From: yangguo@chromium.org <yangguo@chromium.org@ce2b1a6d-e550-0410-aec6-3dcde31c8c00>
Date: Wed, 28 May 2014 10:21:46 +0000 (+0000)
Subject: Move LiveEdit-related code.
X-Git-Tag: upstream/4.7.83~8913
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=eaf8718290e10371f3be2ee101c1f89c0104ebdf;p=platform%2Fupstream%2Fv8.git

Move LiveEdit-related code.

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/300793002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21559 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
---

diff --git a/src/arm/debug-arm.cc b/src/arm/debug-arm.cc
index 204c83d..3421f8b 100644
--- a/src/arm/debug-arm.cc
+++ b/src/arm/debug-arm.cc
@@ -83,8 +83,6 @@ void BreakLocationIterator::ClearDebugBreakAtSlot() {
                      Assembler::kDebugBreakSlotInstructions);
 }
 
-const bool Debug::FramePaddingLayout::kIsSupported = false;
-
 
 #define __ ACCESS_MASM(masm)
 
@@ -292,7 +290,8 @@ void DebugCodegen::GenerateFrameDropperLiveEdit(MacroAssembler* masm) {
   masm->Abort(kLiveEditFrameDroppingIsNotSupportedOnArm);
 }
 
-const bool Debug::kFrameDropperSupported = false;
+
+const bool LiveEdit::kFrameDropperSupported = false;
 
 #undef __
 
diff --git a/src/arm64/debug-arm64.cc b/src/arm64/debug-arm64.cc
index dbf1b6e..d354c42 100644
--- a/src/arm64/debug-arm64.cc
+++ b/src/arm64/debug-arm64.cc
@@ -123,7 +123,6 @@ void BreakLocationIterator::ClearDebugBreakAtSlot() {
                      Assembler::kDebugBreakSlotInstructions);
 }
 
-const bool Debug::FramePaddingLayout::kIsSupported = false;
 
 static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
                                           RegList object_regs,
@@ -350,7 +349,8 @@ void DebugCodegen::GenerateFrameDropperLiveEdit(MacroAssembler* masm) {
   masm->Abort(kLiveEditFrameDroppingIsNotSupportedOnARM64);
 }
 
-const bool Debug::kFrameDropperSupported = false;
+
+const bool LiveEdit::kFrameDropperSupported = false;
 
 } }  // namespace v8::internal
 
diff --git a/src/debug.cc b/src/debug.cc
index 4372cdd..893cd64 100644
--- a/src/debug.cc
+++ b/src/debug.cc
@@ -543,32 +543,6 @@ int Debug::ArchiveSpacePerThread() {
 }
 
 
-// Frame structure (conforms InternalFrame structure):
-//   -- code
-//   -- SMI maker
-//   -- function (slot is called "context")
-//   -- frame base
-Object** Debug::SetUpFrameDropperFrame(StackFrame* bottom_js_frame,
-                                       Handle<Code> code) {
-  ASSERT(bottom_js_frame->is_java_script());
-
-  Address fp = bottom_js_frame->fp();
-
-  // Move function pointer into "context" slot.
-  Memory::Object_at(fp + StandardFrameConstants::kContextOffset) =
-      Memory::Object_at(fp + JavaScriptFrameConstants::kFunctionOffset);
-
-  Memory::Object_at(fp + InternalFrameConstants::kCodeOffset) = *code;
-  Memory::Object_at(fp + StandardFrameConstants::kMarkerOffset) =
-      Smi::FromInt(StackFrame::INTERNAL);
-
-  return reinterpret_cast<Object**>(&Memory::Object_at(
-      fp + StandardFrameConstants::kContextOffset));
-}
-
-const int Debug::kFrameDropperFrameSize = 4;
-
-
 void ScriptCache::Add(Handle<Script> script) {
   GlobalHandles* global_handles = isolate_->global_handles();
   // Create an entry in the hash map for the script.
@@ -837,7 +811,7 @@ Object* Debug::Break(Arguments args) {
   HandleScope scope(isolate_);
   ASSERT(args.length() == 0);
 
-  thread_local_.frame_drop_mode_ = FRAMES_UNTOUCHED;
+  thread_local_.frame_drop_mode_ = LiveEdit::FRAMES_UNTOUCHED;
 
   // Get the top-most JavaScript frame.
   JavaScriptFrameIterator it(isolate_);
@@ -950,26 +924,26 @@ Object* Debug::Break(Arguments args) {
     PrepareStep(step_action, step_count, StackFrame::NO_ID);
   }
 
-  if (thread_local_.frame_drop_mode_ == FRAMES_UNTOUCHED) {
+  if (thread_local_.frame_drop_mode_ == LiveEdit::FRAMES_UNTOUCHED) {
     SetAfterBreakTarget(frame);
   } else if (thread_local_.frame_drop_mode_ ==
-      FRAME_DROPPED_IN_IC_CALL) {
+      LiveEdit::FRAME_DROPPED_IN_IC_CALL) {
     // We must have been calling IC stub. Do not go there anymore.
     Code* plain_return = isolate_->builtins()->builtin(
         Builtins::kPlainReturn_LiveEdit);
     thread_local_.after_break_target_ = plain_return->entry();
   } else if (thread_local_.frame_drop_mode_ ==
-      FRAME_DROPPED_IN_DEBUG_SLOT_CALL) {
+      LiveEdit::FRAME_DROPPED_IN_DEBUG_SLOT_CALL) {
     // Debug break slot stub does not return normally, instead it manually
     // cleans the stack and jumps. We should patch the jump address.
     Code* plain_return = isolate_->builtins()->builtin(
         Builtins::kFrameDropper_LiveEdit);
     thread_local_.after_break_target_ = plain_return->entry();
   } else if (thread_local_.frame_drop_mode_ ==
-      FRAME_DROPPED_IN_DIRECT_CALL) {
+      LiveEdit::FRAME_DROPPED_IN_DIRECT_CALL) {
     // Nothing to do, after_break_target is not used here.
   } else if (thread_local_.frame_drop_mode_ ==
-      FRAME_DROPPED_IN_RETURN_CALL) {
+      LiveEdit::FRAME_DROPPED_IN_RETURN_CALL) {
     Code* plain_return = isolate_->builtins()->builtin(
         Builtins::kFrameDropper_LiveEdit);
     thread_local_.after_break_target_ = plain_return->entry();
@@ -2491,9 +2465,9 @@ bool Debug::IsBreakAtReturn(JavaScriptFrame* frame) {
 
 
 void Debug::FramesHaveBeenDropped(StackFrame::Id new_break_frame_id,
-                                  FrameDropMode mode,
+                                  LiveEdit::FrameDropMode mode,
                                   Object** restarter_frame_function_pointer) {
-  if (mode != CURRENTLY_SET_MODE) {
+  if (mode != LiveEdit::CURRENTLY_SET_MODE) {
     thread_local_.frame_drop_mode_ = mode;
   }
   thread_local_.break_frame_id_ = new_break_frame_id;
@@ -2502,13 +2476,6 @@ void Debug::FramesHaveBeenDropped(StackFrame::Id new_break_frame_id,
 }
 
 
-const int Debug::FramePaddingLayout::kInitialSize = 1;
-
-
-// Any even value bigger than kInitialSize as needed for stack scanning.
-const int Debug::FramePaddingLayout::kPaddingValue = kInitialSize + 1;
-
-
 bool Debug::IsDebugGlobal(GlobalObject* global) {
   return IsLoaded() && global == debug_context()->global_object();
 }
diff --git a/src/debug.h b/src/debug.h
index 03ddc0f..e6c1d26 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -13,6 +13,7 @@
 #include "flags.h"
 #include "frames-inl.h"
 #include "hashmap.h"
+#include "liveedit.h"
 #include "platform.h"
 #include "string-stream.h"
 #include "v8threads.h"
@@ -532,10 +533,9 @@ class Debug {
     return break_on_uncaught_exception_;
   }
 
-  enum AddressId {
-    k_after_break_target_address,
-    k_restarter_frame_function_pointer
-  };
+  void FramesHaveBeenDropped(StackFrame::Id new_break_frame_id,
+                             LiveEdit::FrameDropMode mode,
+                             Object** restarter_frame_function_pointer);
 
   // Support for setting the address to jump to when returning from break point.
   Address after_break_target_address() {
@@ -547,7 +547,6 @@ class Debug {
     return reinterpret_cast<Address>(address);
   }
 
-  static const int kEstimatedNofDebugInfoEntries = 16;
   static const int kEstimatedNofBreakPointsInFunction = 16;
 
   // Passed to MakeWeak.
@@ -578,86 +577,6 @@ class Debug {
   // Garbage collection notifications.
   void AfterGarbageCollection();
 
-  // Describes how exactly a frame has been dropped from stack.
-  enum FrameDropMode {
-    // No frame has been dropped.
-    FRAMES_UNTOUCHED,
-    // The top JS frame had been calling IC stub. IC stub mustn't be called now.
-    FRAME_DROPPED_IN_IC_CALL,
-    // The top JS frame had been calling debug break slot stub. Patch the
-    // address this stub jumps to in the end.
-    FRAME_DROPPED_IN_DEBUG_SLOT_CALL,
-    // The top JS frame had been calling some C++ function. The return address
-    // gets patched automatically.
-    FRAME_DROPPED_IN_DIRECT_CALL,
-    FRAME_DROPPED_IN_RETURN_CALL,
-    CURRENTLY_SET_MODE
-  };
-
-  void FramesHaveBeenDropped(StackFrame::Id new_break_frame_id,
-                                    FrameDropMode mode,
-                                    Object** restarter_frame_function_pointer);
-
-  // Initializes an artificial stack frame. The data it contains is used for:
-  //  a. successful work of frame dropper code which eventually gets control,
-  //  b. being compatible with regular stack structure for various stack
-  //     iterators.
-  // Returns address of stack allocated pointer to restarted function,
-  // the value that is called 'restarter_frame_function_pointer'. The value
-  // 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 Smi storing n -- current size of padding
-   *      - padding: n words filled with kPaddingValue in form of Smi
-   *      - 3 context/type words of a regular InternalFrame
-   *      - fp
-   *   ---
-   *      Topmost JavaScript frame
-   *   ---
-   *   ...
-   *   --- Bottom
-   */
-  class FramePaddingLayout : public AllStatic {
-   public:
-    // 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;
-
-    // A number of words that should be reserved on stack for the LiveEdit use.
-    // Normally equals 1. Stored on stack in form of Smi.
-    static const int kInitialSize;
-    // A value that padding words are filled with (in form of Smi). Going
-    // bottom-top, the first word not having this value is a counter word.
-    static const int kPaddingValue;
-  };
-
  private:
   explicit Debug(Isolate* isolate);
 
@@ -767,6 +686,9 @@ class Debug {
   // Per-thread data.
   class ThreadLocal {
    public:
+    // Top debugger entry.
+    EnterDebugger* debugger_entry_;
+
     // Counter for generating next break id.
     int break_count_;
 
@@ -801,16 +723,13 @@ class Debug {
     // Storage location for jump when exiting debug break calls.
     Address after_break_target_;
 
-    // Stores the way how LiveEdit has patched the stack. It is used when
-    // debugger returns control back to user script.
-    FrameDropMode frame_drop_mode_;
-
-    // Top debugger entry.
-    EnterDebugger* debugger_entry_;
-
     // Pending interrupts scheduled while debugging.
     bool has_pending_interrupt_;
 
+    // Stores the way how LiveEdit has patched the stack. It is used when
+    // debugger returns control back to user script.
+    LiveEdit::FrameDropMode frame_drop_mode_;
+
     // When restarter frame is on stack, stores the address
     // of the pointer to function being restarted. Otherwise (most of the time)
     // stores NULL. This pointer is used with 'step in' implementation.
@@ -831,6 +750,7 @@ class Debug {
 
   friend class Isolate;
   friend class EnterDebugger;
+  friend class FrameDropper;
 
   DISALLOW_COPY_AND_ASSIGN(Debug);
 };
@@ -912,6 +832,7 @@ class DebugCodegen : public AllStatic {
   static void GenerateFrameDropperLiveEdit(MacroAssembler* masm);
 };
 
+
 } }  // namespace v8::internal
 
 #endif  // V8_DEBUG_H_
diff --git a/src/ia32/debug-ia32.cc b/src/ia32/debug-ia32.cc
index 6fdb28c..1e56dc5 100644
--- a/src/ia32/debug-ia32.cc
+++ b/src/ia32/debug-ia32.cc
@@ -67,10 +67,6 @@ void BreakLocationIterator::ClearDebugBreakAtSlot() {
 }
 
 
-// All debug break stubs support padding for LiveEdit.
-const bool Debug::FramePaddingLayout::kIsSupported = true;
-
-
 #define __ ACCESS_MASM(masm)
 
 static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
@@ -82,11 +78,10 @@ static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
     FrameScope scope(masm, StackFrame::INTERNAL);
 
     // Load padding words on stack.
-    for (int i = 0; i < Debug::FramePaddingLayout::kInitialSize; i++) {
-      __ push(Immediate(Smi::FromInt(
-          Debug::FramePaddingLayout::kPaddingValue)));
+    for (int i = 0; i < LiveEdit::kFramePaddingInitialSize; i++) {
+      __ push(Immediate(Smi::FromInt(LiveEdit::kFramePaddingValue)));
     }
-    __ push(Immediate(Smi::FromInt(Debug::FramePaddingLayout::kInitialSize)));
+    __ push(Immediate(Smi::FromInt(LiveEdit::kFramePaddingInitialSize)));
 
     // Store the registers containing live values on the expression stack to
     // make sure that these are correctly updated during GC. Non object values
@@ -331,7 +326,8 @@ void DebugCodegen::GenerateFrameDropperLiveEdit(MacroAssembler* masm) {
   __ jmp(edx);
 }
 
-const bool Debug::kFrameDropperSupported = true;
+
+const bool LiveEdit::kFrameDropperSupported = true;
 
 #undef __
 
diff --git a/src/liveedit.cc b/src/liveedit.cc
index cf7f4c8..e55f24e 100644
--- a/src/liveedit.cc
+++ b/src/liveedit.cc
@@ -1533,6 +1533,38 @@ static bool FixTryCatchHandler(StackFrame* top_frame,
 }
 
 
+// Initializes an artificial stack frame. The data it contains is used for:
+//  a. successful work of frame dropper code which eventually gets control,
+//  b. being compatible with regular stack structure for various stack
+//     iterators.
+// Returns address of stack allocated pointer to restarted function,
+// the value that is called 'restarter_frame_function_pointer'. The value
+// at this address (possibly updated by GC) may be used later when preparing
+// 'step in' operation.
+// Frame structure (conforms InternalFrame structure):
+//   -- code
+//   -- SMI maker
+//   -- function (slot is called "context")
+//   -- frame base
+static Object** SetUpFrameDropperFrame(StackFrame* bottom_js_frame,
+                                       Handle<Code> code) {
+  ASSERT(bottom_js_frame->is_java_script());
+
+  Address fp = bottom_js_frame->fp();
+
+  // Move function pointer into "context" slot.
+  Memory::Object_at(fp + StandardFrameConstants::kContextOffset) =
+      Memory::Object_at(fp + JavaScriptFrameConstants::kFunctionOffset);
+
+  Memory::Object_at(fp + InternalFrameConstants::kCodeOffset) = *code;
+  Memory::Object_at(fp + StandardFrameConstants::kMarkerOffset) =
+      Smi::FromInt(StackFrame::INTERNAL);
+
+  return reinterpret_cast<Object**>(&Memory::Object_at(
+      fp + StandardFrameConstants::kContextOffset));
+}
+
+
 // Removes specified range of frames from stack. There may be 1 or more
 // frames in range. Anyway the bottom frame is restarted rather than dropped,
 // and therefore has to be a JavaScript frame.
@@ -1540,9 +1572,9 @@ static bool FixTryCatchHandler(StackFrame* top_frame,
 static const char* DropFrames(Vector<StackFrame*> frames,
                               int top_frame_index,
                               int bottom_js_frame_index,
-                              Debug::FrameDropMode* mode,
+                              LiveEdit::FrameDropMode* mode,
                               Object*** restarter_frame_function_pointer) {
-  if (!Debug::kFrameDropperSupported) {
+  if (!LiveEdit::kFrameDropperSupported) {
     return "Stack manipulations are not supported in this architecture.";
   }
 
@@ -1555,34 +1587,30 @@ static const char* DropFrames(Vector<StackFrame*> frames,
   // Check the nature of the top frame.
   Isolate* isolate = bottom_js_frame->isolate();
   Code* pre_top_frame_code = pre_top_frame->LookupCode();
-  bool frame_has_padding;
+  bool frame_has_padding = true;
   if (pre_top_frame_code->is_inline_cache_stub() &&
       pre_top_frame_code->is_debug_stub()) {
     // OK, we can drop inline cache calls.
-    *mode = Debug::FRAME_DROPPED_IN_IC_CALL;
-    frame_has_padding = Debug::FramePaddingLayout::kIsSupported;
+    *mode = LiveEdit::FRAME_DROPPED_IN_IC_CALL;
   } else if (pre_top_frame_code ==
              isolate->builtins()->builtin(Builtins::kSlot_DebugBreak)) {
     // OK, we can drop debug break slot.
-    *mode = Debug::FRAME_DROPPED_IN_DEBUG_SLOT_CALL;
-    frame_has_padding = Debug::FramePaddingLayout::kIsSupported;
+    *mode = LiveEdit::FRAME_DROPPED_IN_DEBUG_SLOT_CALL;
   } else if (pre_top_frame_code ==
-      isolate->builtins()->builtin(
-          Builtins::kFrameDropper_LiveEdit)) {
+             isolate->builtins()->builtin(Builtins::kFrameDropper_LiveEdit)) {
     // OK, we can drop our own code.
     pre_top_frame = frames[top_frame_index - 2];
     top_frame = frames[top_frame_index - 1];
-    *mode = Debug::CURRENTLY_SET_MODE;
+    *mode = LiveEdit::CURRENTLY_SET_MODE;
     frame_has_padding = false;
   } else if (pre_top_frame_code ==
-      isolate->builtins()->builtin(Builtins::kReturn_DebugBreak)) {
-    *mode = Debug::FRAME_DROPPED_IN_RETURN_CALL;
-    frame_has_padding = Debug::FramePaddingLayout::kIsSupported;
+             isolate->builtins()->builtin(Builtins::kReturn_DebugBreak)) {
+    *mode = LiveEdit::FRAME_DROPPED_IN_RETURN_CALL;
   } else if (pre_top_frame_code->kind() == Code::STUB &&
       pre_top_frame_code->major_key() == CodeStub::CEntry) {
     // Entry from our unit tests on 'debugger' statement.
     // It's fine, we support this case.
-    *mode = Debug::FRAME_DROPPED_IN_DIRECT_CALL;
+    *mode = LiveEdit::FRAME_DROPPED_IN_DIRECT_CALL;
     // We don't have a padding from 'debugger' statement call.
     // Here the stub is CEntry, it's not debug-only and can't be padded.
     // If anyone would complain, a proxy padded stub could be added.
@@ -1591,19 +1619,19 @@ static const char* DropFrames(Vector<StackFrame*> frames,
     // This must be adaptor that remain from the frame dropping that
     // is still on stack. A frame dropper frame must be above it.
     ASSERT(frames[top_frame_index - 2]->LookupCode() ==
-        isolate->builtins()->builtin(Builtins::kFrameDropper_LiveEdit));
+           isolate->builtins()->builtin(Builtins::kFrameDropper_LiveEdit));
     pre_top_frame = frames[top_frame_index - 3];
     top_frame = frames[top_frame_index - 2];
-    *mode = Debug::CURRENTLY_SET_MODE;
+    *mode = LiveEdit::CURRENTLY_SET_MODE;
     frame_has_padding = false;
   } else {
     return "Unknown structure of stack above changing function";
   }
 
   Address unused_stack_top = top_frame->sp();
+  int new_frame_size = LiveEdit::kFrameDropperFrameSize * kPointerSize;
   Address unused_stack_bottom = bottom_js_frame->fp()
-      - Debug::kFrameDropperFrameSize * kPointerSize  // Size of the new frame.
-      + kPointerSize;  // Bigger address end is exclusive.
+      - new_frame_size + kPointerSize;  // Bigger address end is exclusive.
 
   Address* top_frame_pc_address = top_frame->pc_address();
 
@@ -1616,11 +1644,10 @@ static const char* DropFrames(Vector<StackFrame*> frames,
           static_cast<int>(unused_stack_top - unused_stack_bottom);
 
       Address padding_start = pre_top_frame->fp() -
-          Debug::FramePaddingLayout::kFrameBaseSize * kPointerSize;
+          LiveEdit::kFrameDropperFrameSize * kPointerSize;
 
       Address padding_pointer = padding_start;
-      Smi* padding_object =
-          Smi::FromInt(Debug::FramePaddingLayout::kPaddingValue);
+      Smi* padding_object = Smi::FromInt(LiveEdit::kFramePaddingValue);
       while (Memory::Object_at(padding_pointer) == padding_object) {
         padding_pointer -= kPointerSize;
       }
@@ -1637,7 +1664,7 @@ static const char* DropFrames(Vector<StackFrame*> frames,
 
       MemMove(padding_start + kPointerSize - shortage_bytes,
               padding_start + kPointerSize,
-              Debug::FramePaddingLayout::kFrameBaseSize * kPointerSize);
+              LiveEdit::kFrameDropperFrameSize * kPointerSize);
 
       pre_top_frame->UpdateFp(pre_top_frame->fp() - shortage_bytes);
       pre_pre_frame->SetCallerFp(pre_top_frame->fp());
@@ -1661,7 +1688,7 @@ static const char* DropFrames(Vector<StackFrame*> frames,
   pre_top_frame->SetCallerFp(bottom_js_frame->fp());
 
   *restarter_frame_function_pointer =
-      Debug::SetUpFrameDropperFrame(bottom_js_frame, code);
+      SetUpFrameDropperFrame(bottom_js_frame, code);
 
   ASSERT((**restarter_frame_function_pointer)->IsJSFunction());
 
@@ -1776,7 +1803,7 @@ static const char* DropActivationsInActiveThreadImpl(
     return target.GetNotFoundMessage();
   }
 
-  Debug::FrameDropMode drop_mode = Debug::FRAMES_UNTOUCHED;
+  LiveEdit::FrameDropMode drop_mode = LiveEdit::FRAMES_UNTOUCHED;
   Object** restarter_frame_function_pointer = NULL;
   const char* error_message = DropFrames(frames, top_frame_index,
                                          bottom_js_frame_index, &drop_mode,
diff --git a/src/liveedit.h b/src/liveedit.h
index b22d01a..fed4b4d 100644
--- a/src/liveedit.h
+++ b/src/liveedit.h
@@ -122,6 +122,63 @@ class LiveEdit : AllStatic {
   // of diff chunks.
   static Handle<JSArray> CompareStrings(Handle<String> s1,
                                         Handle<String> s2);
+
+  // 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 Smi storing n -- current size of padding
+   *      - padding: n words filled with kPaddingValue in form of Smi
+   *      - 3 context/type words of a regular InternalFrame
+   *      - fp
+   *   ---
+   *      Topmost JavaScript frame
+   *   ---
+   *   ...
+   *   --- Bottom
+   */
+  // A size of frame base including fp. Padding words starts right above
+  // the base.
+  static const int kFrameDropperFrameSize = 4;
+  // A number of words that should be reserved on stack for the LiveEdit use.
+  // Stored on stack in form of Smi.
+  static const int kFramePaddingInitialSize = 1;
+  // A value that padding words are filled with (in form of Smi). Going
+  // bottom-top, the first word not having this value is a counter word.
+  static const int kFramePaddingValue = kFramePaddingInitialSize + 1;
+
+
+  // Describes how exactly a frame has been dropped from stack.
+  enum FrameDropMode {
+    // No frame has been dropped.
+    FRAMES_UNTOUCHED,
+    // The top JS frame had been calling IC stub. IC stub mustn't be called now.
+    FRAME_DROPPED_IN_IC_CALL,
+    // The top JS frame had been calling debug break slot stub. Patch the
+    // address this stub jumps to in the end.
+    FRAME_DROPPED_IN_DEBUG_SLOT_CALL,
+    // The top JS frame had been calling some C++ function. The return address
+    // gets patched automatically.
+    FRAME_DROPPED_IN_DIRECT_CALL,
+    FRAME_DROPPED_IN_RETURN_CALL,
+    CURRENTLY_SET_MODE
+  };
 };
 
 
diff --git a/src/mips/debug-mips.cc b/src/mips/debug-mips.cc
index d901866..ed4cf12 100644
--- a/src/mips/debug-mips.cc
+++ b/src/mips/debug-mips.cc
@@ -90,8 +90,6 @@ void BreakLocationIterator::ClearDebugBreakAtSlot() {
                      Assembler::kDebugBreakSlotInstructions);
 }
 
-const bool Debug::FramePaddingLayout::kIsSupported = false;
-
 
 #define __ ACCESS_MASM(masm)
 
@@ -301,7 +299,7 @@ void DebugCodegen::GenerateFrameDropperLiveEdit(MacroAssembler* masm) {
 }
 
 
-const bool Debug::kFrameDropperSupported = false;
+const bool LiveEdit::kFrameDropperSupported = false;
 
 #undef __
 
diff --git a/src/x64/debug-x64.cc b/src/x64/debug-x64.cc
index af20154..bf15e95 100644
--- a/src/x64/debug-x64.cc
+++ b/src/x64/debug-x64.cc
@@ -65,8 +65,6 @@ void BreakLocationIterator::ClearDebugBreakAtSlot() {
   rinfo()->PatchCode(original_rinfo()->pc(), Assembler::kDebugBreakSlotLength);
 }
 
-const bool Debug::FramePaddingLayout::kIsSupported = true;
-
 
 #define __ ACCESS_MASM(masm)
 
@@ -80,10 +78,10 @@ static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
     FrameScope scope(masm, StackFrame::INTERNAL);
 
     // Load padding words on stack.
-    for (int i = 0; i < Debug::FramePaddingLayout::kInitialSize; i++) {
-      __ Push(Smi::FromInt(Debug::FramePaddingLayout::kPaddingValue));
+    for (int i = 0; i < LiveEdit::kFramePaddingInitialSize; i++) {
+      __ Push(Smi::FromInt(LiveEdit::kFramePaddingValue));
     }
-    __ Push(Smi::FromInt(Debug::FramePaddingLayout::kInitialSize));
+    __ Push(Smi::FromInt(LiveEdit::kFramePaddingInitialSize));
 
     // Store the registers containing live values on the expression stack to
     // make sure that these are correctly updated during GC. Non object values
@@ -309,7 +307,7 @@ void DebugCodegen::GenerateFrameDropperLiveEdit(MacroAssembler* masm) {
   __ jmp(rdx);
 }
 
-const bool Debug::kFrameDropperSupported = true;
+const bool LiveEdit::kFrameDropperSupported = true;
 
 #undef __