This patch is the propagation version of https://codereview.chromium.org/10824032 patch

src/assembler.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // 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.
 //
@@ skipping 824 matching lines @@
 };
 
 
 class PositionsRecorder BASE_EMBEDDED {
  public:
   explicit PositionsRecorder(Assembler* assembler)
       : assembler_(assembler) {
 #ifdef ENABLE_GDB_JIT_INTERFACE
     gdbjit_lineinfo_ = NULL;
 #endif
+    user_data_ = NULL;

[danno, 2013/02/01 13:43:10]

please call this (and all names of variables derived from it) jit_handler_data_

   }
 
 #ifdef ENABLE_GDB_JIT_INTERFACE
   ~PositionsRecorder() {
     delete gdbjit_lineinfo_;
   }
 
   void StartGDBJITLineInfoRecording() {
     if (FLAG_gdbjit) {
       gdbjit_lineinfo_ = new GDBJITLineInfo();
     }
   }
 
   GDBJITLineInfo* DetachGDBJITLineInfo() {
     GDBJITLineInfo* lineinfo = gdbjit_lineinfo_;
     gdbjit_lineinfo_ = NULL;  // To prevent deallocation in destructor.
     return lineinfo;
   }
 #endif
+  void InitializeUserData(void* user_data) {

[danno, 2013/02/01 13:43:10]

AttachJITHandlerData?

+    user_data_ = user_data;
+  }
 
+  void* DetachJITLineInfo() {

[danno, 2013/02/01 13:43:10]

DetachJITHandlerData?

+    void* old_user_data = user_data_;
+    user_data_ = NULL;
+    return old_user_data;
+  }
   // Set current position to pos.
   void RecordPosition(int pos);
 
   // Set current statement position to pos.
   void RecordStatementPosition(int pos);
 
   // Write recorded positions to relocation information.
   bool WriteRecordedPositions();
 
   int current_position() const { return state_.current_position; }
 
   int current_statement_position() const {
     return state_.current_statement_position;
   }
 
+  Assembler* assembler() {
+    return assembler_;
+  }
+
  private:
   Assembler* assembler_;
   PositionState state_;
 #ifdef ENABLE_GDB_JIT_INTERFACE
   GDBJITLineInfo* gdbjit_lineinfo_;
 #endif
-
+  // Currently user_data_ is used to keep the JITted code line info.

[danno, 2013/02/01 13:43:10]

I don't think this comment is exactly correct. It is used to store
JITHandler-specific data over the lifetime of a PositionsRecorder.

+  void* user_data_;
   friend class PreservePositionScope;
 
   DISALLOW_COPY_AND_ASSIGN(PositionsRecorder);
 };
 
 
 class PreservePositionScope BASE_EMBEDDED {
  public:
   explicit PreservePositionScope(PositionsRecorder* positions_recorder)
       : positions_recorder_(positions_recorder),
@@ skipping 72 matching lines @@
  public:
   NullCallWrapper() { }
   virtual ~NullCallWrapper() { }
   virtual void BeforeCall(int call_size) const { }
   virtual void AfterCall() const { }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_ASSEMBLER_H_