Use a reserved stack local variable to store the Code object so that it can be looked up easily whe…

vm/assembler_macros_x64.h

 // Copyright (c) 2011, 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.
 // The class 'AssemblerMacros' contains assembler instruction groups that
 // are used in Dart.
 
 #ifndef VM_ASSEMBLER_MACROS_X64_H_
 #define VM_ASSEMBLER_MACROS_X64_H_
 
 #ifndef VM_ASSEMBLER_MACROS_H_
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   // Inlined allocation of an instance of class 'cls', code has no runtime
   // calls. Jump to 'failure' if the instance cannot be allocated here.
   // Class must be loaded in 'class_reg'. Allocated instance is returned
   // in 'instance_reg'. Only the class field of the object is initialized.
   // 'class_reg' and 'instance_reg' may not be the same register.
   static void TryAllocate(Assembler* assembler,
                           const Class& cls,
                           Register class_reg,
                           Label* failure,
                           Register instance_reg);
+
+  // Set up a dart frame on entry with a frame pointer and PC information to
+  // enable easy access to the RawInstruction object of code corresponding
+  // to this frame.
+  // The dart frame layout is as follows:
+  //   ....
+  //   ret PC
+  //   saved RBP     <=== RBP
+  //   pc (used to derive the RawInstruction Object of the dart code)
+  //   locals space  <=== RSP
+  //   .....
+  // This code sets this up with the sequence:
+  //   pushq rbp
+  //   movq rbp, rsp
+  //   call L
+  //   L: <code to adjust saved pc if there is any intrinsification code>
+  //   .....
+  static void EnterDartFrame(Assembler* assembler, intptr_t frame_size);
+
+  // Set up a stub frame so that the stack traversal code can easily identify
+  // a stub frame.
+  // The stub frame layout is as follows:
+  //   ....
+  //   ret PC
+  //   saved RBP
+  //   pc (used to derive the RawInstruction Object of the stub)
+  //   .....
+  // This code sets this up with the sequence:
+  //   pushq rbp
+  //   movq rbp, rsp
+  //   pushq immediate(0)
+  //   .....
+  static void EnterStubFrame(Assembler* assembler);
+
+  // Instruction pattern from entrypoint is used in dart frame prologs
+  // to set up the frame and save a PC which can be used to figure out the
+  // RawInstruction object corresponding to the code running in the frame.
+  // entrypoint:
+  //   pushq rbp          (size is 1 byte)
+  //   movq rbp, rsp      (size is 3 bytes)
+  //   call L             (size is 5 bytes)
+  //   L:
+  static const intptr_t kOffsetOfSavedPCfromEntrypoint = 9;
 };
 
 }  // namespace dart.
 
 #endif  // VM_ASSEMBLER_MACROS_X64_H_