Fix liveedit heap traversal bug with write barrier

src/liveedit.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 950 matching lines @@
  private:
   Code* original_;
   Code* substitution_;
 };
 
 
 // Finds all references to original and replaces them with substitution.
 static void ReplaceCodeObject(Code* original, Code* substitution) {
   ASSERT(!HEAP->InNewSpace(substitution));
 
+  // Perform a full GC in order to avoid dead objects and to
+  // notify the GC with a write barrier so that the it can keep track of where
+  // there are pointers in case some of the objects move in a compacting GC.

[Erik Corry, 2012/06/25 11:43:51]

I think this comment should read:

// Perform a full GC in order to ensure that we are not in the middle of an
incremental marking phase when we are replacing the code object.  Since we are
not in an incremental marking phase we can write pointers to code objects (that
are never in new space) without worrying about write barriers.

[Peter Rybin, 2012/06/25 21:43:42]

Thank you!

+  HEAP->CollectAllGarbage(Heap::kMakeHeapIterableMask,
+                          "liveedit.cc ReplaceCodeObject");
+
   AssertNoAllocation no_allocations_please;
 
   ReplacingVisitor visitor(original, substitution);
 
   // Iterate over all roots. Stack frames may have pointer into original code,
   // so temporary replace the pointers with offset numbers
   // in prologue/epilogue.
   HEAP->IterateRoots(&visitor, VISIT_ALL);
 
   // Now iterate over all pointers of all objects, including code_target
@@ skipping 887 matching lines @@
 
 bool LiveEditFunctionTracker::IsActive(Isolate* isolate) {
   return false;
 }
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 
 
 } }  // namespace v8::internal