Fix issue 825 (LiveEdit vs. function with no locals) in core and for ia32.

src/debug.h

 // Copyright 2012 the V8 project authors. All rights reserved.
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 // modification, are permitted provided that the following conditions are
 // met:
 //
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@@ skipping 439 matching lines @@
   // at this address (possibly updated by GC) may be used later when preparing
   // 'step in' operation.
   static Object** SetUpFrameDropperFrame(StackFrame* bottom_js_frame,
                                          Handle<Code> code);
 
   static const int kFrameDropperFrameSize;
 
   // Architecture-specific constant.
   static const bool kFrameDropperSupported;
 
+  /**
+   * Defines layout of a stack frame that supports padding. This is a regular
+   * internal frame that has a flexible stack structure. LiveEdit can shift
+   * its lower part up the stack, taking up the 'padding' space when additional
+   * stack memory is required.
+   * Such frame is expected immediately above the topmost JavaScript frame.
+   *
+   * Stack Layout:
+   *   --- Top
+   *   LiveEdit routine frames
+   *   ---
+   *   C frames of debug handler
+   *   ---
+   *   ...
+   *   ---
+   *      An internal frame that has n padding words:
+   *      - any number of words as needed by code -- upper part of frame
+   *      - padding size: a word storing n*2, n -- current size of padding
+   *      - padding: n words filled with kPaddingValue
+   *      - 3 context/type words of a regular InternalFrame
+   *      - fp
+   *   ---
+   *      Topmost JavaScript frame
+   *   ---
+   *   ...
+   *   --- Bottom
+   */
+  struct FramePaddingLayout {

[Yang, 2012/05/02 11:38:34]

we would typically define this as a class deriving from AllStatic (e.g. class
ArgumentsAdaptorFrameConstants : public AllStatic)

[Peter Rybin, 2012/05/02 23:58:20]

Done.

+    // Architecture-specific constant.
+    static const bool kIsSupported;
+
+    // A size of frame base including fp. Padding words starts right above
+    // the base.
+    static const int kFrameBaseSize = 4;

[Yang, 2012/05/02 11:38:34]

This coincides with Debug::kFrameDropperFrameSize, which is also 4. If they are
derived similarly, can't we consistently use only one of the two?

[Peter Rybin, 2012/05/02 23:58:20]

I'm not sure. Both are derived from the fact that the minimum size of
InternalFrame is 4 words. But they are layouts of different frames. So I would
say it's still more of coincidence here.

+
+    // A number of words that should be reserved on stack for the LiveEdit use.
+    // Normally equals 1.
+    static const int kInitialSize;
+    // A value that padding words are filled with. Going bottom-top, the first
+    // word not having this value is a counter word.
+    static const int kPaddingValue;
+  };
+
  private:
   explicit Debug(Isolate* isolate);
   ~Debug();
 
   static bool CompileDebuggerScript(int index);
   void ClearOneShot();
   void ActivateStepIn(StackFrame* frame);
   void ClearStepIn();
   void ActivateStepOut(StackFrame* frame);
   void ClearStepNext();
@@ skipping 515 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(MessageDispatchHelperThread);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 #endif  // V8_DEBUG_H_