Extracting relocation info from the code object....

src/objects.cc

Index: src/objects.cc
===================================================================
--- src/objects.cc	(revision 5008)
+++ src/objects.cc	(working copy)
@@ -5292,7 +5292,15 @@
                   RelocInfo::ModeMask(RelocInfo::DEBUG_BREAK_SLOT) |
                   RelocInfo::ModeMask(RelocInfo::RUNTIME_ENTRY);
 
-  for (RelocIterator it(this, mode_mask); !it.done(); it.next()) {
+  // Use the relocation info pointer before it is visited by
+  // the heap compaction in the next statement.
+  RelocIterator it(this, mode_mask);
+
+  IteratePointers(v,
+                  kRelocationInfoOffset,
+                  kRelocationInfoOffset + kPointerSize);
+
+  for (; !it.done(); it.next()) {
     it.rinfo()->Visit(v);
   }
 
@@ -5312,14 +5320,6 @@
   // copy code
   memmove(instruction_start(), desc.buffer, desc.instr_size);
 
-  // fill gap with zero bytes
-  { byte* p = instruction_start() + desc.instr_size;
-    byte* q = relocation_start();
-    while (p < q) {
-      *p++ = 0;
-    }
-  }
-
   // copy reloc info
   memmove(relocation_start(),
           desc.buffer + desc.buffer_size - desc.reloc_size,