments
+in the standard mark_roots.c.  Most of the data structures were revamped.
+The treatment of interior pointers was completely changed.  Finalization
+was added.  Support for locking was added.  Object kinds were added.
+We added a black listing facility to avoid allocating at addresses known
+to occur as integers somewhere in the address space.  Much of this
+was accomplished by adapting ideas and code from the PCR collector.
+The test program was changed and expanded.
+
+  Version 2.1 was the first stable version since 1.9, and added support
+for PPCR.
+
+  Version 2.2 added debugging allocation, and fixed various bugs.  Among them:
+- GC_realloc could fail to extend the size of the object for certain large object sizes.
+- A blatant subscript range error in GC_printf, which unfortunately
+  wasn't exercised on machines with sufficient stack alignment constraints.
+- GC_register_displacement did the wrong thing if it was called after
+  any allocation had taken place.
+- The leak finding code would eventually break after 2048 byte
+  byte objects leaked.
+- interface.c didn't compile.
+- The heap size remained much too small for large stacks.
+- The stack clearing code behaved badly for large stacks, and perhaps
+  on HP/PA machines.
+
+  Version 2.3 added ALL_INTERIOR_POINTERS and fixed the following bugs:
+- Missing declaration of etext in the A/UX version.
+- Some PCR root-finding problems.
+- Blacklisting was not 100% effective, because the plausible future
+  heap bounds were being miscalculated.
+- GC_realloc didn't handle out-of-memory correctly.
+- GC_base could return a nonzero value for addresses inside free blocks.
+- test.c wasn't really thread safe, and could erroneously report failure
+  in a multithreaded environment.  (The locking primitives need to be
+  replaced for other threads packages.)
+- GC_CONS was thoroughly broken.
+- On a SPARC with dynamic linking, signals stayed diabled while the
+  client code was running.
+  (Thanks to Manuel Serrano at INRIA for reporting the last two.)
+  
+  Version 2.4 added GC_free_space_divisor as a tuning knob, added
+  support for OS/2 and linux, and fixed the following bugs:
+- On machines with unaligned pointers (e.g. Sun 3), every 128th word could
+  fail to be considered for marking.
+- Dynamic_load.c erroneously added 4 bytes to the length of the data and
+  bss sections of the dynamic library.  This could result in a bad memory
+  reference if the actual length was a multiple of a page.  (Observed on
+  Sun 3.  Can probably also happen on a Sun 4.)
+  (Thanks to Robert Brazile for pointing out that the Sun 3 version
+  was broken.  Dynamic library handling is still broken on Sun 3s
+  under 4.1.1U1, but apparently not 4.1.1.  If you have such a machine,
+  use -Bstatic.)
+  
+  Version 2.5 fixed the following bugs:
+- Removed an explicit call to exit(1)
+- Fixed calls to GC_printf and GC_err_printf, so the correct number of
+  arguments are always supplied.  The OS/2 C compiler gets confused if
+  the number of actuals and the number of formals differ.  (ANSI C
+  doesn't require this to work.  The ANSI sanctioned way of doing things
+  causes too many compatibility problems.)
+  
+  Version 3.0  added generational/incremental collection and stubborn
+  objects.
+
+  Version 3.1 added the following features:
+- A workaround for a SunOS 4.X SPARC C compiler
+  misfeature that caused problems when the collector was turned into
+  a dynamic library.  
+- A fix for a bug in GC_base that could result in a memory fault.
+- A fix for a performance bug (and several other misfeatures) pointed
+  out by Dave Detlefs and Al Dosser.
+- Use of dirty bit information for static data under Solaris 2.X.
+- DEC Alpha/OSF1 support (thanks to Al Dosser).
+- Incremental collection on more platforms.
+- A more refined heap expansion policy.  Less space usage by default.
+- Various minor enhancements to reduce space usage, and to reduce
+  the amount of memory scanned by the collector.
+- Uncollectable allocation without per object overhead.
+- More conscientious handling of out-of-memory conditions.
+- Fixed a bug in debugging stubborn allocation.
+- Fixed a bug that resulted in occasional erroneous reporting of smashed
+  objects with debugging allocation.
+- Fixed bogus leak reports of size 4096 blocks with FIND_LEAK.
+
+  Version 3.2 fixed a serious and not entirely repeatable bug in
+  the incremental collector.  It appeared only when dirty bit info
+  on the roots was available, which is normally only under Solaris.
+  It also added GC_general_register_disappearing_link, and some
+  testing code.  Interface.c disappeared.
+
+  Version 3.3 fixes several bugs and adds new ports:
+- PCR-specific bugs.
+- Missing locking in GC_free, redundant FASTUNLOCK
+  in GC_malloc_stubborn, and 2 bugs in
+  GC_unregister_disappearing_link.
+  All of the above were pointed out by Neil Sharman
+  (neil@cs.mu.oz.au).
+- Common symbols allocated by the SunOS4.X dynamic loader
+  were not included in the root set.
+- Bug in GC_finalize (reported by Brian Beuning and Al Dosser)
+- Merged Amiga port from Jesper Peterson (untested)
+- Merged NeXT port from Thomas Funke (significantly
+  modified and untested)
+
+  Version 3.4:
+- Fixed a performance bug in GC_realloc.
+- Updated the amiga port.
+- Added NetBSD and 386BSD ports.
+- Added cord library.
+- Added trivial performance enhancement for
+  ALL_INTERIOR_POINTERS.  (Don't scan last word.)
+  
+  Version 3.5
+- Minor collections now mark from roots only once, if that
+  doesn't cause an excessive pause.
+- The stack clearing heuristic was refined to prevent anomalies
+  with very heavily recursive programs and sparse stacks.
+- Fixed a bug that prevented mark stack growth in some cases.
+  GC_objects_are_marked should be set to TRUE after a call
+  to GC_push_roots and as part of GC_push_marked, since
+  both can now set mark bits.  I think this is only a performance
+  bug, but I wouldn't bet on it.  It's certainly very hard to argue
+  that the old version was correct.
+- Fixed an incremental collection bug that prevented it from
+  working at all when HBLKSIZE != getpagesize()
+- Changed dynamic_loading.c to include gc_priv.h before testing
+  DYNAMIC_LOADING.  SunOS dynamic library scanning
+  must have been broken in 3.4.
+- Object size rounding now adapts to program behavior.
+- Added a workaround (provided by Manuel Serrano and
+  colleagues) to a long-standing SunOS 4.X (and 3.X?) ld bug
+  that I had incorrectly assumed to have been squished.
+  The collector was broken if the text segment size was within
+  32 bytes of a multiple of 8K bytes, and if the beginning of
+  the data segment contained interesting roots.  The workaround
+  assumes a demand-loadable executable.  The original may have
+  have "worked" in some other cases.
+- Added dynamic library support under IRIX5.
+- Added support for EMX under OS/2 (thanks to Ari Huttunen).
+  
+Version 3.6:
+- fixed a bug in the mark stack growth code that was introduced
+  in 3.4.
+- fixed Makefile to work around DEC AXP compiler tail recursion
+  bug.
+
+Version 3.7:
+- Added a workaround for an HP/UX compiler bug.
+- Fixed another stack clearing performance bug.  Reworked
+  that code once more.
+  
+Version 4.0:
+- Added support for Solaris threads (which was possible
+  only by reimplementing some fraction of Solaris threads,
+  since Sun doesn't currently make the thread debugging
+  interface available).
+- Added non-threads win32 and win32S support.
+- (Grudgingly, with suitable muttering of obscenities) renamed
+  files so that the collector distribution could live on a FAT
+  file system.  Files that are guaranteed to be useless on
+  a PC still have long names.  Gc_inline.h and gc_private.h
+  still exist, but now just include  gc_inl.h and gc_priv.h.
+- Fixed a really obscure bug in finalization that could cause
+  undetected mark stack overflows.  (I would be surprised if
+  any real code ever tickled this one.)
+- Changed finalization code to dynamically resize the hash
+  tables it maintains.  (This probably does not matter for well-
+  -written code.  It no doubt does for C++ code that overuses
+  destructors.)
+- Added typed allocation primitives.  Rewrote the marker to
+  accommodate them with more reasonable efficiency.  This
+  change should also speed up marking for GC_malloc allocated
+  objects a little.  See gc_typed.h for new primitives.
+- Improved debugging facilities slightly.  Allocation time
+  stack traces are now kept by default on SPARC/SUNOS4.
+  (Thanks to Scott Schwartz.)
+- Added better support for small heap applications.
+- Significantly extended cord package.  Fixed a bug in the
+  implementation of lazily read files.  Printf and friends now
+  have cord variants.  Cord traversals are a bit faster.
+- Made ALL_INTERIOR_POINTERS recognition the default.
+- Fixed de so that it can run in constant space, independent
+  of file size.  Added simple string searching to cords and de.
+- Added the Hull-Ellis C++ interface.
+- Added dynamic library support for OSF/1.
+  (Thanks to Al Dosser and Tim Bingham at DEC.)
+- Changed argument to GC_expand_hp to be expressed
+  in units of bytes instead of heap blocks.  (Necessary
+  since the heap block size now varies depending on
+  configuration.  The old version was never very clean.)
+- Added GC_get_heap_size().  The previous "equivalent"
+  was broken.
+- Restructured the Makefile a bit.  
+
+Since version 4.0:
+- Changed finalization implementation to guarantee that
+  finalization procedures are called outside of the allocation
+  lock, making direct use of the interface a little less dangerous.
+  MAY BREAK EXISTING CLIENTS that assume finalizers
+  are protected by a lock.  Since there seem to be few multithreaded
+  clients that use finalization, this is hopefully not much of
+  a problem.
+- Fixed a gross bug in CORD_prev.
+- Fixed a bug in blacklst.c that could result in unbounded
+  heap growth during startup on machines that do not clear
+  memory obtained from the OS (e.g. win32S).
+- Ported de editor to win32/win32S.  (This is now the only
+  version with a mouse-sensitive UI.)
+- Added GC_malloc_ignore_off_page to allocate large arrays
+  in the presence of ALL_INTERIOR_POINTERS.
+- Changed GC_call_with_alloc_lock to not disable signals in
+  the single-threaded case.
+- Reduced retry count in GC_collect_or_expand for garbage
+  collecting when out of memory.
+- Made uncollectable allocations bypass black-listing, as they
+  should.
+- Fixed a bug in typed_test in test.c that could cause (legitimate)
+  GC crashes.
+- Fixed some potential synchronization problems in finalize.c
+- Fixed a real locking problem in typd_mlc.c.
+- Worked around an AIX 3.2 compiler feature that results in
+  out of bounds memory references.
+- Partially worked around an IRIX5.2 beta problem (which may
+  or may not persist to the final release).
+- Fixed a bug in the heap integrity checking code that could
+  result in explicitly deallocated objects being identified as
+  smashed.  Fixed a bug in the dbg_mlc stack saving code
+  that caused old argument pointers to be considered live.
+- Fixed a bug in CORD_ncmp (and hence CORD_str).
+- Repaired the OS2 port, which had suffered from bit rot
+  in 4.0.  Worked around what appears to be CSet/2 V1.0
+  optimizer bug.
+- Fixed a Makefile bug for target "c++".
+
+Since version 4.1:
+- Multiple bug fixes/workarounds in the Solaris threads version.
+  (It occasionally failed to locate some register contents for
+  marking.  It also turns out that thr_suspend and friends are
+  unreliable in Solaris 2.3.  Dirty bit reads appear
+  to be unreliable under some weird 
+  circumstances.  My stack marking code
+  contained a serious performance bug.  The new code is
+  extremely defensive, and has not failed in several cpu
+  hours of testing.  But  no guarantees ...)
+- Added MacOS support (thanks to Patrick Beard.)
+- Fixed several syntactic bugs in gc_c++.h and friends.  (These
+  didn't bother g++, but did bother most other compilers.)
+  Fixed gc_c++.h finalization interface.  (It didn't.)
+- 64 bit alignment for allocated objects was not guaranteed in a
+  few cases in which it should have been.
+- Added GC_malloc_atomic_ignore_off_page.
+- Added GC_collect_a_little.
+- Added some prototypes to gc.h.
+- Some other minor bug fixes (notably in Makefile).
+- Fixed OS/2 / EMX port (thanks to Ari Huttunen).
+- Fixed AmigaDOS port. (thanks to Michel Schinz).
+- Fixed the DATASTART definition under Solaris.  There
+  was a 1 in 16K chance of the collector missing the first
+  64K of static data (and thus crashing).
+- Fixed some blatant anachronisms in the README file.
+- Fixed PCR-Makefile for upcoming PPCR release.
+
+Since version 4.2:
+- Fixed SPARC alignment problem with GC_DEBUG.
+- Fixed Solaris threads /proc workaround.  The real
+  problem was an interaction with mprotect.
+- Incorporated fix from Patrick Beard for gc_c++.h (now gc_cpp.h).
+- Slightly improved allocator space utilization by
+  fixing the GC_size_map mechanism.
+- Integrated some Sony News and MIPS RISCos 4.51
+  patches.  (Thanks to Nobuyuki Hikichi of
+  Software Research Associates, Inc. Japan)
+- Fixed HP_PA alignment problem.  (Thanks to
+  xjam@cork.cs.berkeley.edu.)
+- Added GC_same_obj and friends.  Changed GC_base
+  to return 0 for pointers past the end of large objects.
+  Improved GC_base performance with ALL_INTERIOR_POINTERS
+  on machines with a slow integer mod operation.
+  Added GC_PTR_ADD, GC_PTR_STORE, etc. to prepare
+  for preprocessor.
+- changed the default on most UNIX machines to be that
+  signals are not disabled during critical GC operations.
+  This is still ANSI-conforming, though somewhat dangerous
+  in the presence of signal handlers. But the performance
+  cost of the alternative is sometimes problematic.
+  Can be changed back with a minor Makefile edit.
+- renamed IS_STRING in gc.h, to CORD_IS_STRING, thus
+  following my own naming convention.  Added the function
+  CORD_to_const_char_star.
+- Fixed a gross bug in GC_finalize.  Symptom: occasional
+  address faults in that function.  (Thanks to Anselm
+  Baird-Smith (Anselm.BairdSmith@inria.fr)
+- Added port to ICL DRS6000 running DRS/NX.  Restructured
+  things a bit to factor out common code, and remove obsolete
+  code.  Collector should now run under SUNOS5 with either
+  mprotect or /proc dirty bits.  (Thanks to Douglas Steel
+  (doug@wg.icl.co.uk)).
+- More bug fixes and workarounds for Solaris 2.X.  (These were
+  mostly related to putting the collector in a dynamic library,
+  which didn't really work before.  Also SOLARIS_THREADS
+  didn't interact well with dl_open.)  Thanks to btlewis@eng.sun.com.
+- Fixed a serious performance bug on the DEC Alpha.  The text
+  segment was getting registered as part of the root set.
+  (Amazingly, the result was still fast enough that the bug
+  was not conspicuous.) The fix works on OSF/1, version 1.3.
+  Hopefully it also works on other versions of OSF/1 ...
+- Fixed a bug in GC_clear_roots.
+- Fixed a bug in GC_generic_malloc_words_small that broke
+  gc_inl.h.  (Reported by Antoine de Maricourt.  I broke it
+  in trying to tweak the Mac port.) 
+- Fixed some problems with cord/de under Linux.
+- Fixed some cord problems, notably with CORD_riter4.
+- Added DG/UX port.
+  Thanks to Ben A. Mesander (ben@piglet.cr.usgs.gov)
+- Added finalization registration routines with weaker ordering
+  constraints.  (This is necessary for C++ finalization with
+  multiple inheritance, since the compiler often adds self-cycles.)
+- Filled the holes in the SCO port. (Thanks to Michael Arnoldus
+  <chime@proinf.dk>.)
+- John Ellis' additions to the C++ support:  From John:
+
+* I completely rewrote the documentation in the interface gc_c++.h
+(later renamed gc_cpp.h).  I've tried to make it both clearer and more
+precise.
+
+* The definition of accessibility now ignores pointers from an
+finalizable object (an object with a clean-up function) to itself.
+This allows objects with virtual base classes to be finalizable by the
+collector.  Compilers typically implement virtual base classes using
+pointers from an object to itself, which under the old definition of
+accessibility prevented objects with virtual base classes from ever
+being collected or finalized.
+
+* gc_cleanup now includes gc as a virtual base.  This was enabled by
+the change in the definition of accessibility.
+
+* I added support for operator new[].  Since most (all?) compilers
+don't yet support operator new[], it is conditionalized on
+-DOPERATOR_NEW_ARRAY.  The code is untested, but its trivial and looks
+correct.
+
+* The test program test_gc_c++ (later renamed test_cpp.cc)
+tries to test for the C++-specific functionality not tested by the
+other programs.
+- Added <unistd.h> include to misc.c.  (Needed for ppcr.)
+- Added PowerMac port. (Thanks to Patrick Beard again.)
+- Fixed "srcdir"-related Makefile problems.  Changed things so
+  that all externally visible include files always appear in the
+  include subdirectory of the source.  Made gc.h directly
+  includable from C++ code.  (These were at Per
+  Bothner's suggestion.)
+- Changed Intel code to also mark from ebp (Kevin Warne's
+  suggestion).
+- Renamed C++ related files so they could live in a FAT
+  file system. (Charles Fiterman's suggestion.)
+- Changed Windows NT Makefile to include C++ support in
+  gc.lib.  Added C++ test as Makefile target.
+  
+Since version 4.3:
+ - ASM_CLEAR_CODE was erroneously defined for HP
+   PA machines, resulting in a compile error.
+ - Fixed OS/2 Makefile to create a library.  (Thanks to
+   Mark Boulter (mboulter@vnet.ibm.com)).
+ - Gc_cleanup objects didn't work if they were created on
+   the stack.  Fixed.
+ - One copy of Gc_cpp.h in the distribution was out of 
+   synch, and failed to document some known compiler
+   problems with explicit destructor invocation.  Partially
+   fixed.  There are probably other compilers on which
+   gc_cleanup is miscompiled.
+ - Fixed Makefile to pass C compiler flags to C++ compiler.
+ - Added Mac fixes.
+ - Fixed os_dep.c to work around what appears to be
+   a new and different VirtualQuery bug under newer
+   versions of win32S.
+ - GC_non_gc_bytes was not correctly maintained by
+   GC_free.  Fixed.  Thanks to James Clark (jjc@jclark.com).
+ - Added GC_set_max_heap_size.
+ - Changed allocation code to ignore blacklisting if it is preventing
+   use of a very large block of memory.  This has the advantage
+   that naive code allocating very large objects is much more
+   likely to work.  The downside is you might no
+   longer find out that such code should really use
+   GC_malloc_ignore_off_page.
+ - Changed GC_printf under win32 to close and reopen the file
+   between calls.  FAT file systems otherwise make the log file
+   useless for debugging.
+ - Added GC_try_to_collect and GC_get_bytes_since_gc.  These
+   allow starting an abortable collection during idle times. 
+   This facility does not require special OS support.  (Thanks to
+   Michael Spertus of Geodesic Systems for suggesting this.  It was
+   actually an easy addition.  Kumar Srikantan previously added a similar
+   facility to a now ancient version of the collector.  At the time
+   this was much harder, and the result was less convincing.)
+ - Added some support for the Borland development environment.  (Thanks
+   to John Ellis and Michael Spertus.)
+ - Removed a misfeature from checksums.c that caused unexpected 
+   heap growth.  (Thanks to Scott Schwartz.)
+ - Changed finalize.c to call WARN if it encounters a finalization cycle.
+   WARN is defined in gc_priv.h to write a message, usually to stdout.
+   In many environments, this may be inappropriate.
+ - Renamed NO_PARAMS in gc.h to GC_NO_PARAMS, thus adhering to my own
+   naming convention.
+ - Added GC_set_warn_proc to intercept warnings.
+ - Fixed Amiga port. (Thanks to Michel Schinz (schinz@alphanet.ch).)
+ - Fixed a bug in mark.c that could result in an access to unmapped
+   memory from GC_mark_from_mark_stack on machines with unaligned
+   pointers.
+ - Fixed a win32 specific performance bug that could result in scanning of
+   objects allocated with the system malloc.
+ - Added REDIRECT_MALLOC.
+
+Since version 4.4:
+ - Fixed many minor and one major README bugs. (Thanks to Franklin Chen
+   (chen@adi.com) for pointing out many of them.)
+ - Fixed ALPHA/OSF/1 dynamic library support. (Thanks to Jonathan Bachrach
+   (jonathan@harlequin.com)).
+ - Added incremental GC support (MPROTECT_VDB) for Linux (with some
+   help from Bruno Haible).
+ - Altered SPARC recognition tests in gc.h and config.h (mostly as
+   suggested by Fergus Henderson).
+ - Added basic incremental GC support for win32, as implemented by
+   Windows NT and Windows 95.  GC_enable_incremental is a noop
+   under win32s, which doesn't implement enough of the VM interface.
+ - Added -DLARGE_CONFIG.
+ - Fixed GC_..._ignore_off_page to also function without
+   -DALL_INTERIOR_POINTERS.
+ - (Hopefully) fixed RS/6000 port.  (Only the test was broken.)
+ - Fixed a performance bug in the nonincremental collector running
+   on machines supporting incremental collection with MPROTECT_VDB
+   (e.g. SunOS 4, DEC AXP).  This turned into a correctness bug under
+   win32s with win32 incremental collection.  (Not all memory protection
+   was disabled.)
+ - Fixed some ppcr related bit rot.
+ - Caused dynamic libraries to be unregistered before reregistering.
+   The old way turned out to be a performance bug on some machines.
+ - GC_root_size was not properly maintained under MSWIN32.
+ - Added -DNO_DEBUGGING and GC_dump.
+ - Fixed a couple of bugs arising with SOLARIS_THREADS +
+   REDIRECT_MALLOC.
+ - Added NetBSD/M68K port.  (Thanks to Peter Seebach
+   <seebs@taniemarie.solon.com>.)
+ - Fixed a serious realloc bug.  For certain object sizes, the collector
+   wouldn't scan the expanded part of the object.  (Thanks to Clay Spence
+   (cds@peanut.sarnoff.com) for noticing the problem, and helping me to
+   track it down.)
+   
+Since version 4.5:
+ - Added Linux ELF support.  (Thanks to Arrigo Triulzi <arrigo@ic.ac.uk>.)
+ - GC_base crashed if it was called before any other GC_ routines.
+   This could happen if a gc_cleanup object was allocated outside the heap
+   before any heap allocation.
+ - The heap expansion heuristic was not stable if all objects had finalization
+   enabled.  Fixed finalize.c to count memory in finalization queue and
+   avoid explicit deallocation.  Changed alloc.c to also consider this count.
+   (This is still not recommended.  It's expensive if nothing else.)  Thanks
+   to John Ellis for pointing this out.
+ - GC_malloc_uncollectable(0) was broken.  Thanks to Phong Vo for pointing
+   this out.
+ - The collector didn't compile under Linux 1.3.X.  (Thanks to Fred Gilham for
+   pointing this out.)  The current workaround is ugly, but expected to be
+   temporary.
+ - Fixed a formatting problem for SPARC stack traces.
+ - Fixed some '=='s in os_dep.c that should have been assignments.
+   Fortunately these were in code that should never be executed anyway.
+   (Thanks to Fergus Henderson.)
+ - Fixed the heap block allocator to only drop blacklisted blocks in small
+   chunks.  Made BL_LIMIT self adjusting.  (Both of these were in response
+   to heap growth observed by Paul Graham.)
+ - Fixed the Metrowerks/68K Mac code to also mark from a6.  (Thanks
+   to Patrick Beard.)
+ - Significantly updated README.debugging.
+ - Fixed some problems with longjmps out of signal handlers, especially under
+   Solaris.  Added a workaround for the fact that siglongjmp doesn't appear to
+   do the right thing with -lthread under Solaris.
+ - Added MSDOS/djgpp port.  (Thanks to Mitch Harris  (maharri@uiuc.edu).)
+ - Added "make reserved_namespace" and "make user_namespace".  The
+   first renames ALL "GC_xxx" identifiers as "_GC_xxx".  The second is the
+   inverse transformation.  Note that doing this is guaranteed to break all
+   clients written for the other names.
+ - descriptor field for kind NORMAL in GC_obj_kinds with ADD_BYTE_AT_END
+   defined should be -ALIGNMENT not WORDS_TO_BYTES(-1).  This is
+   a serious bug on machines with pointer alignment of less than a word.
+ - GC_ignore_self_finalize_mark_proc didn't handle pointers to very near the
+   end of the object correctly.  Caused failures of the C++ test on a DEC Alpha
+   with g++.
+ - gc_inl.h still had problems.  Partially fixed.  Added warnings at the
+   beginning to hopefully specify the remaining dangers.
+ - Added DATAEND definition to config.h.
+ - Fixed some of the .h file organization.  Fixed "make floppy".
+ 
+Since version 4.6:
+ - Fixed some compilation problems with -DCHECKSUMS (thanks to Ian Searle)
+ - Updated some Mac specific files to synchronize with Patrick Beard.
+ - Fixed a serious bug for machines with non-word-aligned pointers.
+   (Thanks to Patrick Beard for pointing out the problem.  The collector
+   should fail almost any conceivable test immediately on such machines.)
+
+Since version 4.7:
+ - Changed a "comment" in a MacOS specific part of mach-dep.c that caused
+   gcc to fail on other platforms.
+
+Since version 4.8
+ - More README.debugging fixes.
+ - Objects ready for finalization, but not finalized in the same GC
+   cycle, could be prematurely collected.  This occasionally happened
+   in test_cpp.
+ - Too little memory was obtained from the system for very large
+   objects.  That could cause a heap explosion if these objects were
+   not contiguous (e.g. under PCR), and too much of them was blacklisted.
+ - Due to an improper initialization, the collector was too hesitant to
+   allocate blacklisted objects immediately after system startup.
+ - Moved GC_arrays from the data into the bss segment by not explicitly
+   initializing it to zero.  This significantly
+   reduces the size of executables, and probably avoids some disk accesses
+   on program startup.  It's conceivable that it might break a port that I
+   didn't test.
+ - Fixed EMX_MAKEFILE to reflect the gc_c++.h to gc_cpp.h renaming which
+   occurred a while ago.
+
+Since 4.9:
+ - Fixed a typo around a call to GC_collect_or_expand in alloc.c.  It broke
+   handling of out of memory.  (Thanks to Patrick Beard for noticing.)
+
+Since 4.10:
+ - Rationalized (hopefully) GC_try_to_collect in an incremental collection
+   environment.  It appeared to not handle a call while a collection was in
+   progress, and was otherwise too conservative.
+ - Merged GC_reclaim_or_delete_all into GC_reclaim_all to get rid of some
+   code.
+ - Added Patrick Beard's Mac fixes, with substantial completely untested
+   modifications.
+ - Fixed the MPROTECT_VDB code to deal with large pages and imprecise
+   fault addresses (as on an UltraSPARC running Solaris 2.5).  Note that this
+   was not a problem in the default configuration, which uses PROC_VDB.
+ - The DEC Alpha assembly code needed to restore $gp between calls.
+   Thanks to Fergus Henderson for tracking this down and supplying a
+   patch.
+ - The write command for "de" was completely broken for large files.
+   I used the easiest portable fix, which involved changing the semantics
+   so that f.new is written instead of overwriting f.  That's safer anyway.
+ - Added README.solaris2 with a discussion of the possible problems of
+   mixing the collector's sbrk allocation with malloc/realloc.
+ - Changed the data segment starting address for SGI machines.  The
+   old code failed under IRIX6.
+ - Required double word alignment for MIPS.
+ - Various minor fixes to remove warnings.
+ - Attempted to fix some Solaris threads problems reported by Zhiying Chen.
+   In particular, the collector could try to fork a thread with the
+   world stopped as part of GC_thr_init.  It also failed to deal with
+   the case in which the original thread terminated before the whole
+   process did.
+ - Added -DNO_EXECUTE_PERMISSION.  This has a major performance impact
+   on the incremental collector under Irix, and perhaps under other
+   operating systems.
+ - Added some code to support allocating the heap with mmap.  This may
+   be preferable under some circumstances.
+ - Integrated dynamic library support for HP.
+   (Thanks to Knut Tvedten <knuttv@ifi.uio.no>.)
+ - Integrated James Clark's win32 threads support, and made a number
+   of changes to it, many of which were suggested by Pontus Rydin.
+   This is still not 100% solid.
+ - Integrated Alistair Crooks' support for UTS4 running on an Amdahl
+   370-class machine.
+ - Fixed a serious bug in explicitly typed allocation.  Objects requiring
+   large descriptors where handled in a way that usually resulted in
+   a segmentation fault in the marker.  (Thanks to Jeremy Fitzhardinge
+   for helping to track this down.)
+ - Added partial support for GNU win32 development.  (Thanks to Fergus
+   Henderson.)
+ - Added optional support for Java-style finalization semantics.  (Thanks
+   to Patrick Bridges.)  This is recommended only for Java implementations.
+ - GC_malloc_uncollectable faulted instead of returning 0 when out of
+   memory.  (Thanks to dan@math.uiuc.edu for noticing.)
+ - Calls to GC_base before the collector was initialized failed on a
+   DEC Alpha.  (Thanks to Matthew Flatt.)
+ - Added base pointer checking to GC_REGISTER_FINALIZER in debugging
+   mode, at the suggestion of Jeremy Fitzhardinge.
+ - GC_debug_realloc failed for uncollectable objects.  (Thanks to
+   Jeremy Fitzhardinge.)
+ - Explicitly typed allocation could crash if it ran out of memory.
+   (Thanks to Jeremy Fitzhardinge.)
+ - Added minimal support for a DEC Alpha running Linux.
+ - Fixed a problem with allocation of objects whose size overflowed
+   ptrdiff_t.  (This now fails unconditionally, as it should.)
+ - Added the beginning of Irix pthread support.
+ - Integrated Xiaokun Zhu's fixes for djgpp 2.01.
+ - Added SGI-style STL allocator support (gc_alloc.h).
+ - Fixed a serious bug in README.solaris2.  Multithreaded programs must include
+   gc.h with SOLARIS_THREADS defined.
+ - Changed GC_free so it actually deallocates uncollectable objects.
+   (Thanks to Peter Chubb for pointing out the problem.)
+ - Added Linux ELF support for dynamic libararies.  (Thanks again to
+   Patrick Bridges.)
+ - Changed the Borland cc configuration so that the assembler is not
+   required.
+ - Fixed a bug in the C++ test that caused it to fail in 64-bit
+   environments.
+
+Since 4.11:
+ - Fixed ElfW definition in dyn_load.c. (Thanks to Fergus Henderson.)
+   This prevented the dynamic library support from compiling on some
+   older ELF Linux systems.
+ - Fixed UTS4 port (which I apparently mangled during the integration)
+   (Thanks to again to Alistair Crooks.)
+ - "Make C++" failed on Suns with SC4.0, due to a problem with "bool".
+   Fixed in gc_priv.h.
+ - Added more pieces for GNU win32.  (Thanks to Timothy N. Newsham.)
+   The current state of things should suffice for at least some
+   applications.
+ - Changed the out of memory retry count handling as suggested by
+   Kenjiro Taura.  (This matters only if GC_max_retries > 0, which
+   is no longer the default.)
+ - If a /proc read failed repeatedly, GC_written_pages was not updated
+   correctly.  (Thanks to Peter Chubb for diagnosing this.)
+ - Under unlikely circumstances, the allocator could infinite loop in
+   an out of memory situation.  (Thanks again to Kenjiro Taura for
+   identifying the problem and supplying a fix.)
+ - Fixed a syntactic error in the DJGPP code.  (Thanks to Fergus
+   Henderson for finding this by inspection.)  Also fixed a test program
+   problem with DJGPP (Thanks to Peter Monks.)
+ - Atomic uncollectable objects were not treated correctly by the
+   incremental collector.  This resulted in weird log statistics and
+   occasional performance problems.  (Thanks to Peter Chubb for pointing
+   this out.)
+ - Fixed some problems resulting from compilers that dont define
+   __STDC__.  In this case void * and char * were used inconsistently
+   in some cases.  (Void * should not have been used at all.  If
+   you have an ANSI superset compiler that does not define __STDC__,
+   please compile with -D__STDC__=0. Thanks to Manuel Serrano and others
+   for pointing out the problem.)
+ - Fixed a compilation problem on Irix with -n32 and -DIRIX_THREADS.
+   Also fixed some other IRIX_THREADS problems which may or may not have
+   had observable symptoms.
+ - Fixed an HP PA compilation problem in dyn_load.c.  (Thanks to
+   Philippe Queinnec.)
+ - SEGV fault handlers sometimes did not get reset correctly.  (Thanks
+   to David Pickens.)
+ - Added a fix for SOLARIS_THREADS on Intel.  (Thanks again to David
+   Pickens.)  This probably needs more work to become functional.
+ - Fixed struct sigcontext_struct in os_dep.c for compilation under
+   Linux 2.1.X.	(Thanks to Fergus Henderson.)
+ - Changed the DJGPP STACKBOTTOM and DATASTART values to those suggested
+   by Kristian Kristensen.  These may still not be right, but it is
+   it is likely to work more often than what was there before.  They may
+   even be exactly right.
+ - Added a #include <string.h> to test_cpp.cc.  This appears to help
+   with HP/UX and gcc.  (Thanks to assar@sics.se.)
+ - Version 4.11 failed to run in incremental mode on recent 64-bit Irix
+   kernels.  This was a problem related to page unaligned heap segments.
+   Changed the code to page align heap sections on all platforms.
+   (I had mistakenly identified this as a kernel problem earlier.
+   It was not.)
+ - Version 4.11 did not make allocated storage executable, except on
+   one or two platforms, due to a bug in a #if test.  (Thanks to Dave
+   Grove for pointing this out.)
+ - Added sparc_sunos4_mach_dep.s to support Sun's compilers under SunOS4.
+ - Added GC_exclude_static_roots.
+ - Fixed the object size mapping algorithm.  This shouldn't matter,
+   but the old code was ugly.
+ - Heap checking code could die if one of the allocated objects was
+   larger than its base address.  (Unsigned underflow problem.  Thanks
+   to Clay Spence for isolating the problem.)
+ - Added RS6000 (AIX) dynamic library support and fixed STACK_BOTTOM.
+   (Thanks to Fred Stearns.)
+ - Added Fergus Henderson's patches for improved robustness with large
+   heaps and lots of blacklisting.
+ - Added Peter Chubb's changes to support Solaris Pthreads, to support
+   MMAP allocation in Solaris, to allow Solaris to find dynamic libraries
+   through /proc, to add malloc_typed_ignore_off_page, and a few other
+   minor features and bug fixes.
+ - The Solaris 2 port should not use sbrk.  I received confirmation from
+   Sun that the use of sbrk and malloc in the same program is not
+   supported.  The collector now defines USE_MMAP by default on Solaris.
+ - Replaced the djgpp makefile with Gary Leavens' version.
+ - Fixed MSWIN32 detection test.
+ - Added Fergus Henderson's patches to allow putting the collector into
+   a DLL under GNU win32.
+ - Added Ivan V. Demakov's port to Watcom C on X86.
+ - Added Ian Piumarta's Linux/PowerPC port.
+ - On Brian Burton's suggestion added PointerFreeGC to the placement
+   options in gc_cpp.h.  This is of course unsafe, and may be controversial.
+   On the other hand, it seems to be needed often enough that it's worth
+   adding as a standard facility.
+
+Since 4.12:
+ - Fixed a crucial bug in the Watcom port.  There was a redundant decl
+   of GC_push_one in gc_priv.h.
+ - Added FINALIZE_ON_DEMAND.
+ - Fixed some pre-ANSI cc problems in test.c.
+ - Removed getpagesize() use for Solaris.  It seems to be missing in one
+   or two versions.
+ - Fixed bool handling for SPARCCompiler version 4.2.
+ - Fixed some files in include that had gotten unlinked from the main
+   copy.
+ - Some RS/6000 fixes (missing casts).  Thanks to Toralf Foerster.
+ - Fixed several problems in GC_debug_realloc, affecting mostly the
+   FIND_LEAK case.
+ - GC_exclude_static_roots contained a buggy unsigned comparison to
+   terminate a loop.  (Thanks to Wilson Ho.)
+ - CORD_str failed if the substring occurred at the last possible position.
+   (Only affects cord users.)
+ - Fixed Linux code to deal with RedHat 5.0 and integrated Peter Bigot's
+   os_dep.c code for dealing with various Linux versions.
+ - Added workaround for Irix pthreads sigaction bug and possible signal
+   misdirection problems.
+Since alpha1:
+ - Changed RS6000 STACKBOTTOM.
+ - Integrated Patrick Beard's Mac changes.
+ - Alpha1 didn't compile on Irix m.n, m < 6.
+ - Replaced Makefile.dj with a new one from Gary Leavens.
+ - Added Andrew Stitcher's changes to support SCO OpenServer.
+ - Added PRINT_BLACK_LIST, to allow debugging of high densities of false
+   pointers.
+ - Added code to debug allocator to keep track of return address
+   in GC_malloc caller, thus giving a bit more context.
+ - Changed default behavior of large block allocator to more
+   aggressively avoid fragmentation.  This is likely to slow down the
+   collector when it succeeds at reducing space cost.
+ - Integrated Fergus Henderson's CYGWIN32 changes.  They are untested,
+   but needed for newer versions.
+ - USE_MMAP had some serious bugs.  This caused the collector to fail
+   consistently on Solaris with -DSMALL_CONFIG.
+ - Added Linux threads support, thanks largely to Fergus Henderson.
+Since alpha2:
+ - Fixed more Linux threads problems.
+ - Changed default GC_free_space_divisor to 3 with new large block allocation.
+   (Thanks to Matthew Flatt for some measurements that suggest the old
+   value sometimes favors space too much over time.)
+ - More CYGWIN32 fixes.
+ - Integrated Tyson-Dowd's Linux-M68K port.
+ - Minor HP PA and DEC UNIX fixes from Fergus Henderson.
+ - Integrated Christoffe Raffali's Linux-SPARC changes.
+ - Allowed for one more GC fixup iteration after a full GC in incremental
+   mode.  Some quick measurements suggested that this significantly
+   reduces pause times even with smaller GC_RATE values.
+ - Moved some more GC data structures into GC_arrays.  This decreases
+   pause times and GC overhead, but makes debugging slightly less convenient.
+ - Fixed namespace pollution problem ("excl_table").
+ - Made GC_incremental a constant for -DSMALL_CONFIG, hopefully shrinking
+   that slightly.
+ - Added some win32 threads fixes.
+ - Integrated Ivan Demakov and David Stes' Watcom fixes.
+ - Various other minor fixes contributed by many people.
+ - Renamed config.h to gcconfig.h, since config.h tends to be used for
+   many other things.
+ - Integrated Matthew Flatt's support for 68K MacOS "far globals".
+ - Fixed up some of the dynamic library Makefile targets for consistency
+   across platforms.
+ - Fixed a USE_MMAP typo that caused out-of-memory handling to fail
+   on Solaris.
+ - Added code to test.c to test thread creation a bit more.
+ - Integrated GC_win32_free_heap, as suggested by Ivan Demakov.
+ - Fixed Solaris 2.7 stack base finding problem.  (This may actually
+   have been done in an earlier alpha release.)
+Since alpha3:
+ - Fixed MSWIN32 recognition test, which interfered with cygwin.
+ - Removed unnecessary gc_watcom.asm from distribution.  Removed
+   some obsolete README.win32 text.
+ - Added Alpha Linux incremental GC support.  (Thanks to Philipp Tomsich
+   for code for retrieving the fault address in a signal handler.)
+   Changed Linux signal handler context argument to be a pointer.
+ - Took care of some new warnings generated by the 7.3 SGI compiler.
+ - Integrated Phillip Musumeci's FreeBSD/ELF fixes.
+ - -DIRIX_THREADS was broken with the -o32 ABI (typo in gc_priv.h>
+
+Since 4.13:
+ - Fixed GC_print_source_ptr to not use a prototype.
+ - generalized CYGWIN test.
+ - gc::new did the wrong thing with PointerFreeGC placement.
+   (Thanks to Rauli Ruohonen.)
+ - In the ALL_INTERIOR_POINTERS (default) case, some callee-save register
+   values could fail to be scanned if the register was saved and
+   reused in a GC frame.  This showed up in verbose mode with gctest
+   compiled with an unreleased SGI compiler.  I vaguely recall an old
+   bug report that may have been related.  The bug was probably quite old.
+   (The problem was that the stack scanning could be deferred until
+   after the relevant frame was overwritten, and the new save location
+   might be outside the scanned area.  Fixed by more eager stack scanning.)
+ - PRINT_BLACK_LIST had some problems.  A few source addresses were garbage.
+ - Replaced Makefile.dj and added -I flags to cord make targets.
+   (Thanks to Gary Leavens.)
+ - GC_try_to_collect was broken with the nonincremental collector.
+ - gc_cleanup destructors could pass the wrong address to
+   GC_register_finalizer_ignore_self in the presence of multiple
+   inheritance.  (Thanks to Darrell Schiebel.)
+ - Changed PowerPC Linux stack finding code.
+
+Since 4.14alpha1
+ - -DSMALL_CONFIG did not work reliably with large (> 4K) pages.
+   Recycling the mark stack during expansion could result in a size
+   zero heap segment, which confused things.  (This was probably also an
+   issue with the normal config and huge pages.)
+ - Did more work to make sure that callee-save registers were scanned
+   completely, even with the setjmp-based code.  Added USE_GENERIC_PUSH_REGS
+   macro to facilitate testing on machines I have access to.
+ - Added code to explicitly push register contents for win32 threads.
+   This seems to be necessary.  (Thanks to Pierre de Rop.)
+
+Since 4.14alpha2
+ - changed STACKBOTTOM for DJGPP (Thanks to Salvador Eduardo Tropea).
+ 
+Since 4.14
+ - Reworked large block allocator.  Now uses multiple doubly linked free
+   lists to approximate best fit.
+ - Changed heap expansion heuristic.  Entirely free blocks are no longer
+   counted towards the heap size.  This seems to have a major impact on
+   heap size stability; the old version could expand the heap way too
+   much in the presence of large block fragmentation.
+ - added -DGC_ASSERTIONS and some simple assertions inside the collector.
+   This is mainlyt for collector debugging.
+ - added -DUSE_MUNMAP to allow the heap to shrink.  Suupported on only
+   a few UNIX-like platforms for now.
+ - added GC_dump_regions() for debugging of fragmentation issues.
+ - Changed PowerPC pointer alignment under Linux to 4.  (This needs
+   checking by someone who has one.  The suggestions came to me via a
+   rather circuitous path.)
+ - Changed the Linux/Alpha port to walk the data segment backwards until
+   it encounters a SIGSEGV.  The old way to find the start of the data
+   segment broke with a recent release.
+ - cordxtra.c needed to call GC_REGISTER_FINALIZER instead of
+   GC_register_finalizer, so that it would continue to work with GC_DEBUG.
+ - allochblk sometimes cleared the wrong block for debugging purposes
+   when it dropped blacklisted blocks.  This could result in spurious
+   error reports with GC_DEBUG.
+ - added MACOS X Server support.  (Thanks to Andrew Stone.)
+ - Changed the Solaris threads code to ignore stack limits > 8 MB with
+   a warning.  Empirically, it is not safe to access arbitrary pages
+   in such large stacks.  And the dirty bit implementation does not
+   guarantee that none of them will be accessed.
+ - Integrated Martin Tauchmann's Amiga changes.
+ - Integrated James Dominy's OpenBSD/SPARC port.
+
+Since 5.0alpha1
+ - Fixed bugs introduced in alpha1 (OpenBSD & large block initialization).
+ - Added -DKEEP_BACK_PTRS and backptr.h interface.  (The implementation
+   idea came from Al Demers.)
+
+Since 5.0alpha2
+ - Added some highly incomplete code to support a copied young generation.
+   Comments on nursery.h are appreciated.
+ - Changed -DFIND_LEAK, -DJAVA_FINALIZATION, and -DFINALIZE_ON_DEMAND,
+   so the same effect could be obtained with a runtime switch.   This is
+   a step towards standardizing on a single dynamic GC library.
+ - Significantly changed the way leak detection is handled, as a consequence
+   of the above.
+
+Since 5.0 alpha3
+ - Added protection fault handling patch for Linux/M68K from Fergus
+   Henderson and Roman Hodek.
+ - Removed the tests for SGI_SOURCE in new_gc_alloc.h.  This was causing that
+   interface to fail on nonSGI platforms.
+ - Changed the Linux stack finding code to use /proc, after changing it
+   to use HEURISTIC1.  (Thanks to David Mossberger for pointing out the
+   /proc hook.)
+ - Added HP/UX incremental GC support and HP/UX 11 thread support.
+   Thread support is currently still flakey.
+ - Added basic Linux/IA64 support.
+ - Integrated Anthony Green's PicoJava support.
+ - Integrated Scott Ananian's StrongARM/NetBSD support.
+ - Fixed some fairly serious performance bugs in the incremental
+   collector.  These have probably been there essentially forever.
+   (Mark bits were sometimes set before scanning dirty pages.
+   The reclaim phase unnecessarily dirtied full small object pages.)
+ - Changed the reclaim phase to ignore nearly full pages to avoid
+   touching them.
+ - Limited GC_black_list_spacing to roughly the heap growth increment.
+ - Changed full collection triggering heuristic to decrease full GC
+   frequency by default, but to explicitly trigger full GCs during
+   heap growth.  This doesn't always improve things, but on average it's
+   probably a win.
+ - GC_debug_free(0, ...) failed.  Thanks to Fergus Henderson for the
+   bug report and fix.
+
+Since 5.0 alpha4
+ - GC_malloc_explicitly_typed and friends sometimes failed to
+   initialize first word.
+ - Added allocation routines and support in the marker for mark descriptors
+   in a type structure referenced by the first word of an object.  This was
+   introduced to support gcj, but hopefully in a way that makes it
+   generically useful.
+ - Added GC_requested_heapsize, and inhibited collections in nonincremental
+   mode if the actual used heap size is less than what was explicitly
+   requested.
+ - The Solaris pthreads version of GC_pthread_create didn't handle a NULL
+   attribute pointer.  Solaris thread support used the wrong default thread
+   stack size.  (Thanks to Melissa O'Neill for the patch.)
+ - Changed PUSH_CONTENTS macro to no longer modify first parameter.
+   This usually doesn't matter, but it was certainly an accident waiting
+   to happen ...
+ - Added GC_register_finalizer_no_order and friends to gc.h.  They're
+   needed by Java implementations.
+ - Integrated a fix for a win32 deadlock resulting from clock() calling
+   malloc.  (Thanks to Chris Dodd.)
+ - Integrated Hiroshi Kawashima's port to Linux/MIPS.  This was designed
+   for a handheld platform, and may or may not be sufficient for other
+   machines.
+ - Fixed a va_arg problem with the %c specifier in cordprnt.c.  It appears
+   that this was always broken, but recent versions of gcc are the first to
+   report the (statically detectable) bug.
+ - Added an attempt at a more general solution to dlopen races/deadlocks.
+   GC_dlopen now temporarily disables collection.  Still not ideal, but ...
+ - Added -DUSE_I686_PREFETCH, -DUSE_3DNOW_PREFETCH, and support for IA64
+   prefetch instructions.  May improve performance measurably, but I'm not
+   sure the code will run correctly on processors that don't support the
+   instruction.  Won't build except with very recent gcc.
+ - Added caching for header lookups in the marker.  This seems to result
+   in a barely measurable performance gain.  Added support for interleaved
+   lookups of two pointers, but unconfigured that since the performance
+   gain is currently near zero, and it adds to code size.
+ - Changed Linux DATA_START definition to check both data_start and
+   __data_start, since nothing else seems to be portable.
+ - Added -DUSE_LD_WRAP to optionally take advantage of the GNU ld function
+   wrapping mechanism.  Probably currently useful only on Linux.
+ - Moved some variables for the scratch allocator into GC_arrays, on
+   Martin Hirzel's suggestion.
+ - Fixed a win32 threads bug that caused the collector to not look for
+   interior pointers from one of the thread stacks without
+   ALL_INTERIOR_POINTERS.  (Thanks to Jeff Sturm.)
+ - Added Mingw32 support.  (Thanks again to Jeff Sturm for the patch.)
+ - Changed the alpha port to use the generic register scanning code instead
+   of alpha_mach_dep.s.  Alpha_mach_dep.s doesn't look for pointers in fp
+   registers, but gcc sometimes spills pointers there.  (Thanks to Manuel
+   Serrano for helping me debug this by email.)  Changed the IA64 code to
+   do something similar for similar reasons.
+
+[5.0alpha5 doesn't really exist, but it may have escaped.]
+
+Since 5.0alpha6:
+ - -DREDIRECT_MALLOC was broken in alpha6. Fixed.
+ - Cleaned up gc_ccp.h slightly, thus also causing the HP C++ compiler to
+   accept it.
+ - Removed accidental reference to dbg_mlc.c, which caused dbg_mlc.o to be
+   linked into every executable.
+ - Added PREFETCH to bitmap marker.  Changed it to use the header cache.
+ - GC_push_marked sometimes pushed one object too many, resulting in a
+   segmentation fault in GC_mark_from_mark_stack.  This was probably an old
+   bug.  It finally showed up in gctest on win32.
+ - Gc_priv.h erroneously #defined GC_incremental to be TRUE instead of FALSE
+   when SMALL_CONFIG was defined.  This was no doubt a major performance bug for
+   the default win32 configuration.
+ - Removed -DSMALL_CONFIG from NT_MAKEFILE.  It seemed like an anchronism now
+   that the average PC has 64MB or so.
+ - Integrated Bryce McKinley's patches for linux threads and dynamic loading
+   from the libgcj tree.  Turned on dynamic loading support for Linux/PPC.
+ - Changed the stack finding code to use environ on HP/UX.  (Thanks
+   to Gustavo Rodriguez-Rivera for the suggestion.)  This should probably
+   be done on other platforms, too.  Since I can't test those, that'll
+   wait until after 5.0.
+
+Since 5.0alpha7:
+ - Fixed threadlibs.c for linux threads.  -DUSE_LD_WRAP was broken and
+   -ldl was omitted.  Fixed Linux stack finding code to handle
+   -DUSE_LD_WRAP correctly.
+ - Added MSWIN32 exception handler around marker, so that the collector
+   can recover from root segments that are unmapped during the collection.
+   This caused occasional failures under Windows 98, and may also be
+   an issue under Windows NT/2000.
+
+Since 5.0
+ - Fixed a gc.h header bug which showed up under Irix.  (Thanks to
+   Dan Sullivan.)
+ - Fixed a typo in GC_double_descr in typd_mlc.c.
+   This probably could result in objects described by array descriptors not
+   getting traced correctly.  (Thanks to Ben Hutchings for pointing this out.)
+ - The block nearly full tests in reclaim.c were not correct for 64 bit
+   environments.  This could result in unnecessary heap growth under unlikely
+   conditions.
+
+Since 5.1
+ - dyn_load.c declared GC_scratch_last_end_ptr as an extern even if it
+   was defined as a macro.  This prevented the collector from building on
+   Irix.
+ - We quietly assumed that indirect mark descriptors were never 0.
+   Our own typed allocation interface violated that.  This could result
+   in segmentation faults in the marker with typed allocation.
+ - Fixed a _DUSE_MUNMAP bug in the heap block allocation code.
+   (Thanks to Ben Hutchings for the patch.)
+ - Taught the collector about VC++ handling array operator new.
+   (Thanks again to Ben Hutchings for the patch.)
+ - The two copies of gc_hdrs.h had diverged.  Made one a link to the other
+   again.
+
+Since 5.2  (A few 5.2 patches are not in 6.0alpha1)
+ - Fixed _end declaration for OSF1.
+ - There were lots of spurious leak reports in leak detection mode, caused
+   by the fact that some pages were not being swept, and hence unmarked
+   objects weren't making it onto free lists.  (This bug dated back to 5.0.)
+ - Fixed a typo in the liblinuxgc.so Makefile rule.
+ - Added the GetExitCodeThread to Win32 GC_stop_world to (mostly) work
+   around a Windows 95 GetOpenFileName problem.  (Thanks to Jacob Navia.)
+
+Since 5.3
+ - Fixed a typo that prevented compilation with -DUSE_3DNOW_PREFETCH.
+   (Thanks to Shawn Wagner for actually testing this.)
+ - Fixed GC_is_thread_stack in solaris_threads.c.  It forgot to return a value
+   in the common case.  I wonder why nobody noticed?
+ - Fixed another silly syntax problem in GC_double_descr.  (Thanks to
+   Fergus Henderson for finding it.)
+ - Fixed a GC_gcj_malloc bug: It tended to release the allocator lock twice.
+
+Since 5.4  (A few 5.3 patches are not in 6.0alpha2)
+ - Added HP/PA prefetch support.
+ - Added -DDBG_HDRS_ALL and -DSHORT_DBG_HDRS to reduce the cost and improve
+   the reliability of generating pointer backtrace information, e.g. in
+   the Bigloo environment.
+ - Added parallel marking support (-DPARALLEL_MARK).  This currently
+   works only under IA32 and IA64 Linux, but it shouldn't be hard to adapt
+   to other platforms.  This is intended to be a lighter-weight (less
+   new code, probably not as scalable) solution than the work by Toshio Endo
+   et al, at the University of Tokyo.  A number of their ideas were
+   reused, though the code wasn't, and the underlying data structure
+   is significantly different.  In particular, we keep the global mark
+   stack as a single shared data structure, but most of the work is done
+   on smaller thread-local mark stacks.
+ - Changed GC_malloc_many to be cheaper, and to require less mutual exclusion
+   with -DPARALLEL_MARK.
+ - Added full support for thread local allocation under Linux
+   (-DTHREAD_LOCAL_ALLOC).  This is a thin veneer on GC_malloc_many, and
+   should be easily portable to other platforms, especially those that
+   support pthreads.
+ - CLEAR_DOUBLE was not always getting invoked when it should have been.
+ - GC_gcj_malloc and friends used different out of memory handling than
+   everything else, probably because I forgot about one when I implemented
+   the other.  They now both call GC_oom_fn(), not GC_oom_action().
+ - Integrated Jakub Jelinek's fixes for Linux/SPARC.
+ - Moved GC_objfreelist, GC_aobjfreelist, and GC_words_allocd out of
+   GC_arrays, and separately registered the first two as excluded roots.
+   This makes code compiled with gc_inl.h less dependent on the
+   collector version.  (It would be nice to remove the inclusion of
+   gc_priv.h by gc_inl.h completely, but we're not there yet.  The
+   locking definitions in gc_priv.h are still referenced.)
+   This change was later coniditoned on SEPARATE_GLOBALS, which
+   is not defined by default, since it involves a performance hit.
+ - Register GC_obj_kinds separately as an excluded root region.  The
+   attempt to register it with GC_arrays was usually failing.  (This wasn't
+   serious, but seemed to generate some confusion.) 
+ - Moved backptr.h to gc_backptr.h.
+
+Since 6.0alpha1
+ - Added USE_MARK_BYTES to reduce the need for compare-and-swap on platforms
+   for which that's expensive.
+ - Fixed a locking bug ib GC_gcj_malloc and some locking assertion problems.
+ - Added a missing volatile to OR_WORD and renamed the parameter to
+   GC_compare_and_swap so it's not a C++ reserved word.  (Thanks to
+   Toshio Endo for pointing out both of those.)
+ - Changed Linux dynamic library registration code to look at /proc/self/maps
+   instead of the rld data structures when REDIRECT_MALLOC is defined.
+   Otherwise some of the rld data data structures may be prematurely garbage
+   collected.  (Thanks to Eric Benson for helping to track this down.)
+ - Fixed USE_LD_WRAP a bit more, so it should now work without threads.
+ - Renamed XXX_THREADS macros to GC_XXX_THREADS for namespace correctness.
+   Tomporarily added some backward compatibility definitions.  Renamed
+   USE_LD_WRAP to GC_USE_LD_WRAP.
+ - Many MACOSX POWERPC changes, some additions to the gctest output, and
+   a few minor generic bug fixes.  (Thanks to Dietmar Planitzer.)
+
+Since 6.0 alpha2
+ - Fixed the /proc/self/maps code to not seek, since that apparently is not
+   reliable across all interesting kernels.
+ - Fixed some compilation problems in the absence of PARALLEL_MARK
+   (introduced in alpha2).
+ - Fixed an algorithmic problem with PARALLEL_MARK.  If work needs to
+   be given back to the main mark "stack", the BOTTOM entries of the local
+   stack should be given away, not the top ones.  This has substantial
+   performance impact, especially for > 2 processors, from what I can tell.
+ - Extracted gc_lock.h from gc_priv.h.  This should eventually make it a
+   bit easier to avoid including gc_priv.h in clients.
+ - Moved all include files to include/ and removed duplicate links to the
+   same file.  The old scheme was a bad idea because it was too easy to get the
+   copies out of sync, and many systems don't support hard links.
+   Unfortunately, it's likely that I broke some of the non-Unix Makefiles in
+   the process, although I tried to update them appropriately.
+ - Removed the partial support for a copied nursery.  It's not clear that
+   this would be a tremendous win, since we don't consistently lose to
+   generational copying collectors.  And it would significantly complicate
+   many things.  May be reintroduced if/when it really turns out to win.
+ - Removed references to IRIX_JDK_THREADS, since I believe there never
+   were and never will be any clients.
+ - Added some code to linux_threads.c to possibly support HPUX threads
+   using the Linux code.  Unfortunately, it doesn't work yet, and is
+   currently disabled.
+ - Added support under Linux/X86 for saving the call chain, both in (debug)
+   objects for client debugging, and in GC_arrays._last_stack for GC
+   debugging.  This was previously supported only under Solaris.  It is
+   not enabled by default under X86, since it requires that code be compiled
+   to explicitly dave frame pointers on the call stack.  (With gcc this
+   currently happens by default, but is often turned off explicitly.)
+   To turn it on, define SAVE_CALL_CHAIN.
+ 
+Since 6.0 alpha3
+ - Moved up the detection of mostly full blocks to the initiatiation of the
+   sweep phase.  This eliminates some lock conention in the PARALLEL_MARK case,
+   as multiple threads try to look at mostly full blocks concurrently.
+ - Restored the code in GC_malloc_many that grabs a prefix of the global
+   free list.  This avoids the case in which every GC_malloc_many call
+   tries and fails to allocate a new heap block, and the returns a single
+   object from the global free list.
+ - Some minor fixes in new_hblk.c.  (Attempted to build free lists in order
+   of increasing addresses instead of decreasing addresses for cache performance
+   reasons.  But this seems to be only a very minor gain with -DEAGER_SWEEP,
+   and a loss in other cases.  So the change was backed out.)
+ - Fixed some of the documentation.  (Thanks in large part to Fergus
+   Henderson.)
+ - Fixed the Linux USE_PROC_FOR_LIBRARIES code to deal with apps that perform
+   large numbers of mmaps.  (Thanks to Eric Benson.)  Also fixed that code to
+   deal with short reads.
+ - Added GC_get_total_bytes(). 
+ - Fixed leak detection mode to avoid spurious messages under linuxthreads.
+   (This should also now be easy for the other supported threads packages.
+   But the code is tricky enough that I'm hesitant to do it without being able
+   to test.  Everything allocated in the GC thread support itself should be
+   explicitly deallocated.)
+ - Made it possible (with luck) to redirect malloc to GC_local_malloc.
+
+Since 6.0 alpha4
+ - Changed the definition of GC_pause in linux_threads.c to use a volatile
+   asm.  Some versions of gcc apparently optimize away writes to local volatile
+   variables.  This caused poor locking behaviour starting at about
+   4 processors.
+ - Added GC_start_blocking(), GC_end_blocking() calls and wrapper for sleep
+   to linux_threads.c.
+   The first two calls could be used to generally avoid sending GC signals to
+   blocked threads, avoiding both premature wakeups and unnecessary overhead.
+ - Fixed a serious bug in thread-local allocation.  At thread termination,
+   GC_free could get called on small integers.  Changed the code for thread
+   termination to more efficiently return left-over free-lists.
+ - Integrated Kjetil Matheussen's BeOS support.
+ - Rearranged the directory structure to create the doc and tests
+   subdirectories.
+ - Sort of integrated Eric Benson's patch for OSF1.  This provided basic
+   OSF1 thread support by suitably extending hpux_irix_threads.c.  Based
+   on earlier email conversations with David Butenhof, I suspect that it
+   will be more reliable in the long run to base this on linux_threads.c
+   instead.  Thus I attempted to patch up linux_threads.c based on Eric's code.
+   The result is almost certainly broken, but hopefully close enough that
+   someone with access to a machine can pick it up.
+ - Integrated lots of minor changes from the NetBSD distribution.  (These
+   were supplied by David Brownlee.  I'm not sure about the original
+   authors.)
+ - Hacked a bit more on the HP/UX thread-support in linux_threads.c.  It
+   now appears to work in the absence of incremental collection.  Renamed
+   hpux_irix_threads.c back to irix_threads.c, and removed the attempt to
+   support HPUX there.
+ - Changed gc.h to define _REENTRANT in cases in which it should already
+   have been defined. It is still safer to also define it on the command
+   line. 
+
+Since 6.0alpha5:
+ - Changed the definition of DATASTART on ALPHA and IA64, where data_start
+   and __data_start are not defined by earlier versions of glibc.  This might
+   need to be fixed on other platforms as well.
+ - Changed the way the stack base and backing store base are found on IA64.
+   This should now remain reliable on future kernels.  But since it relies
+   on /proc, it will no longer work in the simulated NUE environment.
+ - Made the call to random() in dbg_mlc.c with -DKEEP_BACK_PTRS dependent
+   on the OS.  On non-Unix systems, rand() should be used instead.  Handled
+   small RAND_MAX.  (Thanks to Peter Ross for pointing this out.)
+ - Fixed the cord make rules to create the cord subdirectory, if necessary.
+   (Thanks to Doug Moen.)
+ - Changed fo_object_size calculation in finalize.c.  Turned finalization
+   of nonheap object into a no-op.  Removed anachronism from GC_size()
+   implementation.
+ - Changed GC_push_dirty call in solaris_threads.c to GC_push_selected.
+   It was missed in a previous renaming. (Thanks to Vladimir Tsichevski
+   for pointing this out.)
+ - Arranged to not not mask SIGABRT in linux_threads.c.  (Thanks to Bryce
+   McKinlay.) 
+ - Added GC_no_dls hook for applications that want to register their own
+   roots.
+ - Integrated Kjetil Matheussen's Amiga changes.
+ - Added FREEBSD_STACKBOTTOM.  Changed the X86/FreeBSD port to use it.
+   (Thanks to Matthew Flatt.)
+ - Added pthread_detach interception for platforms supported by linux_threads.c
+   and irix_threads.c.  Should also be added for Solaris?
+ - Changed the USE_MMAP code to check for the case in which we got the
+   high end of the address space, i.e. mem_ptr + mem_sz == 0.  It appears
+   that this can happen under Solaris 7.  It seems to be allowed by what
+   I would claim is an oversight in the mmap specification.  (Thanks to Toshio
+   Endo for pointing out the problem.)
+ - Cleanup of linux_threads.c.  Some code was originally cloned from
+   irix_threads.c and now unnecessary.  Some comments were obviously wrong.
+ - (Mostly) fixed a longstanding problem with setting of dirty bits from
+   a signal handler.  In the presence of threads, dirty bits could get lost,
+   since the etting of a bit in the bit vector was not atomic with respect
+   to other updates.  The fix is 100% correct only for platforms for which
+   GC_test_and_set is defined.  The goal is to make that all platforms with
+   thread support.  Matters only if incremental GC and threads are both
+   enabled.
+ - made GC_all_interior_pointers (a.k.a. ALL_INTERIOR_POINTERS) an
+   initialization time, instead of build-time option.  This is a 
+   nontrivial, high risk change.  It should slow down the code measurably
+   only if MERGE_SIZES is not defined, which is a very nonstandard
+   configuration.   
+ - Added doc/README.environment, and implemented what it describes.  This
+   allows a number of additional configuration options to be set through
+   the environment.  It documents a few previously undocumented options.
+ - Integrated Eric Benson's leak testing improvements.
+ - Removed the option to throw away the beginning of each page (DISCARD_WORDS).
+   This became less and less useful as processors enforce stricter alignment.
+   And it hadn't been tested in ages, and was thus probably broken anyway.
+
+Since 6.0alpha6:
+ - Added GC_finalizer_notifier.  Fixed GC_finalize_on_demand.  (The variable
+   actually wasn't being tested at the right points.  The build-time flag
+   was.)
+ - Added Tom Tromey's S390 Linux patch.
+ - Added code to push GC_finalize_now in GC_push_finalizer_structures.
+   (Thanks to Matthew Flatt.)
+ - Added GC_push_gc_structures() to push all GC internal roots.
+ - Integrated some FreeBSD changes from Matthew Flatt.
+ - It looks like USRSTACK is not always correctly defined under Solaris.
+   Hacked gcconfig.h to attempt to work around the problem.  The result
+   is not well tested.  (Thanks again to Matthew Flatt for pointing this
+   out.  The gross hack is mine. - HB)
+ - Added Ji-Yong Chung's win32 threads and C++ fixes.
+ - Arranged for hpux_test_and_clear.s to no longer be needed or built.
+   It was causing build problems with gas, and it's not clear this is
+   better than the pthreads alternative on this platform.
+ - Some MINGW32 fixes from Hubert Garavel.
+ - Added Initial Hitachi SH4 port from Kaz Kojima.
+ - Ported thread-local allocation and parallel mark code to HP/UX on PA_RISC.
+ - Made include/gc_mark.h more public and separated out the really private
+   pieces.  This is probably still not quite sufficient for clients that
+   want to supply their own kind of type information.  But it's a start.
+   This involved lots of identifier renaming to make it namespace clean.
+ - Added GC_dont_precollect for clients that need complete control over
+   the root set.
+ - GC_is_visible didn't do the right thing with gcj objects.  (Not that
+   many people are likely to care, but ...)
+ - Don't redefine read with GC_USE_LD_WRAP.
+ - Initial port to LINUX/HP_PA.  Incremental collection and threads are not
+   yet supported.  (Incremental collection should work if you have the
+   right kernel.  Threads may work with a sufficiently patched pthread
+   library.)
+ - Changed gcconfig.h to recognize __i386__ as an alternative to i386 in
+   many places.  (Thanks to Benjamin Lerman.)
+ - Made win32_threads.c more tolerant of detaching a thread that it didn't
+   know about.  (Thanks to Paul Nash.)
+ - Added Makefile.am and configure.in from gcc to the distribution, with
+   minimal changes.  For the moment, those are just placeholders.  In the
+   future, we're planning to switch to a GNU-style build environment for
+   Un*x-like systems, though the old Makefile will remain as a backup.
+ - Turned off STUBBORN_ALLOC by default, and added it back as a Makefile
+   option.
+ - Redistributed some functions between malloc.c and mallocx.c, so that
+   simple statically linked apps no longer pull in mallocx.o.
+ - Changed large object allocation to clear the first and last few words
+   of each block before releassing the lock.  Otherwise the marker could see
+   objects with nonsensical type descriptors.
+ - Fixed a couple of subtle problems that could result in not recognizing
+   interior pointers from the stack.  (I believe these were introduced
+   in 6.0alpha6.)
+ - GC_debug_free_inner called GC_free, which tried to reacquire the
+   allocator lock, and hence deadlocked.  (DBG_HDRS_ALL probably never worked
+   with threads?)
+ - Fixed several problems with back traces.  Accidental references to a free
+   list could cause the free list pointer to be overwritten by a back pointer.
+   There seemed to be some problems with the encoding of root and finalizer
+   references.
+  
+Since 6.0alpha7:
+ - Changed GC_debug_malloc_replacement and GC_debug_realloc_replacement
+   so that they compile under Irix.  (Thanks to Dave Love.)
+ - Updated powerpc_macosx_mach_dep.s so that it works if the collector
+   is in a dynamic library.  (Thanks to Andrew Begel.)
+ - Transformed README.debugging into debugging.html, updating and
+   expanding it in the process.  Added gcdescr.html and tree.html
+   from the web site to the GC distribution.
+ - Fixed several problems related to PRINT_BLACK_LIST. This involved
+   restructuring some of the marker macros.
+ - Fixed some problems with the sizing of objects with debug information.
+   Finalization was broken KEEP_BACK_PTRS or PRINT_BLACK_LIST.  Reduced the
+   object size with SHORT_DEBUG_HDRS by another word.
+ - The "Needed to allocate blacklisted ..." warning had inadvertently
+   been turned off by default, due to a buggy test in allchblk.c.  Turned
+   it back on.
+ - Removed the marker macros to deal with 2 pointers in interleaved fashion.
+   They were messy and the performance improvement seemed minimal.  We'll
+   leave such scheduling issues to the compiler.
+ - Changed Linux/PowerPC test to also check for __powerpc__ in response
+   to a discussion on the gcc mailing list.
+ - On Matthew Flatt's suggestion removed the "static" from the jmp_buf
+   declaration in GC_generic_push_regs.  This was causing problems in
+   systems that register all of their own roots.  It looks far more correct
+   to me without the "static" anyway. 
+ - Fixed several problems with thread local allocation of pointerfree or
+   typed objects.  The collector was reclaiming thread-local free lists, since
+   it wasn't following the link fields.
+ - There was apparently a long-standing race condition related to multithreaded
+   incremental collection.  A collection could be started and a thread stopped
+   between the memory unprotect system call and the setting of the
+   corresponding dirt bit.  I believe this did not affect Solaris or PCR, which
+   use a different dirty-bit implementation.  Fixed this by installing
+   signal handlers with sigaction instead of signal, and disabling the thread
+   suspend signal while in the write-protect handler.  (It is unclear
+   whether this scenario ever actually occurred.  I found it while tracking
+   down the following:)
+ - Incremental collection did not cooperate correctly with the PARALLEL_MARK
+   implementation of GC_malloc_many or the local_malloc primitves.  It still
+   doesn't work well, but it shouldn't lose memory anymore.
+ - Integrated some changes from the gcc source tree that I had previously
+   missed.  (Thanks to Bryce McKinley for the reminder/diff.)
+ - Added Makefile.direct as a copy of the default Makefile, which would
+   normally be overwritten if configure is run.
+ - Changed the gc.tar target in Makefile.direct to embed the version number
+   in the gc directory name.  This will affect future tar file distributions.
+ - Changed the Irix dynamic library finding code to no longer try to
+   eliminate writable text segments under Irix6.x, since that is probably no
+   longer necessary, and can apparently be unsafe on occasion.  (Thanks to
+   Shiro Kawai for pointing this out.)
+ - GC_cleanup with GC_DEBUG enabled passed a real object base address to
+   GC_debug_register_finalizer_ignore_self, which expected a pointer past the
+   debug header.  Call GC_register_finalizer_ignore_self instead, even with
+   debugging enabled.  (Thanks to Jean-Daniel Fekete for catching this.)
+ - The collector didn't build with call chain saving enabled but NARGS=0.
+   (Thanks to Maarten Thibaut.)
+ - Fixed up the GNU-style build files enough so that they work in some
+   obvious cases.
+ - Added initial port to Digital Mars compiler for win32. (Thanks to Walter
+   Bright.)
+
+Since 6.0alpha8:
+ - added README.macros.
+ - Made gc.mak a symbolic link to work around winzip's tendency to ignore
+   hard links.
+ - Simplified the setting of NEED_FIND_LIMIT in os_dep.c, possibly breaking
+   it on untested platforms.
+ - Integrated initial GNU HURD port. (Thanks to Chris Lingard and Igor
+   Khavkine.)
+ - A few more fixes for Digital Mars compiler.
+ - Fixed gcc version recognition.  Renamed OPERATOR_NEW_ARRAY to
+   GC_OPERATOR_NEW_ARRAY.  Changed GC_OPERATOR_NEW_ARRAY to be the default.
+   It can be overridden with -DGC_NO_OPERATOR_NEW_ARRAY.  (Thanks to
+   Cesar Eduardo Barros.) 
+ - Changed the byte size to free-list mapping in thread local allocation
+   so that size 0 allocations are handled correctly.
+ - Fixed Linux/MIPS stackbottom for new toolchain. (Thanks to Ryan Murray.)
+ - Changed finalization registration to invoke GC_oom_fn when it runs out
+   of memory.
+ - Removed lvalue cast in finalize.c.  This caused some debug configurations
+   not to build with some non-gcc compilers.
+
+Since 6.0alpha9:
+ - Two more bug fixes for KEEP_BACK_PTRS and DBG_HDRS_ALL.
+ - Fixed a stack clearing problem that resulted in SIGILL with a
+   misaligned stack pointer for multithreaded SPARC builds.
+ - Integrated another HURD patch (thanks to Igor Khavkine).
+ 
+
+To do:
+ - There seem to be outstanding issues on Solaris/X86, possibly with
+   finding the data segment starting address.  Information/patches would
+   ne appreciated.
+ - New_gc_alloc.h is apparently no longer compatible with the latest C++
+   standard library in gcc3.0.  (This isn't technically a bug, since it only
+   claimed compatibility with the SGI STL.  But we may need a new C++ STL
+   allocator interface.)
+ - Very large root set sizes (> 16 MB or so) could cause the collector
+   to abort with an unexpected mark stack overflow.  (Thanks again to
+   Peter Chubb.)  NOT YET FIXED.  Workaround is to increase the initial
+   size.
+ - The SGI version of the collector marks from mmapped pages, even
+   if they are not part of dynamic library static data areas.  This
+   causes performance problems with some SGI libraries that use mmap
+   as a bitmap allocator.  NOT YET FIXED.  It may be possible to turn
+   off DYNAMIC_LOADING in the collector as a workaround.  It may also
+   be possible to conditionally intercept mmap and use GC_exclude_static_roots.
+   The real fix is to walk rld data structures, which looks possible.
+ - Incremental collector should handle large objects better.  Currently,
+   it looks like the whole object is treated as dirty if any part of it
+   is.
+ - Cord/cordprnt.c doesn't build on a few platforms (notably PowerPC), since
+   we make some unwarranted assumptions about how varargs are handled.  This
+   currently makes the cord-aware versions of printf unusable on some platforms.
+   Fixing this is unfortunately not trivial.