Track prologue offset of Code and use for more precise return addresses

runtime/vm/assembler_x64.h

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_ASSEMBLER_X64_H_
 #define VM_ASSEMBLER_X64_H_
 
 #ifndef VM_ASSEMBLER_H_
 #error Do not include assembler_x64.h directly; use assembler.h instead.
 #endif
@@ skipping 867 matching lines @@
   int PreferredLoopAlignment() { return 16; }
   void Align(int alignment, intptr_t offset);
   void Bind(Label* label);
   void Jump(Label* label) { jmp(label); }
 
   void Comment(const char* format, ...) PRINTF_ATTRIBUTE(2, 3);
   static bool EmittingComments();
 
   const Code::Comments& GetCodeComments() const;
 
+  // Address of code at offset.
+  uword CodeAddress(intptr_t offset) {
+    return buffer_.Address(offset);
+  }
+
   intptr_t CodeSize() const { return buffer_.Size(); }
   intptr_t prologue_offset() const { return prologue_offset_; }
 
   // Count the fixups that produce a pointer offset, without processing
   // the fixups.
   intptr_t CountPointerOffsets() const {
     return buffer_.CountPointerOffsets();
   }
 
   const ZoneGrowableArray<intptr_t>& GetPointerOffsets() const {
@@ skipping 292 matching lines @@
 }
 
 
 inline void Assembler::EmitOperandSizeOverride() {
   EmitUint8(0x66);
 }
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_X64_H_