Track prologue offset of Code and use for more precise return addresses

runtime/vm/instructions_x64.cc

Index: runtime/vm/instructions_x64.cc
diff --git a/runtime/vm/instructions_x64.cc b/runtime/vm/instructions_x64.cc
index f4a0632291fa22618a38b049d1b397c8a315eaf6..98ffcd96c3c62fa8622256c1bef5d43fcc716865 100644
--- a/runtime/vm/instructions_x64.cc
+++ b/runtime/vm/instructions_x64.cc
@@ -79,6 +79,19 @@ const int* ReturnPattern::pattern() const {
   return kReturnPattern;
 }
 
+
+const int* ProloguePattern::pattern() const {
+  static const int kProloguePattern[kLengthInBytes] =
+      { 0x55, 0x48, 0x89, 0xe5 };
+  return kProloguePattern;
+}
+
+
+const int* SetFramePointerPattern::pattern() const {
+  static const int kFramePointerPattern[kLengthInBytes] = { 0x48, 0x89, 0xe5 };
+  return kFramePointerPattern;
+}
+
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64