From 6087adb2aa3cd803c12ac03bdca5d3652beab9d1 Mon Sep 17 00:00:00 2001
From: Aleksey Kliger <alklig@microsoft.com>
Date: Wed, 1 Sep 2021 15:53:55 -0400
Subject: [PATCH 1/2] [mini] Don't add unbox tramopline on generic DIM calls

Don't unbox a valuetype `this` if the generic method is a DIM

Fixes https://github.com/dotnet/runtime/issues/58394
---
 src/mono/mono/mini/mini-trampolines.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/mono/mono/mini/mini-trampolines.c b/src/mono/mono/mini/mini-trampolines.c
index 36fb6ca4d84b5c..07a50524a0feb2 100644
--- a/src/mono/mono/mini/mini-trampolines.c
+++ b/src/mono/mono/mini/mini-trampolines.c
@@ -632,11 +632,13 @@ common_call_trampoline (host_mgreg_t *regs, guint8 *code, MonoMethod *m, MonoVTa
 		return NULL;
 
 	if (generic_virtual || variant_iface) {
-		if (m_class_is_valuetype (vt->klass)) /*FIXME is this required variant iface?*/
+		if (m_class_is_valuetype (vt->klass)  && !mini_method_is_default_method (m)) /*FIXME is this required variant iface?*/
 			need_unbox_tramp = TRUE;
 	} else if (orig_vtable_slot) {
-		if (m_class_is_valuetype (m->klass))
+		if (m_class_is_valuetype (m->klass)) {
+			g_assert (!mini_method_is_default_method (m));
 			need_unbox_tramp = TRUE;
+		}
 	}
 
 	addr = mini_add_method_trampoline (m, compiled_method, need_rgctx_tramp, need_unbox_tramp);

From bd0ccd2e16b4fd3f8da541e7d729813111eb8e5b Mon Sep 17 00:00:00 2001
From: Aleksey Kliger <alklig@microsoft.com>
Date: Wed, 1 Sep 2021 16:31:24 -0400
Subject: [PATCH 2/2] Add regression test

---
 .../regressions/github58394.cs                | 47 +++++++++++++++++++
 .../regressions/github58394.csproj            | 11 +++++
 2 files changed, 58 insertions(+)
 create mode 100644 src/tests/Loader/classloader/DefaultInterfaceMethods/regressions/github58394.cs
 create mode 100644 src/tests/Loader/classloader/DefaultInterfaceMethods/regressions/github58394.csproj

diff --git a/src/tests/Loader/classloader/DefaultInterfaceMethods/regressions/github58394.cs b/src/tests/Loader/classloader/DefaultInterfaceMethods/regressions/github58394.cs
new file mode 100644
index 00000000000000..ee94e5422908dc
--- /dev/null
+++ b/src/tests/Loader/classloader/DefaultInterfaceMethods/regressions/github58394.cs
@@ -0,0 +1,47 @@
+// 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;
+
+namespace GenericDimValuetypeBug
+{
+    class Program
+    {
+        static int Main()
+        {
+            if (RunOne() != 17)
+                return 1;
+            if (RunTwo() != 23)
+                return 2;
+            return 100;
+        }
+
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        public static int RunOne()
+        {
+            return (new Foo() { x = 17 } as IFoo).NoCrash();
+        }
+
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        public static int RunTwo()
+        {
+            return (new Foo() { x = 23 } as IFoo).Crash<int>();
+        }
+    }
+
+    interface IFoo
+    {
+        int Crash<T>() => Bla();
+
+        int NoCrash() => Bla();
+
+        int Bla();
+    }
+
+    struct Foo: IFoo
+    {
+        public int x;
+        public int Bla() => x;
+    }
+}
diff --git a/src/tests/Loader/classloader/DefaultInterfaceMethods/regressions/github58394.csproj b/src/tests/Loader/classloader/DefaultInterfaceMethods/regressions/github58394.csproj
new file mode 100644
index 00000000000000..aab61d4e4497b8
--- /dev/null
+++ b/src/tests/Loader/classloader/DefaultInterfaceMethods/regressions/github58394.csproj
@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <OutputType>Exe</OutputType>
+    <CLRTestKind>BuildAndRun</CLRTestKind>
+    <CLRTestPriority>0</CLRTestPriority>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>