Repeat last debugger command in the arm simulator when command input is empty.

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 542cc302d30f09c8db016b977930181ae76304a8..b4458000fc6a229ec6fb4a74818e78f736b69dee 100644
--- a/src/arm/simulator-arm.cc
+++ b/src/arm/simulator-arm.cc
@@ -53,7 +53,7 @@ namespace internal {
 // code.
 class ArmDebugger {
  public:
-  explicit ArmDebugger(Simulator* sim);
+  explicit ArmDebugger(Simulator* sim) : sim_(sim) { };
   ~ArmDebugger();
 
   void Stop(Instruction* instr);
@@ -84,11 +84,6 @@ class ArmDebugger {
 };
 
 
-ArmDebugger::ArmDebugger(Simulator* sim) {
-  sim_ = sim;
-}
-
-
 ArmDebugger::~ArmDebugger() {
 }
 
@@ -296,6 +291,13 @@ void ArmDebugger::Debug() {
     if (line == NULL) {
       break;
     } else {
+      char* last_input = sim_->last_debugger_input();
+      if (strcmp(line, "\n") == 0 && last_input != NULL) {
+        line = last_input;
+      } else {
+        // Ownership is transferred to sim_;
+        sim_->set_last_debugger_input(line);
+      }
       // Use sscanf to parse the individual parts of the command line. At the
       // moment no command expects more than two parameters.
       int argc = SScanF(line,
@@ -611,7 +613,6 @@ void ArmDebugger::Debug() {
         PrintF("Unknown command: %s\n", cmd);
       }
     }
-    DeleteArray(line);
   }
 
   // Add all the breakpoints back to stop execution and enter the debugger
@@ -645,6 +646,12 @@ static bool AllOnOnePage(uintptr_t start, int size) {
 }
 
 
+void Simulator::set_last_debugger_input(char* input) {
+  DeleteArray(last_debugger_input_);
+  last_debugger_input_ = input;
+}
+
+
 void Simulator::FlushICache(v8::internal::HashMap* i_cache,
                             void* start_addr,
                             size_t size) {
@@ -781,6 +788,8 @@ Simulator::Simulator(Isolate* isolate) : isolate_(isolate) {
   registers_[pc] = bad_lr;
   registers_[lr] = bad_lr;
   InitializeCoverage();
+
+  last_debugger_input_ = NULL;
 }