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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 (Walter Bright).
- - 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).
-
-Since 6.0:
- - Non-debug, atomic allocations could result in bogus smashed object
-   reports with debugging on.  (Thanks to Patrick Doyle for the small
-   test case.)
- - Fixed GC_get_register_stack_base (Itanium only) to work around a glibc
-   2.2.4 bug.
- - Initial port to HP/UX on Itanium.  Thread support and both 32 and 64
-   bit ABIs appear to work.  Parallel mark support doesn't yet, due to
-   some inline assembly code issues.  Thread local allocation does appear
-   to work.
- - ifdef'ed out glibc2.1/Itanium workaround.  I suspect nobody is using
-   that combination anymore.
- - Added a patch to make new_gc_alloc.h usable with gcc3.0.  (Thanks to
-   Dimitris Vyzovitis for the patch.)
- - Debugged 64-bit support on HP/UX PA-RISC.
- - Turned on dynamic loading support for FreeBSD/ELF.  (Thanks to Peter
-   Housel.)
- - Unregistering of finalizers with debugging allocation was broken.
-   (Thanks to Jani Kajala for the test case.)
- - Old finalizers were not returned correctly from GC_debug_register_finalizer.
- - Disabled MPROTECT_VDB for Linux/M68K based on a report that it doesn't work.
- - Cleaned up some statistics gathering code in reclaim.c (Thanks to Walter
-   Bright.)
- - Added some support for OpenBSD/ELF/Linux.  (Thanks to Suzuki Toshiya.)
- - Added Jakub Jelinek's patch to use dl_iterate_phdr for dynamic library
-   traversal to dyn_load.c.  Changed it to weakly reference dl_iterate_phdr,
-   so that the old code is stilll used with old versions of glibc.
- - Cleaned up feature test macros for various threads packages and
-   integrated (partially functional) FreeBSD threads code from Loren Rittle.
-   It's likely that the cleanup broke something, since it touched lots of
-   code.  It's also likelly that it fixed some unreported bugs in the
-   less common thread implementations, since some of the original code
-   didn't stand up to close scrutiny.  Support for the next pthreads
-   implementation should be easier to add.
-
-Since 6.1alpha1:
- - No longer wrap read by default in multithreaded applications.  It was
-   pointed out on the libgcj list that this holds the allocation lock for
-   way too long if the read blocks.  For now, reads into the heap are
-   broken with incremental collection.  It's possible to turn this back on
-   if you make sure that read calls don't block (e.g. by calling select
-   first).
- - Fix ifdef in Solaris_threads.h to refer to GC_SOLARIS_THREADS.
- - Added check for environment variable GC_IGNORE_GCJ_INFO.
- - Added printing of stop-the-world GC times if GC_PRINT_STATS environment
-   variable is set.
- - The calloc definition in leak_detector.h was missing parentheses, and
-   realloc was missing a second argument to GC_REALLOC.
-   (Thanks to Elrond (elrond<at>samba-tng.org).)
- - Added GC_PRINT_BACK_HEIGHT environment variable and associated
-   code, mostly in the new file backgraph.c.  See doc/README.environment.
- - Added -DUSE_GLOBAL_ALLOC to work around a Windows NT issue.  (Thanks to
-   Jonathan Clark.)
- - Integrated port to NEC EWS4800 (MIPS-based workstation, with somewhat
-   different address-space layout). This may help for other machines with
-   holes in the data segment.  (Thanks to Hironori Sakamoto.)
- - Changed the order in which GC_push_roots and friends push things onto
-   the mark stack.  GC_push_all calls need to come first, since we can't
-   necessarily recovere if those overflow the mark stack.  (Thanks to
-   Matthew Flatt for tracking down the problem.)
- - Some minor cleanups to mostly support the Intel compiler on Linux/IA64.
-
-Since 6.1 alpha2:
- - Minor cleanup on the gcconfig.h section for SPARC.
- - Minor fix to support Intel compiler for I386/Linux. (Thanks to Sven
-   Hartrumpf.)
- - Added SPARC V9 (64-bit) support.  (Thanks to Jeff Sturm.)
- - Restructured the way in which we determine whether or not to keep
-   call stacks for debug allocation.  By default SAVE_CALL_COUNT is
-   now zero on all platforms.  Added SAVE_CALL_NARGS parameters.
-   If possible, use execinfo.h to capture call stack.  (This should
-   add support for a number of new platforms, though often at
-   considerable runtime expense.)
- - Try to print symbolic information for call stacks.  On Linux, we
-   do this with a combination of execinfo.h and running addr2line in
-   a separate process.  This is both much more expensive and much more
-   useful.  Amazingly, it seems to be fast enough for most purposes.
- - Redefined strdup if -DREDIRECT_MALLOC is given.
- - Changed incremental collector and MPROTECT_VDB implementation so that,
-   under favorable conditions, pointerfree objects are not protected.
-   Added GC_incremental_protection_needs() to determine ahead of time whether
-   pointerfree objects may be protected.  Replaced GC_write_hint() with
-   GC_remove_protection().
- - Added test for GC_ENABLE_INCREMENTAL environment variable.
- - Made GC_time_limit runtime configurable.  Added GC_PAUSE_TIME_TARGET
-   environment variable.
- - Eliminated GC_page_sz, a duplicate of GC_page_size.
- - Caused the Solaris and Irix thread creation primitives to call
-   GC_init_inner().
- 
-Since 6.1alpha3:
- - Fixed typo in sparc_mach_dep.S, preventing the 64-bit version from
-   building.  Increased 64-bit heap size limit in test.c slightly, since
-   a functional SPARC collector seems to slightly exceed the old limits.
-   (Thanks again to Jeff Sturm.)
- - Use NPRGREG in solaris_threads.c, thus printing all registers if things
-   go wrong.
- - Added GC_MARKERS environment variable to allow use of a single marker
-   thread on an MP without confusing the lock implementation.
- - Collect much less aggressively in incremental mode with GC_TIME_UNLIMITED.
-   This is really a purely generational mode, and we can afford to 
-   postpone the collection until the heap is (nearly) full.
- - Remove read() wrapper for MPROTECT_VDB.  It was causing more harm than
-   good.  It is often no longer needed if system calls avoid writing to
-   pointerfull heap objects.
- - Fix MACOSX test in gcconfig.h. (Thanks to John Clements.)
- - Change GC_test_and_set so that it consistently has one argument.
-   Add spaces to ::: in powerpc assembly code in gc_locks.h.
-   (Thanks to Ryan Murray.)
- - Fixed a formatting error in dbg_mlc.c.  Added prototype to GC_abort()
-   declaration.   (Thanks to Michael Smith.)
- - Removed "source" argument to GC_find_start().  Eliminate GC_FIND_START().
- - Added win32 recognition code in configure.in.  Changed some of the
-   dllimport/export defines in gc.h.  (Thanks to Adam Megacz.)
- - GC_malloc_many didn't set hb_last_reclaimed when it called 
-   GC_reclaim_generic.  (I'm not sure this matters much, but ...)
- - Allocating uncollectable objects with debug information sometimes
-   allocated objects that were one byte too small, since uncollectable
-   objects don't have the extra byte added at the end.  (Thanks to
-   Wink Saville for pointing this out.)
- - Added a bit more assertion checking to make sure that gcj objects
-   on free lists never have a nonzero second word.
- - Replaced BCC_MAKEFILE with an up-to-date one.  (Thanks to 
-   Andre Leiradella.)
- - Upgraded libtool, cinfigure.in and some related files to hopefully
-   support NetBSD/SPARC.  (Thanks to Adrian Bunk.)  Unfortunately,
-   libtool 1.4.2 seemed to be buggy due to missing quotes in several
-   "test" invocations.  Fixed those in the ltmain.sh script.
- - Some win32-specific patches, including the introduction of
-   GC_CreateThread.  (Thanks to Adam Megacz.)
- - Merged in gcj changes from Anthony Green to support embedded systems.
- - Tried to consistently rename preprocessed assembly files with a capital
-   .S extension.
- - Use alpha_mach_dep.S on ALPHA again.  It doesn't really matter, but this
-   makes our distribution consistent with the gcc one, avoiding future merge
-   problems.
- - Move GET_MEM definition into gcconfig.h.  Include gcconfig.h slightly
-   later in gc_priv.h to avoid forward references to ptr_t.
- - Add some testing of local allocation to test.c.
- - Change definition of INVALID_QTID in specific.h.  The -1 value was used
-   inconsistently, and too likely to collide with a valid stack address.
-   Some general clean-up of specific.[ch].  Added assertions.  (Thanks
-   to Michael Smith for tracking down an intermittent bug to this
-   general area.  I'm not sure it has been squashed yet, however.)
- - On Pthread systems it was not safe to call GC_malloc() between fork()
-   and exec().  According to the applicable standards, it doesn't appear
-   to be safe to call malloc() or many other libc functions either, thus
-   it's not clear this is fixable.  Added experimental support for
-   -DHANDLE_FORK in linux_threads.c which tries to support it.  It may
-   succeed if libc does the right thing.  I'm not sure whether it does.
-   (Thanks to Kenneth Schalk for pointing out this issue.)
- - Documented thread local allocation primitives to require an
-   explicit GC_init call.  GC_init_parallel is no longer declared to
-   be a constructor function, since that isn't portable and often
-   seems to lead to initialization order problems.
- - Changed gc_cpp.cc and gc_cpp.h in one more attempt to make them
-   compatible with Visual C++ 6.  (Thanks to Wink Saville for the
-   patch.)
- - Some more patches for Linux on HP PA-RISC.
- - Added include/gc_allocator.h.  It implements (hopefully) standard
-   conforming (as opposed to SGI-style) allocators that allocate
-   collectable (gc_allocator) or GC-traceable, but not collectable
-   (traceable_allocator) objects.  This borrows heavily from libstc++,
-   which borrows heavily from the SGI implementation, this part of
-   which was written by Matt Austern.  Changed test_cpp.cc to very
-   minimally test this.
- - On Linux/X86, retry mmap with a different start argument.  That should
-   allow the collector to use more (closer to 3GB) of the address space.
-   (Thanks to Jeffrey Mark Siskind for tracking this down.)
- - Force 64 bit alignment with GCJ support.  (Reflects Bryce McKinley's
-   patch to the gcc tree.)
- - Refined the choice of sa_handler vs. sa_sigaction in GC_dirty_init
-   to accomodate some glibc5 systems.  (Thanks to Dan Fandrich for the
-   patch.)
- - Compensated for the fact that current versions of glibc set
-   __libc_stack_end incorrectly on Linux/IA64 while initialization code
-   is running.  This could cause the collector to miss 16 bytes of
-   the memory stack if GC_malloc or friends where called before main().
- - Mostly integrated Takis Psarogiannakopoulos' port to DG/UX Inix 86.
-   This will probably take another iteration to work, since his
-   patch conflicted with the libtool upgrade. 
- - Added README.arm.cross containing some information about cross-
-   compiling to an ARM processor from Margaret Fleck.
-
-Since 6.1alpha4:
- - Added GC_finalizer_mem_freed, and changed some of the code that
-   decided on heap expansion to look at it.  Memory explicitly
-   deallocated by finalizers essentially needs to be counted as reclaimed
-   by the GC.  Otherwise there are cases in which the heap can grow
-   unboundedly.  (Thanks to Mark Reichert for the test case.)
- - Integrated Adam Megacz patches to not scan dynamic libraries if
-   we are compiling with gcc on win32.  Otherwise we need structured
-   exception handling to deal with asynchronously unmapped root
-   segments, and gcc doesn't directly support that.
- - Integrated Anthony Green's patch to support Wine.
- - GC_OPERATOR_NEW_ARRAY was misspelled OPERATOR_NEW_ARRAY in several
-   places, including gc_cpp.cc.  (Thanks to Wink Saville for pointing
-   this out.)
- - Integrated Loren James Rittle's Alpha FreeBSD patches.  In
-   response to Richard Henderson's suggestion, these also
-   changed the declarations of symbols like _end on many platforms to
-   that they wouldn't mistakenly be declared as short data symbols.
- - Integrated changes from the Debian distribution.  (Thanks to Ryan Murray
-   for pointing these out.)  Fix C++ comments in POWERPC port.  Add ARM32
-   incremental GC support.  Get rid of USE_GENERIC_PUSH_REGS for alpha/Linux,
-   this time for real.  Use va_copy to get rid of cord printf problems
-   (finally).
- - Close file descriptor used to count cpus.  Thanks to Jeff Sturm for
-   pointing out the omission.
- - Don't just drop gcj free lists in GC_start_reclaim, since that can
-   eventually cause the marker to see a bogus mark descriptor in the 
-   dropped objects.  The usual symptom was a very intermittent segmentation
-   fault in the marker.  This mattered only if one of the GC_gcj_malloc
-   variants was used.  (Thanks to Michael Smith, Jeff Sturm, Bryce
-   McKinley and Tom Tromey for helping to track this down.)
- - Fixed Linux and Solaris/64 SPARC configuration.  (Thanks to David Miller,
-   Jeff Sturm, Tom Tromey, and Christian Joensson.)
- - Fixed a typo in strdup definition.  (Thanks to Gerard A Allan.)
- - Changed Makefile.direct to invoke $(CC) to assemble alpha_mach_dep.S.
-   This is needed on Linux.  I'm not sure whether it's better or worse
-   on Tru64.
- - Changed gc_cpp.h once more to declare operator new and friends only in
-   a Microsoft environment.  This may need further fine tuning.  (Thanks to
-   Johannes Schmidt for pointing out that the older code breaks on gcc3.0.4.)
- - Don't ever override strdup if it's already macro defined.  (Thanks to
-   Adnan Ali for pointing out the problem.)
- - Changed gc_cpp.h yet again to also overload placement new.  Due to the
-   C++ overloading rules, the other overloaded new operations otherwise hide
-   placement new, which causes many STL uses to break.  (Thanks to Reza
-   Shahidi for reporting this, and to Matt Austern for proposing a fix.)
- - Integrated cygwin pthreads support from Dan Bonachea.
- - Turn on DYNAMIC_LOADING for NetBSD.  (Thanks to Krister Walfridsson.)
- - Changed printing code to print more complete GC times.
- - Applied Mark Mitchell's Irix patch to correct some bitrot.
- - Clarified which object-printing routines in dbg_mlc.c should hold
-   the allocation lock.  Restructured the code to allow reasonable object
-   printing with -DREDIRECT_MALLOC.
- - Fix the Linux mmap code to always start with 0x1000 as the initial hint.
-   Minor patches for 64-bit AIX, particularly to STACKBOTTOM.
-   (Thanks again to Jeffrey Mark Siskind.)
- - Renamed "SUSPENDED" flag for Solaris threads support to avoid a conflict
-   with a system header. (Thanks to Philp Brown.)
- 
-
-To do:
- - --enable-redirect-malloc is mostly untested and known not to work
-   on some platforms. 
- - The win32 collector ends up tracing some (most?) objects allocated with
-   the system allocator, in spite if the fact that it tries not to.
-   This costs time and space, though it remains correct.
-   We need a way to identify memory regions used by the system malloc(),
-   or an alternate way to locate dll data areas.  A very partial
-   workaround is to use GC_malloc_atomic_uncollectable() instead of
-   the system malloc() for most allocation.
- - There seem to be outstanding issues on Solaris/X86, possibly with
-   finding the data segment starting address.  Information/patches would
-   be appreciated.
- - 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.
-