Fix RhGetCodeTarget for Unix x64 (#5168)

src/Native/Runtime/MiscHelpers.cpp

@@ -448,8 +448,15 @@ COOP_PINVOKE_HELPER(UInt8 *, RhGetCodeTarget, (UInt8 * pCodeOrg))
 #ifdef _TARGET_AMD64_
     UInt8 * pCode = pCodeOrg;
 
-    // is this "add rcx,8"?
+    // is this "add rcx/rdi,8"?
-    if (pCode[0] == 0x48 && pCode[1] == 0x83 && pCode[2] == 0xc1 && pCode[3] == 0x08)
+    if (pCode[0] == 0x48 &&
+        pCode[1] == 0x83 &&
+#ifdef UNIX_AMD64_ABI
+        pCode[2] == 0xc7 &&
+#else
+        pCode[2] == 0xc1 &&
+#endif
+        pCode[3] == 0x08)
     {
         // unboxing sequence
         unboxingStub = true;

tests/src/Simple/Reflection/Reflection.cs

@@ -358,14 +358,11 @@ internal class ReflectionTest
 
             Type byRefLikeType = GetTestType(nameof(TestByRefLikeTypeMethod), nameof(ByRefLike));
             MethodInfo toStringMethod = byRefLikeType.GetMethod("ToString");
-            /*var toString = (ToStringDelegate)*/toStringMethod.CreateDelegate(typeof(ToStringDelegate));
+            var toString = (ToStringDelegate)toStringMethod.CreateDelegate(typeof(ToStringDelegate));
 
-            // Doesn't work on Unix: https://github.com/dotnet/corert/issues/4379
-#if false
             ByRefLike foo = new ByRefLike(123);
             if (toString(ref foo) != "123")
                 throw new Exception();
-#endif
         }
     }