--- a/src/share/vm/gc_implementation/parNew/parCardTableModRefBS.cpp	Tue May 10 12:26:10 2011 -0700
+++ b/src/share/vm/gc_implementation/parNew/parCardTableModRefBS.cpp	Wed May 11 15:47:12 2011 -0700
@@ -351,7 +351,7 @@
         // covers.
         const uintptr_t last_chunk_index_to_check = addr_to_chunk_index(last_block + last_block_size - 1)
                                                     - lowest_non_clean_base_chunk_index;
-        DEBUG_ONLY(const uintptr_t last_chunk_index = addr_to_chunk_index(used.end())
+        DEBUG_ONLY(const uintptr_t last_chunk_index = addr_to_chunk_index(used.last())
                                                       - lowest_non_clean_base_chunk_index;)
         assert(last_chunk_index_to_check <= last_chunk_index,
                err_msg("Out of bounds: last_chunk_index_to_check " INTPTR_FORMAT

--- a/src/share/vm/memory/blockOffsetTable.cpp	Tue May 10 12:26:10 2011 -0700
+++ b/src/share/vm/memory/blockOffsetTable.cpp	Wed May 11 15:47:12 2011 -0700
@@ -541,20 +541,33 @@
     // to go back by.
     size_t n_cards_back = entry_to_cards_back(offset);
     q -= (N_words * n_cards_back);
-    assert(q >= _sp->bottom(), "Went below bottom!");
+    assert(q >= _sp->bottom(),
+           err_msg("q = " PTR_FORMAT " crossed below bottom = " PTR_FORMAT,
+                   q, _sp->bottom()));
+    assert(q < _sp->end(),
+           err_msg("q = " PTR_FORMAT " crossed above end = " PTR_FORMAT,
+                   q, _sp->end()));
     index -= n_cards_back;
     offset = _array->offset_array(index);
   }
   assert(offset < N_words, "offset too large");
   index--;
   q -= offset;
+  assert(q >= _sp->bottom(),
+         err_msg("q = " PTR_FORMAT " crossed below bottom = " PTR_FORMAT,
+                 q, _sp->bottom()));
+  assert(q < _sp->end(),
+         err_msg("q = " PTR_FORMAT " crossed above end = " PTR_FORMAT,
+                 q, _sp->end()));
   HeapWord* n = q;
 
   while (n <= addr) {
     debug_only(HeapWord* last = q);   // for debugging
     q = n;
     n += _sp->block_size(n);
-    assert(n > q, err_msg("Looping at: " INTPTR_FORMAT, n));
+    assert(n > q,
+           err_msg("Looping at n = " PTR_FORMAT " with last = " PTR_FORMAT " _sp = [" PTR_FORMAT "," PTR_FORMAT ")",
+                   n, last, _sp->bottom(), _sp->end()));
   }
   assert(q <= addr, err_msg("wrong order for current (" INTPTR_FORMAT ") <= arg (" INTPTR_FORMAT ")", q, addr));
   assert(addr <= n, err_msg("wrong order for arg (" INTPTR_FORMAT ") <= next (" INTPTR_FORMAT ")", addr, n));

--- a/src/share/vm/memory/cardTableModRefBS.hpp	Tue May 10 12:26:10 2011 -0700
+++ b/src/share/vm/memory/cardTableModRefBS.hpp	Wed May 11 15:47:12 2011 -0700
@@ -150,7 +150,9 @@
   // Mapping from address to card marking array entry
   jbyte* byte_for(const void* p) const {
     assert(_whole_heap.contains(p),
-           "out of bounds access to card marking array");
+           err_msg("Attempt to access p = "PTR_FORMAT" out of bounds of "
+                   " card marking array's _whole_heap = ["PTR_FORMAT","PTR_FORMAT")",
+                   p, _whole_heap.start(), _whole_heap.end()));
     jbyte* result = &byte_map_base[uintptr_t(p) >> card_shift];
     assert(result >= _byte_map && result < _byte_map + _byte_map_size,
            "out of bounds accessor for card marking array");
@@ -451,14 +453,18 @@
     size_t delta = pointer_delta(p, byte_map_base, sizeof(jbyte));
     HeapWord* result = (HeapWord*) (delta << card_shift);
     assert(_whole_heap.contains(result),
-           "out of bounds accessor from card marking array");
+           err_msg("Returning result = "PTR_FORMAT" out of bounds of "
+                   " card marking array's _whole_heap = ["PTR_FORMAT","PTR_FORMAT")",
+                   result, _whole_heap.start(), _whole_heap.end()));
     return result;
   }
 
   // Mapping from address to card marking array index.
   size_t index_for(void* p) {
     assert(_whole_heap.contains(p),
-           "out of bounds access to card marking array");
+           err_msg("Attempt to access p = "PTR_FORMAT" out of bounds of "
+                   " card marking array's _whole_heap = ["PTR_FORMAT","PTR_FORMAT")",
+                   p, _whole_heap.start(), _whole_heap.end()));
     return byte_for(p) - _byte_map;
   }