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-Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
-Copyright (c) 1991-1996 by Xerox Corporation.  All rights reserved.
-Copyright (c) 1996-1999 by Silicon Graphics.  All rights reserved.
-
-THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
-OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
-
-Permission is hereby granted to use or copy this program
-for any purpose,  provided the above notices are retained on all copies.
-Permission to modify the code and to distribute modified code is granted,
-provided the above notices are retained, and a notice that the code was
-modified is included with the above copyright notice.
-
-This is version 5.0alpha3 of a conservative garbage collector for C and C++.
-
-You might find a more recent version of this at
-
-http://www.hpl.hp.com/personal/Hans_Boehm/gc
-
-HISTORY -
-
-  Early versions of this collector were developed as a part of research
-projects supported in part by the National Science Foundation
-and the Defense Advance Research Projects Agency.
-Much of the code was rewritten by Hans-J. Boehm (boehm@acm.org) at Xerox PARC
-and at SGI.
-
-Some other contributors:  
-
-More recent contributors are mentioned in the modification history at the
-end of this file.  My apologies for any omissions.
-
-The SPARC specific code was contributed by Mark Weiser
-(weiser@parc.xerox.com).  The Encore Multimax modifications were supplied by
-Kevin Kenny (kenny@m.cs.uiuc.edu).  The adaptation to the RT is largely due
-to Vernon Lee (scorpion@rice.edu), on machines made available by IBM.
-Much of the HP specific code and a number of good suggestions for improving the
-generic code are due to Walter Underwood (wunder@hp-ses.sde.hp.com).
-Robert Brazile (brazile@diamond.bbn.com) originally supplied the ULTRIX code.
-Al Dosser (dosser@src.dec.com) and Regis Cridlig (Regis.Cridlig@cl.cam.ac.uk)
-subsequently provided updates and information on variation between ULTRIX
-systems.  Parag Patel (parag@netcom.com) supplied the A/UX code.
-Jesper Peterson(jep@mtiame.mtia.oz.au), Michel Schinz, and
-Martin Tauchmann (martintauchmann@bigfoot.com) supplied the Amiga port.
-Thomas Funke (thf@zelator.in-berlin.de(?)) and
-Brian D.Carlstrom (bdc@clark.lcs.mit.edu) supplied the NeXT ports.
-Douglas Steel (doug@wg.icl.co.uk) provided ICL DRS6000 code.
-Bill Janssen (janssen@parc.xerox.com) supplied the SunOS dynamic loader
-specific code. Manuel Serrano (serrano@cornas.inria.fr) supplied linux and
-Sony News specific code.  Al Dosser provided Alpha/OSF/1 code.  He and
-Dave Detlefs(detlefs@src.dec.com) also provided several generic bug fixes.
-Alistair G. Crooks(agc@uts.amdahl.com) supplied the NetBSD and 386BSD ports.
-Jeffrey Hsu (hsu@soda.berkeley.edu) provided the FreeBSD port.
-Brent Benson (brent@jade.ssd.csd.harris.com) ported the collector to
-a Motorola 88K processor running CX/UX (Harris NightHawk).
-Ari Huttunen (Ari.Huttunen@hut.fi) generalized the OS/2 port to
-nonIBM development environments (a nontrivial task).
-Patrick Beard (beard@cs.ucdavis.edu) provided the initial MacOS port.
-David Chase, then at Olivetti Research, suggested several improvements.
-Scott Schwartz (schwartz@groucho.cse.psu.edu) supplied some of the
-code to save and print call stacks for leak detection on a SPARC.
-Jesse Hull and John Ellis supplied the C++ interface code.
-Zhong Shao performed much of the experimentation that led to the
-current typed allocation facility.  (His dynamic type inference code hasn't
-made it into the released version of the collector, yet.)
-(Blame for misinstallation of these modifications goes to the first author,
-however.)
-
-OVERVIEW
-
-    This is intended to be a general purpose, garbage collecting storage
-allocator.  The algorithms used are described in:
-
-Boehm, H., and M. Weiser, "Garbage Collection in an Uncooperative Environment",
-Software Practice & Experience, September 1988, pp. 807-820.
-
-Boehm, H., A. Demers, and S. Shenker, "Mostly Parallel Garbage Collection",
-Proceedings of the ACM SIGPLAN '91 Conference on Programming Language Design
-and Implementation, SIGPLAN Notices 26, 6 (June 1991), pp. 157-164.
-
-Boehm, H., "Space Efficient Conservative Garbage Collection", Proceedings
-of the ACM SIGPLAN '91 Conference on Programming Language Design and
-Implementation, SIGPLAN Notices 28, 6 (June 1993), pp. 197-206.
-
-  Possible interactions between the collector and optimizing compilers are
-discussed in
-
-Boehm, H., and D. Chase, "A Proposal for GC-safe C Compilation",
-The Journal of C Language Translation 4, 2 (December 1992).
-
-and
-
-Boehm H., "Simple GC-safe Compilation", Proceedings
-of the ACM SIGPLAN '96 Conference on Programming Language Design and
-Implementation.
-
-(Both are also available from
-http://reality.sgi.com/boehm/papers/, among other places.)
-
-  Unlike the collector described in the second reference, this collector
-operates either with the mutator stopped during the entire collection
-(default) or incrementally during allocations.  (The latter is supported
-on only a few machines.)  It does not rely on threads, but is intended
-to be thread-safe.
-
-  Some of the ideas underlying the collector have previously been explored
-by others.  (Doug McIlroy wrote a vaguely similar collector that is part of
-version 8 UNIX (tm).)  However none of this work appears to have been widely
-disseminated.
-
-  Rudimentary tools for use of the collector as a leak detector are included, as
-is a fairly sophisticated string package "cord" that makes use of the collector.
-(See cord/README.)
-
-
-GENERAL DESCRIPTION
-
-  This is a garbage collecting storage allocator that is intended to be
-used as a plug-in replacement for C's malloc.
-
-  Since the collector does not require pointers to be tagged, it does not
-attempt to ensure that all inaccessible storage is reclaimed.  However,
-in our experience, it is typically more successful at reclaiming unused
-memory than most C programs using explicit deallocation.  Unlike manually
-introduced leaks, the amount of unreclaimed memory typically stays
-bounded.
-
-  In the following, an "object" is defined to be a region of memory allocated
-by the routines described below.  
-
-  Any objects not intended to be collected must be pointed to either
-from other such accessible objects, or from the registers,
-stack, data, or statically allocated bss segments.  Pointers from
-the stack or registers may point to anywhere inside an object.
-The same is true for heap pointers if the collector is compiled with
- ALL_INTERIOR_POINTERS defined, as is now the default.
-
-Compiling without ALL_INTERIOR_POINTERS may reduce accidental retention
-of garbage objects, by requiring pointers from the heap to to the beginning
-of an object.  But this no longer appears to be a significant
-issue for most programs.
-
-There are a number of routines which modify the pointer recognition
-algorithm.  GC_register_displacement allows certain interior pointers
-to be recognized even if ALL_INTERIOR_POINTERS is nor defined.
-GC_malloc_ignore_off_page allows some pointers into the middle of large objects
-to be disregarded, greatly reducing the probablility of accidental
-retention of large objects.  For most purposes it seems best to compile
-with ALL_INTERIOR_POINTERS and to use GC_malloc_ignore_off_page if
-you get collector warnings from allocations of very large objects.
-See README.debugging for details.
-
-  Note that pointers inside memory allocated by the standard "malloc" are not
-seen by the garbage collector.  Thus objects pointed to only from such a
-region may be prematurely deallocated.  It is thus suggested that the
-standard "malloc" be used only for memory regions, such as I/O buffers, that
-are guaranteed not to contain pointers to garbage collectable memory.
-Pointers in C language automatic, static, or register variables,
-are correctly recognized.  (Note that GC_malloc_uncollectable has semantics
-similar to standard malloc, but allocates objects that are traced by the
-collector.)
-
-  The collector does not always know how to find pointers in data
-areas that are associated with dynamic libraries.  This is easy to
-remedy IF you know how to find those data areas on your operating
-system (see GC_add_roots).  Code for doing this under SunOS, IRIX 5.X and 6.X,
-HP/UX, Alpha OSF/1, Linux, and win32 is included and used by default.  (See
-README.win32 for win32 details.)  On other systems pointers from dynamic
-library data areas may not be considered by the collector.
-
-  Note that the garbage collector does not need to be informed of shared
-read-only data.  However if the shared library mechanism can introduce
-discontiguous data areas that may contain pointers, then the collector does
-need to be informed.
-
-  Signal processing for most signals may be deferred during collection,
-and during uninterruptible parts of the allocation process.  Unlike
-standard ANSI C mallocs, it can be safe to invoke malloc
-from a signal handler while another malloc is in progress, provided
-the original malloc is not restarted.  (Empirically, many UNIX
-applications already assume this.)  To obtain this level  of signal
-safety, remove the definition of -DNO_SIGNALS in Makefile.  This incurs
-a minor performance penalty, and hence is no longer the default.
-
-  The allocator/collector can also be configured for thread-safe operation.
-(Full signal safety can also be achieved, but only at the cost of two system
-calls per malloc, which is usually unacceptable.)
-
-INSTALLATION AND PORTABILITY
-
-  As distributed, the macro SILENT is defined in Makefile.
-In the event of problems, this can be removed to obtain a moderate
-amount of descriptive output for each collection.
-(The given statistics exhibit a few peculiarities.
-Things don't appear to add up for a variety of reasons, most notably
-fragmentation losses.  These are probably much more significant for the
-contrived program "test.c" than for your application.)
-
-  Note that typing "make test" will automatically build the collector
-and then run setjmp_test and gctest. Setjmp_test will give you information
-about configuring the collector, which is useful primarily if you have
-a machine that's not already supported.  Gctest is a somewhat superficial
-test of collector functionality.  Failure is indicated by a core dump or
-a message to the effect that the collector is broken.  Gctest takes about 
-35 seconds to run on a SPARCstation 2. On a slower machine,
-expect it to take a while.  It may use up to 8 MB of memory.  (The
-multi-threaded version will use more.)  "Make test" will also, as
-its last step, attempt to build and test the "cord" string library.
-This will fail without an ANSI C compiler.
-
-  The Makefile will generate a library gc.a which you should link against.
-Typing "make cords" will add the cord library to gc.a.
-Note that this requires an ANSI C compiler.
-
-  It is suggested that if you need to replace a piece of the collector
-(e.g. GC_mark_rts.c) you simply list your version ahead of gc.a on the
-		work.)
-ld command line, rather than replacing the one in gc.a.  (This will
-generate numerous warnings under some versions of AIX, but it still
-works.)
-
-  All include files that need to be used by clients will be put in the
-include subdirectory.  (Normally this is just gc.h.  "Make cords" adds
-"cord.h" and "ec.h".)
-
-  The collector currently is designed to run essentially unmodified on
-machines that use a flat 32-bit or 64-bit address space.
-That includes the vast majority of Workstations and X86 (X >= 3) PCs.
-(The list here was deleted because it was getting too long and constantly
-out of date.)
-  It does NOT run under plain 16-bit DOS or Windows 3.X.  There are however
-various packages (e.g. win32s, djgpp) that allow flat 32-bit address
-applications to run under those systemsif the have at least an 80386 processor,
-and several of those are compatible with the collector.
-
-  In a few cases (Amiga, OS/2, Win32, MacOS) a separate makefile
-or equivalent is supplied.  Many of these have separate README.system
-files.
-
-  Dynamic libraries are completely supported only under SunOS
-(and even that support is not functional on the last Sun 3 release),
-IRIX 5&6, HP-PA, Win32 (not Win32S) and OSF/1 on DEC AXP machines.
-On other machines we recommend that you do one of the following:
-
-  1) Add dynamic library support (and send us the code).
-  2) Use static versions of the libraries.
-  3) Arrange for dynamic libraries to use the standard malloc.
-     This is still dangerous if the library stores a pointer to a
-     garbage collected object.  But nearly all standard interfaces
-     prohibit this, because they deal correctly with pointers
-     to stack allocated objects.  (Strtok is an exception.  Don't
-     use it.)
-
-  In all cases we assume that pointer alignment is consistent with that
-enforced by the standard C compilers.  If you use a nonstandard compiler
-you may have to adjust the alignment parameters defined in gc_priv.h.
-
-  A port to a machine that is not byte addressed, or does not use 32 bit
-or 64 bit addresses will require a major effort.  A port to plain MSDOS
-or win16 is hard.
-
-  For machines not already mentioned, or for nonstandard compilers, the
-following are likely to require change:
-
-1.  The parameters in gcconfig.h.
-      The parameters that will usually require adjustment are
-   STACKBOTTOM,  ALIGNMENT and DATASTART.  Setjmp_test
-   prints its guesses of the first two.
-      DATASTART should be an expression for computing the
-   address of the beginning of the data segment.  This can often be
-   &etext.  But some memory management units require that there be
-   some unmapped space between the text and the data segment.  Thus
-   it may be more complicated.   On UNIX systems, this is rarely
-   documented.  But the adb "$m" command may be helpful.  (Note
-   that DATASTART will usually be a function of &etext.  Thus a
-   single experiment is usually insufficient.)
-     STACKBOTTOM is used to initialize GC_stackbottom, which
-   should be a sufficient approximation to the coldest stack address.
-   On some machines, it is difficult to obtain such a value that is
-   valid across a variety of MMUs, OS releases, etc.  A number of
-   alternatives exist for using the collector in spite of this.  See the
-   discussion in gcconfig.h immediately preceding the various
-   definitions of STACKBOTTOM.
-   
-2.  mach_dep.c.
-      The most important routine here is one to mark from registers.
-    The distributed file includes a generic hack (based on setjmp) that
-    happens to work on many machines, and may work on yours.  Try
-    compiling and running setjmp_t.c to see whether it has a chance of
-    working.  (This is not correct C, so don't blame your compiler if it
-    doesn't work.  Based on limited experience, register window machines
-    are likely to cause trouble.  If your version of setjmp claims that
-    all accessible variables, including registers, have the value they
-    had at the time of the longjmp, it also will not work.  Vanilla 4.2 BSD
-    on Vaxen makes such a claim.  SunOS does not.)
-      If your compiler does not allow in-line assembly code, or if you prefer
-    not to use such a facility, mach_dep.c may be replaced by a .s file
-    (as we did for the MIPS machine and the PC/RT).
-      At this point enough architectures are supported by mach_dep.c
-    that you will rarely need to do more than adjust for assembler
-    syntax.
-
-3.  os_dep.c (and gc_priv.h).
-  	  Several kinds of operating system dependent routines reside here.
-  	Many are optional.  Several are invoked only through corresponding
-  	macros in gc_priv.h, which may also be redefined as appropriate.
-      The routine GC_register_data_segments is crucial.  It registers static
-    data areas that must be traversed by the collector. (User calls to
-    GC_add_roots may sometimes be used for similar effect.)
-      Routines to obtain memory from the OS also reside here.
-    Alternatively this can be done entirely by the macro GET_MEM
-    defined in gc_priv.h.  Routines to disable and reenable signals
-    also reside here if they are need by the macros DISABLE_SIGNALS
-    and ENABLE_SIGNALS defined in gc_priv.h.
-      In a multithreaded environment, the macros LOCK and UNLOCK
-    in gc_priv.h will need to be suitably redefined.
-      The incremental collector requires page dirty information, which
-    is acquired through routines defined in os_dep.c.  Unless directed
-    otherwise by gcconfig.h, these are implemented as stubs that simply
-    treat all pages as dirty.  (This of course makes the incremental
-    collector much less useful.)
-
-4.  dyn_load.c
-	This provides a routine that allows the collector to scan data
-	segments associated with dynamic libraries.  Often it is not
-	necessary to provide this routine unless user-written dynamic
-	libraries are used.
-
-  For a different version of UN*X or different machines using the
-Motorola 68000, Vax, SPARC, 80386, NS 32000, PC/RT, or MIPS architecture,
-it should frequently suffice to change definitions in gcconfig.h.
-
-
-THE C INTERFACE TO THE ALLOCATOR
-
-  The following routines are intended to be directly called by the user.
-Note that usually only GC_malloc is necessary.  GC_clear_roots and GC_add_roots
-calls may be required if the collector has to trace from nonstandard places
-(e.g. from dynamic library data areas on a machine on which the 
-collector doesn't already understand them.)  On some machines, it may
-be desirable to set GC_stacktop to a good approximation of the stack base. 
-(This enhances code portability on HP PA machines, since there is no
-good way for the collector to compute this value.)  Client code may include
-"gc.h", which defines all of the following, plus many others.
-
-1)  GC_malloc(nbytes)
-    - allocate an object of size nbytes.  Unlike malloc, the object is
-      cleared before being returned to the user.  Gc_malloc will
-      invoke the garbage collector when it determines this to be appropriate.
-      GC_malloc may return 0 if it is unable to acquire sufficient
-      space from the operating system.  This is the most probable
-      consequence of running out of space.  Other possible consequences
-      are that a function call will fail due to lack of stack space,
-      or that the collector will fail in other ways because it cannot
-      maintain its internal data structures, or that a crucial system
-      process will fail and take down the machine.  Most of these
-      possibilities are independent of the malloc implementation.
-
-2)  GC_malloc_atomic(nbytes)
-    - allocate an object of size nbytes that is guaranteed not to contain any
-      pointers.  The returned object is not guaranteed to be cleared.
-      (Can always be replaced by GC_malloc, but results in faster collection
-      times.  The collector will probably run faster if large character
-      arrays, etc. are allocated with GC_malloc_atomic than if they are
-      statically allocated.)
-
-3)  GC_realloc(object, new_size)
-    - change the size of object to be new_size.  Returns a pointer to the
-      new object, which may, or may not, be the same as the pointer to
-      the old object.  The new object is taken to be atomic iff the old one
-      was.  If the new object is composite and larger than the original object,
-      then the newly added bytes are cleared (we hope).  This is very likely
-      to allocate a new object, unless MERGE_SIZES is defined in gc_priv.h.
-      Even then, it is likely to recycle the old object only if the object
-      is grown in small additive increments (which, we claim, is generally bad
-      coding practice.)
-
-4)  GC_free(object)
-    - explicitly deallocate an object returned by GC_malloc or
-      GC_malloc_atomic.  Not necessary, but can be used to minimize
-      collections if performance is critical.  Probably a performance
-      loss for very small objects (<= 8 bytes).
-
-5)  GC_expand_hp(bytes)
-    - Explicitly increase the heap size.  (This is normally done automatically
-      if a garbage collection failed to GC_reclaim enough memory.  Explicit
-      calls to GC_expand_hp may prevent unnecessarily frequent collections at
-      program startup.)
-
-6)  GC_malloc_ignore_off_page(bytes)
-	- identical to GC_malloc, but the client promises to keep a pointer to
-	  the somewhere within the first 256 bytes of the object while it is
-	  live.  (This pointer should nortmally be declared volatile to prevent
-	  interference from compiler optimizations.)  This is the recommended
-	  way to allocate anything that is likely to be larger than 100Kbytes
-	  or so.  (GC_malloc may result in failure to reclaim such objects.)
-
-7)  GC_set_warn_proc(proc)
-	- Can be used to redirect warnings from the collector.  Such warnings
-	  should be rare, and should not be ignored during code development.
-      
-8) GC_enable_incremental()
-    - Enables generational and incremental collection.  Useful for large
-      heaps on machines that provide access to page dirty information.
-      Some dirty bit implementations may interfere with debugging
-      (by catching address faults) and place restrictions on heap arguments
-      to system calls (since write faults inside a system call may not be
-      handled well).
-
-9) Several routines to allow for registration of finalization code.
-   User supplied finalization code may be invoked when an object becomes
-   unreachable.  To call (*f)(obj, x) when obj becomes inaccessible, use
-	GC_register_finalizer(obj, f, x, 0, 0);
-   For more sophisticated uses, and for finalization ordering issues,
-   see gc.h.
-
-  The global variable GC_free_space_divisor may be adjusted up from its
-default value of 4 to use less space and more collection time, or down for
-the opposite effect.  Setting it to 1 or 0 will effectively disable collections
-and cause all allocations to simply grow the heap.
-
-  The variable GC_non_gc_bytes, which is normally 0, may be changed to reflect
-the amount of memory allocated by the above routines that should not be
-considered as a candidate for collection.  Careless use may, of course, result
-in excessive memory consumption.
-
-  Some additional tuning is possible through the parameters defined
-near the top of gc_priv.h.
-  
-  If only GC_malloc is intended to be used, it might be appropriate to define:
-
-#define malloc(n) GC_malloc(n)
-#define calloc(m,n) GC_malloc((m)*(n))
-
-  For small pieces of VERY allocation intensive code, gc_inl.h
-includes some allocation macros that may be used in place of GC_malloc
-and friends.
-
-  All externally visible names in the garbage collector start with "GC_".
-To avoid name conflicts, client code should avoid this prefix, except when
-accessing garbage collector routines or variables.
-
-  There are provisions for allocation with explicit type information.
-This is rarely necessary.  Details can be found in gc_typed.h.
-
-THE C++ INTERFACE TO THE ALLOCATOR:
-
-  The Ellis-Hull C++ interface to the collector is included in
-the collector distribution.  If you intend to use this, type
-"make c++" after the initial build of the collector is complete.
-See gc_cpp.h for the definition of the interface.  This interface
-tries to approximate the Ellis-Detlefs C++ garbage collection
-proposal without compiler changes.
-
-Cautions:
-1. Arrays allocated without new placement syntax are
-allocated as uncollectable objects.  They are traced by the
-collector, but will not be reclaimed.
-
-2. Failure to use "make c++" in combination with (1) will
-result in arrays allocated using the default new operator.
-This is likely to result in disaster without linker warnings.
-
-3. If your compiler supports an overloaded new[] operator,
-then gc_cpp.cc and gc_cpp.h should be suitably modified.
-
-4. Many current C++ compilers have deficiencies that
-break some of the functionality.  See the comments in gc_cpp.h
-for suggested workarounds.
-
-USE AS LEAK DETECTOR:
-
-  The collector may be used to track down leaks in C programs that are
-intended to run with malloc/free (e.g. code with extreme real-time or
-portability constraints).  To do so define FIND_LEAK in Makefile
-This will cause the collector to invoke the report_leak
-routine defined near the top of reclaim.c whenever an inaccessible
-object is found that has not been explicitly freed.  The collector will
-no longer reclaim inaccessible memory; in this form it is purely a
-debugging tool.
-  Productive use of this facility normally involves redefining report_leak
-to do something more intelligent.  This typically requires annotating
-objects with additional information (e.g. creation time stack trace) that
-identifies their origin.  Such code is typically not very portable, and is
-not included here, except on SPARC machines.
-  If all objects are allocated with GC_DEBUG_MALLOC (see next section),
-then the default version of report_leak will report the source file
-and line number at which the leaked object was allocated.  This may
-sometimes be sufficient.  (On SPARC/SUNOS4 machines, it will also report
-a cryptic stack trace.  This can often be turned into a sympolic stack
-trace by invoking program "foo" with "callprocs foo".  Callprocs is
-a short shell script that invokes adb to expand program counter values
-to symbolic addresses.  It was largely supplied by Scott Schwartz.)
-  Note that the debugging facilities described in the next section can
-sometimes be slightly LESS effective in leak finding mode, since in
-leak finding mode, GC_debug_free actually results in reuse of the object.
-(Otherwise the object is simply marked invalid.)  Also note that the test
-program is not designed to run meaningfully in FIND_LEAK mode.
-Use "make gc.a" to build the collector.
-
-DEBUGGING FACILITIES:
-
-  The routines GC_debug_malloc, GC_debug_malloc_atomic, GC_debug_realloc,
-and GC_debug_free provide an alternate interface to the collector, which
-provides some help with memory overwrite errors, and the like.
-Objects allocated in this way are annotated with additional
-information.  Some of this information is checked during garbage
-collections, and detected inconsistencies are reported to stderr.
-
-  Simple cases of writing past the end of an allocated object should
-be caught if the object is explicitly deallocated, or if the
-collector is invoked while the object is live.  The first deallocation
-of an object will clear the debugging info associated with an
-object, so accidentally repeated calls to GC_debug_free will report the
-deallocation of an object without debugging information.  Out of
-memory errors will be reported to stderr, in addition to returning
-NIL.
-
-  GC_debug_malloc checking  during garbage collection is enabled
-with the first call to GC_debug_malloc.  This will result in some
-slowdown during collections.  If frequent heap checks are desired,
-this can be achieved by explicitly invoking GC_gcollect, e.g. from
-the debugger.
-
-  GC_debug_malloc allocated objects should not be passed to GC_realloc
-or GC_free, and conversely.  It is however acceptable to allocate only
-some objects with GC_debug_malloc, and to use GC_malloc for other objects,
-provided the two pools are kept distinct.  In this case, there is a very
-low probablility that GC_malloc allocated objects may be misidentified as
-having been overwritten.  This should happen with probability at most
-one in 2**32.  This probability is zero if GC_debug_malloc is never called.
-
-  GC_debug_malloc, GC_malloc_atomic, and GC_debug_realloc take two
-additional trailing arguments, a string and an integer.  These are not
-interpreted by the allocator.  They are stored in the object (the string is
-not copied).  If an error involving the object is detected, they are printed.
-
-  The macros GC_MALLOC, GC_MALLOC_ATOMIC, GC_REALLOC, GC_FREE, and
-GC_REGISTER_FINALIZER are also provided.  These require the same arguments
-as the corresponding (nondebugging) routines.  If gc.h is included
-with GC_DEBUG defined, they call the debugging versions of these
-functions, passing the current file name and line number as the two
-extra arguments, where appropriate.  If gc.h is included without GC_DEBUG
-defined, then all these macros will instead be defined to their nondebugging
-equivalents.  (GC_REGISTER_FINALIZER is necessary, since pointers to
-objects with debugging information are really pointers to a displacement
-of 16 bytes form the object beginning, and some translation is necessary
-when finalization routines are invoked.  For details, about what's stored
-in the header, see the definition of the type oh in debug_malloc.c)
-
-INCREMENTAL/GENERATIONAL COLLECTION:
-
-The collector normally interrupts client code for the duration of 
-a garbage collection mark phase.  This may be unacceptable if interactive
-response is needed for programs with large heaps.  The collector
-can also run in a "generational" mode, in which it usually attempts to
-collect only objects allocated since the last garbage collection.
-Furthermore, in this mode, garbage collections run mostly incrementally,
-with a small amount of work performed in response to each of a large number of
-GC_malloc requests.
-
-This mode is enabled by a call to GC_enable_incremental().
-
-Incremental and generational collection is effective in reducing
-pause times only if the collector has some way to tell which objects
-or pages have been recently modified.  The collector uses two sources
-of information:
-
-1. Information provided by the VM system.  This may be provided in
-one of several forms.  Under Solaris 2.X (and potentially under other
-similar systems) information on dirty pages can be read from the
-/proc file system.  Under other systems (currently SunOS4.X) it is
-possible to write-protect the heap, and catch the resulting faults.
-On these systems we require that system calls writing to the heap
-(other than read) be handled specially by client code.
-See os_dep.c for details.
-
-2. Information supplied by the programmer.  We define "stubborn"
-objects to be objects that are rarely changed.  Such an object
-can be allocated (and enabled for writing) with GC_malloc_stubborn.
-Once it has been initialized, the collector should be informed with
-a call to GC_end_stubborn_change.  Subsequent writes that store
-pointers into the object must be preceded by a call to
-GC_change_stubborn.
-
-This mechanism performs best for objects that are written only for
-initialization, and such that only one stubborn object is writable
-at once.  It is typically not worth using for short-lived
-objects.  Stubborn objects are treated less efficiently than pointerfree
-(atomic) objects.
-
-A rough rule of thumb is that, in the absence of VM information, garbage
-collection pauses are proportional to the amount of pointerful storage
-plus the amount of modified "stubborn" storage that is reachable during
-the collection.  
-
-Initial allocation of stubborn objects takes longer than allocation
-of other objects, since other data structures need to be maintained.
-
-We recommend against random use of stubborn objects in client
-code, since bugs caused by inappropriate writes to stubborn objects
-are likely to be very infrequently observed and hard to trace.  
-However, their use may be appropriate in a few carefully written
-library routines that do not make the objects themselves available
-for writing by client code.
-
-
-BUGS:
-
-  Any memory that does not have a recognizable pointer to it will be
-reclaimed.  Exclusive-or'ing forward and backward links in a list
-doesn't cut it.
-  Some C optimizers may lose the last undisguised pointer to a memory
-object as a consequence of clever optimizations.  This has almost
-never been observed in practice.  Send mail to boehm@acm.org
-for suggestions on how to fix your compiler.
-  This is not a real-time collector.  In the standard configuration,
-percentage of time required for collection should be constant across
-heap sizes.  But collection pauses will increase for larger heaps.
-(On SPARCstation 2s collection times will be on the order of 300 msecs
-per MB of accessible memory that needs to be scanned.  Your mileage
-may vary.)  The incremental/generational collection facility helps,
-but is portable only if "stubborn" allocation is used.
-  Please address bug reports to boehm@acm.org.  If you are
-contemplating a major addition, you might also send mail to ask whether
-it's already been done (or whether we tried and discarded it).
-
-RECENT VERSIONS:
-
-  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.
-
-To do:
- - 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.
- - Integrate MIT and DEC pthreads ports.
- - Deal with very uneven black-listing distributions.  If all the black listed
-   blocks reside in the newly allocated heap section, the heuristic for
-   temporarily ignoring black-listing fails, and the heap grows too much.
-   (This was observed in only one case, and could be worked around, but ...)
- - Some platform specific updates are waiting for 4.15alpha1.