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diff --git a/src/mscorlib/shared/System/Runtime/Versioning/NonVersionableAttribute.cs b/src/mscorlib/shared/System/Runtime/Versioning/NonVersionableAttribute.cs
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+++ b/src/mscorlib/shared/System/Runtime/Versioning/NonVersionableAttribute.cs
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+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+/*============================================================
+**
+**
+**
+** The [NonVersionable] attribute is applied to indicate that the implementation 
+** of a particular member or layout of a struct cannot be changed for given platform in incompatible way.
+** This allows cross-module inlining of methods and data structures whose implementation 
+** is never changed in ReadyToRun native images. Any changes to such members or types would be 
+** breaking changes for ReadyToRun.
+**
+** Applying this type also has the side effect that the inlining tables in R2R images will not
+** report that inlining of NonVersionable attributed methods occured. These inlining tables are used
+** by profilers to figure out the set of methods that need to be rejited when one method is instrumented,
+** so in effect NonVersionable methods are also non-instrumentable. Generally this is OK for
+** extremely trivial low level methods where NonVersionable gets used, but if there is any plan to 
+** significantly extend its usage or allow 3rd parties to use it please discuss with the diagnostics team.
+===========================================================*/
+
+using System;
+using System.Diagnostics;
+
+namespace System.Runtime.Versioning
+{
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Method | AttributeTargets.Constructor,
+                    AllowMultiple = false, Inherited = false)]
+    internal sealed class NonVersionableAttribute : Attribute
+    {
+        public NonVersionableAttribute()
+        {
+        }
+    }
+}