When cloning method descs be careful with fields that have different offsets between the source and destination.

src/coreclr/vm/methodtablebuilder.cpp

@@ -7148,16 +7148,14 @@ VOID MethodTableBuilder::AllocAndInitMethodDescChunk(COUNT_T startIndex, COUNT_T
             // and should not be used.  We should go to the effort of having proper constructors
             // in the MethodDesc class. </NICE>
 
-            memcpy(pUnboxedMD, pMD, pMD->SizeOf());
-
-            // Reset the chunk index
-            pUnboxedMD->SetChunkIndex(pChunk);
-
-            if (bmtGenerics->GetNumGenericArgs() == 0) {
-                pUnboxedMD->SetHasNonVtableSlot();
+            if (bmtGenerics->GetNumGenericArgs() == 0)
+            {
+                memcpy(pUnboxedMD, pMD, pMD->GetBaseSize());
 
                 // By settings HasNonVTableSlot, the following chunks of data have been shifted around.
                 // This is an example of the fragility noted in the memcpy comment above
+                pUnboxedMD->SetHasNonVtableSlot();
+
                 if (pUnboxedMD->HasNativeCodeSlot())
                 {
                     *pUnboxedMD->GetAddrOfNativeCodeSlot() = *pMD->GetAddrOfNativeCodeSlot();
@@ -7171,6 +7169,13 @@ VOID MethodTableBuilder::AllocAndInitMethodDescChunk(COUNT_T startIndex, COUNT_T
                     *pUnboxedMD->GetAddrOfAsyncMethodData() = *pMD->GetAddrOfAsyncMethodData();
                 }
             }
+            else
+            {
+                memcpy(pUnboxedMD, pMD, pMD->SizeOf());
+            }
+
+            // Reset the chunk index
+            pUnboxedMD->SetChunkIndex(pChunk);
 
             //////////////////////////////////////////////////////////
             // Modify the original MethodDesc to be an unboxing stub

src/tests/Regressions/coreclr/GitHub_115667/test115667.cs

@@ -0,0 +1,55 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+using Xunit;
+using System.Threading.Tasks;
+
+public interface I0
+{
+    Task<bool> M8();
+}
+
+public struct S1 : I0
+{
+#pragma warning disable CS1998 // Async method lacks 'await' operators and will run synchronously
+    public async Task<bool> M8()
+#pragma warning restore CS1998 // Async method lacks 'await' operators and will run synchronously
+    {
+        return false;
+    }
+}
+
+public class Runtime_115667
+{
+    [Fact]
+    public static void TestEntryPoint()
+    {
+        System.Runtime.Loader.AssemblyLoadContext alc = new CollectibleALC();
+        System.Reflection.Assembly asm = alc.LoadFromAssemblyPath(System.Reflection.Assembly.GetExecutingAssembly().Location);
+        System.Reflection.MethodInfo mi = asm.GetType(typeof(Runtime_115667).FullName).GetMethod(nameof(MainInner));
+        System.Type runtimeTy = asm.GetType(typeof(Runtime).FullName);
+        mi.Invoke(null, new object[] { System.Activator.CreateInstance(runtimeTy) });
+    }
+
+    public static void MainInner(IRuntime rt)
+    {
+        bool vr1 = new S1().M8().GetAwaiter().GetResult();
+    }
+}
+
+public interface IRuntime
+{
+    void WriteLine<T>(string site, T value);
+}
+
+public class Runtime : IRuntime
+{
+    public void WriteLine<T>(string site, T value) => System.Console.WriteLine(value);
+}
+
+public class CollectibleALC : System.Runtime.Loader.AssemblyLoadContext
+{
+    public CollectibleALC() : base(true)
+    {
+    }
+}

src/tests/Regressions/coreclr/GitHub_115667/test115667.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <Optimize>True</Optimize>
+    <CLRTestPriority>1</CLRTestPriority>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="test115667.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(TestSourceDir)Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
+  </ItemGroup>
+</Project>

src/tests/issues.targets

@@ -952,6 +952,9 @@
         <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/JitBlue/Runtime_90219/Runtime_90219/**">
             <Issue>https://github.com/dotnet/runtimelab/issues/155: Assembly.Load</Issue>
         </ExcludeList>
+        <ExcludeList Include="$(XunitTestBinBase)/Regressions/coreclr/GitHub_115667/**">
+            <Issue>https://github.com/dotnet/runtimelab/issues/155: Assembly.Load</Issue>
+        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/reflection\DefaultInterfaceMethods\Emit\*">
             <Issue>https://github.com/dotnet/runtimelab/issues/155: Reflection.Emit</Issue>
         </ExcludeList>
@@ -3064,6 +3067,9 @@
         <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/JitBlue/Runtime_90219/Runtime_90219/*">
             <Issue>Loads an assembly from file</Issue>
         </ExcludeList>
+        <ExcludeList Include="$(XunitTestBinBase)/Regressions/coreclr/GitHub_115667/**">
+          <Issue>Loads an assembly from file</Issue>
+        </ExcludeList>
     </ItemGroup>
 
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