Port some more code to x64

syzygy/agent/common/agent.cc

 // Copyright 2014 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 11 matching lines @@
 // This is to ensure that we have our own version of the CRT so as not to
 // conflict with instrumented code.
 #ifdef _DLL
 #error Must be statically linked to the CRT.
 #endif
 
 void InitializeCrt() {
   // Disable SSE2 instructions. This is to ensure that our instrumentation
   // doesn't inadvertently tinker with SSE2 registers via the CRT, causing
   // instrumented SSE2 enabled instructions to screw up.
+#ifndef _WIN64
+  // SSE registers are a part of the x64 calling convention, so they
+  // cannot be disabled.
+  // The 64-bit version of the runtime is intended to run with LLVM/Clang
+  // provided instrumentation, and doesn't suffer to same problem as the
+  // Syzygy instrumentation.
   const int kDisableSSE2 = 0;
   _set_SSE2_enable(kDisableSSE2);
+#endif
 }
 
 }  // namespace common
 }  // namespace agent