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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. 
diff --git a/gc/README.Mac b/gc/README.Mac
new file mode 100644
index 0000000..04f4682
--- /dev/null
+++ b/gc/README.Mac
@@ -0,0 +1,385 @@
+Patrick Beard's Notes for building GC v4.12 with CodeWarrior Pro 2:
+----------------------------------------------------------------------------
+The current build environment for the collector is CodeWarrior Pro 2.
+Projects for CodeWarrior Pro 2 (and for quite a few older versions)
+are distributed in the file Mac_projects.sit.hqx. The project file
+:Mac_projects:gc.prj builds static library versions of the collector.
+:Mac_projects:gctest.prj builds the GC test suite.
+
+Configuring the collector is still done by editing the files
+:Mac_files:MacOS_config.h and :Mac_files:MacOS_Test_config.h.
+
+Lars Farm's suggestions on building the collector:
+----------------------------------------------------------------------------
+Garbage Collection on MacOS - a manual 'MakeFile'
+-------------------------------------------------
+
+Project files and IDE's are great on the Macintosh, but they do have
+problems when used as distribution media. This note tries to provide
+porting instructions in pure TEXT form to avoid those problems. A manual
+'makefile' if you like.
+
+    GC version:     4.12a2
+    Codewarrior:    CWPro1
+    date:           18 July 1997
+
+The notes may or may not apply to earlier or later versions of the
+GC/CWPro. Actually, they do apply to earlier versions of both except that
+until recently a project could only build one target so each target was a
+separate project. The notes will most likely apply to future versions too.
+Possibly with minor tweaks.
+
+This is just to record my experiences. These notes do not mean I now
+provide a supported port of the GC to MacOS. It works for me. If it works
+for you, great. If it doesn't, sorry, try again...;-) Still, if you find
+errors, please let me know.
+
+    mailto:         lars.farm@ite.mh.se
+
+    address:        Lars Farm
+                    Krönvägen 33b
+                    856 44 Sundsvall
+                    Sweden
+
+Porting to MacOS is a bit more complex than it first seems. Which MacOS?
+68K/PowerPC? Which compiler? Each supports both 68K and PowerPC and offer a
+large number of (unique to each environment) compiler settings. Each
+combination of compiler/68K/PPC/settings require a unique combination of
+standard libraries. And the IDE's does not select them for you. They don't
+even check that the library is built with compatible setting and this is
+the major source of problems when porting the GC (and otherwise too).
+
+You will have to make choices when you configure the GC. I've made some
+choices here, but there are other combinations of settings and #defines
+that work too.
+
+As for target settings the major obstacles may be:
+- 68K Processor: check "4-byte Ints".
+- PPC Processor: uncheck "Store Static Data in TOC".
+
+What you need to do:
+===================
+
+1) Build the GC as a library
+2) Test that the library works with 'test.c'.
+3) Test that the C++ interface 'gc_cpp.cc/h' works with 'test_cpp.cc'.
+
+1) The Libraries:
+=================
+I made one project with four targets (68K/PPC tempmem or appheap). One target
+will suffice if you're able to decide which one you want. I wasn't...
+
+Codewarrior allows a large number of compiler/linker settings. I used these:
+
+Settings shared by all targets:
+------------------------------
+o Access Paths:
+  - User Paths:   the GC folder
+  - System Paths: {Compiler}:Metrowerks Standard Library:
+                  {Compiler}:MacOS Support:Headers:
+                  {Compiler}:MacOS Support:MacHeaders:
+o C/C++ language:
+  - inlining: normal
+  - direct to SOM: off
+  - enable/check: exceptions, RTTI, bool (and if you like pool strings)
+
+PowerPC target settings
+-----------------------
+o Target Settings:
+  - name of target
+  - MacOS PPC Linker
+o PPC Target
+  - name of library
+o C/C++ language
+  - prefix file as described below
+o PPC Processor
+  - Struct Alignment: PowerPC
+  - uncheck "Store Static Data in TOC" -- important!
+    I don't think the others matter, I use full optimization and its ok
+o PPC Linker
+  - Factory Settings (SYM file with full paths, faster linking, dead-strip
+    static init, Main: __start)
+
+
+68K target settings
+-------------------
+o Target Settings:
+  - name of target
+  - MacOS 68K Linker
+o 68K Target
+  - name of library
+  - A5 relative data
+o C/C++ language
+  - prefix file as described below
+o 68K Processor
+  - Code model: smart
+  - Struct alignment: 68K
+  - FP: SANE
+  - enable 4-Byte Ints -- important!
+    I don't think the others matter. I selected...
+  - enable: 68020
+  - enable: global register allocation
+o IR Optimizer
+  - enable: Optimize Space, Optimize Speed
+    I suppose the others would work too, but haven't tried...
+o 68K Linker
+  - Factory Settings (New Style MacsBug,SYM file with full paths,
+    A6 Frames, fast link, Merge compiler glue into segment 1,
+    dead-strip static init)
+
+Prefix Files to configure the GC sources
+----------------------------------------
+The Codewarrior equivalent of commandline compilers -DNAME=X is to use
+prefix-files. A TEXT file that is automatically #included before the first byte
+of every source file. I used these:
+
+---- ( cut here ) ----  gc_prefix_tempmem.h     -- 68K and PPC -----
+    #include "gc_prefix_common.h"
+    #undef USE_TEMPORARY_MEMORY
+    #define USE_TEMPORARY_MEMORY
+---- ( cut here ) ----  gc_prefix_appmem.h      -- 68K and PPC -----
+    #include "gc_prefix_common.h"
+    #undef USE_TEMPORARY_MEMORY
+//  #define USE_TEMPORARY_MEMORY
+
+---- ( cut here ) ----  gc_prefix_common.h      --------------------
+// gc_prefix_common.h
+// ------------------
+// Codewarrior prefix file to configure the GC libraries
+//
+//   prefix files are the Codewarrior equivalent of the
+//   command line option -Dname=x frequently seen in makefiles
+
+#if !__MWERKS__
+  #error only tried this with Codewarrior
+#endif
+
+#if macintosh
+  #define MSL_USE_PRECOMPILED_HEADERS 0
+  #include <ansi_prefix.mac.h>
+  #ifndef __STDC__
+    #define __STDC__ 0
+  #endif
+
+  //  See list of #defines to configure the library in: 'MakeFile'
+  //  see also README
+
+  #define SILENT                // no collection messages. In case
+                                // of trouble you might want this off
+  #define ALL_INTERIOR_POINTERS // follows interior pointers.
+//#define DONT_ADD_BYTE_AT_END  // disables the padding if defined.
+//#define SMALL_CONFIG          // whether to use a smaller heap.
+  #define NO_SIGNALS            // signals aren't real on the Macintosh.
+  #define ATOMIC_UNCOLLECTABLE  // GC_malloc_atomic_uncollectable()
+
+  // define either or none as per personal preference
+  //   used in malloc.c
+  #define REDIRECT_MALLOC GC_malloc
+//#define REDIRECT_MALLOC GC_malloc_uncollectable
+  // if REDIRECT_MALLOC is #defined make sure that the GC library
+  // is listed before the ANSI/ISO libs in the Codewarrior
+  // 'Link order' panel
+//#define IGNORE_FREE
+
+  // mac specific configs
+//#define USE_TEMPORARY_MEMORY    // use Macintosh temporary memory.
+//#define SHARED_LIBRARY_BUILD    // build for use in a shared library.
+
+#else
+  // could build Win32 here too, or in the future
+  // Rhapsody PPC-mach, Rhapsody PPC-MacOS,
+  // Rhapsody Intel-mach, Rhapsody Intel-Win32,...
+  // ... ugh this will get messy ...
+#endif
+
+// make sure ints are at least 32-bit
+// ( could be set to 16-bit by compiler settings (68K) )
+
+struct gc_private_assert_intsize_{ char x[ sizeof(int)>=4 ? 1 : 0 ]; };
+
+#if __powerc
+  #if __option(toc_data)
+    #error turn off "store static data in TOC" when using GC
+    //     ... or find a way to add TOC to the root set...(?)
+  #endif
+#endif
+---- ( cut here ) ----  end of gc_prefix_common.h  -----------------
+
+Files to  build the GC libraries:
+--------------------------------
+    allchblk.c
+    alloc.c
+    blacklst.c
+    checksums.c
+    dbg_mlc.c
+    finalize.c
+    headers.c
+    mach_dep.c
+    MacOS.c    -- contains MacOS code
+    malloc.c
+    mallocx.c
+    mark.c
+    mark_rts.c
+    misc.c
+    new_hblk.c
+    obj_map.c
+    os_dep.c   -- contains MacOS code
+    ptr_chck.c
+    reclaim.c
+    stubborn.c
+    typd_mlc.c
+    gc++.cc    -- this is 'gc_cpp.cc' with less 'inline' and
+               -- throw std::bad_alloc when out of memory
+               -- gc_cpp.cc works just fine too
+
+2) Test that the library works with 'test.c'.
+=============================================
+
+The test app is just an ordinary ANSI-C console app. Make sure settings
+match the library you're testing.
+
+Files
+-----
+    test.c
+    the GC library to test        -- link order before ANSI libs
+    suitable Mac+ANSI libraries
+
+prefix:
+------
+---- ( cut here ) ----  gc_prefix_testlib.h     -- all libs -----
+#define MSL_USE_PRECOMPILED_HEADERS 0
+#include <ansi_prefix.mac.h>
+#undef NDEBUG
+
+#define ALL_INTERIOR_POINTERS	/* for GC_priv.h */
+---- ( cut here ) ----
+
+3) Test that the C++ interface 'gc_cpp.cc/h' works with 'test_cpp.cc'.
+
+The test app is just an ordinary ANSI-C console app. Make sure settings match
+the library you're testing.
+
+Files
+-----
+    test_cpp.cc
+    the GC library to test        -- link order before ANSI libs
+    suitable Mac+ANSI libraries
+
+prefix:
+------
+same as for test.c
+
+For convenience I used one test-project with several targets so that all
+test apps are build at once. Two for each library to test: test.c and
+gc_app.cc. When I was satisfied that the libraries were ok. I put the
+libraries + gc.h + the c++ interface-file in a folder that I then put into
+the MSL hierarchy so that I don't have to alter access-paths in projects
+that use the GC.
+
+After that, just add the proper GC library to your project and the GC is in
+action! malloc will call GC_malloc and free GC_free, new/delete too. You
+don't have to call free or delete. You may have to be a bit cautious about
+delete if you're freeing other resources than RAM. See gc_cpp.h. You can
+also keep coding as always with delete/free. That works too. If you want,
+"include <gc.h> and tweak it's use a bit.
+
+Symantec SPM
+============
+It has been a while since I tried the GC in SPM, but I think that the above
+instructions should be sufficient to guide you through in SPM too. SPM
+needs to know where the global data is. Use the files 'datastart.c' and
+'dataend.c'. Put 'datastart.c' at the top of your project and 'dataend.c'
+at the bottom  of your project so that all data is surrounded. This is not
+needed in Codewarrior because it provides intrinsic variables
+__datastart__, __data_end__ that wraps all globals.
+
+Source Changes (GC 4.12a2)
+==========================
+Very few. Just one tiny in the GC, not strictly needed.
+- MacOS.c line 131 in routine GC_MacFreeTemporaryMemory()
+  change #       if !defined(SHARED_LIBRARY_BUILD)
+  to     #       if !defined(SILENT) && !defined(SHARED_LIBRARY_BUILD)
+  To turn off a message when the application quits (actually, I faked
+  this change by #defining SHARED_LIBRARY_BUILD in a statically linked
+  library for more than a year without ill effects but perhaps this is
+  better).
+
+- test_cpp.cc
+  made the first lines of main() look like this:
+  ------------
+  int main( int argc, char* argv[] ) {
+  #endif
+  #if macintosh                             // MacOS
+    char* argv_[] = {"test_cpp","10"};      //   doesn't
+    argv=argv_;                             //     have a
+    argc = sizeof(argv_)/sizeof(argv_[0]);  //       commandline
+  #endif                                    //
+
+  int i, iters, n;
+  # ifndef __GNUC__
+   alloc dummy_to_fool_the_compiler_into_doing_things_it_currently_cant_handle;
+  ------------
+
+- config.h [now gcconfig.h]
+  __MWERKS__ does not have to mean MACOS. You can use Codewarrior to
+  build a Win32 or BeOS library and soon a Rhapsody library. You may
+  have to change that #if...
+
+
+
+   It worked for me, hope it works for you.
+
+   Lars Farm
+   18 July 1997
+----------------------------------------------------------------------------
+
+
+Patrick Beard's instructions (may be dated):
+
+v4.3 of the collector now runs under Symantec C++/THINK C v7.0.4, and
+Metrowerks C/C++ v4.5 both 68K and PowerPC. Project files are provided
+to build and test the collector under both development systems.
+
+Configuration
+-------------
+
+To configure the collector, under both development systems, a prefix file
+is used to set preprocessor directives. This file is called "MacOS_config.h".
+Also to test the collector, "MacOS_Test_config.h" is provided.
+
+Testing
+-------
+
+To test the collector (always a good idea), build one of the gctest projects,
+gctest.¹ (Symantec C++/THINK C), mw/gctest.68K.¹, or mw/gctest.PPC.¹. The
+test will ask you how many times to run; 1 should be sufficient.
+
+Building 
+--------
+
+For your convenience project files for the major Macintosh development
+systems are provided.
+
+For Symantec C++/THINK C, you must build the two projects gclib-1.¹ and
+gclib-2.¹. It has to be split up because the collector has more than 32k
+of static data and no library can have more than this in the Symantec
+environment. (Future versions will probably fix this.)
+
+For Metrowerks C/C++ 4.5 you build gc.68K.¹/gc.PPC.¹ and the result will
+be a library called gc.68K.lib/gc.PPC.lib.
+
+Using
+-----
+
+Under Symantec C++/THINK C, you can just add the gclib-1.¹ and gclib-2.¹
+projects to your own project. Under Metrowerks, you add gc.68K.lib or
+gc.PPC.lib and two additional files. You add the files called datastart.c
+and dataend.c to your project, bracketing all files that use the collector.
+See mw/gctest.¹ for an example.
+
+Include the projects/libraries you built above into your own project,
+#include "gc.h", and call GC_malloc. You don't have to call GC_free.
+
+
+Patrick C. Beard
+January 4, 1995
diff --git a/gc/README.OS2 b/gc/README.OS2
new file mode 100644
index 0000000..5345bbd
--- /dev/null
+++ b/gc/README.OS2
@@ -0,0 +1,6 @@
+The code assumes static linking, and a single thread.  The editor de has
+not been ported.  The cord test program has.  The supplied OS2_MAKEFILE
+assumes the IBM C Set/2 environment, but the code shouldn't.
+
+Since we haven't figured out hoe to do perform partial links or to build static
+libraries, clients currently need to link against a long list of executables.
diff --git a/gc/README.QUICK b/gc/README.QUICK
new file mode 100644
index 0000000..3273c8b
--- /dev/null
+++ b/gc/README.QUICK
@@ -0,0 +1,41 @@
+Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
+Copyright (c) 1991-1994 by Xerox Corporation.  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.
+
+
+For more details and the names of other contributors, see the
+README file and gc.h.  This file describes typical use of
+the collector on a machine that is already supported.
+
+INSTALLATION:
+Under UN*X, type "make test".  Under OS/2 or Windows NT, copy the
+appropriate makefile to MAKEFILE, read it, and type "nmake test".
+Read the machine specific README if one exists.  The only way to
+develop code with the collector for Windows 3.1 is to develop under
+Windows NT, and then to use win32S.
+
+If you wish to use the cord (structured string) library type
+"make cords". (This requires an ANSI C compiler.  You may need
+to redefine CC in the Makefile.)
+
+If you wish to use the collector from C++, type
+"make c++".  These add further files to gc.a and to the include
+subdirectory.  See cord/cord.h and gc_c++.h.
+
+TYPICAL USE:
+Include "gc.h" from this directory.  Link against the appropriate library
+("gc.a" under UN*X).  Replace calls to malloc by calls to GC_MALLOC,
+and calls to realloc by calls to GC_REALLOC.  If the object is known
+to never contain pointers, use GC_MALLOC_ATOMIC instead of
+GC_MALLOC.
+
+Define GC_DEBUG before including gc.h for additional checking.
+
diff --git a/gc/README.alpha b/gc/README.alpha
new file mode 100644
index 0000000..213a13e
--- /dev/null
+++ b/gc/README.alpha
@@ -0,0 +1,22 @@
+Should work under OSF/1 and Linux.  Currently no VMS or NT support, though
+the latter shouldn't be hard.
+
+Incremental gc not yet supported under Linux because signal handler
+for SIGSEGV can't get a hold of fault address.  Dynamic library support
+is also missing from Linux/alpha, probably for no good reason.
+
+Currently there is no thread support in the standard distribution.  There
+exists a separate port to DEC Unix pthreads.  It should be possible to
+port the X86 Linux threads support to Alpha without much trouble.
+
+If you get asssembler errors, be sure to read the first few lines of the
+Makefile.
+
+From Philippe Queinnec:
+
+System: DEC/Alpha OSF1 v3.2, vendor cc
+Problem: can't link if libgc has been compiled with "cc -std1".
+         It works if the library has been compiled with either gcc or "cc"
+         alone. The problem is because the variable "end" is not defined if
+         compiling in std1 mode (see man ld).
+Proposed fix: none. Don't use cc -std1 !
diff --git a/gc/README.amiga b/gc/README.amiga
new file mode 100644
index 0000000..47b1588
--- /dev/null
+++ b/gc/README.amiga
@@ -0,0 +1,180 @@
+===========================================================================
+			   Martin Tauchmann's notes		(1-Apr-99)
+===========================================================================
+
+Works now, also with the GNU-C compiler V2.7.2.1. <ftp://ftp.unina.it/pub/amiga/geekgadgets/amiga/m68k/snapshots/971125/amiga-bin/>
+Modify the `Makefile`
+CC=cc $(ABI_FLAG)
+to
+CC=gcc $(ABI_FLAG)
+
+TECHNICAL NOTES
+
+- `GC_get_stack_base()`, `GC_register_data_segments()` works now with every
+   C compiler; also Workbench.
+
+- Removed AMIGA_SKIP_SEG, but the Code-Segment must not be scanned by GC.
+
+
+PROBLEMS
+- When the Linker, does`t merge all Code-Segments to an single one. LD of GCC
+  do it always.
+
+- With ixemul.library V47.3, when an GC program launched from another program
+  (example: `Make` or `if_mach M68K AMIGA gctest`), `GC_register_data_segments()`
+  found the Segment-List of the caller program.
+  Can be fixed, if the run-time initialization code (for C programs, usually *crt0*)
+  support `__data` and `__bss`.
+
+- PowerPC Amiga currently not supported.
+
+- Dynamic libraries (dyn_load.c) not supported.
+
+
+TESTED WITH SOFTWARE
+
+`Optimized Oberon 2 C` (oo2c) <http://cognac.informatik.uni-kl.de/download/index.html>
+
+
+TESTED WITH HARDWARE
+
+MC68030
+
+
+CONTACT
+
+Please, contact me at <martintauchmann@bigfoot.com>, when you change the
+Amiga port. <http://martintauchmann.home.pages.de>
+ 
+===========================================================================
+			   Michel Schinz's notes
+===========================================================================
+WHO DID WHAT
+
+The original Amiga port was made by Jesper Peterson. I (Michel Schinz)
+modified it slightly to reflect the changes made in the new official
+distributions, and to take advantage of the new SAS/C 6.x features. I also
+created a makefile to compile the "cord" package (see the cord
+subdirectory).
+
+TECHNICAL NOTES
+
+In addition to Jesper's notes, I have the following to say:
+
+- Starting with version 4.3, gctest checks to see if the code segment is
+  added to the root set or not, and complains if it is. Previous versions
+  of this Amiga port added the code segment to the root set, so I tried to
+  fix that. The only problem is that, as far as I know, it is impossible to
+  know which segments are code segments and which are data segments (there
+  are indeed solutions to this problem, like scanning the program on disk
+  or patch the LoadSeg functions, but they are rather complicated). The
+  solution I have chosen (see os_dep.c) is to test whether the program
+  counter is in the segment we are about to add to the root set, and if it
+  is, to skip the segment. The problems are that this solution is rather
+  awkward and that it works only for one code segment. This means that if
+  your program has more than one code segment, all of them but one will be
+  added to the root set. This isn't a big problem in fact, since the
+  collector will continue to work correctly, but it may be slower.
+
+  Anyway, the code which decides whether to skip a segment or not can be
+  removed simply by not defining AMIGA_SKIP_SEG. But notice that if you do
+  so, gctest will complain (it will say that "GC_is_visible produced wrong
+  failure indication"). However, it may be useful if you happen to have
+  pointers stored in a code segment (you really shouldn't).
+
+  If anyone has a good solution to the problem of finding, when a program
+  is loaded in memory, whether a segment is a code or a data segment,
+  please let me know.
+
+PROBLEMS
+
+If you have any problem with this version, please contact me at
+schinz@alphanet.ch (but do *not* send long files, since we pay for
+every mail!).
+
+===========================================================================
+			  Jesper Peterson's notes
+===========================================================================
+
+ADDITIONAL NOTES FOR AMIGA PORT
+
+These notes assume some familiarity with Amiga internals.
+
+WHY I PORTED TO THE AMIGA
+
+The sole reason why I made this port was as a first step in getting
+the Sather(*) language on the Amiga. A port of this language will
+be done as soon as the Sather 1.0 sources are made available to me.
+Given this motivation, the garbage collection (GC) port is rather
+minimal.
+
+(*) For information on Sather read the comp.lang.sather newsgroup.
+
+LIMITATIONS
+
+This port assumes that the startup code linked with target programs
+is that supplied with SAS/C versions 6.0 or later. This allows
+assumptions to be made about where to find the stack base pointer
+and data segments when programs are run from WorkBench, as opposed
+to running from the CLI. The compiler dependent code is all in the
+GC_get_stack_base() and GC_register_data_segments() functions, but
+may spread as I add Amiga specific features.
+
+Given that SAS/C was assumed, the port is set up to be built with
+"smake" using the "SMakefile". Compiler options in "SCoptions" can
+be set with "scopts" program. Both "smake" and "scopts" are part of
+the SAS/C commercial development system.
+
+In keeping with the porting philosophy outlined above, this port
+will not behave well with Amiga specific code. Especially not inter-
+process comms via messages, and setting up public structures like
+Intuition objects or anything else in the system lists. For the
+time being the use of this library is limited to single threaded
+ANSI/POSIX  compliant or near-complient code. (ie. Stick to stdio
+for now). Given this limitation there is currently no mechanism for
+allocating "CHIP" or "PUBLIC" memory under the garbage collector.
+I'll add this after giving it considerable thought. The major
+problem is the entire physical address space may have to me scanned,
+since there is no telling who we may have passed memory to.
+
+If you allocate your own stack in client code, you will have to
+assign the pointer plus stack size to GC_stackbottom.
+
+The initial stack size of the target program can be compiled in by
+setting the __stack symbol (see SAS documentaion). It can be over-
+ridden from the CLI by running the AmigaDOS "stack" program, or from
+the WorkBench by setting the stack size in the tool types window.
+
+SAS/C COMPILER OPTIONS (SCoptions)
+
+You may wish to check the "CPU" code option is appropriate for your
+intended target system.
+
+Under no circumstances set the "StackExtend" code option in either
+compiling the library or *ANY* client code.
+
+All benign compiler warnings have been suppressed. These mainly
+involve lack of prototypes in the code, and dead assignments
+detected by the optimizer.
+
+THE GOOD NEWS
+
+The library as it stands is compatible with the GigaMem commercial
+virtual memory software, and probably similar PD software.
+
+The performance of "gctest" on an Amiga 2630 (68030 @ 25Mhz)
+compares favourably with an HP9000 with similar architecture (a 325
+with a 68030 I think).
+
+-----------------------------------------------------------------------
+
+The Amiga port has been brought to you by:
+
+Jesper Peterson.
+
+jep@mtiame.mtia.oz.au		(preferred, but 1 week turnaround)
+jep@orca1.vic.design.telecom.au (that's orca<one>, 1 day turnaround)
+
+At least one of these addresses should be around for a while, even
+though I don't work for either of the companies involved.
+
diff --git a/gc/README.debugging b/gc/README.debugging
new file mode 100644
index 0000000..80635c2
--- /dev/null
+++ b/gc/README.debugging
@@ -0,0 +1,58 @@
+Debugging suggestions:
+
+****If you get a segmentation fault or bus error while debugging with a debugger:
+If the fault occurred in GC_find_limit, or with incremental collection enabled, this is probably normal.  The collector installs handlers to take care of these.  You will not see these unless you are using a debugger.  Your debugger should allow you to continue.  It's preferable to tell the debugger to ignore SIGBUS and SIGSEGV ("handle" in gdb, "ignore" in most versions of dbx) and set a breakpoint in abort.  The collector will call abort if the signal had another cause, and there was not other handler previously installed.  I recommend debugging without incremental collection if possible.  (This applies directly to UNIX systems.  Debugging with incremental collection under win32 is worse.  See README.win32.)  
+
+****If you get warning messages informing you that the collector needed to allocate blacklisted blocks:
+
+0) Ignore these warnings while you are using GC_DEBUG.  Some of the routines mentioned below don't have debugging equivalents.  (Alternatively, write the missing routines and send them to me.)
+
+1) Replace allocator calls that request large blocks with calls to GC_malloc_ignore_off_page or GC_malloc_atomic_ignore_off_page.  You may want to set a breakpoint in GC_default_warn_proc to help you identify such calls.  Make sure that a pointer to somewhere near the beginning of the resulting block is maintained in a (preferably volatile) variable as long as the block is needed.
+
+2) If the large blocks are allocated with realloc, I suggest instead allocating them with something like the following.  Note that the realloc size increment should be fairly large (e.g. a factor of 3/2) for this to exhibit reasonable performance.  But we all know we should do that anyway.
+
+void * big_realloc(void *p, size_t new_size)
+{
+    size_t old_size = GC_size(p);
+    void * result;
+ 
+    if (new_size <= 10000) return(GC_realloc(p, new_size));
+    if (new_size <= old_size) return(p);
+    result = GC_malloc_ignore_off_page(new_size);
+    if (result == 0) return(0);
+    memcpy(result,p,old_size);
+    GC_free(p);
+    return(result);
+}
+
+3) In the unlikely case that even relatively small object (<20KB) allocations are triggering these warnings, then your address space contains lots of "bogus pointers", i.e. values that appear to be pointers but aren't.  Usually this can be solved by using GC_malloc_atomic or the routines in gc_typed.h to allocate large pointerfree regions of bitmaps, etc.  Sometimes the problem can be solved with trivial changes of encoding in certain values.  It is possible, though not pleasant, to identify the source of the bogus pointers by setting a breakpoint in GC_add_to_black_list_stack, and looking at the value of current_p in the GC_mark_from_mark_stack frame.  Current_p contains the address of the bogus pointer.
+
+4) If you get only a fixed number of these warnings, you are probably only introducing a bounded leak by ignoring them.  If the data structures being allocated are intended to be permanent, then it is also safe to ignore them.  The warnings can be turned off by calling GC_set_warn_proc with a procedure that ignores these warnings (e.g. by doing absolutely nothing).
+
+
+****If the collector dies in GC_malloc while trying to remove a free list element:
+
+1) With > 99% probability, you wrote past the end of an allocated object.  Try setting GC_DEBUG and using the debugging facilities in gc.h.
+
+
+****If the heap grows too much:
+
+1) Consider using GC_malloc_atomic for objects containing nonpointers.  This is especially important for large arrays containg compressed data, pseudo-random numbers, and the like.  (This isn't all that likely to solve your problem, but it's a useful and easy optimization anyway, and this is a good time to try it.)   If you allocate large objects containg only one or two pointers at the beginning, either try the typed allocation primitives is gc.h, or separate out the pointerfree component.
+2) If you are using the collector in its default mode, with interior pointer recognition enabled, consider using GC_malloc_ignore_off_page to allocate large objects.  (See gc.h and above for details.  Large means > 100K in most environments.)
+3) GC_print_block_list() will print a list of all currently allocated heap blocks and what size objects they contain.  GC_print_hblkfreelist() will print a list of free heap blocks, and whether they are blacklisted.  GC_dump calls both of these, and also prints information about heap sections, and root segments.
+4) Write a tool that traces back references to the appropriate root.  Send me the code.  (I have code that does this for old PCR.)
+
+
+****If the collector appears to be losing objects:
+
+1) Replace all calls to GC_malloc_atomic and typed allocation by GC_malloc calls.  If this fixes the problem, gradually reinsert your optimizations.
+2) You may also want to try the safe(r) pointer manipulation primitives in gc.h.  But those are hard to use until the preprocessor becomes available.
+3) Try using the GC_DEBUG facilities.  This is less likely to be successful here than if the collector crashes.
+[The rest of these are primarily for wizards.  You shouldn't need them unless you're doing something really strange, or debugging a collector port.]
+4) Don't turn on incremental collection.  If that fixes the problem, suspect a bug in the dirty bit implementation.  Try compiling with -DCHECKSUMS to check for modified, but supposedly clean, pages.
+5) On a SPARC, in a single-threaded environment, GC_print_callers(GC_arrays._last_stack) prints a cryptic stack trace as of the time of the last collection.  (You will need a debugger to decipher the result.)  The question to ask then is "why should this object have been accessible at the time of the last collection?  Where was a pointer to it stored?".  This facility should be easy to add for some other collector ports (namely if it's easy to traverse stack frames), but will be hard for others.
+6) "print *GC_find_header(p)" in dbx or gdb will print the garbage collector block header information associated with the object p (e.g. object size, etc.)
+7) GC_is_marked(p) determines whether p is the base address of a marked object.  Note that objects allocated since the last collection should not be marked, and that unmarked objects are reclaimed incrementally.  It's usually most interesting to set a breakpoint in GC_finish_collection and then to determine how much of the damaged data structure is marked at that point.
+8) Look at the tracing facility in mark.c.  (Ignore this suggestion unless you are very familiar with collector internals.)
+
+
diff --git a/gc/README.dj b/gc/README.dj
new file mode 100644
index 0000000..613bc42
--- /dev/null
+++ b/gc/README.dj
@@ -0,0 +1,12 @@
+[Original version supplied by Xiaokun Zhu <xiaokun@aero.gla.ac.uk>]
+[This version came mostly from Gary Leavens.			  ]
+
+Look first at Makefile.dj, and possibly change the definitions of
+RM and MV if you don't have rm and mv installed.
+Then use Makefile.dj to compile the garbage collector.
+For example, you can do:
+
+	make -f Makefile.dj test
+
+All the tests should work fine.
+
diff --git a/gc/README.hp b/gc/README.hp
new file mode 100644
index 0000000..b290590
--- /dev/null
+++ b/gc/README.hp
@@ -0,0 +1,11 @@
+Dynamic loading support requires that executables be linked with -ldld.
+The alternative is to build the collector without defining DYNAMIC_LOADING
+in gcconfig.h and ensuring that all garbage collectable objects are
+accessible without considering statically allocated variables in dynamic
+libraries.
+
+The collector should compile with either plain cc or cc -Ae.  CC -Aa
+fails to define _HPUX_SOURCE and thus will not configure the collector
+correctly.
+
+There is currently no thread support.
diff --git a/gc/README.linux b/gc/README.linux
new file mode 100644
index 0000000..b4f136a
--- /dev/null
+++ b/gc/README.linux
@@ -0,0 +1,50 @@
+See README.alpha for Linux on DEC AXP info.
+
+This file applies mostly to Linux/Intel IA32.  Ports to Linux on an M68K
+and PowerPC are also integrated.  They should behave similarly, except that
+the PowerPC port lacks incremental GC support, and it is unknown to what
+extent the Linux threads code is functional.
+
+Incremental GC is supported on Intel IA32 and M68K.
+
+Dynamic libraries are supported on an ELF system.  A static executable
+should be linked with the gcc option "-Wl,-defsym,_DYNAMIC=0".
+
+The collector appears to work with Linux threads.  We have seen
+intermittent hangs in sem_wait.  So far we have been unable to reproduce
+these unless the process was being debugged or traced.  Thus it's
+possible that the only real issue is that the debugger loses
+signals on rare occasions.
+
+The garbage collector uses SIGPWR and SIGXCPU if it is used with
+Linux threads.  These should not be touched by the client program.
+
+To use threads, you need to abide by the following requirements:
+
+1) You need to use LinuxThreads (which are included in libc6).
+
+   The collector relies on some implementation details of the LinuxThreads
+   package.  It is unlikely that this code will work on other
+   pthread implementations (in particular it will *not* work with
+   MIT pthreads).
+
+2) You must compile the collector with -DLINUX_THREADS and -D_REENTRANT
+   specified in the Makefile.
+
+3) Every file that makes thread calls should define LINUX_THREADS and 
+   _REENTRANT and then include gc.h.  Gc.h redefines some of the
+   pthread primitives as macros which also provide the collector with
+   information it requires.
+
+4) Currently dlopen() is probably not safe.  The collector must traverse
+   the list of libraries maintained by the runtime loader.  That can
+   probably be an inconsistent state when a thread calling the loader is
+   is stopped for GC.  (It's possible that this is fixable in the
+   same way it is handled for SOLARIS_THREADS, with GC_dlopen.)
+
+5) The combination of LINUX_THREADS, REDIRECT_MALLOC, and incremental
+   collection fails in seemingly random places.  This hasn't been tracked
+   down yet, but is perhaps not completely astonishing.  The thread package
+   uses malloc, and thus can presumably get SIGSEGVs while inside the
+   package.  There is no real guarantee that signals are handled properly
+   at that point.
diff --git a/gc/README.rs6000 b/gc/README.rs6000
new file mode 100644
index 0000000..f5630b2
--- /dev/null
+++ b/gc/README.rs6000
@@ -0,0 +1,9 @@
+We have so far failed to find a good way to determine the stack base.
+It is highly recommended that GC_stackbottom be set explicitly on program
+startup.  The supplied value sometimes causes failure under AIX 4.1, though
+it appears to work under 3.X.  HEURISTIC2 seems to work under 4.1, but
+involves a substantial performance penalty, and will fail if there is
+no limit on stack size.
+
+There is no thread support.  (I assume recent versions of AIX provide
+pthreads?  I no longer have access to a machine ...)
diff --git a/gc/README.sgi b/gc/README.sgi
new file mode 100644
index 0000000..e67124b
--- /dev/null
+++ b/gc/README.sgi
@@ -0,0 +1,41 @@
+Performance of the incremental collector can be greatly enhanced with
+-DNO_EXECUTE_PERMISSION.
+
+The collector should run with all of the -32, -n32 and -64 ABIs.  Remember to
+define the AS macro in the Makefile to be "as -64", or "as -n32".
+
+If you use -DREDIRECT_MALLOC=GC_malloc with C++ code, your code should make
+at least one explicit call to malloc instead of new to ensure that the proper
+version of malloc is linked in.
+
+Sproc threads are not supported in this version, though there may exist other
+ports.
+
+Pthreads support is provided.  This requires that:
+
+1) You compile the collector with -DIRIX_THREADS specified in the Makefile.
+
+2) You have the latest pthreads patches installed.  
+
+(Though the collector makes only documented pthread calls,
+it relies on signal/threads interactions working just right in ways
+that are not required by the standard.  It is unlikely that this code
+will run on other pthreads platforms.  But please tell me if it does.)
+
+3) Every file that makes thread calls should define IRIX_THREADS and then
+include gc.h.  Gc.h redefines some of the pthread primitives as macros which
+also provide the collector with information it requires.
+
+4) pthread_cond_wait and pthread_cond_timed_wait should be prepared for
+premature wakeups.  (I believe the pthreads and realted standards require this
+anyway.  Irix pthreads often terminate a wait if a signal arrives.
+The garbage collector uses signals to stop threads.)
+
+5) It is expensive to stop a thread waiting in IO at the time the request is
+initiated.  Applications with many such threads may not exhibit acceptable
+performance with the collector.  (Increasing the heap size may help.)
+
+6) The collector should not be compiled with -DREDIRECT_MALLOC.  This
+confuses some library calls made by the pthreads implementation, which
+expect the standard malloc.
+
diff --git a/gc/README.solaris2 b/gc/README.solaris2
new file mode 100644
index 0000000..e593513
--- /dev/null
+++ b/gc/README.solaris2
@@ -0,0 +1,65 @@
+The collector supports both incremental collection and threads under
+Solaris 2.  The incremental collector normally retrieves page dirty information
+through the appropriate /proc calls.  But it can also be configured
+(by defining MPROTECT_VDB instead of PROC_VDB in gcconfig.h) to use mprotect
+and signals.  This may result in shorter pause times, but it is no longer
+safe to issue arbitrary system calls that write to the heap.
+
+Under other UNIX versions,
+the collector normally obtains memory through sbrk.  There is some reason
+to expect that this is not safe if the client program also calls the system
+malloc, or especially realloc.  The sbrk man page strongly suggests this is
+not safe: "Many library routines use malloc() internally, so use brk()
+and sbrk() only when you know  that malloc() definitely will not be used by
+any library routine."  This doesn't make a lot of sense to me, since there
+seems to be no documentation as to which routines can transitively call malloc.
+Nonetheless, under Solaris2, the collector now (since 4.12) allocates
+memory using mmap by default.  (It defines USE_MMAP in gcconfig.h.)
+You may want to reverse this decisions if you use -DREDIRECT_MALLOC=...
+
+
+SOLARIS THREADS:
+
+The collector must be compiled with -DSOLARIS_THREADS to be thread safe.
+It is also essential that gc.h be included in files that call thr_create,
+thr_join, thr_suspend, thr_continue, or dlopen.  Gc.h macro defines
+these to also do GC bookkeeping, etc.  Gc.h must be included with
+SOLARIS_THREADS defined, otherwise these replacements are not visible.
+A collector built in this way way only be used by programs that are
+linked with the threads library.
+
+If you are using the Pthreads interface, also define _SOLARIS_PTHREADS.
+
+In this mode, the collector contains various workarounds for older Solaris
+bugs.  Mostly, these should not be noticeable unless you look at system
+call traces.  However, it cannot protect a guard page at the end of
+a thread stack.  If you know that you will only be running Solaris2.5
+or later, it should be possible to fix this by compiling the collector
+with -DSOLARIS23_MPROTECT_BUG_FIXED.
+
+Jeremy Fitzhardinge points out that there is a problem with the dlopen
+replacement, in that startup code in the library is run while the allocation
+lock is held.  This appears to be difficult to fix, since the collector does
+look at data structures maintained by dlopen, and hence some locking is needed
+around the dlopen call.  Defining USE_PROC_FOR_LIBRARIES will get address
+space layout information from /proc avoiding the dlopen lock.  But this has
+other disadvanatages, e.g. mmapped files may be scanned.
+
+If solaris_threads are used on an X86 processor with malloc redirected to
+GC_malloc, it is necessary to call GC_thr_init explicitly before forking the
+first thread.  (This avoids a deadlock arising from calling GC_thr_init
+with the allocation lock held.)
+
+It appears that there is a problem in using gc_cpp.h in conjunction with
+Solaris threads and Sun's C++ runtime.  Apparently the overloaded new operator
+is invoked by some iostream initialization code before threads are correctly
+initialized.  As a result, call to thr_self() in garbage collector
+initialization  segfaults.  Currently the only known workaround is to not
+invoke the garbage collector from a user defined global operator new, or to
+have it invoke the garbage-collector's allocators only after main has started.
+(Note that the latter requires a moderately expensive test in operator
+delete.)
+
+Hans-J. Boehm
+(The above contains my personal opinions, which are probably not shared
+by anyone else.)
diff --git a/gc/README.uts b/gc/README.uts
new file mode 100644
index 0000000..6be4966
--- /dev/null
+++ b/gc/README.uts
@@ -0,0 +1,2 @@
+Alistair Crooks supplied the port.  He used Lexa C version 2.1.3 with
+-Xa to compile.
diff --git a/gc/README.win32 b/gc/README.win32
new file mode 100644
index 0000000..d78816b
--- /dev/null
+++ b/gc/README.win32
@@ -0,0 +1,149 @@
+The collector has only been compiled under Windows NT, with the
+original Microsoft SDK, with Visual C++ 2.0 and later, with
+the GNU win32 environment, with Borland 4.5, and recently with
+Watcom C.
+
+It runs under both win32s and win32, but with different semantics.
+Under win32, all writable pages outside of the heaps and stack are
+scanned for roots.  Thus the collector sees pointers in DLL data
+segments.  Under win32s, only the main data segment is scanned.
+(The main data segment should always be scanned.  Under some
+versions of win32s, other regions may also be scanned.)
+Thus all accessible objects should be accessible from local variables
+or variables in the main data segment.  Alternatively, other data
+segments (e.g. in DLLs) may be registered with the collector by
+calling GC_init() and then GC_register_root_section(a), where
+a is the address of some variable inside the data segment.  (Duplicate
+registrations are ignored, but not terribly quickly.)
+
+(There are two reasons for this.  We didn't want to see many 16:16
+pointers.  And the VirtualQuery call has different semantics under
+the two systems, and under different versions of win32s.)
+
+The collector test program "gctest" is linked as a GUI application,
+but does not open any windows.  Its output appears in the file
+"gc.log".  It may be started from the file manager.  The hour glass
+cursor will appear as long as it's running.  If it is started from the
+command line, it will usually run in the background.  Wait a few
+minutes (a few seconds on a modern machine) before you check the output.
+You should see either a failure indication or a "Collector appears to
+work" message.
+
+The cord test program has not been ported (but should port
+easily).  A toy editor (cord/de.exe) based on cords (heavyweight
+strings represented as trees) has been ported and is included.
+It runs fine under either win32 or win32S.  It serves as an example
+of a true Windows application, except that it was written by a
+nonexpert Windows programmer.  (There are some peculiarities
+in the way files are displayed.  The <cr> is displayed explicitly
+for standard DOS text files.  As in the UNIX version, control
+characters are displayed explicitly, but in this case as red text.
+This may be suboptimal for some tastes and/or sets of default
+window colors.)
+
+For Microsoft development tools, rename NT_MAKEFILE as
+MAKEFILE.  (Make sure that the CPU environment variable is defined
+to be i386.)
+
+For GNU-win32, use the regular makefile, possibly after uncommenting
+the line "include Makefile.DLLs".  The latter should be necessary only
+if you want to package the collector as a DLL.  The GNU-win32 port is
+believed to work only for b18, not b19, probably dues to linker changes
+in b19.  This is probably fixable with a different definition of
+DATASTART and DATAEND in gcconfig.h.
+
+For Borland tools, use BCC_MAKEFILE.  Note that
+Borland's compiler defaults to 1 byte alignment in structures (-a1),
+whereas Visual C++ appears to default to 8 byte alignment (/Zp8).
+The garbage collector in its default configuration EXPECTS AT
+LEAST 4 BYTE ALIGNMENT.  Thus the BORLAND DEFAULT MUST
+BE OVERRIDDEN.  (In my opinion, it should usually be anyway.
+I expect that -a1 introduces major performance penalties on a
+486 or Pentium.)  Note that this changes structure layouts.  (As a last
+resort, gcconfig.h can be changed to allow 1 byte alignment.  But
+this has significant negative performance implications.)
+The Makefile is set up to assume Borland 4.5.  If you have another
+version, change the line near the top.  By default, it does not
+require the assembler.  If you do have the assembler, I recommend
+removing the -DUSE_GENERIC.
+
+Incremental collection support was recently added.  This is
+currently pretty simpleminded.  Pages are protected.  Protection
+faults are caught by a handler installed at the bottom of the handler
+stack.  This is both slow and interacts poorly with a debugger.
+Whenever possible, I recommend adding a call to
+GC_enable_incremental at the last possible moment, after most
+debugging is complete.  Unlike the UNIX versions, no system
+calls are wrapped by the collector itself.  It may be necessary
+to wrap ReadFile calls that use a buffer in the heap, so that the
+call does not encounter a protection fault while it's running.
+(As usual, none of this is an issue unless GC_enable_incremental
+is called.)
+
+Note that incremental collection is disabled with -DSMALL_CONFIG,
+which is the default for win32.  If you need incremental collection,
+undefine SMALL_CONFIG.
+
+Incremental collection is not supported under win32s, and it may not
+be possible to do so.  However, win32 applications that attempt to use
+incremental collection should continue to run, since the
+collector detects if it's running under win32s and turns calls to
+GC_enable_incremental() into noops.
+
+James Clark has contributed the necessary code to support win32 threads.
+This code is known to exhibit some problems with incremental collection
+enabled.  Use NT_THREADS_MAKEFILE (a.k.a gc.mak) instead of NT_MAKEFILE
+to build this version.  Note that this requires some files whose names
+are more than 8 + 3 characters long.  Thus you should unpack the tar file
+so that long file names are preserved.  To build the garbage collector
+test with VC++ from the command line, use
+
+nmake /F ".\gc.mak" CFG="gctest - Win32 Release"
+
+This requires that the subdirectory gctest\Release exist.
+The test program and DLL will reside in the Release directory.
+
+This version relies on the collector residing in a dll.
+
+This version currently supports incremental collection only if it is
+enabled before any additional threads are created.
+Version 4.13 attempts to fix some of the earlier problems, but there
+may be other issues.  If you need solid support for win32 threads, you
+might check with Geodesic Systems.  Their collector must be licensed,
+but they have invested far more time in win32-specific issues.
+
+Hans
+
+Ivan V. Demakov's README for the Watcom port:
+
+The collector has been compiled with Watcom C 10.6 and 11.0.
+It runs under win32, win32s, and even under msdos with dos4gw
+dos-extender. It should also run under OS/2, though this isn't
+tested. Under win32 the collector can be built either as dll
+or as static library.
+
+Note that all compilations were done under Windows 95 or NT.
+For unknown reason compiling under Windows 3.11 for NT (one
+attempt has been made) leads to broken executables.
+
+Incremental collection is not supported.
+
+cord is not ported.
+
+Before compiling you may need to edit WCC_MAKEFILE to set target
+platform, library type (dynamic or static), calling conventions, and
+optimization options.
+
+To compile the collector and testing programs use the command:
+    wmake -f WCC_MAKEFILE
+
+All programs using gc should be compiled with 4-byte alignment.
+For further explanations on this see comments about Borland.
+
+If gc compiled as dll, the macro ``GC_DLL'' should be defined before
+including "gc.h" (for example, with -DGC_DLL compiler option). It's
+important, otherwise resulting programs will not run.
+
+Ivan Demakov (email: ivan@tgrad.nsk.su)
+
+