Fix nested non-byref like VC with no pointer fields (#80642) (#80873)

* Fix nested non-byref like VC with no pointer fields

src/coreclr/vm/methodtablebuilder.cpp

@@ -8743,29 +8743,30 @@ MethodTableBuilder::HandleExplicitLayout(
  if (pMT->IsByRefLike())
  return CheckByRefLikeValueClassLayout(pMT, pFieldLayout);
 
- // This method assumes there is a GC desc associated with the MethodTable.
- _ASSERTE(pMT->ContainsPointers());
-
  // Build a layout of the value class (vc). Don't know the sizes of all the fields easily, but
  // do know (a) vc is already consistent so don't need to check it's overlaps and
  // (b) size and location of all objectrefs. So build it by setting all non-oref
- // then fill in the orefs later
+ // then fill in the orefs later if present.
  UINT fieldSize = pMT->GetNumInstanceFieldBytes();
 
  CQuickBytes qb;
  bmtFieldLayoutTag *vcLayout = (bmtFieldLayoutTag*) qb.AllocThrows(fieldSize * sizeof(bmtFieldLayoutTag));
  memset((void*)vcLayout, nonoref, fieldSize);
 
- // use pointer series to locate the orefs
- CGCDesc* map = CGCDesc::GetCGCDescFromMT(pMT);
- CGCDescSeries *pSeries = map->GetLowestSeries();
-
- for (SIZE_T j = 0; j < map->GetNumSeries(); j++)
+ // If the type contains pointers fill it out from the GC data
+ if (pMT->ContainsPointers())
  {
- CONSISTENCY_CHECK(pSeries <= map->GetHighestSeries());
+ // use pointer series to locate the orefs
+ CGCDesc* map = CGCDesc::GetCGCDescFromMT(pMT);
+ CGCDescSeries *pSeries = map->GetLowestSeries();
 
- memset((void*)&vcLayout[pSeries->GetSeriesOffset() - OBJECT_SIZE], oref, pSeries->GetSeriesSize() + pMT->GetBaseSize());
- pSeries++;
+ for (SIZE_T j = 0; j < map->GetNumSeries(); j++)
+ {
+ CONSISTENCY_CHECK(pSeries <= map->GetHighestSeries());
+
+ memset((void*)&vcLayout[pSeries->GetSeriesOffset() - OBJECT_SIZE], oref, pSeries->GetSeriesSize() + pMT->GetBaseSize());
+ pSeries++;
+ }
  }
 
  ExplicitClassTrust explicitClassTrust;

src/tests/Loader/classloader/explicitlayout/objrefandnonobjrefoverlap/case13.cs

@@ -0,0 +1,92 @@
+// 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 System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+using Xunit;
+
+public class Test
+{
+ public struct WithORefs
+ {
+ public object F;
+ }
+
+ public struct WithNoORefs
+ {
+ public int F;
+ }
+
+ public ref struct WithByRefs
+ {
+ public ref int F;
+ }
+
+ [StructLayout(LayoutKind.Explicit)]
+ public ref struct Explicit1
+ {
+ [FieldOffset(0)] public Inner1 Field1;
+ public ref struct Inner1
+ {
+ public WithORefs Field2;
+ }
+ }
+
+ [StructLayout(LayoutKind.Explicit)]
+ public ref struct Explicit2
+ {
+ [FieldOffset(0)] public Inner2 Field1;
+ public ref struct Inner2
+ {
+ public WithNoORefs Field2;
+ }
+ }
+
+ [StructLayout(LayoutKind.Explicit)]
+ public ref struct Explicit3
+ {
+ [FieldOffset(0)] public Inner3 Field1;
+ public ref struct Inner3
+ {
+ public WithByRefs Field2;
+ }
+ }
+
+ [Fact]
+ public static void Validate_Explicit1()
+ {
+ Load1();
+
+ [MethodImpl(MethodImplOptions.NoInlining)]
+ static string Load1()
+ {
+ return typeof(Explicit1).ToString();
+ }
+ }
+
+ [Fact]
+ public static void Validate_Explicit2()
+ {
+ Load2();
+
+ [MethodImpl(MethodImplOptions.NoInlining)]
+ static string Load2()
+ {
+ return typeof(Explicit2).ToString();
+ }
+ }
+
+ [Fact]
+ public static void Validate_Explicit3()
+ {
+ Load3();
+
+ [MethodImpl(MethodImplOptions.NoInlining)]
+ static string Load3()
+ {
+ return typeof(Explicit3).ToString();
+ }
+ }
+}

src/tests/Loader/classloader/explicitlayout/objrefandnonobjrefoverlap/case13.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+ <PropertyGroup>
+ <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+ <OutputType>Exe</OutputType>
+ <MonoAotIncompatible>false</MonoAotIncompatible>
+ </PropertyGroup>
+ <ItemGroup>
+ <Compile Include="case13.cs" />
+ </ItemGroup>
+</Project>