Introduce a switch for the new snapshot code and switch...

src/x64/assembler-x64.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 440 matching lines @@
 
   // Read/Modify the code target in the relative branch/call instruction at pc.
   // On the x64 architecture, we use relative jumps with a 32-bit displacement
   // to jump to other Code objects in the Code space in the heap.
   // Jumps to C functions are done indirectly through a 64-bit register holding
   // the absolute address of the target.
   // These functions convert between absolute Addresses of Code objects and
   // the relative displacements stored in the code.
   static inline Address target_address_at(Address pc);
   static inline void set_target_address_at(Address pc, Address target);
+
   // This sets the branch destination (which is in the instruction on x64).
+  // This is for calls and branches within generated code.
   inline static void set_target_at(Address instruction_payload,
                                    Address target) {
     set_target_address_at(instruction_payload, target);
   }
+
+  // This sets the branch destination (which is a load instruction on x64).
+  // This is for calls and branches to runtime code.
+  inline static void set_external_target_at(Address instruction_payload,
+                                            Address target) {
+    *reinterpret_cast<Address*>(instruction_payload) = target;
+  }
+
   inline Handle<Object> code_target_object_handle_at(Address pc);
   // Number of bytes taken up by the branch target in the code.
-  static const int kCallTargetSize = 4;  // Use 32-bit displacement.
+  static const int kCallTargetSize = 4;      // Use 32-bit displacement.
+  static const int kExternalTargetSize = 8;  // Use 64-bit absolute.
   // Distance between the address of the code target in the call instruction
   // and the return address pushed on the stack.
   static const int kCallTargetAddressOffset = 4;  // Use 32-bit displacement.
   // Distance between the start of the JS return sequence and where the
   // 32-bit displacement of a near call would be, relative to the pushed
   // return address.  TODO: Use return sequence length instead.
   // Should equal Debug::kX64JSReturnSequenceLength - kCallTargetAddressOffset;
   static const int kPatchReturnSequenceAddressOffset = 13 - 4;
   // TODO(X64): Rename this, removing the "Real", after changing the above.
   static const int kRealPatchReturnSequenceAddressOffset = 2;
@@ skipping 897 matching lines @@
  private:
   Assembler* assembler_;
 #ifdef DEBUG
   int space_before_;
 #endif
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_ASSEMBLER_X64_H_