update bjam source code. Copied from boost 1.54

1 files changed, 1866 insertions, 0 deletions

diff --git a/jam-files/engine/boehm_gc/mark.c b/jam-files/engine/boehm_gc/mark.c
new file mode 100644
index 000000000..3e5c46d1b
--- /dev/null
+++ b/jam-files/engine/boehm_gc/mark.c
@@ -0,0 +1,1866 @@
+
+/*
+ * 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.
+ *
+ * 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.
+ *
+ */
+
+
+# include <stdio.h>
+# include "private/gc_pmark.h"
+
+#if defined(MSWIN32) && defined(__GNUC__)
+# include <excpt.h>
+#endif
+
+/* We put this here to minimize the risk of inlining. */
+/*VARARGS*/
+#ifdef __WATCOMC__
+  void GC_noop(void *p, ...) {}
+#else
+  void GC_noop() {}
+#endif
+
+/* Single argument version, robust against whole program analysis. */
+void GC_noop1(word x)
+{
+    static volatile word sink;
+
+    sink = x;
+}
+
+/* mark_proc GC_mark_procs[MAX_MARK_PROCS] = {0} -- declared in gc_priv.h */
+
+unsigned GC_n_mark_procs = GC_RESERVED_MARK_PROCS;
+
+/* 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.		*/
+struct obj_kind GC_obj_kinds[MAXOBJKINDS] = {
+/* PTRFREE */ { &GC_aobjfreelist[0], 0 /* filled in dynamically */,
+		0 | GC_DS_LENGTH, FALSE, FALSE },
+/* NORMAL  */ { &GC_objfreelist[0], 0,
+		0 | GC_DS_LENGTH,  /* Adjusted in GC_init_inner for EXTRA_BYTES */
+		TRUE /* add length to descr */, TRUE },
+/* UNCOLLECTABLE */
+	      { &GC_uobjfreelist[0], 0,
+		0 | GC_DS_LENGTH, TRUE /* add length to descr */, TRUE },
+# ifdef ATOMIC_UNCOLLECTABLE
+   /* AUNCOLLECTABLE */
+	      { &GC_auobjfreelist[0], 0,
+		0 | GC_DS_LENGTH, FALSE /* add length to descr */, FALSE },
+# endif
+# ifdef STUBBORN_ALLOC
+/*STUBBORN*/ { &GC_sobjfreelist[0], 0,
+		0 | GC_DS_LENGTH, TRUE /* add length to descr */, TRUE },
+# endif
+};
+
+# ifdef ATOMIC_UNCOLLECTABLE
+#   ifdef STUBBORN_ALLOC
+      unsigned GC_n_kinds = 5;
+#   else
+      unsigned GC_n_kinds = 4;
+#   endif
+# else
+#   ifdef STUBBORN_ALLOC
+      unsigned GC_n_kinds = 4;
+#   else
+      unsigned GC_n_kinds = 3;
+#   endif
+# 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 want to push all marked dirty objs	*/
+		/* before marking anything new.  Currently we let it	*/
+		/* grow dynamically.					*/
+# endif
+
+/*
+ * Limits of stack for GC_mark routine.
+ * All ranges between GC_mark_stack(incl.) and GC_mark_stack_top(incl.) still
+ * need to be marked from.
+ */
+
+word GC_n_rescuing_pages;	/* Number of dirty pages we marked from */
+				/* excludes ptrfree pages, etc.		*/
+
+mse * GC_mark_stack;
+
+mse * GC_mark_stack_limit;
+
+size_t GC_mark_stack_size = 0;
+ 
+#ifdef PARALLEL_MARK
+# include "atomic_ops.h"
+
+  mse * volatile GC_mark_stack_top;
+  /* Updated only with mark lock held, but read asynchronously.	*/
+  volatile AO_t GC_first_nonempty;
+  	/* Lowest entry on mark stack	*/
+	/* that may be nonempty.	*/
+	/* Updated only by initiating 	*/
+	/* thread.			*/
+#else
+  mse * GC_mark_stack_top;
+#endif
+
+static struct hblk * scan_ptr;
+
+mark_state_t GC_mark_state = MS_NONE;
+
+GC_bool GC_mark_stack_too_small = FALSE;
+
+GC_bool GC_objects_are_marked = FALSE;	/* Are there collectable marked	*/
+					/* objects in the heap?		*/
+
+/* Is a collection in progress?  Note that this can return true in the	*/
+/* nonincremental case, if a collection has been abandoned and the	*/
+/* mark state is now MS_INVALID.					*/
+GC_bool GC_collection_in_progress(void)
+{
+    return(GC_mark_state != MS_NONE);
+}
+
+/* clear all mark bits in the header */
+void GC_clear_hdr_marks(hdr *hhdr)
+{
+    size_t last_bit = FINAL_MARK_BIT(hhdr -> hb_sz);
+
+#   ifdef USE_MARK_BYTES
+      BZERO(hhdr -> hb_marks, MARK_BITS_SZ);
+      hhdr -> hb_marks[last_bit] = 1;
+#   else
+      BZERO(hhdr -> hb_marks, MARK_BITS_SZ*sizeof(word));
+      set_mark_bit_from_hdr(hhdr, last_bit);
+#   endif
+    hhdr -> hb_n_marks = 0;
+}
+
+/* Set all mark bits in the header.  Used for uncollectable blocks. */
+void GC_set_hdr_marks(hdr *hhdr)
+{
+    unsigned i;
+    size_t sz = hhdr -> hb_sz;
+    size_t n_marks = FINAL_MARK_BIT(sz);
+
+#   ifdef USE_MARK_BYTES
+      for (i = 0; i <= n_marks; i += MARK_BIT_OFFSET(sz)) {
+    	hhdr -> hb_marks[i] = 1;
+      }
+#   else
+      for (i = 0; i < divWORDSZ(n_marks + WORDSZ); ++i) {
+    	hhdr -> hb_marks[i] = ONES;
+      }
+#   endif
+#   ifdef MARK_BIT_PER_OBJ
+      hhdr -> hb_n_marks = n_marks - 1;
+#   else
+      hhdr -> hb_n_marks = HBLK_OBJS(sz);
+#   endif
+}
+
+/*
+ * Clear all mark bits associated with block h.
+ */
+/*ARGSUSED*/
+static void clear_marks_for_block(struct hblk *h, word dummy)
+{
+    register 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 */
+void GC_set_mark_bit(ptr_t p)
+{
+    struct hblk *h = HBLKPTR(p);
+    hdr * hhdr = HDR(h);
+    word bit_no = MARK_BIT_NO(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;
+    }
+}
+
+void GC_clear_mark_bit(ptr_t p)
+{
+    struct hblk *h = HBLKPTR(p);
+    hdr * hhdr = HDR(h);
+    word bit_no = MARK_BIT_NO(p - (ptr_t)h, hhdr -> hb_sz);
+    
+    if (mark_bit_from_hdr(hhdr, bit_no)) {
+      size_t n_marks;
+      clear_mark_bit_from_hdr(hhdr, bit_no);
+      n_marks = hhdr -> hb_n_marks - 1;
+#     ifdef PARALLEL_MARK
+        if (n_marks != 0)
+          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_bool GC_is_marked(ptr_t p)
+{
+    struct hblk *h = HBLKPTR(p);
+    hdr * hhdr = HDR(h);
+    word bit_no = MARK_BIT_NO(p - (ptr_t)h, hhdr -> hb_sz);
+    
+    return((GC_bool)mark_bit_from_hdr(hhdr, bit_no));
+}
+
+
+/*
+ * 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.)
+ */
+void GC_clear_marks(void)
+{
+    GC_apply_to_all_blocks(clear_marks_for_block, (word)0);
+    GC_objects_are_marked = FALSE;
+    GC_mark_state = MS_INVALID;
+    scan_ptr = 0;
+}
+
+/* Initiate a garbage collection.  Initiates a full collection if the	*/
+/* mark	state is invalid.						*/
+/*ARGSUSED*/
+void GC_initiate_gc(void)
+{
+    if (GC_dirty_maintained) GC_read_dirty();
+#   ifdef STUBBORN_ALLOC
+    	GC_read_changed();
+#   endif
+#   ifdef CHECKSUMS
+	{
+	    extern void GC_check_dirty();
+	    
+	    if (GC_dirty_maintained) GC_check_dirty();
+	}
+#   endif
+    GC_n_rescuing_pages = 0;
+    if (GC_mark_state == MS_NONE) {
+        GC_mark_state = MS_PUSH_RESCUERS;
+    } else if (GC_mark_state != MS_INVALID) {
+    	ABORT("unexpected state");
+    } /* else this is really a full collection, and mark	*/
+      /* bits are invalid.					*/
+    scan_ptr = 0;
+}
+
+
+static void alloc_mark_stack(size_t);
+
+# if defined(MSWIN32) || defined(USE_PROC_FOR_LIBRARIES) && defined(THREADS)
+    /* Under rare conditions, we may end up marking from nonexistent memory. */
+    /* Hence we need to be prepared to recover by running GC_mark_some	     */
+    /* with a suitable handler in place.				     */
+#   define WRAP_MARK_SOME
+# endif
+
+/* 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.					*/
+/* We hold the allocation lock.  In the case of 	*/
+/* incremental collection, the world may not be stopped.*/
+#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.  See below.  In either case, we acquire the 	*/
+  /* allocator lock long before we get here.			*/
+  GC_bool GC_mark_some_inner(ptr_t cold_gc_frame)
+#else
+  GC_bool GC_mark_some(ptr_t cold_gc_frame)
+#endif
+{
+    switch(GC_mark_state) {
+    	case MS_NONE:
+    	    return(FALSE);
+    	    
+    	case MS_PUSH_RESCUERS:
+    	    if (GC_mark_stack_top
+    	        >= 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();
+    	        return(FALSE);
+    	    } else {
+    	        scan_ptr = GC_push_next_marked_dirty(scan_ptr);
+    	        if (scan_ptr == 0) {
+		    if (GC_print_stats) {
+			GC_log_printf("Marked from %u dirty pages\n",
+				      GC_n_rescuing_pages);
+		    }
+    	    	    GC_push_roots(FALSE, cold_gc_frame);
+    	    	    GC_objects_are_marked = TRUE;
+    	    	    if (GC_mark_state != MS_INVALID) {
+    	    	        GC_mark_state = MS_ROOTS_PUSHED;
+    	    	    }
+    	    	}
+    	    }
+    	    return(FALSE);
+    	
+    	case MS_PUSH_UNCOLLECTABLE:
+    	    if (GC_mark_stack_top
+    	        >= 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();
+    	        return(FALSE);
+    	    } else {
+    	        scan_ptr = GC_push_next_marked_uncollectable(scan_ptr);
+    	        if (scan_ptr == 0) {
+    	    	    GC_push_roots(TRUE, cold_gc_frame);
+    	    	    GC_objects_are_marked = TRUE;
+    	    	    if (GC_mark_state != MS_INVALID) {
+    	    	        GC_mark_state = MS_ROOTS_PUSHED;
+    	    	    }
+    	    	}
+    	    }
+    	    return(FALSE);
+    	
+    	case MS_ROOTS_PUSHED:
+#	    ifdef PARALLEL_MARK
+	      /* In the incremental GC case, this currently doesn't	*/
+	      /* quite do the right thing, since it runs to		*/
+	      /* completion.  On the other hand, starting a		*/
+	      /* parallel marker is expensive, so perhaps it is		*/
+	      /* the right thing?					*/
+	      /* Eventually, incremental marking should run		*/
+	      /* asynchronously in multiple threads, without grabbing	*/
+	      /* the allocation lock.					*/
+	        if (GC_parallel) {
+		  GC_do_parallel_mark();
+		  GC_ASSERT(GC_mark_stack_top < (mse *)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);
+		  } else {
+		    return(FALSE);
+	          }
+		}
+#	    endif
+    	    if (GC_mark_stack_top >= GC_mark_stack) {
+    	        MARK_FROM_MARK_STACK();
+    	        return(FALSE);
+    	    } else {
+    	        GC_mark_state = MS_NONE;
+    	        if (GC_mark_stack_too_small) {
+    	            alloc_mark_stack(2*GC_mark_stack_size);
+    	        }
+    	        return(TRUE);
+    	    }
+    	    
+    	case MS_INVALID:
+    	case MS_PARTIALLY_INVALID:
+	    if (!GC_objects_are_marked) {
+		GC_mark_state = MS_PUSH_UNCOLLECTABLE;
+		return(FALSE);
+	    }
+    	    if (GC_mark_stack_top >= GC_mark_stack) {
+    	        MARK_FROM_MARK_STACK();
+    	        return(FALSE);
+    	    }
+    	    if (scan_ptr == 0 && 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;
+    	    }
+    	    scan_ptr = GC_push_next_marked(scan_ptr);
+    	    if (scan_ptr == 0 && GC_mark_state == MS_PARTIALLY_INVALID) {
+    	    	GC_push_roots(TRUE, cold_gc_frame);
+    	    	GC_objects_are_marked = TRUE;
+    	    	if (GC_mark_state != MS_INVALID) {
+    	    	    GC_mark_state = MS_ROOTS_PUSHED;
+    	    	}
+    	    }
+    	    return(FALSE);
+    	default:
+    	    ABORT("GC_mark_some: bad state");
+    	    return(FALSE);
+    }
+}
+
+
+#if defined(MSWIN32) && 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)
+    {
+        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 */
+
+#ifdef GC_WIN32_THREADS
+  extern GC_bool GC_started_thread_while_stopped(void);
+  /* In win32_threads.c.  Did we invalidate mark phase with an	*/
+  /* unexpected thread start?					*/
+#endif
+
+# ifdef WRAP_MARK_SOME
+  GC_bool GC_mark_some(ptr_t cold_gc_frame)
+  {
+      GC_bool ret_val;
+
+#   ifdef MSWIN32
+#    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.                          */
+      /* 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;
+      }
+#     ifdef GC_WIN32_THREADS
+	/* 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_ex;
+#     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;
+
+      er.alt_path = &&handle_ex;
+      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;
+    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.						*/
+      if (GC_incremental)
+	      WARN("Incremental GC incompatible with /proc roots\n", 0);
+      	/* I'm not sure if this could still work ...	*/
+      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. */
+      if (GC_print_stats) {
+        GC_log_printf("Caught ACCESS_VIOLATION in marker. "
+		      "Memory mapping disappeared.\n");
+      }
+
+      /* We have bad roots on the stack.  Discard mark stack.	*/
+      /* Rescan from marked objects.  Redetermine roots.	*/
+      GC_invalidate_mark_state();	
+      scan_ptr = 0;
+
+      ret_val = FALSE;
+      goto rm_handler;  // Back to platform-specific code.
+  }
+#endif /* WRAP_MARK_SOME */
+
+
+GC_bool GC_mark_stack_empty(void)
+{
+    return(GC_mark_stack_top < GC_mark_stack);
+}	
+
+void GC_invalidate_mark_state(void)
+{
+    GC_mark_state = MS_INVALID;
+    GC_mark_stack_top = GC_mark_stack-1;
+}
+
+mse * GC_signal_mark_stack_overflow(mse *msp)
+{
+    GC_mark_state = MS_INVALID;
+    GC_mark_stack_too_small = TRUE;
+    if (GC_print_stats) {
+	GC_log_printf("Mark stack overflow; current size = %lu entries\n",
+	    	      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. 
+ */
+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;	/* (Incl) limit of current candidate 	*/
+  				/* range				*/
+  word descr;
+  ptr_t greatest_ha = GC_greatest_plausible_heap_addr;
+  ptr_t least_ha = 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 (mark_stack_top >= mark_stack && credit >= 0) {
+# else
+  while ((((ptr_t)mark_stack_top - (ptr_t)mark_stack) | credit)
+  	>= 0) {
+# endif
+    current_p = mark_stack_top -> mse_start;
+    descr = mark_stack_top -> mse_descr;
+  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;
+      
+      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);
+#	  ifdef ENABLE_TRACE
+	    if (GC_trace_addr >= current_p
+		&& GC_trace_addr < current_p + descr) {
+		GC_log_printf("GC:%d Large section; start %p len %lu\n",
+			      GC_gc_no, current_p, (unsigned long) descr);
+	    }
+#	  endif /* ENABLE_TRACE */
+#	  ifdef PARALLEL_MARK
+#	    define SHARE_BYTES 2048
+	    if (descr > SHARE_BYTES && GC_parallel
+		&& mark_stack_top < mark_stack_limit - 1) {
+	      int new_size = (descr/2) & ~(sizeof(word)-1);
+	      mark_stack_top -> mse_start = current_p;
+	      mark_stack_top -> mse_descr = new_size + sizeof(word);
+					/* makes sure we handle 	*/
+					/* misaligned pointers.		*/
+	      mark_stack_top++;
+#	      ifdef ENABLE_TRACE
+	        if (GC_trace_addr >= current_p
+		    && GC_trace_addr < current_p + descr) {
+		    GC_log_printf("GC:%d splitting (parallel) %p at %p\n",
+				  GC_gc_no, current_p, current_p + new_size);
+	        }
+#	      endif /* ENABLE_TRACE */
+	      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 =
+          		descr - WORDS_TO_BYTES(SPLIT_RANGE_WORDS-1);
+#	  ifdef ENABLE_TRACE
+	    if (GC_trace_addr >= current_p
+		&& GC_trace_addr < current_p + descr) {
+		GC_log_printf("GC:%d splitting %p at %p\n",
+			      GC_gc_no, current_p, limit);
+	    }
+#	  endif /* ENABLE_TRACE */
+          /* 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 (GC_trace_addr >= current_p
+		&& GC_trace_addr < current_p + WORDS_TO_BYTES(WORDSZ-2)) {
+		GC_log_printf("GC:%d Tracing from %p bitmap descr %lu\n",
+			      GC_gc_no, current_p, (unsigned long) descr);
+	    }
+#	  endif /* ENABLE_TRACE */
+          descr &= ~GC_DS_TAGS;
+          credit -= WORDS_TO_BYTES(WORDSZ/2); /* guess */
+          while (descr != 0) {
+            if ((signed_word)descr < 0) {
+              current = *(word *)current_p;
+	      FIXUP_POINTER(current);
+	      if ((ptr_t)current >= least_ha && (ptr_t)current < greatest_ha) {
+		PREFETCH((ptr_t)current);
+#               ifdef ENABLE_TRACE
+	          if (GC_trace_addr == current_p) {
+	            GC_log_printf("GC:%d Considering(3) %p -> %p\n",
+			          GC_gc_no, current_p, (ptr_t) current);
+	          }
+#               endif /* ENABLE_TRACE */
+                PUSH_CONTENTS((ptr_t)current, mark_stack_top,
+			      mark_stack_limit, current_p, exit1);
+	      }
+            }
+	    descr <<= 1;
+	    current_p += sizeof(word);
+          }
+          continue;
+        case GC_DS_PROC:
+          mark_stack_top--;
+#	  ifdef ENABLE_TRACE
+	    if (GC_trace_addr >= current_p
+		&& GC_base(current_p) != 0
+		&& GC_base(current_p) == GC_base(GC_trace_addr)) {
+		GC_log_printf("GC:%d Tracing from %p proc descr %lu\n",
+			      GC_gc_no, 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 	*/
+	    /* 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 (0 == type_descr) {
+		/* Rarely executed.	*/
+		mark_stack_top--;
+		continue;
+	    }
+            descr = *(word *)(type_descr
+			      - (descr - (GC_DS_PER_OBJECT
+					  - GC_INDIR_PER_OBJ_BIAS)));
+	  }
+	  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--;
+      limit = current_p + (word)descr;
+    }
+#   ifdef ENABLE_TRACE
+	if (GC_trace_addr >= current_p
+	    && GC_trace_addr < limit) {
+	    GC_log_printf("GC:%d Tracing from %p len %lu\n",
+			  GC_gc_no, current_p, (unsigned long) descr);
+	}
+#   endif /* ENABLE_TRACE */
+    /* 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
+
+#     ifndef SMALL_CONFIG
+        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(limit >= current_p);
+	  deferred = *(word *)limit;
+	  FIXUP_POINTER(deferred);
+	  limit -= ALIGNMENT;
+	  if ((ptr_t)deferred >= least_ha && (ptr_t)deferred <  greatest_ha) {
+	    PREFETCH((ptr_t)deferred);
+	    break;
+	  }
+	  if (current_p > 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 ((ptr_t)deferred >= least_ha && (ptr_t)deferred <  greatest_ha) {
+	    PREFETCH((ptr_t)deferred);
+	    break;
+	  }
+	  if (current_p > limit) goto next_object;
+	}
+#     endif
+
+      while (current_p <= limit) {
+	/* Empirically, unrolling this loop doesn't help a lot.	*/
+	/* Since PUSH_CONTENTS expands to a lot of code,	*/
+	/* we don't.						*/
+        current = *(word *)current_p;
+	FIXUP_POINTER(current);
+        PREFETCH(current_p + PREF_DIST*CACHE_LINE_SIZE);
+        if ((ptr_t)current >= least_ha && (ptr_t)current <  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:%d Considering(1) %p -> %p\n",
+			      GC_gc_no, current_p, (ptr_t) current);
+	    }
+#         endif /* ENABLE_TRACE */
+          PUSH_CONTENTS((ptr_t)current, mark_stack_top,
+  		           mark_stack_limit, current_p, exit2);
+        }
+        current_p += ALIGNMENT;
+      }
+
+#     ifndef SMALL_CONFIG
+	/* 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:%d Considering(2) %p -> %p\n",
+			      GC_gc_no, current_p, (ptr_t) deferred);
+	    }
+#       endif /* ENABLE_TRACE */
+        PUSH_CONTENTS((ptr_t)deferred, mark_stack_top,
+  		         mark_stack_limit, current_p, exit4);
+	next_object:;
+#     endif
+    }
+  }
+  return mark_stack_top;
+}
+
+#ifdef PARALLEL_MARK
+
+/* We assume we have an ANSI C Compiler.	*/
+GC_bool GC_help_wanted = FALSE;
+unsigned GC_helper_count = 0;
+unsigned GC_active_count = 0;
+word GC_mark_no = 0;
+
+#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.						*/
+
+
+/* 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.								*/
+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(high >= low-1 && high - low + 1 <= GC_mark_stack_size);
+    for (p = low; p <= high && i <= max; ++p) {
+	word descr = AO_load((volatile AO_t *) &(p -> mse_descr));
+	if (descr != 0) {
+	    /* Must be ordered after read of descr: */
+	    AO_store_release_write((volatile AO_t *) &(p -> mse_descr), 0);
+	    /* More than one thread may get this entry, but that's only */
+	    /* a minor performance problem.				*/
+	    ++top;
+	    top -> mse_descr = descr;
+	    top -> mse_start = p -> mse_start;
+	    GC_ASSERT((top -> mse_descr & GC_DS_TAGS) != GC_DS_LENGTH || 
+		      top -> mse_descr < (ptr_t)GC_greatest_plausible_heap_addr
+			                 - (ptr_t)GC_least_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 += (descr >> 8);
+	}
+    }
+    *next = p;
+    return top;
+}
+
+/* Copy back a local mark stack.	*/
+/* low and high are inclusive bounds.	*/
+void GC_return_mark_stack(mse * low, mse * high)
+{
+    mse * my_top;
+    mse * my_start;
+    size_t stack_size;
+
+    if (high < 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 (my_start - GC_mark_stack + stack_size > GC_mark_stack_size) {
+      if (GC_print_stats) {
+	  GC_log_printf("No room to copy back mark stack.");
+      }
+      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();
+}
+
+/* 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.	*/
+void GC_do_local_mark(mse *local_mark_stack, mse *local_top)
+{
+    unsigned n;
+#   define N_LOCAL_ITERS 1
+
+#   ifdef GC_ASSERTIONS
+      /* Make sure we don't hold mark lock. */
+	GC_acquire_mark_lock();
+	GC_release_mark_lock();
+#   endif
+    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 (local_top < local_mark_stack) return;
+	    if (local_top - local_mark_stack >= LOCAL_MARK_STACK_SIZE/2) {
+	 	GC_return_mark_stack(local_mark_stack, local_top);
+		return;
+	    }
+	}
+	if ((mse *)AO_load((volatile AO_t *)(&GC_mark_stack_top))
+	    < (mse *)AO_load(&GC_first_nonempty)
+	    && GC_active_count < GC_helper_count
+	    && local_top > local_mark_stack + 1) {
+	    /* 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, eventhough	*/
+	    /* it's harder.						*/
+ 	    mse * new_bottom = local_mark_stack
+				+ (local_top - local_mark_stack)/2;
+	    GC_ASSERT(new_bottom > local_mark_stack
+		      && new_bottom < 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);
+	}
+    }
+}
+
+#define ENTRIES_TO_GET 5
+
+long GC_markers = 2;		/* Normally changed by thread-library-	*/
+				/* -specific code.			*/
+
+/* 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 does not hold mark lock.					*/
+/* Caller has already incremented GC_helper_count.  We decrement it,	*/
+/* and maintain GC_active_count.					*/
+void GC_mark_local(mse *local_mark_stack, int id)
+{
+    mse * my_first_nonempty;
+
+    GC_acquire_mark_lock();
+    GC_active_count++;
+    my_first_nonempty = (mse *)AO_load(&GC_first_nonempty);
+    GC_ASSERT((mse *)AO_load(&GC_first_nonempty) >= GC_mark_stack && 
+	      (mse *)AO_load(&GC_first_nonempty) <=
+	      (mse *)AO_load((volatile AO_t *)(&GC_mark_stack_top)) + 1);
+    if (GC_print_stats == VERBOSE)
+	GC_log_printf("Starting mark helper %lu\n", (unsigned long)id);
+    GC_release_mark_lock();
+    for (;;) {
+  	size_t n_on_stack;
+        size_t n_to_get;
+	mse * my_top;
+	mse * local_top;
+        mse * global_first_nonempty = (mse *)AO_load(&GC_first_nonempty);
+
+    	GC_ASSERT(my_first_nonempty >= GC_mark_stack && 
+		  my_first_nonempty <=
+		  (mse *)AO_load((volatile AO_t *)(&GC_mark_stack_top))  + 1);
+    	GC_ASSERT(global_first_nonempty >= GC_mark_stack && 
+		  global_first_nonempty <= 
+		  (mse *)AO_load((volatile AO_t *)(&GC_mark_stack_top))  + 1);
+	if (my_first_nonempty < global_first_nonempty) {
+	    my_first_nonempty = global_first_nonempty;
+        } else if (global_first_nonempty < my_first_nonempty) {
+	    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));
+	n_on_stack = my_top - my_first_nonempty + 1;
+        if (0 == n_on_stack) {
+	    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
+		       && (mse *)AO_load(&GC_first_nonempty)
+		          > 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 &&
+		    (mse *)AO_load(&GC_first_nonempty) > 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;
+		    if (GC_print_stats == VERBOSE)
+		      GC_log_printf(
+		        "Finished mark helper %lu\n", (unsigned long)id);
+		    GC_release_mark_lock();
+		    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();
+	    }
+	}
+	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(my_first_nonempty >= GC_mark_stack && 
+	          my_first_nonempty <=
+		    (mse *)AO_load((volatile AO_t *)(&GC_mark_stack_top)) + 1);
+	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.					*/
+void GC_do_parallel_mark()
+{
+    mse local_mark_stack[LOCAL_MARK_STACK_SIZE];
+
+    GC_acquire_mark_lock();
+    GC_ASSERT(I_HOLD_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");
+    if (GC_print_stats == VERBOSE)
+	GC_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_release_mark_lock();
+    GC_notify_all_marker();
+	/* Wake up potential helpers.	*/
+    GC_mark_local(local_mark_stack, 0);
+    GC_acquire_mark_lock();
+    GC_help_wanted = FALSE;
+    /* Done; clean up.	*/
+    while (GC_helper_count > 0) GC_wait_marker();
+    /* GC_helper_count cannot be incremented while GC_help_wanted == FALSE */
+    if (GC_print_stats == VERBOSE)
+	GC_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 do not hold the GC lock, but the requestor does.	*/
+void GC_help_marker(word my_mark_no)
+{
+    mse local_mark_stack[LOCAL_MARK_STACK_SIZE];
+    unsigned my_id;
+
+    if (!GC_parallel) return;
+    GC_acquire_mark_lock();
+    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 >= GC_markers) {
+      /* Second test is useful only if original threads can also	*/
+      /* act as helpers.  Under Linux they can't.			*/
+      GC_release_mark_lock();
+      return;
+    }
+    GC_helper_count = my_id + 1;
+    GC_release_mark_lock();
+    GC_mark_local(local_mark_stack, my_id);
+    /* GC_mark_local decrements GC_helper_count. */
+}
+
+#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)
+{
+    mse * 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.		*/
+      static GC_bool GC_incremental_at_stack_alloc = 0;
+      GC_bool recycle_old = (!GC_incremental || GC_incremental_at_stack_alloc);
+
+      GC_incremental_at_stack_alloc = GC_incremental;
+#   else
+#     define recycle_old 1
+#   endif
+    
+    GC_mark_stack_too_small = FALSE;
+    if (GC_mark_stack_size != 0) {
+        if (new_stack != 0) {
+	  if (recycle_old) {
+            /* Recycle old space */
+              size_t page_offset = (word)GC_mark_stack & (GC_page_size - 1);
+              size_t size = GC_mark_stack_size * sizeof(struct GC_ms_entry);
+	      size_t displ = 0;
+          
+	      if (0 != page_offset) displ = GC_page_size - page_offset;
+	      size = (size - displ) & ~(GC_page_size - 1);
+	      if (size > 0) {
+	        GC_add_to_heap((struct hblk *)
+	      			((word)GC_mark_stack + displ), (word)size);
+	      }
+	  }
+          GC_mark_stack = new_stack;
+          GC_mark_stack_size = n;
+	  GC_mark_stack_limit = new_stack + n;
+	  if (GC_print_stats) {
+	      GC_log_printf("Grew mark stack to %lu frames\n",
+		    	    (unsigned long) GC_mark_stack_size);
+	  }
+        } else {
+	  if (GC_print_stats) {
+	      GC_log_printf("Failed to grow mark stack to %lu frames\n",
+		    	    (unsigned long) n);
+	  }
+        }
+    } else {
+        if (new_stack == 0) {
+            GC_err_printf("No space for mark stack\n");
+            EXIT();
+        }
+        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;
+}
+
+void GC_mark_init()
+{
+    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.
+ */
+void GC_push_all(ptr_t bottom, ptr_t top)
+{
+    register word length;
+    
+    bottom = (ptr_t)(((word) bottom + ALIGNMENT-1) & ~(ALIGNMENT-1));
+    top = (ptr_t)(((word) top) & ~(ALIGNMENT-1));
+    if (top == 0 || bottom == top) return;
+    GC_mark_stack_top++;
+    if (GC_mark_stack_top >= GC_mark_stack_limit) {
+	ABORT("unexpected mark stack overflow");
+    }
+    length = top - bottom;
+#   if GC_DS_TAGS > ALIGNMENT - 1
+	length += GC_DS_TAGS;
+	length &= ~GC_DS_TAGS;
+#   endif
+    GC_mark_stack_top -> mse_start = bottom;
+    GC_mark_stack_top -> mse_descr = length;
+}
+
+/*
+ * Analogous to the above, but push only those pages h with dirty_fn(h) != 0.
+ * We use push_fn 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 push_fn pushes a small fixed number
+ * of entries.  (This is invoked only if push_fn pushes a single entry,
+ * or if it marks each object before pushing it, thus ensuring progress
+ * in the event of a stack overflow.)
+ */
+void GC_push_selected(ptr_t bottom, ptr_t top,
+		      int (*dirty_fn) (struct hblk *),
+		      void (*push_fn) (ptr_t, ptr_t))
+{
+    struct hblk * h;
+
+    bottom = (ptr_t)(((word) bottom + ALIGNMENT-1) & ~(ALIGNMENT-1));
+    top = (ptr_t)(((word) top) & ~(ALIGNMENT-1));
+
+    if (top == 0 || bottom == top) return;
+    h = HBLKPTR(bottom + HBLKSIZE);
+    if (top <= (ptr_t) h) {
+  	if ((*dirty_fn)(h-1)) {
+	    (*push_fn)(bottom, top);
+	}
+	return;
+    }
+    if ((*dirty_fn)(h-1)) {
+        (*push_fn)(bottom, (ptr_t)h);
+    }
+    while ((ptr_t)(h+1) <= 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 */
+		(*push_fn)((ptr_t)h, top);
+		return;
+	    } else {
+		(*push_fn)((ptr_t)h, (ptr_t)(h+1));
+	    }
+	}
+	h++;
+    }
+    if ((ptr_t)h != top) {
+	if ((*dirty_fn)(h)) {
+            (*push_fn)((ptr_t)h, top);
+        }
+    }
+    if (GC_mark_stack_top >= GC_mark_stack_limit) {
+        ABORT("unexpected mark stack overflow");
+    }
+}
+
+# ifndef SMALL_CONFIG
+
+#ifdef PARALLEL_MARK
+    /* Break up root sections into page size chunks to better spread 	*/
+    /* out work.							*/
+    GC_bool GC_true_func(struct hblk *h) { return TRUE; }
+#   define GC_PUSH_ALL(b,t) GC_push_selected(b,t,GC_true_func,GC_push_all);
+#else
+#   define GC_PUSH_ALL(b,t) GC_push_all(b,t);
+#endif
+
+
+void GC_push_conditional(ptr_t bottom, ptr_t top, GC_bool all)
+{
+    if (all) {
+      if (GC_dirty_maintained) {
+#	ifdef PROC_VDB
+	    /* Pages that were never dirtied cannot contain pointers	*/
+	    GC_push_selected(bottom, top, GC_page_was_ever_dirty, GC_push_all);
+#	else
+	    GC_push_all(bottom, top);
+#	endif
+      } else {
+      	GC_push_all(bottom, top);
+      }
+    } else {
+	GC_push_selected(bottom, top, GC_page_was_dirty, GC_push_all);
+    }
+}
+#endif
+
+# if defined(MSWIN32) || defined(MSWINCE)
+  void __cdecl GC_push_one(word p)
+# else
+  void GC_push_one(word p)
+# endif
+{
+    GC_PUSH_ONE_STACK((ptr_t)p, MARKED_FROM_REGISTER);
+}
+
+struct GC_ms_entry *GC_mark_and_push(void *obj,
+				     mse *mark_stack_ptr,
+				     mse *mark_stack_limit,
+				     void **src)
+{
+    hdr * hhdr;
+
+    PREFETCH(obj);
+    GET_HDR(obj, hhdr);
+    if (EXPECT(IS_FORWARDING_ADDR_OR_NIL(hhdr),FALSE)) {
+      if (GC_all_interior_pointers) {
+	hhdr = GC_find_header(GC_base(obj));
+	if (hhdr == 0) {
+          GC_ADD_TO_BLACK_LIST_NORMAL(obj, src);
+	  return mark_stack_ptr;
+	}
+      } else {
+        GC_ADD_TO_BLACK_LIST_NORMAL(obj, src);
+	return mark_stack_ptr;
+      }
+    }
+    if (EXPECT(HBLK_IS_FREE(hhdr),0)) {
+	GC_ADD_TO_BLACK_LIST_NORMAL(obj, src);
+	return mark_stack_ptr;
+    }
+
+    PUSH_CONTENTS_HDR(obj, mark_stack_ptr /* modified */, mark_stack_limit,
+		      src, was_marked, hhdr, TRUE);
+ was_marked:
+    return mark_stack_ptr;
+}
+
+/* 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)
+    void GC_mark_and_push_stack(ptr_t p, ptr_t source)
+# else
+    void GC_mark_and_push_stack(ptr_t p)
+#   define source 0
+# endif
+{
+    hdr * hhdr; 
+    ptr_t r = p;
+  
+    PREFETCH(p);
+    GET_HDR(p, hhdr);
+    if (EXPECT(IS_FORWARDING_ADDR_OR_NIL(hhdr),FALSE)) {
+        if (hhdr != 0) {
+          r = GC_base(p);
+	  hhdr = HDR(r);
+	}
+        if (hhdr == 0) {
+            GC_ADD_TO_BLACK_LIST_STACK(p, source);
+	    return;
+	}
+    }
+    if (EXPECT(HBLK_IS_FREE(hhdr),0)) {
+	GC_ADD_TO_BLACK_LIST_NORMAL(p, src);
+	return;
+    }
+#   if defined(MANUAL_VDB) && defined(THREADS)
+      /* Pointer is on the stack.  We may have dirtied the object	*/
+      /* it points to, but not yet have called GC_dirty();	*/
+      GC_dirty(p);	/* Implicitly affects entire object.	*/
+#   endif
+    PUSH_CONTENTS_HDR(r, GC_mark_stack_top, GC_mark_stack_limit,
+		      source, mark_and_push_exit, hhdr, FALSE);
+  mark_and_push_exit: ;
+    /* 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.							*/
+}
+
+# ifdef TRACE_BUF
+
+# define TRACE_ENTRIES 1000
+
+struct trace_entry {
+    char * kind;
+    word gc_no;
+    word bytes_allocd;
+    word arg1;
+    word arg2;
+} GC_trace_buf[TRACE_ENTRIES];
+
+int GC_trace_buf_ptr = 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;
+}
+
+void GC_print_trace(word gc_no, GC_bool lock)
+{
+    int i;
+    struct trace_entry *p;
+    
+    if (lock) LOCK();
+    for (i = GC_trace_buf_ptr-1; i != GC_trace_buf_ptr; i--) {
+    	if (i < 0) i = TRACE_ENTRIES-1;
+    	p = GC_trace_buf + i;
+    	if (p -> gc_no < gc_no || p -> kind == 0) return;
+    	printf("Trace:%s (gc:%d,bytes:%d) 0x%X, 0x%X\n",
+    		p -> kind, p -> gc_no, p -> bytes_allocd,
+    		(p -> arg1) ^ 0x80000000, (p -> arg2) ^ 0x80000000);
+    }
+    printf("Trace incomplete\n");
+    if (lock) 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.
+ */
+void GC_push_all_eager(ptr_t bottom, ptr_t top)
+{
+    word * b = (word *)(((word) bottom + ALIGNMENT-1) & ~(ALIGNMENT-1));
+    word * t = (word *)(((word) top) & ~(ALIGNMENT-1));
+    register word *p;
+    register ptr_t q;
+    register word *lim;
+    register ptr_t greatest_ha = GC_greatest_plausible_heap_addr;
+    register ptr_t least_ha = 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 = t - 1 /* longword */;
+      for (p = b; p <= lim; p = (word *)(((ptr_t)p) + ALIGNMENT)) {
+	q = (ptr_t)(*p);
+	GC_PUSH_ONE_STACK((ptr_t)q, p);
+      }
+#   undef GC_greatest_plausible_heap_addr
+#   undef GC_least_plausible_heap_addr
+}
+
+#ifndef THREADS
+/*
+ * A version of GC_push_all that treats all interior pointers as valid
+ * and scans part of the area immediately, to make sure that saved
+ * register values are not lost.
+ * Cold_gc_frame delimits the stack section that must be scanned
+ * eagerly.  A zero value indicates that no eager scanning is needed.
+ * We don't need to worry about the MANUAL_VDB case here, since this
+ * is only called in the single-threaded case.  We assume that we
+ * cannot collect between an assignment and the corresponding
+ * GC_dirty() call.
+ */
+void GC_push_all_stack_partially_eager(ptr_t bottom, ptr_t top,
+				       ptr_t cold_gc_frame)
+{
+  if (!NEED_FIXUP_POINTER && GC_all_interior_pointers) {
+    /* Push the hot end of the stack eagerly, so that register values   */
+    /* saved inside GC frames are marked before they disappear.		*/
+    /* The rest of the marking can be deferred until later.		*/
+    if (0 == cold_gc_frame) {
+	GC_push_all_stack(bottom, top);
+	return;
+    }
+    GC_ASSERT(bottom <= cold_gc_frame && cold_gc_frame <= top);
+#   ifdef STACK_GROWS_DOWN
+	GC_push_all(cold_gc_frame - sizeof(ptr_t), top);
+	GC_push_all_eager(bottom, cold_gc_frame);
+#   else /* STACK_GROWS_UP */
+	GC_push_all(bottom, cold_gc_frame + sizeof(ptr_t));
+	GC_push_all_eager(cold_gc_frame, top);
+#   endif /* STACK_GROWS_UP */
+  } else {
+    GC_push_all_eager(bottom, top);
+  }
+# ifdef TRACE_BUF
+      GC_add_trace_entry("GC_push_all_stack", bottom, top);
+# endif
+}
+#endif /* !THREADS */
+
+void GC_push_all_stack(ptr_t bottom, ptr_t top)
+{
+# if defined(THREADS) && defined(MPROTECT_VDB)
+    GC_push_all_eager(bottom, top);
+# else
+    if (!NEED_FIXUP_POINTER && GC_all_interior_pointers) {
+      GC_push_all(bottom, top);
+    } else {
+      GC_push_all_eager(bottom, top);
+    }
+# endif
+}
+
+#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) \
+		{ ptr_t qcontents = (ptr_t)((q)[0]); \
+	          GC_PUSH_ONE_HEAP(qcontents, (q)); }
+# elif GC_GRANULE_WORDS == 2
+#   define USE_PUSH_MARKED_ACCELERATORS
+#   define PUSH_GRANULE(q) \
+		{ ptr_t qcontents = (ptr_t)((q)[0]); \
+	          GC_PUSH_ONE_HEAP(qcontents, (q)); \
+		  qcontents = (ptr_t)((q)[1]); \
+	          GC_PUSH_ONE_HEAP(qcontents, (q)+1); }
+# elif GC_GRANULE_WORDS == 4
+#   define USE_PUSH_MARKED_ACCELERATORS
+#   define PUSH_GRANULE(q) \
+		{ ptr_t qcontents = (ptr_t)((q)[0]); \
+	          GC_PUSH_ONE_HEAP(qcontents, (q)); \
+		  qcontents = (ptr_t)((q)[1]); \
+	          GC_PUSH_ONE_HEAP(qcontents, (q)+1); \
+		  qcontents = (ptr_t)((q)[2]); \
+	          GC_PUSH_ONE_HEAP(qcontents, (q)+2); \
+		  qcontents = (ptr_t)((q)[3]); \
+	          GC_PUSH_ONE_HEAP(qcontents, (q)+3); }
+# endif
+#endif
+
+#ifdef USE_PUSH_MARKED_ACCELERATORS
+/* Push all objects reachable from marked objects in the given block */
+/* containing objects of size 1 granule.			     */
+void GC_push_marked1(struct hblk *h, hdr *hhdr)
+{
+    word * mark_word_addr = &(hhdr->hb_marks[0]);
+    word *p;
+    word *plim;
+    word *q;
+    word mark_word;
+
+    /* Allow registers to be used for some frequently acccessed	*/
+    /* global variables.  Otherwise aliasing issues are likely	*/
+    /* to prevent that.						*/
+    ptr_t greatest_ha = GC_greatest_plausible_heap_addr;
+    ptr_t least_ha = GC_least_plausible_heap_addr;
+    mse * mark_stack_top = GC_mark_stack_top;
+    mse * mark_stack_limit = 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( p < plim )  {
+	    mark_word = *mark_word_addr++;
+	    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
+
+    GC_mark_stack_top = mark_stack_top;
+}
+
+
+#ifndef UNALIGNED
+
+/* Push all objects reachable from marked objects in the given block */
+/* of size 2 (granules) objects.				     */
+void GC_push_marked2(struct hblk *h, hdr *hhdr)
+{
+    word * mark_word_addr = &(hhdr->hb_marks[0]);
+    word *p;
+    word *plim;
+    word *q;
+    word mark_word;
+
+    ptr_t greatest_ha = GC_greatest_plausible_heap_addr;
+    ptr_t least_ha = GC_least_plausible_heap_addr;
+    mse * mark_stack_top = GC_mark_stack_top;
+    mse * mark_stack_limit = 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( p < plim )  {
+	    mark_word = *mark_word_addr++;
+	    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
+
+    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.    */
+void GC_push_marked4(struct hblk *h, hdr *hhdr)
+{
+    word * mark_word_addr = &(hhdr->hb_marks[0]);
+    word *p;
+    word *plim;
+    word *q;
+    word mark_word;
+
+    ptr_t greatest_ha = GC_greatest_plausible_heap_addr;
+    ptr_t least_ha = GC_least_plausible_heap_addr;
+    mse * mark_stack_top = GC_mark_stack_top;
+    mse * mark_stack_limit = 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( p < plim )  {
+	    mark_word = *mark_word_addr++;
+	    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
+    GC_mark_stack_top = mark_stack_top;
+}
+
+#endif /* GC_GRANULE_WORDS < 4 */
+
+#endif /* UNALIGNED */
+
+#endif /* USE_PUSH_MARKED_ACCELERATORS */
+
+/* Push all objects reachable from marked objects in the given block */
+void GC_push_marked(struct hblk *h, hdr *hhdr)
+{
+    size_t 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;
+    GC_n_rescuing_pages++;
+    GC_objects_are_marked = TRUE;
+    if (sz > MAXOBJBYTES) {
+        lim = h -> hb_body;
+    } else {
+        lim = (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)
+       case 2:
+         GC_push_marked2(h, hhdr);
+         break;
+#     if GC_GRANULE_WORDS < 4
+       case 4:
+         GC_push_marked4(h, hhdr);
+         break;
+#     endif
+#    endif
+#   endif       
+     default:
+      GC_mark_stack_top_reg = GC_mark_stack_top;
+      for (p = h -> hb_body, bit_no = 0; p <= lim;
+	   p += sz, bit_no += MARK_BIT_OFFSET(sz)) {
+         if (mark_bit_from_hdr(hhdr, bit_no)) {
+           /* Mark from fields inside the object */
+             PUSH_OBJ(p, hhdr, GC_mark_stack_top_reg, mark_stack_limit);
+         }
+      }
+      GC_mark_stack_top = GC_mark_stack_top_reg;
+    }
+}
+
+#ifndef SMALL_CONFIG
+/* Test whether any page in the given block is dirty	*/
+GC_bool GC_block_was_dirty(struct hblk *h, hdr *hhdr)
+{
+    size_t sz = hhdr -> hb_sz;
+    
+    if (sz <= MAXOBJBYTES) {
+         return(GC_page_was_dirty(h));
+    } else {
+    	 ptr_t p = (ptr_t)h;
+         while (p < (ptr_t)h + sz) {
+             if (GC_page_was_dirty((struct hblk *)p)) return(TRUE);
+             p += HBLKSIZE;
+         }
+         return(FALSE);
+    }
+}
+#endif /* SMALL_CONFIG */
+
+/* Similar to GC_push_next_marked, but return address of next block	*/
+struct hblk * GC_push_next_marked(struct hblk *h)
+{
+    hdr * hhdr = HDR(h);
+    
+    if (EXPECT(IS_FORWARDING_ADDR_OR_NIL(hhdr), FALSE)) {
+      h = GC_next_used_block(h);
+      if (h == 0) return(0);
+      hhdr = GC_find_header((ptr_t)h);
+    }
+    GC_push_marked(h, hhdr);
+    return(h + OBJ_SZ_TO_BLOCKS(hhdr -> hb_sz));
+}
+
+#ifndef SMALL_CONFIG
+/* Identical to above, but mark only from dirty pages	*/
+struct hblk * GC_push_next_marked_dirty(struct hblk *h)
+{
+    hdr * hhdr = HDR(h);
+    
+    if (!GC_dirty_maintained) { ABORT("dirty bits not set up"); }
+    for (;;) {
+	if (EXPECT(IS_FORWARDING_ADDR_OR_NIL(hhdr), FALSE)) {
+          h = GC_next_used_block(h);
+          if (h == 0) return(0);
+          hhdr = GC_find_header((ptr_t)h);
+	}
+#	ifdef STUBBORN_ALLOC
+          if (hhdr -> hb_obj_kind == STUBBORN) {
+            if (GC_page_was_changed(h) && GC_block_was_dirty(h, hhdr)) {
+                break;
+            }
+          } else {
+            if (GC_block_was_dirty(h, hhdr)) break;
+          }
+#	else
+	  if (GC_block_was_dirty(h, hhdr)) break;
+#	endif
+        h += OBJ_SZ_TO_BLOCKS(hhdr -> hb_sz);
+	hhdr = HDR(h);
+    }
+    GC_push_marked(h, hhdr);
+    return(h + OBJ_SZ_TO_BLOCKS(hhdr -> hb_sz));
+}
+#endif
+
+/* Similar to above, but for uncollectable pages.  Needed since we	*/
+/* do not clear marks for such pages, even for full collections.	*/
+struct hblk * GC_push_next_marked_uncollectable(struct hblk *h)
+{
+    hdr * hhdr = HDR(h);
+    
+    for (;;) {
+	if (EXPECT(IS_FORWARDING_ADDR_OR_NIL(hhdr), FALSE)) {
+          h = GC_next_used_block(h);
+          if (h == 0) return(0);
+          hhdr = GC_find_header((ptr_t)h);
+	}
+	if (hhdr -> hb_obj_kind == UNCOLLECTABLE) break;
+        h += OBJ_SZ_TO_BLOCKS(hhdr -> hb_sz);
+	hhdr = HDR(h);
+    }
+    GC_push_marked(h, hhdr);
+    return(h + OBJ_SZ_TO_BLOCKS(hhdr -> hb_sz));
+}
+