Setup R10/EDX to be valid Oops before stub calls

runtime/vm/stub_code_x64.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
@@ skipping 65 matching lines @@
   // Reserve space for arguments and align frame before entering C++ world.
   __ subq(RSP, Immediate(sizeof(NativeArguments)));
   if (OS::ActivationFrameAlignment() > 1) {
     __ andq(RSP, Immediate(~(OS::ActivationFrameAlignment() - 1)));
   }
 
   // Pass NativeArguments structure by value and call runtime.
   __ movq(Address(RSP, isolate_offset), CTX);  // Set isolate in NativeArgs.
   // There are no runtime calls to closures, so we do not need to set the tag
   // bits kClosureFunctionBit and kInstanceFunctionBit in argc_tag_.
+  __ SmiUntag(R10);
   __ movq(Address(RSP, argc_tag_offset), R10);  // Set argc in NativeArguments.
   __ leaq(RAX, Address(RBP, R10, TIMES_8, 1 * kWordSize));  // Compute argv.
   __ movq(Address(RSP, argv_offset), RAX);  // Set argv in NativeArguments.
   __ addq(RAX, Immediate(1 * kWordSize));  // Retval is next to 1st argument.
   __ movq(Address(RSP, retval_offset), RAX);  // Set retval in NativeArguments.
 #if defined(_WIN64)
   ASSERT(sizeof(NativeArguments) > CallingConventions::kRegisterTransferLimit);
   __ movq(CallingConventions::kArg1Reg, RSP);
 #endif
   __ CallCFunction(RBX);
@@ skipping 1761 matching lines @@
 
   __ movq(left, Address(RSP, 2 * kWordSize));
   __ movq(right, Address(RSP, 1 * kWordSize));
   GenerateIdenticalWithNumberCheckStub(assembler, left, right);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64