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+This is a rough history of garbage collector bugs and versions.
+This has been maintained with varying diligence over the years.
+I made an attempt to include recent contributors here. I apologize for any
+ 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
+ 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
+ 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
+ All of the above were pointed out by Neil Sharman
+- 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).
+- 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
+- Added a workaround for an HP/UX compiler bug.
+- Fixed another stack clearing performance bug. Reworked
+ that code once more.
+- 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
+- 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
+- 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
+- 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
+- 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
+- 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 firstname.lastname@example.org.
+- 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 (email@example.com)
+- 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
+- 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
+* 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
+* The test program test_gc_c++ (later renamed test_cpp.cc)
+tries to test for the C++-specific functionality not tested by the
+- 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
+- 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 (firstname.lastname@example.org)).
+ - 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 (email@example.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
+ - 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 (firstname.lastname@example.org).)
+ - 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
+ - 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
+ (email@example.com) for pointing out many of them.)
+ - Fixed ALPHA/OSF/1 dynamic library support. (Thanks to Jonathan Bachrach
+ - 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
+ - (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 +
+ - Added NetBSD/M68K port. (Thanks to Peter Seebach
+ - Fixed a serious realloc bug. For certain object sizes, the collector
+ wouldn't scan the expanded part of the object. (Thanks to Clay Spence
+ (firstname.lastname@example.org) for noticing the problem, and helping me to
+ track it down.)
+Since version 4.5:
+ - Added Linux ELF support. (Thanks to Arrigo Triulzi <email@example.com>.)
+ - 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
+ - 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 (firstname.lastname@example.org).)
+ - 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.
+ - 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.)
+ - 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
+ - Added Patrick Beard's Mac fixes, with substantial completely untested
+ - 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
+ - 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 <email@example.com>.)
+ - 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
+ - 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 firstname.lastname@example.org 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
+ - Fixed a bug in the C++ test that caused it to fail in 64-bit
+ - 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
+ - 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 email@example.com.)
+ - 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.
+ - 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
+ - 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.
+ - 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
+ - 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.
+ - 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.)
+ - 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>
+ - 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.
+ - -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.)
+ - changed STACKBOTTOM for DJGPP (Thanks to Salvador Eduardo Tropea).
+ - 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.
+ - Fixed bugs introduced in alpha1 (OpenBSD & large block initialization).
+ - Added -DKEEP_BACK_PTRS and backptr.h interface. (The implementation
+ idea came from Al Demers.)
+ - Added some highly incomplete code to support a copied young generation.
+ Comments on nursery.h are appreciated.
+ - Changed -DFIND_LEAK, -DJAVA_FINALIZATION, and -DFINALIZE_ON_DEMAND,
+ so the same effect could be obtained with a runtime switch. This is
+ a step towards standardizing on a single dynamic GC library.
+ - Significantly changed the way leak detection is handled, as a consequence
+ of the above.
+Since 5.0 alpha3
+ - Added protection fault handling patch for Linux/M68K from Fergus
+ Henderson and Roman Hodek.
+ - Removed the tests for SGI_SOURCE in new_gc_alloc.h. This was causing that
+ interface to fail on nonSGI platforms.
+ - Changed the Linux stack finding code to use /proc, after changing it
+ to use HEURISTIC1. (Thanks to David Mossberger for pointing out the
+ /proc hook.)
+ - Added HP/UX incremental GC support and HP/UX 11 thread support.
+ Thread support is currently still flakey.
+ - Added basic Linux/IA64 support.
+ - Integrated Anthony Green's PicoJava support.
+ - Integrated Scott Ananian's StrongARM/NetBSD support.
+ - Fixed some fairly serious performance bugs in the incremental
+ collector. These have probably been there essentially forever.
+ (Mark bits were sometimes set before scanning dirty pages.
+ The reclaim phase unnecessarily dirtied full small object pages.)
+ - Changed the reclaim phase to ignore nearly full pages to avoid
+ touching them.
+ - Limited GC_black_list_spacing to roughly the heap growth increment.
+ - Changed full collection triggering heuristic to decrease full GC
+ frequency by default, but to explicitly trigger full GCs during
+ heap growth. This doesn't always improve things, but on average it's
+ probably a win.
+ - GC_debug_free(0, ...) failed. Thanks to Fergus Henderson for the
+ bug report and fix.
+Since 5.0 alpha4
+ - GC_malloc_explicitly_typed and friends sometimes failed to
+ initialize first word.
+ - Added allocation routines and support in the marker for mark descriptors
+ in a type structure referenced by the first word of an object. This was
+ introduced to support gcj, but hopefully in a way that makes it
+ generically useful.
+ - Added GC_requested_heapsize, and inhibited collections in nonincremental
+ mode if the actual used heap size is less than what was explicitly
+ - The Solaris pthreads version of GC_pthread_create didn't handle a NULL
+ attribute pointer. Solaris thread support used the wrong default thread
+ stack size. (Thanks to Melissa O'Neill for the patch.)
+ - Changed PUSH_CONTENTS macro to no longer modify first parameter.
+ This usually doesn't matter, but it was certainly an accident waiting
+ to happen ...
+ - Added GC_register_finalizer_no_order and friends to gc.h. They're
+ needed by Java implementations.
+ - Integrated a fix for a win32 deadlock resulting from clock() calling
+ malloc. (Thanks to Chris Dodd.)
+ - Integrated Hiroshi Kawashima's port to Linux/MIPS. This was designed
+ for a handheld platform, and may or may not be sufficient for other
+ - Fixed a va_arg problem with the %c specifier in cordprnt.c. It appears
+ that this was always broken, but recent versions of gcc are the first to
+ report the (statically detectable) bug.
+ - Added an attempt at a more general solution to dlopen races/deadlocks.
+ GC_dlopen now temporarily disables collection. Still not ideal, but ...
+ - Added -DUSE_I686_PREFETCH, -DUSE_3DNOW_PREFETCH, and support for IA64
+ prefetch instructions. May improve performance measurably, but I'm not
+ sure the code will run correctly on processors that don't support the
+ instruction. Won't build except with very recent gcc.
+ - Added caching for header lookups in the marker. This seems to result
+ in a barely measurable performance gain. Added support for interleaved
+ lookups of two pointers, but unconfigured that since the performance
+ gain is currently near zero, and it adds to code size.
+ - Changed Linux DATA_START definition to check both data_start and
+ __data_start, since nothing else seems to be portable.
+ - Added -DUSE_LD_WRAP to optionally take advantage of the GNU ld function
+ wrapping mechanism. Probably currently useful only on Linux.
+ - Moved some variables for the scratch allocator into GC_arrays, on
+ Martin Hirzel's suggestion.
+ - Fixed a win32 threads bug that caused the collector to not look for
+ interior pointers from one of the thread stacks without
+ ALL_INTERIOR_POINTERS. (Thanks to Jeff Sturm.)
+ - Added Mingw32 support. (Thanks again to Jeff Sturm for the patch.)
+ - Changed the alpha port to use the generic register scanning code instead
+ of alpha_mach_dep.s. Alpha_mach_dep.s doesn't look for pointers in fp
+ registers, but gcc sometimes spills pointers there. (Thanks to Manuel
+ Serrano for helping me debug this by email.) Changed the IA64 code to
+ do something similar for similar reasons.
+[5.0alpha5 doesn't really exist, but it may have escaped.]
+ - -DREDIRECT_MALLOC was broken in alpha6. Fixed.
+ - Cleaned up gc_ccp.h slightly, thus also causing the HP C++ compiler to
+ accept it.
+ - Removed accidental reference to dbg_mlc.c, which caused dbg_mlc.o to be
+ linked into every executable.
+ - Added PREFETCH to bitmap marker. Changed it to use the header cache.
+ - GC_push_marked sometimes pushed one object too many, resulting in a
+ segmentation fault in GC_mark_from_mark_stack. This was probably an old
+ bug. It finally showed up in gctest on win32.
+ - Gc_priv.h erroneously #defined GC_incremental to be TRUE instead of FALSE
+ when SMALL_CONFIG was defined. This was no doubt a major performance bug for
+ the default win32 configuration.
+ - Removed -DSMALL_CONFIG from NT_MAKEFILE. It seemed like an anchronism now
+ that the average PC has 64MB or so.
+ - Integrated Bryce McKinley's patches for linux threads and dynamic loading
+ from the libgcj tree. Turned on dynamic loading support for Linux/PPC.
+ - Changed the stack finding code to use environ on HP/UX. (Thanks
+ to Gustavo Rodriguez-Rivera for the suggestion.) This should probably
+ be done on other platforms, too. Since I can't test those, that'll
+ wait until after 5.0.
+ - Fixed threadlibs.c for linux threads. -DUSE_LD_WRAP was broken and
+ -ldl was omitted. Fixed Linux stack finding code to handle
+ -DUSE_LD_WRAP correctly.
+ - Added MSWIN32 exception handler around marker, so that the collector
+ can recover from root segments that are unmapped during the collection.
+ This caused occasional failures under Windows 98, and may also be
+ an issue under Windows NT/2000.
+ - Fixed a gc.h header bug which showed up under Irix. (Thanks to
+ Dan Sullivan.)
+ - Fixed a typo in GC_double_descr in typd_mlc.c.
+ This probably could result in objects described by array descriptors not
+ getting traced correctly. (Thanks to Ben Hutchings for pointing this out.)
+ - The block nearly full tests in reclaim.c were not correct for 64 bit
+ environments. This could result in unnecessary heap growth under unlikely
+ - dyn_load.c declared GC_scratch_last_end_ptr as an extern even if it
+ was defined as a macro. This prevented the collector from building on
+ - We quietly assumed that indirect mark descriptors were never 0.
+ Our own typed allocation interface violated that. This could result
+ in segmentation faults in the marker with typed allocation.
+ - Fixed a _DUSE_MUNMAP bug in the heap block allocation code.
+ (Thanks to Ben Hutchings for the patch.)
+ - Taught the collector about VC++ handling array operator new.
+ (Thanks again to Ben Hutchings for the patch.)
+ - The two copies of gc_hdrs.h had diverged. Made one a link to the other
+Since 5.2 (A few 5.2 patches are not in 6.0alpha1)
+ - Fixed _end declaration for OSF1.
+ - There were lots of spurious leak reports in leak detection mode, caused
+ by the fact that some pages were not being swept, and hence unmarked
+ objects weren't making it onto free lists. (This bug dated back to 5.0.)
+ - Fixed a typo in the liblinuxgc.so Makefile rule.
+ - Added the GetExitCodeThread to Win32 GC_stop_world to (mostly) work
+ around a Windows 95 GetOpenFileName problem. (Thanks to Jacob Navia.)
+ - Fixed a typo that prevented compilation with -DUSE_3DNOW_PREFETCH.
+ (Thanks to Shawn Wagner for actually testing this.)
+ - Fixed GC_is_thread_stack in solaris_threads.c. It forgot to return a value
+ in the common case. I wonder why nobody noticed?
+ - Fixed another silly syntax problem in GC_double_descr. (Thanks to
+ Fergus Henderson for finding it.)
+ - Fixed a GC_gcj_malloc bug: It tended to release the allocator lock twice.
+Since 5.4 (A few 5.3 patches are not in 6.0alpha2)
+ - Added HP/PA prefetch support.
+ - Added -DDBG_HDRS_ALL and -DSHORT_DBG_HDRS to reduce the cost and improve
+ the reliability of generating pointer backtrace information, e.g. in
+ the Bigloo environment.
+ - Added parallel marking support (-DPARALLEL_MARK). This currently
+ works only under IA32 and IA64 Linux, but it shouldn't be hard to adapt
+ to other platforms. This is intended to be a lighter-weight (less
+ new code, probably not as scalable) solution than the work by Toshio Endo
+ et al, at the University of Tokyo. A number of their ideas were
+ reused, though the code wasn't, and the underlying data structure
+ is significantly different. In particular, we keep the global mark
+ stack as a single shared data structure, but most of the work is done
+ on smaller thread-local mark stacks.
+ - Changed GC_malloc_many to be cheaper, and to require less mutual exclusion
+ with -DPARALLEL_MARK.
+ - Added full support for thread local allocation under Linux
+ (-DTHREAD_LOCAL_ALLOC). This is a thin veneer on GC_malloc_many, and
+ should be easily portable to other platforms, especially those that
+ support pthreads.
+ - CLEAR_DOUBLE was not always getting invoked when it should have been.
+ - GC_gcj_malloc and friends used different out of memory handling than
+ everything else, probably because I forgot about one when I implemented
+ the other. They now both call GC_oom_fn(), not GC_oom_action().
+ - Integrated Jakub Jelinek's fixes for Linux/SPARC.
+ - Moved GC_objfreelist, GC_aobjfreelist, and GC_words_allocd out of
+ GC_arrays, and separately registered the first two as excluded roots.
+ This makes code compiled with gc_inl.h less dependent on the
+ collector version. (It would be nice to remove the inclusion of
+ gc_priv.h by gc_inl.h completely, but we're not there yet. The
+ locking definitions in gc_priv.h are still referenced.)
+ This change was later coniditoned on SEPARATE_GLOBALS, which
+ is not defined by default, since it involves a performance hit.
+ - Register GC_obj_kinds separately as an excluded root region. The
+ attempt to register it with GC_arrays was usually failing. (This wasn't
+ serious, but seemed to generate some confusion.)
+ - Moved backptr.h to gc_backptr.h.
+ - Added USE_MARK_BYTES to reduce the need for compare-and-swap on platforms
+ for which that's expensive.
+ - Fixed a locking bug ib GC_gcj_malloc and some locking assertion problems.
+ - Added a missing volatile to OR_WORD and renamed the parameter to
+ GC_compare_and_swap so it's not a C++ reserved word. (Thanks to
+ Toshio Endo for pointing out both of those.)
+ - Changed Linux dynamic library registration code to look at /proc/self/maps
+ instead of the rld data structures when REDIRECT_MALLOC is defined.
+ Otherwise some of the rld data data structures may be prematurely garbage
+ collected. (Thanks to Eric Benson for helping to track this down.)
+ - Fixed USE_LD_WRAP a bit more, so it should now work without threads.
+ - Renamed XXX_THREADS macros to GC_XXX_THREADS for namespace correctness.
+ Tomporarily added some backward compatibility definitions. Renamed
+ USE_LD_WRAP to GC_USE_LD_WRAP.
+ - Many MACOSX POWERPC changes, some additions to the gctest output, and
+ a few minor generic bug fixes. (Thanks to Dietmar Planitzer.)
+Since 6.0 alpha2
+ - Fixed the /proc/self/maps code to not seek, since that apparently is not
+ reliable across all interesting kernels.
+ - Fixed some compilation problems in the absence of PARALLEL_MARK
+ (introduced in alpha2).
+ - Fixed an algorithmic problem with PARALLEL_MARK. If work needs to
+ be given back to the main mark "stack", the BOTTOM entries of the local
+ stack should be given away, not the top ones. This has substantial
+ performance impact, especially for > 2 processors, from what I can tell.
+ - Extracted gc_lock.h from gc_priv.h. This should eventually make it a
+ bit easier to avoid including gc_priv.h in clients.
+ - Moved all include files to include/ and removed duplicate links to the
+ same file. The old scheme was a bad idea because it was too easy to get the
+ copies out of sync, and many systems don't support hard links.
+ Unfortunately, it's likely that I broke some of the non-Unix Makefiles in
+ the process, although I tried to update them appropriately.
+ - Removed the partial support for a copied nursery. It's not clear that
+ this would be a tremendous win, since we don't consistently lose to
+ generational copying collectors. And it would significantly complicate
+ many things. May be reintroduced if/when it really turns out to win.
+ - Removed references to IRIX_JDK_THREADS, since I believe there never
+ were and never will be any clients.
+ - Added some code to linux_threads.c to possibly support HPUX threads
+ using the Linux code. Unfortunately, it doesn't work yet, and is
+ currently disabled.
+ - Added support under Linux/X86 for saving the call chain, both in (debug)
+ objects for client debugging, and in GC_arrays._last_stack for GC
+ debugging. This was previously supported only under Solaris. It is
+ not enabled by default under X86, since it requires that code be compiled
+ to explicitly dave frame pointers on the call stack. (With gcc this
+ currently happens by default, but is often turned off explicitly.)
+ To turn it on, define SAVE_CALL_CHAIN.
+Since 6.0 alpha3
+ - Moved up the detection of mostly full blocks to the initiatiation of the
+ sweep phase. This eliminates some lock conention in the PARALLEL_MARK case,
+ as multiple threads try to look at mostly full blocks concurrently.
+ - Restored the code in GC_malloc_many that grabs a prefix of the global
+ free list. This avoids the case in which every GC_malloc_many call
+ tries and fails to allocate a new heap block, and the returns a single
+ object from the global free list.
+ - Some minor fixes in new_hblk.c. (Attempted to build free lists in order
+ of increasing addresses instead of decreasing addresses for cache performance
+ reasons. But this seems to be only a very minor gain with -DEAGER_SWEEP,
+ and a loss in other cases. So the change was backed out.)
+ - Fixed some of the documentation. (Thanks in large part to Fergus
+ - Fixed the Linux USE_PROC_FOR_LIBRARIES code to deal with apps that perform
+ large numbers of mmaps. (Thanks to Eric Benson.) Also fixed that code to
+ deal with short reads.
+ - Added GC_get_total_bytes().
+ - Fixed leak detection mode to avoid spurious messages under linuxthreads.
+ (This should also now be easy for the other supported threads packages.
+ But the code is tricky enough that I'm hesitant to do it without being able
+ to test. Everything allocated in the GC thread support itself should be
+ explicitly deallocated.)
+ - Made it possible (with luck) to redirect malloc to GC_local_malloc.
+Since 6.0 alpha4
+ - Changed the definition of GC_pause in linux_threads.c to use a volatile
+ asm. Some versions of gcc apparently optimize away writes to local volatile
+ variables. This caused poor locking behaviour starting at about
+ 4 processors.
+ - Added GC_start_blocking(), GC_end_blocking() calls and wrapper for sleep
+ to linux_threads.c.
+ The first two calls could be used to generally avoid sending GC signals to
+ blocked threads, avoiding both premature wakeups and unnecessary overhead.
+ - Fixed a serious bug in thread-local allocation. At thread termination,
+ GC_free could get called on small integers. Changed the code for thread
+ termination to more efficiently return left-over free-lists.
+ - Integrated Kjetil Matheussen's BeOS support.
+ - Rearranged the directory structure to create the doc and tests
+ - Sort of integrated Eric Benson's patch for OSF1. This provided basic
+ OSF1 thread support by suitably extending hpux_irix_threads.c. Based
+ on earlier email conversations with David Butenhof, I suspect that it
+ will be more reliable in the long run to base this on linux_threads.c
+ instead. Thus I attempted to patch up linux_threads.c based on Eric's code.
+ The result is almost certainly broken, but hopefully close enough that
+ someone with access to a machine can pick it up.
+ - Integrated lots of minor changes from the NetBSD distribution. (These
+ were supplied by David Brownlee. I'm not sure about the original
+ - Hacked a bit more on the HP/UX thread-support in linux_threads.c. It
+ now appears to work in the absence of incremental collection. Renamed
+ hpux_irix_threads.c back to irix_threads.c, and removed the attempt to
+ support HPUX there.
+ - Changed gc.h to define _REENTRANT in cases in which it should already
+ have been defined. It is still safer to also define it on the command
+ - Changed the definition of DATASTART on ALPHA and IA64, where data_start
+ and __data_start are not defined by earlier versions of glibc. This might
+ need to be fixed on other platforms as well.
+ - Changed the way the stack base and backing store base are found on IA64.
+ This should now remain reliable on future kernels. But since it relies
+ on /proc, it will no longer work in the simulated NUE environment.
+ - Made the call to random() in dbg_mlc.c with -DKEEP_BACK_PTRS dependent
+ on the OS. On non-Unix systems, rand() should be used instead. Handled
+ small RAND_MAX. (Thanks to Peter Ross for pointing this out.)
+ - Fixed the cord make rules to create the cord subdirectory, if necessary.
+ (Thanks to Doug Moen.)
+ - Changed fo_object_size calculation in finalize.c. Turned finalization
+ of nonheap object into a no-op. Removed anachronism from GC_size()
+ - Changed GC_push_dirty call in solaris_threads.c to GC_push_selected.
+ It was missed in a previous renaming. (Thanks to Vladimir Tsichevski
+ for pointing this out.)
+ - Arranged to not not mask SIGABRT in linux_threads.c. (Thanks to Bryce
+ - Added GC_no_dls hook for applications that want to register their own
+ - Integrated Kjetil Matheussen's Amiga changes.
+ - Added FREEBSD_STACKBOTTOM. Changed the X86/FreeBSD port to use it.
+ (Thanks to Matthew Flatt.)
+ - Added pthread_detach interception for platforms supported by linux_threads.c
+ and irix_threads.c. Should also be added for Solaris?
+ - Changed the USE_MMAP code to check for the case in which we got the
+ high end of the address space, i.e. mem_ptr + mem_sz == 0. It appears
+ that this can happen under Solaris 7. It seems to be allowed by what
+ I would claim is an oversight in the mmap specification. (Thanks to Toshio
+ Endo for pointing out the problem.)
+ - Cleanup of linux_threads.c. Some code was originally cloned from
+ irix_threads.c and now unnecessary. Some comments were obviously wrong.
+ - (Mostly) fixed a longstanding problem with setting of dirty bits from
+ a signal handler. In the presence of threads, dirty bits could get lost,
+ since the etting of a bit in the bit vector was not atomic with respect
+ to other updates. The fix is 100% correct only for platforms for which
+ GC_test_and_set is defined. The goal is to make that all platforms with
+ thread support. Matters only if incremental GC and threads are both
+ - made GC_all_interior_pointers (a.k.a. ALL_INTERIOR_POINTERS) an
+ initialization time, instead of build-time option. This is a
+ nontrivial, high risk change. It should slow down the code measurably
+ only if MERGE_SIZES is not defined, which is a very nonstandard
+ - Added doc/README.environment, and implemented what it describes. This
+ allows a number of additional configuration options to be set through
+ the environment. It documents a few previously undocumented options.
+ - Integrated Eric Benson's leak testing improvements.
+ - Removed the option to throw away the beginning of each page (DISCARD_WORDS).
+ This became less and less useful as processors enforce stricter alignment.
+ And it hadn't been tested in ages, and was thus probably broken anyway.
+ - Added GC_finalizer_notifier. Fixed GC_finalize_on_demand. (The variable
+ actually wasn't being tested at the right points. The build-time flag
+ - Added Tom Tromey's S390 Linux patch.
+ - Added code to push GC_finalize_now in GC_push_finalizer_structures.
+ (Thanks to Matthew Flatt.)
+ - Added GC_push_gc_structures() to push all GC internal roots.
+ - Integrated some FreeBSD changes from Matthew Flatt.
+ - It looks like USRSTACK is not always correctly defined under Solaris.
+ Hacked gcconfig.h to attempt to work around the problem. The result
+ is not well tested. (Thanks again to Matthew Flatt for pointing this
+ out. The gross hack is mine. - HB)
+ - Added Ji-Yong Chung's win32 threads and C++ fixes.
+ - Arranged for hpux_test_and_clear.s to no longer be needed or built.
+ It was causing build problems with gas, and it's not clear this is
+ better than the pthreads alternative on this platform.
+ - Some MINGW32 fixes from Hubert Garavel.
+ - Added Initial Hitachi SH4 port from Kaz Kojima.
+ - Ported thread-local allocation and parallel mark code to HP/UX on PA_RISC.
+ - Made include/gc_mark.h more public and separated out the really private
+ pieces. This is probably still not quite sufficient for clients that
+ want to supply their own kind of type information. But it's a start.
+ This involved lots of identifier renaming to make it namespace clean.
+ - Added GC_dont_precollect for clients that need complete control over
+ the root set.
+ - GC_is_visible didn't do the right thing with gcj objects. (Not that
+ many people are likely to care, but ...)
+ - Don't redefine read with GC_USE_LD_WRAP.
+ - Initial port to LINUX/HP_PA. Incremental collection and threads are not
+ yet supported. (Incremental collection should work if you have the
+ right kernel. Threads may work with a sufficiently patched pthread
+ - Changed gcconfig.h to recognize __i386__ as an alternative to i386 in
+ many places. (Thanks to Benjamin Lerman.)
+ - Made win32_threads.c more tolerant of detaching a thread that it didn't
+ know about. (Thanks to Paul Nash.)
+ - Added Makefile.am and configure.in from gcc to the distribution, with
+ minimal changes. For the moment, those are just placeholders. In the
+ future, we're planning to switch to a GNU-style build environment for
+ Un*x-like systems, though the old Makefile will remain as a backup.
+ - Turned off STUBBORN_ALLOC by default, and added it back as a Makefile
+ - Redistributed some functions between malloc.c and mallocx.c, so that
+ simple statically linked apps no longer pull in mallocx.o.
+ - Changed large object allocation to clear the first and last few words
+ of each block before releassing the lock. Otherwise the marker could see
+ objects with nonsensical type descriptors.
+ - Fixed a couple of subtle problems that could result in not recognizing
+ interior pointers from the stack. (I believe these were introduced
+ in 6.0alpha6.)
+ - GC_debug_free_inner called GC_free, which tried to reacquire the
+ allocator lock, and hence deadlocked. (DBG_HDRS_ALL probably never worked
+ with threads?)
+ - Fixed several problems with back traces. Accidental references to a free
+ list could cause the free list pointer to be overwritten by a back pointer.
+ There seemed to be some problems with the encoding of root and finalizer
+ - Changed GC_debug_malloc_replacement and GC_debug_realloc_replacement
+ so that they compile under Irix. (Thanks to Dave Love.)
+ - Updated powerpc_macosx_mach_dep.s so that it works if the collector
+ is in a dynamic library. (Thanks to Andrew Begel.)
+ - Transformed README.debugging into debugging.html, updating and
+ expanding it in the process. Added gcdescr.html and tree.html
+ from the web site to the GC distribution.
+ - Fixed several problems related to PRINT_BLACK_LIST. This involved
+ restructuring some of the marker macros.
+ - Fixed some problems with the sizing of objects with debug information.
+ Finalization was broken KEEP_BACK_PTRS or PRINT_BLACK_LIST. Reduced the
+ object size with SHORT_DEBUG_HDRS by another word.
+ - The "Needed to allocate blacklisted ..." warning had inadvertently
+ been turned off by default, due to a buggy test in allchblk.c. Turned
+ it back on.
+ - Removed the marker macros to deal with 2 pointers in interleaved fashion.
+ They were messy and the performance improvement seemed minimal. We'll
+ leave such scheduling issues to the compiler.
+ - Changed Linux/PowerPC test to also check for __powerpc__ in response
+ to a discussion on the gcc mailing list.
+ - On Matthew Flatt's suggestion removed the "static" from the jmp_buf
+ declaration in GC_generic_push_regs. This was causing problems in
+ systems that register all of their own roots. It looks far more correct
+ to me without the "static" anyway.
+ - Fixed several problems with thread local allocation of pointerfree or
+ typed objects. The collector was reclaiming thread-local free lists, since
+ it wasn't following the link fields.
+ - There was apparently a long-standing race condition related to multithreaded
+ incremental collection. A collection could be started and a thread stopped
+ between the memory unprotect system call and the setting of the
+ corresponding dirt bit. I believe this did not affect Solaris or PCR, which
+ use a different dirty-bit implementation. Fixed this by installing
+ signal handlers with sigaction instead of signal, and disabling the thread
+ suspend signal while in the write-protect handler. (It is unclear
+ whether this scenario ever actually occurred. I found it while tracking
+ down the following:)
+ - Incremental collection did not cooperate correctly with the PARALLEL_MARK
+ implementation of GC_malloc_many or the local_malloc primitves. It still
+ doesn't work well, but it shouldn't lose memory anymore.
+ - Integrated some changes from the gcc source tree that I had previously
+ missed. (Thanks to Bryce McKinley for the reminder/diff.)
+ - Added Makefile.direct as a copy of the default Makefile, which would
+ normally be overwritten if configure is run.
+ - Changed the gc.tar target in Makefile.direct to embed the version number
+ in the gc directory name. This will affect future tar file distributions.
+ - Changed the Irix dynamic library finding code to no longer try to
+ eliminate writable text segments under Irix6.x, since that is probably no
+ longer necessary, and can apparently be unsafe on occasion. (Thanks to
+ Shiro Kawai for pointing this out.)
+ - GC_cleanup with GC_DEBUG enabled passed a real object base address to
+ GC_debug_register_finalizer_ignore_self, which expected a pointer past the
+ debug header. Call GC_register_finalizer_ignore_self instead, even with
+ debugging enabled. (Thanks to Jean-Daniel Fekete for catching this.)
+ - The collector didn't build with call chain saving enabled but NARGS=0.
+ (Thanks to Maarten Thibaut.)
+ - Fixed up the GNU-style build files enough so that they work in some
+ obvious cases.
+ - Added initial port to Digital Mars compiler for win32. (Thanks to Walter
+ - added README.macros.
+ - Made gc.mak a symbolic link to work around winzip's tendency to ignore
+ hard links.
+ - Simplified the setting of NEED_FIND_LIMIT in os_dep.c, possibly breaking
+ it on untested platforms.
+ - Integrated initial GNU HURD port. (Thanks to Chris Lingard and Igor
+ - A few more fixes for Digital Mars compiler.
+ - Fixed gcc version recognition. Renamed OPERATOR_NEW_ARRAY to
+ GC_OPERATOR_NEW_ARRAY. Changed GC_OPERATOR_NEW_ARRAY to be the default.
+ It can be overridden with -DGC_NO_OPERATOR_NEW_ARRAY. (Thanks to
+ Cesar Eduardo Barros.)
+ - Changed the byte size to free-list mapping in thread local allocation
+ so that size 0 allocations are handled correctly.
+ - Fixed Linux/MIPS stackbottom for new toolchain. (Thanks to Ryan Murray.)
+ - Changed finalization registration to invoke GC_oom_fn when it runs out
+ of memory.
+ - Removed lvalue cast in finalize.c. This caused some debug configurations
+ not to build with some non-gcc compilers.
+ - Two more bug fixes for KEEP_BACK_PTRS and DBG_HDRS_ALL.
+ - Fixed a stack clearing problem that resulted in SIGILL with a
+ misaligned stack pointer for multithreaded SPARC builds.
+ - Integrated another HURD patch (thanks to Igor Khavkine).
+ - There seem to be outstanding issues on Solaris/X86, possibly with
+ finding the data segment starting address. Information/patches would
+ ne appreciated.
+ - New_gc_alloc.h is apparently no longer compatible with the latest C++
+ standard library in gcc3.0. (This isn't technically a bug, since it only
+ claimed compatibility with the SGI STL. But we may need a new C++ STL
+ allocator interface.)
+ - Very large root set sizes (> 16 MB or so) could cause the collector
+ to abort with an unexpected mark stack overflow. (Thanks again to
+ Peter Chubb.) NOT YET FIXED. Workaround is to increase the initial
+ - The SGI version of the collector marks from mmapped pages, even
+ if they are not part of dynamic library static data areas. This
+ causes performance problems with some SGI libraries that use mmap
+ as a bitmap allocator. NOT YET FIXED. It may be possible to turn
+ off DYNAMIC_LOADING in the collector as a workaround. It may also
+ be possible to conditionally intercept mmap and use GC_exclude_static_roots.
+ The real fix is to walk rld data structures, which looks possible.
+ - Incremental collector should handle large objects better. Currently,
+ it looks like the whole object is treated as dirty if any part of it
+ - Cord/cordprnt.c doesn't build on a few platforms (notably PowerPC), since
+ we make some unwarranted assumptions about how varargs are handled. This
+ currently makes the cord-aware versions of printf unusable on some platforms.
+ Fixing this is unfortunately not trivial.