In reporting step-in positions be more accurate with a position the debugger paused at

src/runtime.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 12058 matching lines @@
   Object* check;
   { MaybeObject* maybe_check = Runtime_CheckExecutionState(
       RUNTIME_ARGUMENTS(isolate, args));
     if (!maybe_check->ToObject(&check)) return maybe_check;
   }
   CONVERT_SMI_ARG_CHECKED(wrapped_id, 1);
 
   // Get the frame where the debugging is performed.
   StackFrame::Id id = UnwrapFrameId(wrapped_id);
   JavaScriptFrameIterator frame_it(isolate, id);
+  RUNTIME_ASSERT(!frame_it.done());
+
   JavaScriptFrame* frame = frame_it.frame();
 
   Handle<JSFunction> fun =
       Handle<JSFunction>(frame->function());
   Handle<SharedFunctionInfo> shared =
       Handle<SharedFunctionInfo>(fun->shared());
 
   if (!isolate->debug()->EnsureDebugInfo(shared, fun)) {
     return isolate->heap()->undefined_value();
   }
 
   Handle<DebugInfo> debug_info = Debug::GetDebugInfo(shared);
 
   int len = 0;
   Handle<JSArray> array(isolate->factory()->NewJSArray(10));
   // Find the break point where execution has stopped.
   BreakLocationIterator break_location_iterator(debug_info,
                                                 ALL_BREAK_LOCATIONS);
 
-  break_location_iterator.FindBreakLocationFromAddress(frame->pc());
+  break_location_iterator.FindBreakLocationFromAddress(frame->pc() - 1);
   int current_statement_pos = break_location_iterator.statement_position();
 
   while (!break_location_iterator.Done()) {
+    bool accept;
     if (break_location_iterator.pc() > frame->pc()) {
+      accept = true;
+    } else {
+      StackFrame::Id break_frame_id = isolate->debug()->break_frame_id();
+      // The break point is near our pc. Could be a step-in possibility,
+      // that is currently taken by active debugger call.
+      if (break_frame_id == StackFrame::NO_ID) {
+        // We are not stepping.
+        accept = false;
+      } else {
+        JavaScriptFrameIterator additional_frame_it(isolate, break_frame_id);
+        // If our frame is a top frame and we are stepping, we can do step-in
+        // at this place.
+        accept = additional_frame_it.frame()->id() == id;
+      }
+    }
+    if (accept) {
       if (break_location_iterator.IsStepInLocation(isolate)) {
         Smi* position_value = Smi::FromInt(break_location_iterator.position());
         JSObject::SetElement(array, len,
             Handle<Object>(position_value, isolate),
             NONE, kNonStrictMode);
         len++;
       }
     }
     // Advance iterator.
     break_location_iterator.Next();
@@ skipping 2582 matching lines @@
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                        "Runtime::PerformGC");
   }
 }
 
 
 } }  // namespace v8::internal