X64: Obey WIN64 ABI more exactly, in WIN64 build.

src/x64/macro-assembler-x64.cc

 // 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 992 matching lines @@
     // TODO(1243899): This should be symmetric to
     // CopyRegistersFromStackToMemory() but it isn't! esp is assumed
     // correct here, but computed for the other call. Very error
     // prone! FIX THIS.  Actually there are deeper problems with
     // register saving than this asymmetry (see the bug report
     // associated with this issue).
     PushRegistersFromMemory(kJSCallerSaved);
   }
 #endif
 
-  // Reserve space for the Arguments object.  The Windows 64-bit ABI
-  // requires us to pass this structure as a pointer to its location on
-  // the stack.  We also need backing space for the pointer, even though
-  // it is passed in a register.
-  subq(rsp, Immediate(3 * kPointerSize));
-
   // Get the required frame alignment for the OS.
   static const int kFrameAlignment = OS::ActivationFrameAlignment();
   if (kFrameAlignment > 0) {
     ASSERT(IsPowerOf2(kFrameAlignment));
     movq(kScratchRegister, Immediate(-kFrameAlignment));
     and_(rsp, kScratchRegister);
   }
 
+#ifdef _WIN64
+  // Reserve space for the Arguments object.  The Windows 64-bit ABI
+  // requires us to pass this structure as a pointer to its location on
+  // the stack.  The structure contains 2 pointers.
+  // The structure on the stack must be 16-byte aligned.
+  // We also need backing space for 4 parameters, even though
+  // we only pass one parameter, and it is in a register.
+  subq(rsp, Immediate(6 * kPointerSize));
+  ASSERT(kFrameAlignment == 2 * kPointerSize);  // Change the padding if needed.
+#endif
+
   // Patch the saved entry sp.
   movq(Operand(rbp, ExitFrameConstants::kSPOffset), rsp);
 }
 
 
 void MacroAssembler::LeaveExitFrame(StackFrame::Type type) {
   // Registers:
   // r15 : argv
 #ifdef ENABLE_DEBUGGER_SUPPORT
   // Restore the memory copy of the registers by digging them out from
@@ skipping 329 matching lines @@
   movq(kScratchRegister, new_space_allocation_top);
 #ifdef DEBUG
   cmpq(object, Operand(kScratchRegister, 0));
   Check(below, "Undo allocation of non allocated memory");
 #endif
   movq(Operand(kScratchRegister, 0), object);
 }
 
 
 } }  // namespace v8::internal