8332401: G1: TestFromCardCacheIndex.java with -XX:GCCardSizeInBytes=1…

…28 triggers underflow assertion

Reviewed-by: tschatzl, iwalulya

src/hotspot/share/gc/g1/g1BlockOffsetTable.inline.hpp

@@ -62,7 +62,8 @@ inline uint8_t* G1BlockOffsetTable::entry_for_addr(const void* const p) const {
 }
 
 inline HeapWord* G1BlockOffsetTable::addr_for_entry(const uint8_t* const p) const {
-  size_t delta = pointer_delta(p, _offset_base, sizeof(uint8_t));
+  // _offset_base can be "negative", so can't use pointer_delta().
+  size_t delta = p - _offset_base;
   HeapWord* result = (HeapWord*) (delta << CardTable::card_shift());
   assert(_reserved.contains(result),
          "out of bounds accessor from block offset table");

src/hotspot/share/gc/parallel/objectStartArray.hpp

@@ -57,7 +57,8 @@ class ObjectStartArray : public CHeapObj<mtGC> {
 
   // Mapping from object start array entry to address of first word
   HeapWord* addr_for_entry(const uint8_t* const p) const {
-    size_t delta = pointer_delta(p, _offset_base, sizeof(uint8_t));
+    // _offset_base can be "negative", so can't use pointer_delta().
+    size_t delta = p - _offset_base;
     HeapWord* result = (HeapWord*) (delta << CardTable::card_shift());
     assert(_covered_region.contains(result),
            "out of bounds accessor from card marking array");

src/hotspot/share/gc/serial/serialBlockOffsetTable.inline.hpp

@@ -35,7 +35,8 @@ inline uint8_t* SerialBlockOffsetTable::entry_for_addr(const void* const p) cons
 }
 
 inline HeapWord* SerialBlockOffsetTable::addr_for_entry(const uint8_t* const p) const {
-  size_t delta = pointer_delta(p, _offset_base, sizeof(uint8_t));
+  // _offset_base can be "negative", so can't use pointer_delta().
+  size_t delta = p - _offset_base;
   HeapWord* result = (HeapWord*) (delta << CardTable::card_shift());
   assert(_reserved.contains(result),
          "out of bounds accessor from block offset array");