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

src/debug.h

Index: src/debug.h
diff --git a/src/debug.h b/src/debug.h
index 7ec78015c6d2d65794b8f0f299444ccf570683b2..500fae297d8b77b8a35fa061e7c7d28115964547 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -457,6 +457,49 @@ class Debug {
   // 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();