text: /*
   * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
   * Copyright (c) 1991-1995 by Xerox Corporation.  All rights reserved.
   * Copyright (c) 2000 by Hewlett-Packard Company.  All rights reserved.
   * Copyright (c) 2008-2022 Ivan Maidanski
   *
   * 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.
   *
   */
  
  #if defined(__MINGW32__) && !defined(__MINGW_EXCPT_DEFINE_PSDK) \
      && defined(__i386__) /* cannot use macros from gcconfig.h */
    /* Otherwise EXCEPTION_REGISTRATION type declaration from winnt.h     */
    /* might be used.  That declaration has "handler" callback with NTAPI */
    /* attribute.  The proper type (with "handler" field compatible with  */
    /* GC mark_ex_handler) is declared in excpt.h.  The given macro is    */
    /* defined before any system header include.                          */
  # define __MINGW_EXCPT_DEFINE_PSDK 1
  #endif
  
  #include "private/gc_pmark.h"
  
  #include <stdio.h>
  
  #if defined(MSWIN32) && defined(__GNUC__)
  # include <excpt.h>
  #endif
  
  /* Make arguments appear live to compiler.  Put here to minimize the    */
  /* risk of inlining.  Used to minimize junk left in registers.          */
  GC_ATTR_NOINLINE
  void GC_noop6(word arg1 GC_ATTR_UNUSED, word arg2 GC_ATTR_UNUSED,
                word arg3 GC_ATTR_UNUSED, word arg4 GC_ATTR_UNUSED,
                word arg5 GC_ATTR_UNUSED, word arg6 GC_ATTR_UNUSED)
  {
    /* Avoid GC_noop6 calls to be optimized away. */
  # if defined(AO_HAVE_compiler_barrier) && !defined(BASE_ATOMIC_OPS_EMULATED)
      AO_compiler_barrier(); /* to serve as a special side-effect */
  # else
      GC_noop1(0);
  # endif
  }
  
  #if defined(AO_HAVE_store) && defined(THREAD_SANITIZER)
    volatile AO_t GC_noop_sink;
  #else
    volatile word GC_noop_sink;
  #endif
  
  /* Make the argument appear live to compiler.  This is similar  */
  /* to GC_noop6(), but with a single argument.  Robust against   */
  /* whole program analysis.                                      */
  GC_API void GC_CALL GC_noop1(word x)
  {
  # if defined(AO_HAVE_store) && defined(THREAD_SANITIZER)
      AO_store(&GC_noop_sink, (AO_t)x);
  # else
      GC_noop_sink = x;
  # endif
  }
  
  /* Initialize GC_obj_kinds properly and standard free lists properly.   */
  /* This must be done statically since they may be accessed before       */
  /* GC_init is called.                                                   */
  /* It's done here, since we need to deal with mark descriptors.         */
  GC_INNER struct obj_kind GC_obj_kinds[MAXOBJKINDS] = {
  /* PTRFREE */ { &GC_aobjfreelist[0], 0 /* filled in dynamically */,
                  /* 0 | */ GC_DS_LENGTH, FALSE, FALSE
                  /*, */ OK_DISCLAIM_INITZ },
  /* NORMAL */  { &GC_objfreelist[0], 0,
                  /* 0 | */ GC_DS_LENGTH,
                                  /* adjusted in GC_init for EXTRA_BYTES  */
                  TRUE /* add length to descr */, TRUE
                  /*, */ OK_DISCLAIM_INITZ },
  /* UNCOLLECTABLE */
                { &GC_uobjfreelist[0], 0,
                  /* 0 | */ GC_DS_LENGTH, TRUE /* add length to descr */, TRUE
                  /*, */ OK_DISCLAIM_INITZ },
  # ifdef GC_ATOMIC_UNCOLLECTABLE
                { &GC_auobjfreelist[0], 0,
                  /* 0 | */ GC_DS_LENGTH, FALSE /* add length to descr */, FALSE
                  /*, */ OK_DISCLAIM_INITZ },
  # endif
  };
  
  # ifndef INITIAL_MARK_STACK_SIZE
  #   define INITIAL_MARK_STACK_SIZE (1*HBLKSIZE)
                  /* INITIAL_MARK_STACK_SIZE * sizeof(mse) should be a    */
                  /* multiple of HBLKSIZE.                                */
                  /* The incremental collector actually likes a larger    */
                  /* size, since it wants to push all marked dirty        */
                  /* objects before marking anything new.  Currently we   */
                  /* let it grow dynamically.                             */
  # endif
  
  #if !defined(GC_DISABLE_INCREMENTAL)
    STATIC word GC_n_rescuing_pages = 0;
                                  /* Number of dirty pages we marked from */
                                  /* excludes ptrfree pages, etc.         */
                                  /* Used for logging only.               */
  #endif
  
  #ifdef PARALLEL_MARK
    GC_INNER GC_bool GC_parallel_mark_disabled = FALSE;
  #endif
  
  /* Is a collection in progress?  Note that this can return true in the  */
  /* non-incremental case, if a collection has been abandoned and the     */
  /* mark state is now MS_INVALID.                                        */
  GC_INNER GC_bool GC_collection_in_progress(void)
  {
      return GC_mark_state != MS_NONE;
  }
  
  /* Clear all mark bits in the header.   */
  GC_INNER void GC_clear_hdr_marks(hdr *hhdr)
  {
    size_t last_bit;
  
  # ifdef AO_HAVE_load
      /* Atomic access is used to avoid racing with GC_realloc.   */
      last_bit = FINAL_MARK_BIT((size_t)AO_load((volatile AO_t *)&hhdr->hb_sz));
  # else
      /* No race as GC_realloc holds the lock while updating hb_sz.   */
      last_bit = FINAL_MARK_BIT((size_t)hhdr->hb_sz);
  # endif
  
      BZERO(hhdr -> hb_marks, sizeof(hhdr->hb_marks));
      set_mark_bit_from_hdr(hhdr, last_bit);
      hhdr -> hb_n_marks = 0;
  }
  
  /* Set all mark bits in the header.  Used for uncollectible blocks. */
  GC_INNER void GC_set_hdr_marks(hdr *hhdr)
  {
      unsigned i;
      size_t sz = (size_t)hhdr->hb_sz;
      unsigned n_marks = (unsigned)FINAL_MARK_BIT(sz);
  
  #   ifdef USE_MARK_BYTES
        for (i = 0; i <= n_marks; i += (unsigned)MARK_BIT_OFFSET(sz)) {
          hhdr -> hb_marks[i] = 1;
        }
  #   else
        /* Note that all bits are set even in case of MARK_BIT_PER_GRANULE,   */
        /* instead of setting every n-th bit where n is MARK_BIT_OFFSET(sz).  */
        /* This is done for a performance reason.                             */
        for (i = 0; i < divWORDSZ(n_marks); ++i) {
          hhdr -> hb_marks[i] = GC_WORD_MAX;
        }
        /* Set the remaining bits near the end (plus one bit past the end).   */
        hhdr -> hb_marks[i] = ((((word)1 << modWORDSZ(n_marks)) - 1) << 1) | 1;
  #   endif
  #   ifdef MARK_BIT_PER_OBJ
        hhdr -> hb_n_marks = n_marks;
  #   else
        hhdr -> hb_n_marks = HBLK_OBJS(sz);
  #   endif
  }
  
  /* Clear all mark bits associated with block h. */
  static void clear_marks_for_block(struct hblk *h, word dummy GC_ATTR_UNUSED)
  {
      hdr * hhdr = HDR(h);
  
      if (IS_UNCOLLECTABLE(hhdr -> hb_obj_kind)) return;
          /* Mark bit for these is cleared only once the object is        */
          /* explicitly deallocated.  This either frees the block, or     */
          /* the bit is cleared once the object is on the free list.      */
      GC_clear_hdr_marks(hhdr);
  }
  
  /* Slow but general routines for setting/clearing/asking about mark bits. */
  GC_API void GC_CALL GC_set_mark_bit(const void *p)
  {
      struct hblk *h = HBLKPTR(p);
      hdr * hhdr = HDR(h);
      word bit_no = MARK_BIT_NO((ptr_t)p - (ptr_t)h, hhdr -> hb_sz);
  
      if (!mark_bit_from_hdr(hhdr, bit_no)) {
        set_mark_bit_from_hdr(hhdr, bit_no);
        ++hhdr -> hb_n_marks;
      }
  }
  
  GC_API void GC_CALL GC_clear_mark_bit(const void *p)
  {
      struct hblk *h = HBLKPTR(p);
      hdr * hhdr = HDR(h);
      word bit_no = MARK_BIT_NO((ptr_t)p - (ptr_t)h, hhdr -> hb_sz);
  
      if (mark_bit_from_hdr(hhdr, bit_no)) {
        size_t n_marks = hhdr -> hb_n_marks;
  
        GC_ASSERT(n_marks != 0);
        clear_mark_bit_from_hdr(hhdr, bit_no);
        n_marks--;
  #     ifdef PARALLEL_MARK
          if (n_marks != 0 || !GC_parallel)
            hhdr -> hb_n_marks = n_marks;
          /* Don't decrement to zero.  The counts are approximate due to  */
          /* concurrency issues, but we need to ensure that a count of    */
          /* zero implies an empty block.                                 */
  #     else
            hhdr -> hb_n_marks = n_marks;
  #     endif
      }
  }
  
  GC_API int GC_CALL GC_is_marked(const void *p)
  {
      struct hblk *h = HBLKPTR(p);
      hdr * hhdr = HDR(h);
      word bit_no = MARK_BIT_NO((ptr_t)p - (ptr_t)h, hhdr -> hb_sz);
  
      return (int)mark_bit_from_hdr(hhdr, bit_no); /* 0 or 1 */
  }
  
  /* Clear mark bits in all allocated heap blocks.  This invalidates the  */
  /* marker invariant, and sets GC_mark_state to reflect this.  (This     */
  /* implicitly starts marking to reestablish the invariant.)             */
  GC_INNER void GC_clear_marks(void)
  {
      GC_ASSERT(GC_is_initialized); /* needed for GC_push_roots */
      GC_apply_to_all_blocks(clear_marks_for_block, (word)0);
      GC_objects_are_marked = FALSE;
      GC_mark_state = MS_INVALID;
      GC_scan_ptr = NULL;
  }
  
  /* Initiate a garbage collection.  Initiates a full collection if the   */
  /* mark state is invalid.                                               */
  GC_INNER void GC_initiate_gc(void)
  {
      GC_ASSERT(I_HOLD_LOCK());
      GC_ASSERT(GC_is_initialized);
  #   ifndef GC_DISABLE_INCREMENTAL
          if (GC_incremental) {
  #         ifdef CHECKSUMS
              GC_read_dirty(FALSE);
              GC_check_dirty();
  #         else
              GC_read_dirty(GC_mark_state == MS_INVALID);
  #         endif
          }
          GC_n_rescuing_pages = 0;
  #   endif
      if (GC_mark_state == MS_NONE) {
          GC_mark_state = MS_PUSH_RESCUERS;
      } else {
          GC_ASSERT(GC_mark_state == MS_INVALID);
          /* This is really a full collection, and mark bits are invalid. */
      }
      GC_scan_ptr = NULL;
  }
  
  #ifdef PARALLEL_MARK
      STATIC void GC_do_parallel_mark(void); /* Initiate parallel marking. */
  #endif /* PARALLEL_MARK */
  
  #ifdef GC_DISABLE_INCREMENTAL
  # define GC_push_next_marked_dirty(h) GC_push_next_marked(h)
  #else
    STATIC struct hblk * GC_push_next_marked_dirty(struct hblk *h);
                  /* Invoke GC_push_marked on next dirty block above h.   */
                  /* Return a pointer just past the end of this block.    */
  #endif /* !GC_DISABLE_INCREMENTAL */
  STATIC struct hblk * GC_push_next_marked(struct hblk *h);
                  /* Ditto, but also mark from clean pages.       */
  STATIC struct hblk * GC_push_next_marked_uncollectable(struct hblk *h);
                  /* Ditto, but mark only from uncollectible pages.       */
  
  static void alloc_mark_stack(size_t);
  
  static void push_roots_and_advance(GC_bool push_all, ptr_t cold_gc_frame)
  {
    if (GC_scan_ptr != NULL) return; /* not ready to push */
  
    GC_push_roots(push_all, cold_gc_frame);
    GC_objects_are_marked = TRUE;
    if (GC_mark_state != MS_INVALID)
      GC_mark_state = MS_ROOTS_PUSHED;
  }
  
  /* Perform a small amount of marking.                   */
  /* We try to touch roughly a page of memory.            */
  /* Return TRUE if we just finished a mark phase.        */
  /* Cold_gc_frame is an address inside a GC frame that   */
  /* remains valid until all marking is complete.         */
  /* A zero value indicates that it's OK to miss some     */
  /* register values.  In the case of an incremental      */
  /* collection, the world may be running.                */
  #ifdef WRAP_MARK_SOME
    /* For win32, this is called after we establish a structured  */
    /* exception handler, in case Windows unmaps one of our root  */
    /* segments.                                                  */
    STATIC GC_bool GC_mark_some_inner(ptr_t cold_gc_frame)
  #else
    GC_INNER GC_bool GC_mark_some(ptr_t cold_gc_frame)
  #endif
  {
      GC_ASSERT(I_HOLD_LOCK());
      switch (GC_mark_state) {
          case MS_NONE:
              return TRUE;
  
          case MS_PUSH_RESCUERS:
              if ((word)GC_mark_stack_top
                  >= (word)(GC_mark_stack_limit - INITIAL_MARK_STACK_SIZE/2)) {
                  /* Go ahead and mark, even though that might cause us to */
                  /* see more marked dirty objects later on.  Avoid this   */
                  /* in the future.                                        */
                  GC_mark_stack_too_small = TRUE;
                  MARK_FROM_MARK_STACK();
              } else {
                  GC_scan_ptr = GC_push_next_marked_dirty(GC_scan_ptr);
  #               ifndef GC_DISABLE_INCREMENTAL
                    if (NULL == GC_scan_ptr) {
                      GC_COND_LOG_PRINTF("Marked from %lu dirty pages\n",
                                         (unsigned long)GC_n_rescuing_pages);
                    }
  #               endif
                  push_roots_and_advance(FALSE, cold_gc_frame);
              }
              GC_ASSERT(GC_mark_state == MS_PUSH_RESCUERS
                        || GC_mark_state == MS_ROOTS_PUSHED
                        || GC_mark_state == MS_INVALID);
              break;
  
          case MS_PUSH_UNCOLLECTABLE:
              if ((word)GC_mark_stack_top
                  >= (word)(GC_mark_stack + GC_mark_stack_size/4)) {
  #               ifdef PARALLEL_MARK
                    /* Avoid this, since we don't parallelize the marker  */
                    /* here.                                              */
                    if (GC_parallel) GC_mark_stack_too_small = TRUE;
  #               endif
                  MARK_FROM_MARK_STACK();
              } else {
                  GC_scan_ptr = GC_push_next_marked_uncollectable(GC_scan_ptr);
                  push_roots_and_advance(TRUE, cold_gc_frame);
              }
              GC_ASSERT(GC_mark_state == MS_PUSH_UNCOLLECTABLE
                        || GC_mark_state == MS_ROOTS_PUSHED
                        || GC_mark_state == MS_INVALID);
              break;
  
          case MS_ROOTS_PUSHED:
  #           ifdef PARALLEL_MARK
                /* Eventually, incremental marking should run             */
                /* asynchronously in multiple threads, without grabbing   */
                /* the allocation lock.                                   */
                /* For now, parallel marker is disabled if there is       */
                /* a chance that marking could be interrupted by          */
                /* a client-supplied time limit or custom stop function.  */
                  if (GC_parallel && !GC_parallel_mark_disabled) {
                    GC_do_parallel_mark();
                    GC_ASSERT((word)GC_mark_stack_top < (word)GC_first_nonempty);
                    GC_mark_stack_top = GC_mark_stack - 1;
                    if (GC_mark_stack_too_small) {
                      alloc_mark_stack(2*GC_mark_stack_size);
                    }
                    if (GC_mark_state == MS_ROOTS_PUSHED) {
                      GC_mark_state = MS_NONE;
                      return TRUE;
                    }
                    GC_ASSERT(GC_mark_state == MS_INVALID);
                    break;
                  }
  #           endif
              if ((word)GC_mark_stack_top >= (word)GC_mark_stack) {
                  MARK_FROM_MARK_STACK();
              } else {
                  GC_mark_state = MS_NONE;
                  if (GC_mark_stack_too_small) {
                      alloc_mark_stack(2*GC_mark_stack_size);
                  }
                  return TRUE;
              }
              GC_ASSERT(GC_mark_state == MS_ROOTS_PUSHED
                        || GC_mark_state == MS_INVALID);
              break;
  
          case MS_INVALID:
          case MS_PARTIALLY_INVALID:
              if (!GC_objects_are_marked) {
                  GC_mark_state = MS_PUSH_UNCOLLECTABLE;
                  break;
              }
              if ((word)GC_mark_stack_top >= (word)GC_mark_stack) {
                  MARK_FROM_MARK_STACK();
                  GC_ASSERT(GC_mark_state == MS_PARTIALLY_INVALID
                            || GC_mark_state == MS_INVALID);
                  break;
              }
              if (NULL == GC_scan_ptr && GC_mark_state == MS_INVALID) {
                  /* About to start a heap scan for marked objects. */
                  /* Mark stack is empty.  OK to reallocate.        */
                  if (GC_mark_stack_too_small) {
                      alloc_mark_stack(2*GC_mark_stack_size);
                  }
                  GC_mark_state = MS_PARTIALLY_INVALID;
              }
              GC_scan_ptr = GC_push_next_marked(GC_scan_ptr);
              if (GC_mark_state == MS_PARTIALLY_INVALID)
                  push_roots_and_advance(TRUE, cold_gc_frame);
              GC_ASSERT(GC_mark_state == MS_ROOTS_PUSHED
                        || GC_mark_state == MS_PARTIALLY_INVALID
                        || GC_mark_state == MS_INVALID);
              break;
  
          default:
              ABORT("GC_mark_some: bad state");
      }
      return FALSE;
  }
  
  #ifdef WRAP_MARK_SOME
  
  # if (defined(MSWIN32) || defined(MSWINCE)) && defined(__GNUC__)
  
      typedef struct {
        EXCEPTION_REGISTRATION ex_reg;
        void *alt_path;
      } ext_ex_regn;
  
      static EXCEPTION_DISPOSITION mark_ex_handler(
          struct _EXCEPTION_RECORD *ex_rec,
          void *est_frame,
          struct _CONTEXT *context,
          void *disp_ctxt GC_ATTR_UNUSED)
      {
          if (ex_rec->ExceptionCode == STATUS_ACCESS_VIOLATION) {
            ext_ex_regn *xer = (ext_ex_regn *)est_frame;
  
            /* Unwind from the inner function assuming the standard */
            /* function prologue.                                   */
            /* Assumes code has not been compiled with              */
            /* -fomit-frame-pointer.                                */
            context->Esp = context->Ebp;
            context->Ebp = *((DWORD *)context->Esp);
            context->Esp = context->Esp - 8;
  
            /* Resume execution at the "real" handler within the    */
            /* wrapper function.                                    */
            context->Eip = (DWORD )(xer->alt_path);
  
            return ExceptionContinueExecution;
  
          } else {
              return ExceptionContinueSearch;
          }
      }
  # endif /* __GNUC__ && MSWIN32 */
  
    GC_INNER GC_bool GC_mark_some(ptr_t cold_gc_frame)
    {
      GC_bool ret_val;
  
  #   if defined(MSWIN32) || defined(MSWINCE)
  #     ifndef __GNUC__
          /* Windows 98 appears to asynchronously create and remove   */
          /* writable memory mappings, for reasons we haven't yet     */
          /* understood.  Since we look for writable regions to       */
          /* determine the root set, we may try to mark from an       */
          /* address range that disappeared since we started the      */
          /* collection.  Thus we have to recover from faults here.   */
          /* This code does not appear to be necessary for Windows    */
          /* 95/NT/2000+. Note that this code should never generate   */
          /* an incremental GC write fault.                           */
          /* This code seems to be necessary for WinCE (at least in   */
          /* the case we'd decide to add MEM_PRIVATE sections to      */
          /* data roots in GC_register_dynamic_libraries()).          */
          /* It's conceivable that this is the same issue with        */
          /* terminating threads that we see with Linux and           */
          /* USE_PROC_FOR_LIBRARIES.                                  */
  
          __try {
            ret_val = GC_mark_some_inner(cold_gc_frame);
          } __except (GetExceptionCode() == EXCEPTION_ACCESS_VIOLATION ?
                  EXCEPTION_EXECUTE_HANDLER : EXCEPTION_CONTINUE_SEARCH) {
            goto handle_ex;
          }
  #       if defined(GC_WIN32_THREADS) && !defined(GC_PTHREADS)
            /* With DllMain-based thread tracking, a thread may have  */
            /* started while we were marking.  This is logically      */
            /* equivalent to the exception case; our results are      */
            /* invalid and we have to start over.  This cannot be     */
            /* prevented since we can't block in DllMain.             */
            if (GC_started_thread_while_stopped())
              goto handle_thr_start;
  #       endif
        rm_handler:
          return ret_val;
  
  #     else /* __GNUC__ */
  
          /* Manually install an exception handler since GCC does     */
          /* not yet support Structured Exception Handling (SEH) on   */
          /* Win32.                                                   */
          ext_ex_regn er;
  
  #       if GC_GNUC_PREREQ(4, 7) || GC_CLANG_PREREQ(3, 3)
  #         pragma GCC diagnostic push
            /* Suppress "taking the address of label is non-standard" warning. */
  #         if defined(__clang__) || GC_GNUC_PREREQ(6, 0)
  #           pragma GCC diagnostic ignored "-Wpedantic"
  #         else
              /* GCC before ~4.8 does not accept "-Wpedantic" quietly.    */
  #           pragma GCC diagnostic ignored "-pedantic"
  #         endif
            er.alt_path = &&handle_ex;
  #         pragma GCC diagnostic pop
  #       elif !defined(CPPCHECK) /* pragma diagnostic is not supported */
            er.alt_path = &&handle_ex;
  #       endif
          er.ex_reg.handler = mark_ex_handler;
          __asm__ __volatile__ ("movl %%fs:0, %0" : "=r" (er.ex_reg.prev));
          __asm__ __volatile__ ("movl %0, %%fs:0" : : "r" (&er));
          ret_val = GC_mark_some_inner(cold_gc_frame);
          /* Prevent GCC from considering the following code unreachable  */
          /* and thus eliminating it.                                     */
          if (er.alt_path == 0)
            goto handle_ex;
  #       if defined(GC_WIN32_THREADS) && !defined(GC_PTHREADS)
            if (GC_started_thread_while_stopped())
              goto handle_thr_start;
  #       endif
        rm_handler:
          /* Uninstall the exception handler.       */
          __asm__ __volatile__ ("mov %0, %%fs:0" : : "r" (er.ex_reg.prev));
          return ret_val;
  #     endif /* __GNUC__ */
  
  #   else /* !MSWIN32 */
        /* Here we are handling the case in which /proc is used for root  */
        /* finding, and we have threads.  We may find a stack for a       */
        /* thread that is in the process of exiting, and disappears       */
        /* while we are marking it.  This seems extremely difficult to    */
        /* avoid otherwise.                                               */
  #     ifndef DEFAULT_VDB
          if (GC_auto_incremental) {
            static GC_bool is_warned = FALSE;
  
            if (!is_warned) {
              is_warned = TRUE;
              WARN("Incremental GC incompatible with /proc roots\n", 0);
            }
            /* I'm not sure if this could still work ...  */
          }
  #     endif
        GC_setup_temporary_fault_handler();
        if(SETJMP(GC_jmp_buf) != 0) goto handle_ex;
        ret_val = GC_mark_some_inner(cold_gc_frame);
      rm_handler:
        GC_reset_fault_handler();
        return ret_val;
  #   endif /* !MSWIN32 */
  
  handle_ex:
      /* Exception handler starts here for all cases. */
        {
          static word warned_gc_no;
  
          /* Warn about it at most once per collection. */
          if (warned_gc_no != GC_gc_no) {
            WARN("Caught ACCESS_VIOLATION in marker;"
                 " memory mapping disappeared\n", 0);
            warned_gc_no = GC_gc_no;
          }
        }
  #   if (defined(MSWIN32) || defined(MSWINCE)) && defined(GC_WIN32_THREADS) \
         && !defined(GC_PTHREADS)
        handle_thr_start:
  #   endif
        /* We have bad roots on the stack.  Discard mark stack.   */
        /* Rescan from marked objects.  Redetermine roots.        */
  #     ifdef REGISTER_LIBRARIES_EARLY
          START_WORLD();
          GC_cond_register_dynamic_libraries();
          STOP_WORLD();
  #     endif
        GC_invalidate_mark_state();
        GC_scan_ptr = NULL;
        ret_val = FALSE;
        goto rm_handler;  /* Back to platform-specific code. */
    }
  #endif /* WRAP_MARK_SOME */
  
  GC_INNER void GC_invalidate_mark_state(void)
  {
      GC_mark_state = MS_INVALID;
      GC_mark_stack_top = GC_mark_stack-1;
  }
  
  GC_INNER mse * GC_signal_mark_stack_overflow(mse *msp)
  {
      GC_mark_state = MS_INVALID;
  #   ifdef PARALLEL_MARK
        /* We are using a local_mark_stack in parallel mode, so   */
        /* do not signal the global mark stack to be resized.     */
        /* That will be done if required in GC_return_mark_stack. */
        if (!GC_parallel)
          GC_mark_stack_too_small = TRUE;
  #   else
        GC_mark_stack_too_small = TRUE;
  #   endif
      GC_COND_LOG_PRINTF("Mark stack overflow; current size: %lu entries\n",
                         (unsigned long)GC_mark_stack_size);
      return msp - GC_MARK_STACK_DISCARDS;
  }
  
  /*
   * Mark objects pointed to by the regions described by
   * mark stack entries between mark_stack and mark_stack_top,
   * inclusive.  Assumes the upper limit of a mark stack entry
   * is never 0.  A mark stack entry never has size 0.
   * We try to traverse on the order of a hblk of memory before we return.
   * Caller is responsible for calling this until the mark stack is empty.
   * Note that this is the most performance critical routine in the
   * collector.  Hence it contains all sorts of ugly hacks to speed
   * things up.  In particular, we avoid procedure calls on the common
   * path, we take advantage of peculiarities of the mark descriptor
   * encoding, we optionally maintain a cache for the block address to
   * header mapping, we prefetch when an object is "grayed", etc.
   */
  GC_ATTR_NO_SANITIZE_ADDR GC_ATTR_NO_SANITIZE_MEMORY GC_ATTR_NO_SANITIZE_THREAD
  GC_INNER mse * GC_mark_from(mse *mark_stack_top, mse *mark_stack,
                              mse *mark_stack_limit)
  {
    signed_word credit = HBLKSIZE;  /* Remaining credit for marking work. */
    ptr_t current_p;      /* Pointer to current candidate ptr.            */
    word current;         /* Candidate pointer.                           */
    ptr_t limit = 0;      /* (Incl) limit of current candidate range.     */
    word descr;
    ptr_t greatest_ha = (ptr_t)GC_greatest_plausible_heap_addr;
    ptr_t least_ha = (ptr_t)GC_least_plausible_heap_addr;
    DECLARE_HDR_CACHE;
  
  # define SPLIT_RANGE_WORDS 128  /* Must be power of 2.          */
  
    GC_objects_are_marked = TRUE;
    INIT_HDR_CACHE;
  # ifdef OS2 /* Use untweaked version to circumvent compiler problem.    */
      while ((word)mark_stack_top >= (word)mark_stack && credit >= 0)
  # else
      while (((((word)mark_stack_top - (word)mark_stack) | (word)credit)
              & SIGNB) == 0)
  # endif
    {
      current_p = mark_stack_top -> mse_start;
      descr = mark_stack_top -> mse_descr.w;
    retry:
      /* current_p and descr describe the current object.                 */
      /* (*mark_stack_top) is vacant.                                     */
      /* The following is 0 only for small objects described by a simple  */
      /* length descriptor.  For many applications this is the common     */
      /* case, so we try to detect it quickly.                            */
      if (descr & ((~(WORDS_TO_BYTES(SPLIT_RANGE_WORDS) - 1)) | GC_DS_TAGS)) {
        word tag = descr & GC_DS_TAGS;
  
        GC_STATIC_ASSERT(GC_DS_TAGS == 0x3);
        switch(tag) {
          case GC_DS_LENGTH:
            /* Large length.                                              */
            /* Process part of the range to avoid pushing too much on the */
            /* stack.                                                     */
            GC_ASSERT(descr < (word)GC_greatest_plausible_heap_addr
                              - (word)GC_least_plausible_heap_addr
                  || (word)(current_p + descr)
                              <= (word)GC_least_plausible_heap_addr
                  || (word)current_p >= (word)GC_greatest_plausible_heap_addr);
  #         ifdef PARALLEL_MARK
  #           define SHARE_BYTES 2048
              if (descr > SHARE_BYTES && GC_parallel
                  && (word)mark_stack_top < (word)(mark_stack_limit - 1)) {
                word new_size = (descr/2) & ~(word)(sizeof(word)-1);
  
                mark_stack_top -> mse_start = current_p;
                mark_stack_top -> mse_descr.w = new_size + sizeof(word);
                                          /* Makes sure we handle         */
                                          /* misaligned pointers.         */
                mark_stack_top++;
  #             ifdef ENABLE_TRACE
                  if ((word)GC_trace_addr >= (word)current_p
                      && (word)GC_trace_addr < (word)(current_p + descr)) {
                    GC_log_printf("GC #%lu: large section; start %p, len %lu,"
                                  " splitting (parallel) at %p\n",
                                  (unsigned long)GC_gc_no, (void *)current_p,
                                  (unsigned long)descr,
                                  (void *)(current_p + new_size));
                  }
  #             endif
                current_p += new_size;
                descr -= new_size;
                goto retry;
              }
  #         endif /* PARALLEL_MARK */
            mark_stack_top -> mse_start =
                  limit = current_p + WORDS_TO_BYTES(SPLIT_RANGE_WORDS-1);
            mark_stack_top -> mse_descr.w =
                                  descr - WORDS_TO_BYTES(SPLIT_RANGE_WORDS-1);
  #         ifdef ENABLE_TRACE
              if ((word)GC_trace_addr >= (word)current_p
                  && (word)GC_trace_addr < (word)(current_p + descr)) {
                GC_log_printf("GC #%lu: large section; start %p, len %lu,"
                              " splitting at %p\n",
                              (unsigned long)GC_gc_no, (void *)current_p,
                              (unsigned long)descr, (void *)limit);
              }
  #         endif
            /* Make sure that pointers overlapping the two ranges are     */
            /* considered.                                                */
            limit += sizeof(word) - ALIGNMENT;
            break;
          case GC_DS_BITMAP:
            mark_stack_top--;
  #         ifdef ENABLE_TRACE
              if ((word)GC_trace_addr >= (word)current_p
                  && (word)GC_trace_addr < (word)(current_p
                                                  + WORDS_TO_BYTES(WORDSZ-2))) {
                GC_log_printf("GC #%lu: tracing from %p bitmap descr %lu\n",
                              (unsigned long)GC_gc_no, (void *)current_p,
                              (unsigned long)descr);
              }
  #         endif /* ENABLE_TRACE */
            descr &= ~GC_DS_TAGS;
            credit -= WORDS_TO_BYTES(WORDSZ/2); /* guess */
            for (; descr != 0; descr <<= 1, current_p += sizeof(word)) {
              if ((descr & SIGNB) == 0) continue;
              LOAD_WORD_OR_CONTINUE(current, current_p);
              FIXUP_POINTER(current);
              if (current >= (word)least_ha && current < (word)greatest_ha) {
                  PREFETCH((ptr_t)current);
  #               ifdef ENABLE_TRACE
                    if (GC_trace_addr == current_p) {
                      GC_log_printf("GC #%lu: considering(3) %p -> %p\n",
                                    (unsigned long)GC_gc_no, (void *)current_p,
                                    (void *)current);
                    }
  #               endif /* ENABLE_TRACE */
                  PUSH_CONTENTS((ptr_t)current, mark_stack_top,
                                mark_stack_limit, current_p);
              }
            }
            continue;
          case GC_DS_PROC:
            mark_stack_top--;
  #         ifdef ENABLE_TRACE
              if ((word)GC_trace_addr >= (word)current_p
                  && GC_base(current_p) != 0
                  && GC_base(current_p) == GC_base(GC_trace_addr)) {
                GC_log_printf("GC #%lu: tracing from %p, proc descr %lu\n",
                              (unsigned long)GC_gc_no, (void *)current_p,
                              (unsigned long)descr);
              }
  #         endif /* ENABLE_TRACE */
            credit -= GC_PROC_BYTES;
            mark_stack_top = (*PROC(descr))((word *)current_p, mark_stack_top,
                                            mark_stack_limit, ENV(descr));
            continue;
          case GC_DS_PER_OBJECT:
            if ((signed_word)descr >= 0) {
              /* Descriptor is in the object.     */
              descr = *(word *)(current_p + descr - GC_DS_PER_OBJECT);
            } else {
              /* Descriptor is in type descriptor pointed to by first     */
              /* word in object.                                          */
              ptr_t type_descr = *(ptr_t *)current_p;
              /* type_descr is either a valid pointer to the descriptor   */
              /* structure, or this object was on a free list.            */
              /* If it was anything but the last object on the free list, */
              /* we will misinterpret the next object on the free list as */
              /* the type descriptor, and get a 0 GC descriptor, which    */
              /* is ideal.  Unfortunately, we need to check for the last  */
              /* object case explicitly.                                  */
              if (EXPECT(0 == type_descr, FALSE)) {
                  mark_stack_top--;
                  continue;
              }
              descr = *(word *)(type_descr
                                - ((signed_word)descr + (GC_INDIR_PER_OBJ_BIAS
                                                         - GC_DS_PER_OBJECT)));
            }
            if (0 == descr) {
                /* Can happen either because we generated a 0 descriptor  */
                /* or we saw a pointer to a free object.                  */
                mark_stack_top--;
                continue;
            }
            goto retry;
        }
      } else {
        /* Small object with length descriptor.   */
        mark_stack_top--;
  #     ifndef SMALL_CONFIG
          if (descr < sizeof(word))
            continue;
  #     endif
  #     ifdef ENABLE_TRACE
          if ((word)GC_trace_addr >= (word)current_p
              && (word)GC_trace_addr < (word)(current_p + descr)) {
            GC_log_printf("GC #%lu: small object; start %p, len %lu\n",
                          (unsigned long)GC_gc_no, (void *)current_p,
                          (unsigned long)descr);
          }
  #     endif
        limit = current_p + (word)descr;
      }
      /* The simple case in which we're scanning a range. */
      GC_ASSERT(!((word)current_p & (ALIGNMENT-1)));
      credit -= limit - current_p;
      limit -= sizeof(word);
      {
  #     define PREF_DIST 4
  
  #     if !defined(SMALL_CONFIG) && !defined(USE_PTR_HWTAG)
          word deferred;
  
          /* Try to prefetch the next pointer to be examined ASAP.        */
          /* Empirically, this also seems to help slightly without        */
          /* prefetches, at least on linux/X86.  Presumably this loop     */
          /* ends up with less register pressure, and gcc thus ends up    */
          /* generating slightly better code.  Overall gcc code quality   */
          /* for this loop is still not great.                            */
          for(;;) {
            PREFETCH(limit - PREF_DIST*CACHE_LINE_SIZE);
            GC_ASSERT((word)limit >= (word)current_p);
            deferred = *(word *)limit;
            FIXUP_POINTER(deferred);
            limit -= ALIGNMENT;
            if (deferred >= (word)least_ha && deferred < (word)greatest_ha) {
              PREFETCH((ptr_t)deferred);
              break;
            }
            if ((word)current_p > (word)limit) goto next_object;
            /* Unroll once, so we don't do too many of the prefetches     */
            /* based on limit.                                            */
            deferred = *(word *)limit;
            FIXUP_POINTER(deferred);
            limit -= ALIGNMENT;
            if (deferred >= (word)least_ha && deferred < (word)greatest_ha) {
              PREFETCH((ptr_t)deferred);
              break;
            }
            if ((word)current_p > (word)limit) goto next_object;
          }
  #     endif
  
        for (; (word)current_p <= (word)limit; current_p += ALIGNMENT) {
          /* Empirically, unrolling this loop doesn't help a lot. */
          /* Since PUSH_CONTENTS expands to a lot of code,        */
          /* we don't.                                            */
          LOAD_WORD_OR_CONTINUE(current, current_p);
          FIXUP_POINTER(current);
          PREFETCH(current_p + PREF_DIST*CACHE_LINE_SIZE);
          if (current >= (word)least_ha && current < (word)greatest_ha) {
            /* Prefetch the contents of the object we just pushed.  It's  */
            /* likely we will need them soon.                             */
            PREFETCH((ptr_t)current);
  #         ifdef ENABLE_TRACE
              if (GC_trace_addr == current_p) {
                GC_log_printf("GC #%lu: considering(1) %p -> %p\n",
                              (unsigned long)GC_gc_no, (void *)current_p,
                              (void *)current);
              }
  #         endif /* ENABLE_TRACE */
            PUSH_CONTENTS((ptr_t)current, mark_stack_top,
                          mark_stack_limit, current_p);
          }
        }
  
  #     if !defined(SMALL_CONFIG) && !defined(USE_PTR_HWTAG)
          /* We still need to mark the entry we previously prefetched.    */
          /* We already know that it passes the preliminary pointer       */
          /* validity test.                                               */
  #       ifdef ENABLE_TRACE
              if (GC_trace_addr == current_p) {
                GC_log_printf("GC #%lu: considering(2) %p -> %p\n",
                              (unsigned long)GC_gc_no, (void *)current_p,
                              (void *)deferred);
              }
  #       endif /* ENABLE_TRACE */
          PUSH_CONTENTS((ptr_t)deferred, mark_stack_top,
                        mark_stack_limit, current_p);
          next_object:;
  #     endif
      }
    }
    return mark_stack_top;
  }
  
  #ifdef PARALLEL_MARK
  
  STATIC GC_bool GC_help_wanted = FALSE;  /* Protected by mark lock.      */
  STATIC unsigned GC_helper_count = 0;    /* Number of running helpers.   */
                                          /* Protected by mark lock.      */
  STATIC unsigned GC_active_count = 0;    /* Number of active helpers.    */
                                          /* Protected by mark lock.      */
                                          /* May increase and decrease    */
                                          /* within each mark cycle.  But */
                                          /* once it returns to 0, it     */
                                          /* stays zero for the cycle.    */
  
  GC_INNER word GC_mark_no = 0;
  
  #ifdef LINT2
  # define LOCAL_MARK_STACK_SIZE (HBLKSIZE / 8)
  #else
  # define LOCAL_MARK_STACK_SIZE HBLKSIZE
          /* Under normal circumstances, this is big enough to guarantee  */
          /* we don't overflow half of it in a single call to             */
          /* GC_mark_from.                                                */
  #endif
  
  /* Wait all markers to finish initialization (i.e. store        */
  /* marker_[b]sp, marker_mach_threads, GC_marker_Id).            */
  GC_INNER void GC_wait_for_markers_init(void)
  {
    signed_word count;
  
    GC_ASSERT(I_HOLD_LOCK());
    if (GC_markers_m1 == 0)
      return;
  
    /* Allocate the local mark stack for the thread that holds GC lock.   */
  # ifndef CAN_HANDLE_FORK
      GC_ASSERT(NULL == GC_main_local_mark_stack);
  # else
      if (NULL == GC_main_local_mark_stack)
  # endif
    {
      size_t bytes_to_get =
                  ROUNDUP_PAGESIZE_IF_MMAP(LOCAL_MARK_STACK_SIZE * sizeof(mse));
  
      GC_ASSERT(GC_page_size != 0);
      GC_main_local_mark_stack = (mse *)GET_MEM(bytes_to_get);
      if (NULL == GC_main_local_mark_stack)
        ABORT("Insufficient memory for main local_mark_stack");
      GC_add_to_our_memory((ptr_t)GC_main_local_mark_stack, bytes_to_get);
    }
  
    /* Reuse marker lock and builders count to synchronize        */
    /* marker threads startup.                                    */
    GC_acquire_mark_lock();
    GC_fl_builder_count += GC_markers_m1;
    count = GC_fl_builder_count;
    GC_release_mark_lock();
    if (count != 0) {
      GC_ASSERT(count > 0);
      GC_wait_for_reclaim();
    }
  }
  
  /* Steal mark stack entries starting at mse low into mark stack local   */
  /* until we either steal mse high, or we have max entries.              */
  /* Return a pointer to the top of the local mark stack.                 */
  /* (*next) is replaced by a pointer to the next unscanned mark stack    */
  /* entry.                                                               */
  STATIC mse * GC_steal_mark_stack(mse * low, mse * high, mse * local,
                                   unsigned max, mse **next)
  {
      mse *p;
      mse *top = local - 1;
      unsigned i = 0;
  
      GC_ASSERT((word)high >= (word)(low - 1)
                && (word)(high - low + 1) <= GC_mark_stack_size);
      for (p = low; (word)p <= (word)high && i <= max; ++p) {
          word descr = (word)AO_load(&p->mse_descr.ao);
          if (descr != 0) {
              /* Must be ordered after read of descr: */
              AO_store_release_write(&p->mse_descr.ao, 0);
              /* More than one thread may get this entry, but that's only */
              /* a minor performance problem.                             */
              ++top;
              top -> mse_descr.w = descr;
              top -> mse_start = p -> mse_start;
              GC_ASSERT((descr & GC_DS_TAGS) != GC_DS_LENGTH
                        || descr < (word)GC_greatest_plausible_heap_addr
                                          - (word)GC_least_plausible_heap_addr
                        || (word)(p->mse_start + descr)
                              <= (word)GC_least_plausible_heap_addr
                        || (word)p->mse_start
                              >= (word)GC_greatest_plausible_heap_addr);
              /* If this is a big object, count it as                     */
              /* size/256 + 1 objects.                                    */
              ++i;
              if ((descr & GC_DS_TAGS) == GC_DS_LENGTH) i += (int)(descr >> 8);
          }
      }
      *next = p;
      return top;
  }
  
  /* Copy back a local mark stack.        */
  /* low and high are inclusive bounds.   */
  STATIC void GC_return_mark_stack(mse * low, mse * high)
  {
      mse * my_top;
      mse * my_start;
      size_t stack_size;
  
      if ((word)high < (word)low) return;
      stack_size = high - low + 1;
      GC_acquire_mark_lock();
      my_top = GC_mark_stack_top; /* Concurrent modification impossible. */
      my_start = my_top + 1;
      if ((word)(my_start - GC_mark_stack + stack_size)
                  > (word)GC_mark_stack_size) {
        GC_COND_LOG_PRINTF("No room to copy back mark stack\n");
        GC_mark_state = MS_INVALID;
        GC_mark_stack_too_small = TRUE;
        /* We drop the local mark stack.  We'll fix things later. */
      } else {
        BCOPY(low, my_start, stack_size * sizeof(mse));
        GC_ASSERT((mse *)AO_load((volatile AO_t *)(&GC_mark_stack_top))
                  == my_top);
        AO_store_release_write((volatile AO_t *)(&GC_mark_stack_top),
                               (AO_t)(my_top + stack_size));
                  /* Ensures visibility of previously written stack contents. */
      }
      GC_release_mark_lock();
      GC_notify_all_marker();
  }
  
  #ifndef N_LOCAL_ITERS
  # define N_LOCAL_ITERS 1
  #endif
  
  /* This function is only called when the local  */
  /* and the main mark stacks are both empty.     */
  static GC_bool has_inactive_helpers(void)
  {
    GC_bool res;
  
    GC_acquire_mark_lock();
    res = GC_active_count < GC_helper_count;
    GC_release_mark_lock();
    return res;
  }
  
  /* Mark from the local mark stack.              */
  /* On return, the local mark stack is empty.    */
  /* But this may be achieved by copying the      */
  /* local mark stack back into the global one.   */
  /* We do not hold the mark lock.                */
  STATIC void GC_do_local_mark(mse *local_mark_stack, mse *local_top)
  {
      unsigned n;
  
      for (;;) {
          for (n = 0; n < N_LOCAL_ITERS; ++n) {
              local_top = GC_mark_from(local_top, local_mark_stack,
                                       local_mark_stack + LOCAL_MARK_STACK_SIZE);
              if ((word)local_top < (word)local_mark_stack) return;
              if ((word)(local_top - local_mark_stack)
                          >= LOCAL_MARK_STACK_SIZE / 2) {
                  GC_return_mark_stack(local_mark_stack, local_top);
                  return;
              }
          }
          if ((word)AO_load((volatile AO_t *)&GC_mark_stack_top)
              < (word)AO_load(&GC_first_nonempty)
              && (word)local_top > (word)(local_mark_stack + 1)
              && has_inactive_helpers()) {
              /* Try to share the load, since the main stack is empty,    */
              /* and helper threads are waiting for a refill.             */
              /* The entries near the bottom of the stack are likely      */
              /* to require more work.  Thus we return those, even though */
              /* it's harder.                                             */
              mse * new_bottom = local_mark_stack
                                  + (local_top - local_mark_stack)/2;
              GC_ASSERT((word)new_bottom > (word)local_mark_stack
                        && (word)new_bottom < (word)local_top);
              GC_return_mark_stack(local_mark_stack, new_bottom - 1);
              memmove(local_mark_stack, new_bottom,
                      (local_top - new_bottom + 1) * sizeof(mse));
              local_top -= (new_bottom - local_mark_stack);
          }
      }
  }
  
  #ifndef ENTRIES_TO_GET
  # define ENTRIES_TO_GET 5
  #endif
  
  /* Mark using the local mark stack until the global mark stack is empty */
  /* and there are no active workers. Update GC_first_nonempty to reflect */
  /* progress.  Caller holds the mark lock.                               */
  /* Caller has already incremented GC_helper_count.  We decrement it,    */
  /* and maintain GC_active_count.                                        */
  STATIC void GC_mark_local(mse *local_mark_stack, int id)
  {
      mse * my_first_nonempty;
  
      GC_active_count++;
      my_first_nonempty = (mse *)AO_load(&GC_first_nonempty);
      GC_ASSERT((word)GC_mark_stack <= (word)my_first_nonempty);
      GC_ASSERT((word)my_first_nonempty
          <= (word)AO_load((volatile AO_t *)&GC_mark_stack_top) + sizeof(mse));
      GC_VERBOSE_LOG_PRINTF("Starting mark helper %d\n", id);
      GC_release_mark_lock();
      for (;;) {
          size_t n_on_stack;
          unsigned n_to_get;
          mse * my_top;
          mse * local_top;
          mse * global_first_nonempty = (mse *)AO_load(&GC_first_nonempty);
  
          GC_ASSERT((word)my_first_nonempty >= (word)GC_mark_stack &&
                    (word)my_first_nonempty <=
                          (word)AO_load((volatile AO_t *)&GC_mark_stack_top)
                          + sizeof(mse));
          GC_ASSERT((word)global_first_nonempty >= (word)GC_mark_stack);
          if ((word)my_first_nonempty < (word)global_first_nonempty) {
              my_first_nonempty = global_first_nonempty;
          } else if ((word)global_first_nonempty < (word)my_first_nonempty) {
              (void)AO_compare_and_swap(&GC_first_nonempty,
                                        (AO_t)global_first_nonempty,
                                        (AO_t)my_first_nonempty);
              /* If this fails, we just go ahead, without updating        */
              /* GC_first_nonempty.                                       */
          }
          /* Perhaps we should also update GC_first_nonempty, if it */
          /* is less.  But that would require using atomic updates. */
          my_top = (mse *)AO_load_acquire((volatile AO_t *)(&GC_mark_stack_top));
          if ((word)my_top < (word)my_first_nonempty) {
              GC_acquire_mark_lock();
              my_top = GC_mark_stack_top;
                  /* Asynchronous modification impossible here,   */
                  /* since we hold mark lock.                     */
              n_on_stack = my_top - my_first_nonempty + 1;
              if (0 == n_on_stack) {
                  GC_active_count--;
                  GC_ASSERT(GC_active_count <= GC_helper_count);
                  /* Other markers may redeposit objects          */
                  /* on the stack.                                */
                  if (0 == GC_active_count) GC_notify_all_marker();
                  while (GC_active_count > 0
                         && (word)AO_load(&GC_first_nonempty)
                                  > (word)GC_mark_stack_top) {
                      /* We will be notified if either GC_active_count    */
                      /* reaches zero, or if more objects are pushed on   */
                      /* the global mark stack.                           */
                      GC_wait_marker();
                  }
                  if (GC_active_count == 0
                      && (word)AO_load(&GC_first_nonempty)
                          > (word)GC_mark_stack_top) {
                      GC_bool need_to_notify = FALSE;
                      /* The above conditions can't be falsified while we */
                      /* hold the mark lock, since neither                */
                      /* GC_active_count nor GC_mark_stack_top can        */
                      /* change.  GC_first_nonempty can only be           */
                      /* incremented asynchronously.  Thus we know that   */
                      /* both conditions actually held simultaneously.    */
                      GC_helper_count--;
                      if (0 == GC_helper_count) need_to_notify = TRUE;
                      GC_VERBOSE_LOG_PRINTF("Finished mark helper %d\n", id);
                      if (need_to_notify) GC_notify_all_marker();
                      return;
                  }
                  /* Else there's something on the stack again, or        */
                  /* another helper may push something.                   */
                  GC_active_count++;
                  GC_ASSERT(GC_active_count > 0);
                  GC_release_mark_lock();
                  continue;
              } else {
                  GC_release_mark_lock();
              }
          } else {
              n_on_stack = my_top - my_first_nonempty + 1;
          }
          n_to_get = ENTRIES_TO_GET;
          if (n_on_stack < 2 * ENTRIES_TO_GET) n_to_get = 1;
          local_top = GC_steal_mark_stack(my_first_nonempty, my_top,
                                          local_mark_stack, n_to_get,
                                          &my_first_nonempty);
          GC_ASSERT((word)my_first_nonempty >= (word)GC_mark_stack &&
                    (word)my_first_nonempty <=
                          (word)AO_load((volatile AO_t *)&GC_mark_stack_top)
                          + sizeof(mse));
          GC_do_local_mark(local_mark_stack, local_top);
      }
  }
  
  /* Perform parallel mark.  We hold the GC lock, not the mark lock.      */
  /* Currently runs until the mark stack is empty.                        */
  STATIC void GC_do_parallel_mark(void)
  {
      GC_ASSERT(I_HOLD_LOCK());
      GC_acquire_mark_lock();
  
      /* This could be a GC_ASSERT, but it seems safer to keep it on      */
      /* all the time, especially since it's cheap.                       */
      if (GC_help_wanted || GC_active_count != 0 || GC_helper_count != 0)
          ABORT("Tried to start parallel mark in bad state");
      GC_VERBOSE_LOG_PRINTF("Starting marking for mark phase number %lu\n",
                            (unsigned long)GC_mark_no);
      GC_first_nonempty = (AO_t)GC_mark_stack;
      GC_active_count = 0;
      GC_helper_count = 1;
      GC_help_wanted = TRUE;
      GC_notify_all_marker();
          /* Wake up potential helpers.   */
      GC_mark_local(GC_main_local_mark_stack, 0);
      GC_help_wanted = FALSE;
      /* Done; clean up.  */
      while (GC_helper_count > 0) {
        GC_wait_marker();
      }
      /* GC_helper_count cannot be incremented while not GC_help_wanted.  */
      GC_VERBOSE_LOG_PRINTF("Finished marking for mark phase number %lu\n",
                            (unsigned long)GC_mark_no);
      GC_mark_no++;
      GC_release_mark_lock();
      GC_notify_all_marker();
  }
  
  /* Try to help out the marker, if it's running.  We hold the mark lock  */
  /* only, the initiating thread holds the allocation lock.               */
  GC_INNER void GC_help_marker(word my_mark_no)
  {
  #   define my_id my_id_mse.mse_descr.w
      mse my_id_mse;  /* align local_mark_stack explicitly */
      mse local_mark_stack[LOCAL_MARK_STACK_SIZE];
                  /* Note: local_mark_stack is quite big (up to 128 KiB). */
  
      GC_ASSERT(I_DONT_HOLD_LOCK());
      GC_ASSERT(GC_parallel);
      while (GC_mark_no < my_mark_no
             || (!GC_help_wanted && GC_mark_no == my_mark_no)) {
        GC_wait_marker();
      }
      my_id = GC_helper_count;
      if (GC_mark_no != my_mark_no || my_id > (unsigned)GC_markers_m1) {
        /* Second test is useful only if original threads can also        */
        /* act as helpers.  Under Linux they can't.                       */
        return;
      }
      GC_helper_count = (unsigned)my_id + 1;
      GC_mark_local(local_mark_stack, (int)my_id);
      /* GC_mark_local decrements GC_helper_count. */
  #   undef my_id
  }
  
  #endif /* PARALLEL_MARK */
  
  /* Allocate or reallocate space for mark stack of size n entries.  */
  /* May silently fail.                                              */
  static void alloc_mark_stack(size_t n)
  {
  #   ifdef GWW_VDB
        static GC_bool GC_incremental_at_stack_alloc = FALSE;
  
        GC_bool recycle_old;
  #   endif
      mse * new_stack;
  
      GC_ASSERT(I_HOLD_LOCK());
      new_stack = (mse *)GC_scratch_alloc(n * sizeof(struct GC_ms_entry));
  #   ifdef GWW_VDB
        /* Don't recycle a stack segment obtained with the wrong flags.   */
        /* Win32 GetWriteWatch requires the right kind of memory.         */
        recycle_old = !GC_auto_incremental || GC_incremental_at_stack_alloc;
        GC_incremental_at_stack_alloc = GC_auto_incremental;
  #   endif
  
      GC_mark_stack_too_small = FALSE;
      if (GC_mark_stack != NULL) {
          if (new_stack != 0) {
  #         ifdef GWW_VDB
              if (recycle_old)
  #         endif
            {
              /* Recycle old space.       */
              GC_scratch_recycle_inner(GC_mark_stack,
                          GC_mark_stack_size * sizeof(struct GC_ms_entry));
            }
            GC_mark_stack = new_stack;
            GC_mark_stack_size = n;
            /* FIXME: Do we need some way to reset GC_mark_stack_size?    */
            GC_mark_stack_limit = new_stack + n;
            GC_COND_LOG_PRINTF("Grew mark stack to %lu frames\n",
                               (unsigned long)GC_mark_stack_size);
          } else {
            WARN("Failed to grow mark stack to %" WARN_PRIdPTR " frames\n", n);
          }
      } else if (NULL == new_stack) {
          GC_err_printf("No space for mark stack\n");
          EXIT();
      } else {
          GC_mark_stack = new_stack;
          GC_mark_stack_size = n;
          GC_mark_stack_limit = new_stack + n;
      }
      GC_mark_stack_top = GC_mark_stack-1;
  }
  
  GC_INNER void GC_mark_init(void)
  {
      alloc_mark_stack(INITIAL_MARK_STACK_SIZE);
  }
  
  /*
   * Push all locations between b and t onto the mark stack.
   * b is the first location to be checked. t is one past the last
   * location to be checked.
   * Should only be used if there is no possibility of mark stack
   * overflow.
   */
  GC_API void GC_CALL GC_push_all(void *bottom, void *top)
  {
      word length;
  
      bottom = (void *)(((word)bottom + ALIGNMENT-1) & ~(ALIGNMENT-1));
      top = (void *)((word)top & ~(ALIGNMENT-1));
      if ((word)bottom >= (word)top) return;
  
      GC_mark_stack_top++;
      if ((word)GC_mark_stack_top >= (word)GC_mark_stack_limit) {
          ABORT("Unexpected mark stack overflow");
      }
      length = (word)top - (word)bottom;
  #   if GC_DS_TAGS > ALIGNMENT - 1
          length += GC_DS_TAGS;
          length &= ~GC_DS_TAGS;
  #   endif
      GC_mark_stack_top -> mse_start = (ptr_t)bottom;
      GC_mark_stack_top -> mse_descr.w = length;
  }
  
  #ifndef GC_DISABLE_INCREMENTAL
  
    /* Analogous to the above, but push only those pages h with           */
    /* dirty_fn(h) != 0.  We use GC_push_all to actually push the block.  */
    /* Used both to selectively push dirty pages, or to push a block in   */
    /* piecemeal fashion, to allow for more marking concurrency.          */
    /* Will not overflow mark stack if GC_push_all pushes a small fixed   */
    /* number of entries.  (This is invoked only if GC_push_all pushes    */
    /* a single entry, or if it marks each object before pushing it, thus */
    /* ensuring progress in the event of a stack overflow.)               */
    STATIC void GC_push_selected(ptr_t bottom, ptr_t top,
                                 GC_bool (*dirty_fn)(struct hblk *))
    {
      struct hblk * h;
  
      bottom = (ptr_t)(((word) bottom + ALIGNMENT-1) & ~(ALIGNMENT-1));
      top = (ptr_t)(((word) top) & ~(ALIGNMENT-1));
      if ((word)bottom >= (word)top) return;
  
      h = HBLKPTR(bottom + HBLKSIZE);
      if ((word)top <= (word)h) {
          if ((*dirty_fn)(h-1)) {
              GC_push_all(bottom, top);
          }
          return;
      }
      if ((*dirty_fn)(h-1)) {
          if ((word)(GC_mark_stack_top - GC_mark_stack)
              > 3 * GC_mark_stack_size / 4) {
              GC_push_all(bottom, top);
              return;
          }
          GC_push_all(bottom, h);
      }
  
      while ((word)(h+1) <= (word)top) {
          if ((*dirty_fn)(h)) {
              if ((word)(GC_mark_stack_top - GC_mark_stack)
                  > 3 * GC_mark_stack_size / 4) {
                  /* Danger of mark stack overflow.       */
                  GC_push_all(h, top);
                  return;
              } else {
                  GC_push_all(h, h + 1);
              }
          }
          h++;
      }
  
      if ((ptr_t)h != top && (*dirty_fn)(h)) {
         GC_push_all(h, top);
      }
    }
  
    GC_API void GC_CALL GC_push_conditional(void *bottom, void *top, int all)
    {
      if (!all) {
        GC_push_selected((ptr_t)bottom, (ptr_t)top, GC_page_was_dirty);
      } else {
  #     ifdef PROC_VDB
          if (GC_auto_incremental) {
            /* Pages that were never dirtied cannot contain pointers.     */
            GC_push_selected((ptr_t)bottom, (ptr_t)top, GC_page_was_ever_dirty);
          } else
  #     endif
        /* else */ {
          GC_push_all(bottom, top);
        }
      }
    }
  
  # ifndef NO_VDB_FOR_STATIC_ROOTS
  #   ifndef PROC_VDB
        /* Same as GC_page_was_dirty but h is allowed to point to some    */
        /* page in the registered static roots only.  Not used if         */
        /* manual VDB is on.                                              */
        STATIC GC_bool GC_static_page_was_dirty(struct hblk *h)
        {
          return get_pht_entry_from_index(GC_grungy_pages, PHT_HASH(h));
        }
  #   endif
  
      GC_INNER void GC_push_conditional_static(void *bottom, void *top,
                                               GC_bool all)
      {
  #     ifdef PROC_VDB
          /* Just redirect to the generic routine because PROC_VDB        */
          /* implementation gets the dirty bits map for the whole         */
          /* process memory.                                              */
          GC_push_conditional(bottom, top, all);
  #     else
          if (all || !GC_is_vdb_for_static_roots()) {
            GC_push_all(bottom, top);
          } else {
            GC_push_selected((ptr_t)bottom, (ptr_t)top,
                             GC_static_page_was_dirty);
          }
  #     endif
      }
  # endif /* !NO_VDB_FOR_STATIC_ROOTS */
  
  #else
    GC_API void GC_CALL GC_push_conditional(void *bottom, void *top,
                                            int all GC_ATTR_UNUSED)
    {
      GC_push_all(bottom, top);
    }
  #endif /* GC_DISABLE_INCREMENTAL */
  
  #if defined(AMIGA) || defined(MACOS) || defined(GC_DARWIN_THREADS)
    void GC_push_one(word p)
    {
      GC_PUSH_ONE_STACK(p, MARKED_FROM_REGISTER);
    }
  #endif
  
  #ifdef GC_WIN32_THREADS
    GC_INNER void GC_push_many_regs(const word *regs, unsigned count)
    {
      unsigned i;
      for (i = 0; i < count; i++)
        GC_PUSH_ONE_STACK(regs[i], MARKED_FROM_REGISTER);
    }
  #endif
  
  GC_API struct GC_ms_entry * GC_CALL GC_mark_and_push(void *obj,
                                                  mse *mark_stack_ptr,
                                                  mse *mark_stack_limit,
                                                  void ** src GC_ATTR_UNUSED)
  {
      hdr * hhdr;
  
      PREFETCH(obj);
      GET_HDR(obj, hhdr);
      if ((EXPECT(IS_FORWARDING_ADDR_OR_NIL(hhdr), FALSE)
           && (!GC_all_interior_pointers
               || NULL == (hhdr = GC_find_header((ptr_t)GC_base(obj)))))
          || EXPECT(HBLK_IS_FREE(hhdr), FALSE)) {
        GC_ADD_TO_BLACK_LIST_NORMAL(obj, (ptr_t)src);
        return mark_stack_ptr;
      }
      return GC_push_contents_hdr((ptr_t)obj, mark_stack_ptr, mark_stack_limit,
                                  (ptr_t)src, hhdr, TRUE);
  }
  
  /* Mark and push (i.e. gray) a single object p onto the main    */
  /* mark stack.  Consider p to be valid if it is an interior     */
  /* pointer.                                                     */
  /* The object p has passed a preliminary pointer validity       */
  /* test, but we do not definitely know whether it is valid.     */
  /* Mark bits are NOT atomically updated.  Thus this must be the */
  /* only thread setting them.                                    */
  # if defined(PRINT_BLACK_LIST) || defined(KEEP_BACK_PTRS)
      GC_INNER void GC_mark_and_push_stack(ptr_t p, ptr_t source)
  # else
      GC_INNER void GC_mark_and_push_stack(ptr_t p)
  #   define source ((ptr_t)0)
  # endif
  {
      hdr * hhdr;
      ptr_t r = p;
  
      PREFETCH(p);
      GET_HDR(p, hhdr);
      if (EXPECT(IS_FORWARDING_ADDR_OR_NIL(hhdr), FALSE)) {
        if (NULL == hhdr
              || (r = (ptr_t)GC_base(p)) == NULL
              || (hhdr = HDR(r)) == NULL) {
          GC_ADD_TO_BLACK_LIST_STACK(p, source);
          return;
        }
      }
      if (EXPECT(HBLK_IS_FREE(hhdr), FALSE)) {
          GC_ADD_TO_BLACK_LIST_NORMAL(p, source);
          return;
      }
  #   ifdef THREADS
        /* Pointer is on the stack.  We may have dirtied the object       */
        /* it points to, but have not called GC_dirty yet.                */
        GC_dirty(p); /* entire object */
  #   endif
      GC_mark_stack_top = GC_push_contents_hdr(r, GC_mark_stack_top,
                                               GC_mark_stack_limit,
                                               source, hhdr, FALSE);
      /* We silently ignore pointers to near the end of a block,  */
      /* which is very mildly suboptimal.                         */
      /* FIXME: We should probably add a header word to address   */
      /* this.                                                    */
  }
  # undef source
  
  #ifdef TRACE_BUF
  
  # ifndef TRACE_ENTRIES
  #   define TRACE_ENTRIES 1000
  # endif
  
  struct trace_entry {
      char * kind;
      word gc_no;
      word bytes_allocd;
      word arg1;
      word arg2;
  } GC_trace_buf[TRACE_ENTRIES] = { { NULL, 0, 0, 0, 0 } };
  
  void GC_add_trace_entry(char *kind, word arg1, word arg2)
  {
      GC_trace_buf[GC_trace_buf_ptr].kind = kind;
      GC_trace_buf[GC_trace_buf_ptr].gc_no = GC_gc_no;
      GC_trace_buf[GC_trace_buf_ptr].bytes_allocd = GC_bytes_allocd;
      GC_trace_buf[GC_trace_buf_ptr].arg1 = arg1 ^ 0x80000000;
      GC_trace_buf[GC_trace_buf_ptr].arg2 = arg2 ^ 0x80000000;
      GC_trace_buf_ptr++;
      if (GC_trace_buf_ptr >= TRACE_ENTRIES) GC_trace_buf_ptr = 0;
  }
  
  GC_API void GC_CALL GC_print_trace_inner(word gc_no)
  {
      int i;
  
      for (i = GC_trace_buf_ptr-1; i != GC_trace_buf_ptr; i--) {
          struct trace_entry *p;
  
          if (i < 0) i = TRACE_ENTRIES-1;
          p = GC_trace_buf + i;
          if (p -> gc_no < gc_no || p -> kind == 0) {
              return;
          }
          GC_printf("Trace:%s (gc:%u, bytes:%lu) 0x%lX, 0x%lX\n",
                    p -> kind, (unsigned)p -> gc_no,
                    (unsigned long)p -> bytes_allocd,
                    (long)p->arg1 ^ 0x80000000L, (long)p->arg2 ^ 0x80000000L);
      }
      GC_printf("Trace incomplete\n");
  }
  
  GC_API void GC_CALL GC_print_trace(word gc_no)
  {
      DCL_LOCK_STATE;
  
      LOCK();
      GC_print_trace_inner(gc_no);
      UNLOCK();
  }
  
  #endif /* TRACE_BUF */
  
  /* A version of GC_push_all that treats all interior pointers as valid  */
  /* and scans the entire region immediately, in case the contents change.*/
  GC_ATTR_NO_SANITIZE_ADDR GC_ATTR_NO_SANITIZE_MEMORY GC_ATTR_NO_SANITIZE_THREAD
  GC_API void GC_CALL GC_push_all_eager(void *bottom, void *top)
  {
      REGISTER ptr_t current_p;
      REGISTER word *lim;
      REGISTER ptr_t greatest_ha = (ptr_t)GC_greatest_plausible_heap_addr;
      REGISTER ptr_t least_ha = (ptr_t)GC_least_plausible_heap_addr;
  #   define GC_greatest_plausible_heap_addr greatest_ha
  #   define GC_least_plausible_heap_addr least_ha
  
      if (top == 0) return;
  
      /* Check all pointers in range and push if they appear to be valid. */
      lim = (word *)(((word)top) & ~(ALIGNMENT-1)) - 1;
      for (current_p = (ptr_t)(((word)bottom + ALIGNMENT-1) & ~(ALIGNMENT-1));
           (word)current_p <= (word)lim; current_p += ALIGNMENT) {
        REGISTER word q;
  
        LOAD_WORD_OR_CONTINUE(q, current_p);
        GC_PUSH_ONE_STACK(q, current_p);
      }
  #   undef GC_greatest_plausible_heap_addr
  #   undef GC_least_plausible_heap_addr
  }
  
  GC_INNER void GC_push_all_stack(ptr_t bottom, ptr_t top)
  {
  #   ifndef NEED_FIXUP_POINTER
        if (GC_all_interior_pointers
  #         if defined(THREADS) && defined(MPROTECT_VDB)
              && !GC_auto_incremental
  #         endif
            && (word)GC_mark_stack_top
               < (word)(GC_mark_stack_limit - INITIAL_MARK_STACK_SIZE/8)) {
          GC_push_all(bottom, top);
        } else
  #   endif
      /* else */ {
        GC_push_all_eager(bottom, top);
      }
  }
  
  #if defined(WRAP_MARK_SOME) && defined(PARALLEL_MARK)
    /* Similar to GC_push_conditional but scans the whole region immediately. */
    GC_ATTR_NO_SANITIZE_ADDR GC_ATTR_NO_SANITIZE_MEMORY
    GC_ATTR_NO_SANITIZE_THREAD
    GC_INNER void GC_push_conditional_eager(void *bottom, void *top,
                                            GC_bool all)
    {
      REGISTER ptr_t current_p;
      REGISTER word *lim;
      REGISTER ptr_t greatest_ha = (ptr_t)GC_greatest_plausible_heap_addr;
      REGISTER ptr_t least_ha = (ptr_t)GC_least_plausible_heap_addr;
  #   define GC_greatest_plausible_heap_addr greatest_ha
  #   define GC_least_plausible_heap_addr least_ha
  
      if (top == NULL)
        return;
      (void)all; /* TODO: If !all then scan only dirty pages. */
  
      lim = (word *)(((word)top) & ~(ALIGNMENT-1)) - 1;
      for (current_p = (ptr_t)(((word)bottom + ALIGNMENT-1) & ~(ALIGNMENT-1));
           (word)current_p <= (word)lim; current_p += ALIGNMENT) {
        REGISTER word q;
  
        LOAD_WORD_OR_CONTINUE(q, current_p);
        GC_PUSH_ONE_HEAP(q, current_p, GC_mark_stack_top);
      }
  #   undef GC_greatest_plausible_heap_addr
  #   undef GC_least_plausible_heap_addr
    }
  #endif /* WRAP_MARK_SOME && PARALLEL_MARK */
  
  #if !defined(SMALL_CONFIG) && !defined(USE_MARK_BYTES) && \
      defined(MARK_BIT_PER_GRANULE)
  # if GC_GRANULE_WORDS == 1
  #   define USE_PUSH_MARKED_ACCELERATORS
  #   define PUSH_GRANULE(q) \
                  do { \
                    word qcontents = (q)[0]; \
                    GC_PUSH_ONE_HEAP(qcontents, q, GC_mark_stack_top); \
                  } while (0)
  # elif GC_GRANULE_WORDS == 2
  #   define USE_PUSH_MARKED_ACCELERATORS
  #   define PUSH_GRANULE(q) \
                  do { \
                    word qcontents = (q)[0]; \
                    GC_PUSH_ONE_HEAP(qcontents, q, GC_mark_stack_top); \
                    qcontents = (q)[1]; \
                    GC_PUSH_ONE_HEAP(qcontents, (q)+1, GC_mark_stack_top); \
                  } while (0)
  # elif GC_GRANULE_WORDS == 4
  #   define USE_PUSH_MARKED_ACCELERATORS
  #   define PUSH_GRANULE(q) \
                  do { \
                    word qcontents = (q)[0]; \
                    GC_PUSH_ONE_HEAP(qcontents, q, GC_mark_stack_top); \
                    qcontents = (q)[1]; \
                    GC_PUSH_ONE_HEAP(qcontents, (q)+1, GC_mark_stack_top); \
                    qcontents = (q)[2]; \
                    GC_PUSH_ONE_HEAP(qcontents, (q)+2, GC_mark_stack_top); \
                    qcontents = (q)[3]; \
                    GC_PUSH_ONE_HEAP(qcontents, (q)+3, GC_mark_stack_top); \
                  } while (0)
  # endif
  #endif /* !USE_MARK_BYTES && MARK_BIT_PER_GRANULE */
  
  #ifdef USE_PUSH_MARKED_ACCELERATORS
  /* Push all objects reachable from marked objects in the given block */
  /* containing objects of size 1 granule.                             */
  GC_ATTR_NO_SANITIZE_THREAD
  STATIC void GC_push_marked1(struct hblk *h, hdr *hhdr)
  {
      word * mark_word_addr = &(hhdr->hb_marks[0]);
      word *p;
      word *plim;
  
      /* Allow registers to be used for some frequently accessed  */
      /* global variables.  Otherwise aliasing issues are likely  */
      /* to prevent that.                                         */
      ptr_t greatest_ha = (ptr_t)GC_greatest_plausible_heap_addr;
      ptr_t least_ha = (ptr_t)GC_least_plausible_heap_addr;
      mse * mark_stack_top = GC_mark_stack_top;
      mse * mark_stack_limit = GC_mark_stack_limit;
  
  #   undef GC_mark_stack_top
  #   undef GC_mark_stack_limit
  #   define GC_mark_stack_top mark_stack_top
  #   define GC_mark_stack_limit mark_stack_limit
  #   define GC_greatest_plausible_heap_addr greatest_ha
  #   define GC_least_plausible_heap_addr least_ha
  
      p = (word *)(h->hb_body);
      plim = (word *)(((word)h) + HBLKSIZE);
  
      /* Go through all words in block.   */
          while ((word)p < (word)plim) {
              word mark_word = *mark_word_addr++;
              word *q = p;
  
              while(mark_word != 0) {
                if (mark_word & 1) {
                    PUSH_GRANULE(q);
                }
                q += GC_GRANULE_WORDS;
                mark_word >>= 1;
              }
              p += WORDSZ*GC_GRANULE_WORDS;
          }
  
  #   undef GC_greatest_plausible_heap_addr
  #   undef GC_least_plausible_heap_addr
  #   undef GC_mark_stack_top
  #   undef GC_mark_stack_limit
  #   define GC_mark_stack_limit GC_arrays._mark_stack_limit
  #   define GC_mark_stack_top GC_arrays._mark_stack_top
      GC_mark_stack_top = mark_stack_top;
  }
  
  
  #ifndef UNALIGNED_PTRS
  
  /* Push all objects reachable from marked objects in the given block */
  /* of size 2 (granules) objects.                                     */
  GC_ATTR_NO_SANITIZE_THREAD
  STATIC void GC_push_marked2(struct hblk *h, hdr *hhdr)
  {
      word * mark_word_addr = &(hhdr->hb_marks[0]);
      word *p;
      word *plim;
  
      ptr_t greatest_ha = (ptr_t)GC_greatest_plausible_heap_addr;
      ptr_t least_ha = (ptr_t)GC_least_plausible_heap_addr;
      mse * mark_stack_top = GC_mark_stack_top;
      mse * mark_stack_limit = GC_mark_stack_limit;
  
  #   undef GC_mark_stack_top
  #   undef GC_mark_stack_limit
  #   define GC_mark_stack_top mark_stack_top
  #   define GC_mark_stack_limit mark_stack_limit
  #   define GC_greatest_plausible_heap_addr greatest_ha
  #   define GC_least_plausible_heap_addr least_ha
  
      p = (word *)(h->hb_body);
      plim = (word *)(((word)h) + HBLKSIZE);
  
      /* Go through all words in block.   */
          while ((word)p < (word)plim) {
              word mark_word = *mark_word_addr++;
              word *q = p;
  
              while(mark_word != 0) {
                if (mark_word & 1) {
                    PUSH_GRANULE(q);
                    PUSH_GRANULE(q + GC_GRANULE_WORDS);
                }
                q += 2 * GC_GRANULE_WORDS;
                mark_word >>= 2;
              }
              p += WORDSZ*GC_GRANULE_WORDS;
          }
  
  #   undef GC_greatest_plausible_heap_addr
  #   undef GC_least_plausible_heap_addr
  #   undef GC_mark_stack_top
  #   undef GC_mark_stack_limit
  #   define GC_mark_stack_limit GC_arrays._mark_stack_limit
  #   define GC_mark_stack_top GC_arrays._mark_stack_top
      GC_mark_stack_top = mark_stack_top;
  }
  
  # if GC_GRANULE_WORDS < 4
  /* Push all objects reachable from marked objects in the given block */
  /* of size 4 (granules) objects.                                     */
  /* There is a risk of mark stack overflow here.  But we handle that. */
  /* And only unmarked objects get pushed, so it's not very likely.    */
  GC_ATTR_NO_SANITIZE_THREAD
  STATIC void GC_push_marked4(struct hblk *h, hdr *hhdr)
  {
      word * mark_word_addr = &(hhdr->hb_marks[0]);
      word *p;
      word *plim;
  
      ptr_t greatest_ha = (ptr_t)GC_greatest_plausible_heap_addr;
      ptr_t least_ha = (ptr_t)GC_least_plausible_heap_addr;
      mse * mark_stack_top = GC_mark_stack_top;
      mse * mark_stack_limit = GC_mark_stack_limit;
  
  #   undef GC_mark_stack_top
  #   undef GC_mark_stack_limit
  #   define GC_mark_stack_top mark_stack_top
  #   define GC_mark_stack_limit mark_stack_limit
  #   define GC_greatest_plausible_heap_addr greatest_ha
  #   define GC_least_plausible_heap_addr least_ha
  
      p = (word *)(h->hb_body);
      plim = (word *)(((word)h) + HBLKSIZE);
  
      /* Go through all words in block.   */
          while ((word)p < (word)plim) {
              word mark_word = *mark_word_addr++;
              word *q = p;
  
              while(mark_word != 0) {
                if (mark_word & 1) {
                    PUSH_GRANULE(q);
                    PUSH_GRANULE(q + GC_GRANULE_WORDS);
                    PUSH_GRANULE(q + 2*GC_GRANULE_WORDS);
                    PUSH_GRANULE(q + 3*GC_GRANULE_WORDS);
                }
                q += 4 * GC_GRANULE_WORDS;
                mark_word >>= 4;
              }
              p += WORDSZ*GC_GRANULE_WORDS;
          }
  #   undef GC_greatest_plausible_heap_addr
  #   undef GC_least_plausible_heap_addr
  #   undef GC_mark_stack_top
  #   undef GC_mark_stack_limit
  #   define GC_mark_stack_limit GC_arrays._mark_stack_limit
  #   define GC_mark_stack_top GC_arrays._mark_stack_top
      GC_mark_stack_top = mark_stack_top;
  }
  
  #endif /* GC_GRANULE_WORDS < 4 */
  
  #endif /* UNALIGNED_PTRS */
  
  #endif /* USE_PUSH_MARKED_ACCELERATORS */
  
  /* Push all objects reachable from marked objects in the given block.   */
  STATIC void GC_push_marked(struct hblk *h, hdr *hhdr)
  {
      word sz = hhdr -> hb_sz;
      word descr = hhdr -> hb_descr;
      ptr_t p;
      word bit_no;
      ptr_t lim;
      mse * GC_mark_stack_top_reg;
      mse * mark_stack_limit = GC_mark_stack_limit;
  
      /* Some quick shortcuts: */
          if ((/* 0 | */ GC_DS_LENGTH) == descr) return;
          if (GC_block_empty(hhdr)/* nothing marked */) return;
  #   if !defined(GC_DISABLE_INCREMENTAL)
        GC_n_rescuing_pages++;
  #   endif
      GC_objects_are_marked = TRUE;
      if (sz > MAXOBJBYTES) {
          lim = h -> hb_body;
      } else {
          lim = (ptr_t)((word)(h + 1)->hb_body - sz);
      }
  
      switch(BYTES_TO_GRANULES(sz)) {
  #   if defined(USE_PUSH_MARKED_ACCELERATORS)
        case 1:
          GC_push_marked1(h, hhdr);
          break;
  #     if !defined(UNALIGNED_PTRS)
          case 2:
            GC_push_marked2(h, hhdr);
            break;
  #       if GC_GRANULE_WORDS < 4
            case 4:
              GC_push_marked4(h, hhdr);
              break;
  #       endif
  #     endif /* !UNALIGNED_PTRS */
  #   else
        case 1: /* to suppress "switch statement contains no case" warning */
  #   endif
      default:
        GC_mark_stack_top_reg = GC_mark_stack_top;
        for (p = h -> hb_body, bit_no = 0; (word)p <= (word)lim;
             p += sz, bit_no += MARK_BIT_OFFSET(sz)) {
          if (mark_bit_from_hdr(hhdr, bit_no)) {
            /* Mark from fields inside the object. */
            GC_mark_stack_top_reg = GC_push_obj(p, hhdr, GC_mark_stack_top_reg,
                                                mark_stack_limit);
          }
        }
        GC_mark_stack_top = GC_mark_stack_top_reg;
      }
  }
  
  #ifdef ENABLE_DISCLAIM
  /* Unconditionally mark from all objects which have not been reclaimed. */
  /* This is useful in order to retain pointers which are reachable from  */
  /* the disclaim notifiers.                                              */
  /* To determine whether an object has been reclaimed, we require that   */
  /* any live object has a non-zero as one of the two lowest bits of the  */
  /* first word.  On the other hand, a reclaimed object is a members of   */
  /* free-lists, and thus contains a word-aligned next-pointer as the     */
  /* first word.                                                          */
   GC_ATTR_NO_SANITIZE_THREAD
   STATIC void GC_push_unconditionally(struct hblk *h, hdr *hhdr)
   {
      word sz = hhdr -> hb_sz;
      word descr = hhdr -> hb_descr;
      ptr_t p;
      ptr_t lim;
      mse * GC_mark_stack_top_reg;
      mse * mark_stack_limit = GC_mark_stack_limit;
  
      if ((/* 0 | */ GC_DS_LENGTH) == descr)
          return;
  
  #   if !defined(GC_DISABLE_INCREMENTAL)
        GC_n_rescuing_pages++;
  #   endif
      GC_objects_are_marked = TRUE;
      if (sz > MAXOBJBYTES)
          lim = h -> hb_body;
      else
          lim = (ptr_t)((word)(h + 1)->hb_body - sz);
  
      GC_mark_stack_top_reg = GC_mark_stack_top;
      for (p = h -> hb_body; (word)p <= (word)lim; p += sz)
        if ((*(word *)p & 0x3) != 0)
          GC_mark_stack_top_reg = GC_push_obj(p, hhdr, GC_mark_stack_top_reg,
                                              mark_stack_limit);
      GC_mark_stack_top = GC_mark_stack_top_reg;
    }
  #endif /* ENABLE_DISCLAIM */
  
  #ifndef GC_DISABLE_INCREMENTAL
    /* Test whether any page in the given block is dirty.   */
    STATIC GC_bool GC_block_was_dirty(struct hblk *h, hdr *hhdr)
    {
      word sz = hhdr -> hb_sz;
      ptr_t p;
  
      if (sz <= MAXOBJBYTES) {
        return GC_page_was_dirty(h);
      }
  
      for (p = (ptr_t)h; (word)p < (word)h + sz; p += HBLKSIZE) {
        if (GC_page_was_dirty((struct hblk *)p)) return TRUE;
      }
      return FALSE;
    }
  #endif /* GC_DISABLE_INCREMENTAL */
  
  /* Similar to GC_push_marked, but skip over unallocated blocks  */
  /* and return address of next plausible block.                  */
  STATIC struct hblk * GC_push_next_marked(struct hblk *h)
  {
      hdr * hhdr = HDR(h);
  
      if (EXPECT(IS_FORWARDING_ADDR_OR_NIL(hhdr) || HBLK_IS_FREE(hhdr), FALSE)) {
        h = GC_next_block(h, FALSE);
        if (NULL == h) return NULL;
        hhdr = GC_find_header((ptr_t)h);
      } else {
  #     ifdef LINT2
          if (NULL == h) ABORT("Bad HDR() definition");
  #     endif
      }
      GC_push_marked(h, hhdr);
      return h + OBJ_SZ_TO_BLOCKS(hhdr -> hb_sz);
  }
  
  #ifndef GC_DISABLE_INCREMENTAL
    /* Identical to above, but mark only from dirty pages.        */
    STATIC struct hblk * GC_push_next_marked_dirty(struct hblk *h)
    {
      hdr * hhdr = HDR(h);
  
      if (!GC_incremental) ABORT("Dirty bits not set up");
      for (;;) {
          if (EXPECT(IS_FORWARDING_ADDR_OR_NIL(hhdr)
                     || HBLK_IS_FREE(hhdr), FALSE)) {
            h = GC_next_block(h, FALSE);
            if (NULL == h) return NULL;
            hhdr = GC_find_header((ptr_t)h);
          } else {
  #         ifdef LINT2
              if (NULL == h) ABORT("Bad HDR() definition");
  #         endif
          }
          if (GC_block_was_dirty(h, hhdr))
            break;
          h += OBJ_SZ_TO_BLOCKS(hhdr -> hb_sz);
          hhdr = HDR(h);
      }
  #   ifdef ENABLE_DISCLAIM
        if ((hhdr -> hb_flags & MARK_UNCONDITIONALLY) != 0) {
          GC_push_unconditionally(h, hhdr);
  
          /* Then we may ask, why not also add the MARK_UNCONDITIONALLY   */
          /* case to GC_push_next_marked, which is also applied to        */
          /* uncollectible blocks?  But it seems to me that the function  */
          /* does not need to scan uncollectible (and unconditionally     */
          /* marked) blocks since those are already handled in the        */
          /* MS_PUSH_UNCOLLECTABLE phase.                                 */
        } else
  #   endif
      /* else */ {
        GC_push_marked(h, hhdr);
      }
      return h + OBJ_SZ_TO_BLOCKS(hhdr -> hb_sz);
    }
  #endif /* !GC_DISABLE_INCREMENTAL */
  
  /* Similar to above, but for uncollectible pages.  Needed since we      */
  /* do not clear marks for such pages, even for full collections.        */
  STATIC struct hblk * GC_push_next_marked_uncollectable(struct hblk *h)
  {
      hdr * hhdr = HDR(h);
  
      for (;;) {
          if (EXPECT(IS_FORWARDING_ADDR_OR_NIL(hhdr)
                     || HBLK_IS_FREE(hhdr), FALSE)) {
            h = GC_next_block(h, FALSE);
            if (NULL == h) return NULL;
            hhdr = GC_find_header((ptr_t)h);
          } else {
  #         ifdef LINT2
              if (NULL == h) ABORT("Bad HDR() definition");
  #         endif
          }
          if (hhdr -> hb_obj_kind == UNCOLLECTABLE) {
              GC_push_marked(h, hhdr);
              break;
          }
  #       ifdef ENABLE_DISCLAIM
              if ((hhdr -> hb_flags & MARK_UNCONDITIONALLY) != 0) {
                  GC_push_unconditionally(h, hhdr);
                  break;
              }
  #       endif
          h += OBJ_SZ_TO_BLOCKS(hhdr -> hb_sz);
          hhdr = HDR(h);
      }
      return h + OBJ_SZ_TO_BLOCKS(hhdr -> hb_sz);
  }
  