X64: Implement CEntryStub and JSEntryTrampoline.

src/x64/simulator-x64.h

 // Copyright 2009 the V8 project authors. 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.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 13 matching lines @@
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #ifndef V8_X64_SIMULATOR_X64_H_
 #define V8_X64_SIMULATOR_X64_H_
 
 
 // Since there is no simulator for the ia32 architecture the only thing we can
 // do is to call the entry directly.
+// TODO(X64): Don't pass p0, since it isn't used?
 #define CALL_GENERATED_CODE(entry, p0, p1, p2, p3, p4) \
   entry(p0, p1, p2, p3, p4);
 
 // Calculated the stack limit beyond which we will throw stack overflow errors.
 // This macro must be called from a C++ method. It relies on being able to take
 // the address of "this" to get a value on the current execution stack and then
 // calculates the stack limit based on that value.
 // NOTE: The check for overflow is not safe as there is no guarantee that the
 // running thread has its stack in all memory up to address 0x00000000.
 #define GENERATED_CODE_STACK_LIMIT(limit) \
   (reinterpret_cast<uintptr_t>(this) >= limit ? \
       reinterpret_cast<uintptr_t>(this) - limit : 0)
 
 #endif  // V8_X64_SIMULATOR_X64_H_