Adds an API for setting the stack limit per-thread.

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 17 matching lines @@
 #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)
+// The stack limit beyond which we will throw stack overflow errors in
+// generated code. Because generated code on x64 uses the C stack, we
+// just use the C stack limit.
+#define GENERATED_CODE_STACK_LIMIT(c_limit) \
+  (c_limit)
 
 // Call the generated regexp code directly. The entry function pointer should
 // expect seven int/pointer sized arguments and return an int.
 #define CALL_GENERATED_REGEXP_CODE(entry, p0, p1, p2, p3, p4, p5, p6) \
   entry(p0, p1, p2, p3, p4, p5, p6)
 
 #endif  // V8_X64_SIMULATOR_X64_H_