Use 16 instead of 4 for determining member offsets.

src/base/macros.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_BASE_MACROS_H_
 #define V8_BASE_MACROS_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <cstring>
 
 #include "src/base/build_config.h"
 #include "src/base/compiler-specific.h"
 #include "src/base/logging.h"
 
 
 // The expression OFFSET_OF(type, field) computes the byte-offset
 // of the specified field relative to the containing type. This
 // corresponds to 'offsetof' (in stddef.h), except that it doesn't
 // use 0 or NULL, which causes a problem with the compiler warnings
 // we have enabled (which is also why 'offsetof' doesn't seem to work).
-// Here we simply use the non-zero value 4, which seems to work.
-#define OFFSET_OF(type, field)                                          \
-  (reinterpret_cast<intptr_t>(&(reinterpret_cast<type*>(4)->field)) - 4)
+// Here we simply use the aligned, non-zero value 16.
+#define OFFSET_OF(type, field) \
+  (reinterpret_cast<intptr_t>(&(reinterpret_cast<type*>(16)->field)) - 16)
 
 
 #if V8_OS_NACL
 
 // ARRAYSIZE_UNSAFE performs essentially the same calculation as arraysize,
 // but can be used on anonymous types or types defined inside
 // functions.  It's less safe than arraysize as it accepts some
 // (although not all) pointers.  Therefore, you should use arraysize
 // whenever possible.
 //
@@ skipping 373 matching lines @@
 }
 
 template <>
 inline bool is_fundamental<uint8_t>() {
   return true;
 }
 }
 }  // namespace v8::base
 
 #endif   // V8_BASE_MACROS_H_