--- old/src/share/vm/gc_implementation/parallelScavenge/objectStartArray.cpp	2015-02-12 22:25:30.669173848 -0800
+++ new/src/share/vm/gc_implementation/parallelScavenge/objectStartArray.cpp	2015-02-12 22:25:30.585173845 -0800
@@ -126,7 +126,10 @@
 
 bool ObjectStartArray::object_starts_in_range(HeapWord* start_addr,
                                               HeapWord* end_addr) const {
-  assert(start_addr <= end_addr, "range is wrong");
+  assert(start_addr <= end_addr,
+          err_msg("Range is wrong. start_addr (" PTR_FORMAT ") is after end_addr (" PTR_FORMAT ")",
+                 p2i(start_addr), p2i(end_addr)));
+
   if (start_addr > end_addr) {
     return false;
   }
--- old/src/share/vm/gc_implementation/parallelScavenge/objectStartArray.hpp	2015-02-12 22:25:31.009173859 -0800
+++ new/src/share/vm/gc_implementation/parallelScavenge/objectStartArray.hpp	2015-02-12 22:25:30.921173856 -0800
@@ -120,7 +120,9 @@
   MemRegion covered_region() { return _covered_region; }
 
   void allocate_block(HeapWord* p) {
-    assert(_covered_region.contains(p), "Must be in covered region");
+    assert(_covered_region.contains(p), 
+          err_msg("p (" PTR_FORMAT ") is not in covered region [" PTR_FORMAT ", " PTR_FORMAT ")",
+                 p2i(p), p2i(_covered_region.start()), p2i(_covered_region.end())));
     jbyte* block = block_for_addr(p);
     HeapWord* block_base = addr_for_block(block);
     size_t offset = pointer_delta(p, block_base, sizeof(HeapWord*));
@@ -135,7 +137,9 @@
   // object in that block. Scroll backwards by one, and the first
   // object hit should be at the beginning of the block
   HeapWord* object_start(HeapWord* addr) const {
-    assert(_covered_region.contains(addr), "Must be in covered region");
+    assert(_covered_region.contains(addr), 
+          err_msg("addr (" PTR_FORMAT ") is not in covered region [" PTR_FORMAT ", " PTR_FORMAT ")",
+                 p2i(addr), p2i(_covered_region.start()), p2i(_covered_region.end())));
     jbyte* block = block_for_addr(addr);
     HeapWord* scroll_forward = offset_addr_for_block(block--);
     while (scroll_forward > addr) {
@@ -153,7 +157,9 @@
   }
 
   bool is_block_allocated(HeapWord* addr) {
-    assert(_covered_region.contains(addr), "Must be in covered region");
+    assert(_covered_region.contains(addr), 
+          err_msg("addr (" PTR_FORMAT ") is not in covered region [" PTR_FORMAT ", " PTR_FORMAT ")",
+                 p2i(addr), p2i(_covered_region.start()), p2i(_covered_region.end())));
     jbyte* block = block_for_addr(addr);
     if (*block == clean_block)
       return false;