Check for valid PC when stepping in the ARM sim debugger.

src/arm/simulator-arm.cc

Index: src/arm/simulator-arm.cc
diff --git a/src/arm/simulator-arm.cc b/src/arm/simulator-arm.cc
index 629c209ea2f30a3949ad123e51315d0e80bff0f3..394ef27eb5cfee3c09b7fb1e422a81a13ca58218 100644
--- a/src/arm/simulator-arm.cc
+++ b/src/arm/simulator-arm.cc
@@ -1,4 +1,4 @@
-// Copyright 2011 the V8 project authors. All rights reserved.
+// 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:
@@ -276,7 +276,7 @@ void ArmDebugger::Debug() {
   // make them invisible to all commands.
   UndoBreakpoints();
 
-  while (!done) {
+  while (!done && !sim_->has_bad_pc()) {
     if (last_pc != sim_->get_pc()) {
       disasm::NameConverter converter;
       disasm::Disassembler dasm(converter);