Guard against undefined fields in global context.

src/deoptimizer.cc

 // Copyright 2011 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 246 matching lines @@
         GlobalObject::cast(object)->global_context(), visitor);
   }
 }
 
 
 void Deoptimizer::VisitAllOptimizedFunctions(
     OptimizedFunctionVisitor* visitor) {
   AssertNoAllocation no_allocation;
 
   // Run through the list of all global contexts and deoptimize.
-  Object* global = Isolate::Current()->heap()->global_contexts_list();
-  while (!global->IsUndefined()) {
-    VisitAllOptimizedFunctionsForGlobalObject(Context::cast(global)->global(),
-                                              visitor);
-    global = Context::cast(global)->get(Context::NEXT_CONTEXT_LINK);
+  Object* context = Isolate::Current()->heap()->global_contexts_list();
+  while (!context->IsUndefined()) {
+    // GC can happen when the context is not fully initialized,
+    // so the global field of the context can be undefined.
+    Object* global = Context::cast(context)->get(Context::GLOBAL_INDEX);
+    if (!global->IsUndefined()) {
+      VisitAllOptimizedFunctionsForGlobalObject(JSObject::cast(global),
+                                                visitor);
+    }
+    context = Context::cast(context)->get(Context::NEXT_CONTEXT_LINK);
   }
 }
 
 
 void Deoptimizer::HandleWeakDeoptimizedCode(
     v8::Persistent<v8::Value> obj, void* data) {
   DeoptimizingCodeListNode* node =
       reinterpret_cast<DeoptimizingCodeListNode*>(data);
   RemoveDeoptimizingCode(*node->code());
 #ifdef DEBUG
@@ skipping 1211 matching lines @@
 
 void DeoptimizedFrameInfo::Iterate(ObjectVisitor* v) {
   v->VisitPointer(BitCast<Object**>(&function_));
   v->VisitPointers(parameters_, parameters_ + parameters_count_);
   v->VisitPointers(expression_stack_, expression_stack_ + expression_count_);
 }
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 } }  // namespace v8::internal