[mono] [imt] Don't increment vt_slot for non-virtual generic methods

src/mono/mono/metadata/object.c

@@ -1430,8 +1430,8 @@ print_imt_entry (const char* message, MonoImtBuilderEntry *e, int num) {
 				message,
 				num,
 				method,
-				method->klass->name_space,
-				method->klass->name,
+				m_class_get_name_space (method->klass),
+				m_class_get_name (method->klass),
 				method->name);
 	} else {
 		printf ("  * %s: NULL\n", message);
@@ -1543,12 +1543,11 @@ get_generic_virtual_entries (MonoMemoryManager *mem_manager, gpointer *vtable_sl
  *
 */
 static void
-build_imt_slots (MonoClass *klass, MonoVTable *vt, gpointer* imt, GSList *extra_interfaces, int slot_num)
+build_imt_slots (MonoClass *klass, MonoVTable *vt, gpointer* imt, int slot_num)
 {
 	MONO_REQ_GC_NEUTRAL_MODE;
 
 	int i;
-	GSList *list_item;
 	guint32 imt_collisions_bitmap = 0;
 	MonoImtBuilderEntry **imt_builder = (MonoImtBuilderEntry **)g_calloc (MONO_IMT_SIZE, sizeof (MonoImtBuilderEntry*));
 	int method_count = 0;
@@ -1596,8 +1595,10 @@ build_imt_slots (MonoClass *klass, MonoVTable *vt, gpointer* imt, GSList *extra_
 			}
 			method = mono_class_get_method_by_index (iface, method_slot_in_interface);
 			if (method->is_generic) {
-				has_generic_virtual = TRUE;
-				vt_slot ++;
+				if (m_method_is_virtual (method)) {
+					has_generic_virtual = TRUE;
+					vt_slot ++;
+				}
 				continue;
 			}
 
@@ -1613,23 +1614,6 @@ build_imt_slots (MonoClass *klass, MonoVTable *vt, gpointer* imt, GSList *extra_
 			}
 		}
 	}
-	if (extra_interfaces) {
-		int interface_offset = m_class_get_vtable_size (klass);
-
-		for (list_item = extra_interfaces; list_item != NULL; list_item=list_item->next) {
-			MonoClass* iface = (MonoClass *)list_item->data;
-			int method_slot_in_interface;
-			int mcount = mono_class_get_method_count (iface);
-			for (method_slot_in_interface = 0; method_slot_in_interface < mcount; method_slot_in_interface++) {
-				MonoMethod *method = mono_class_get_method_by_index (iface, method_slot_in_interface);
-
-				if (method->is_generic)
-					has_generic_virtual = TRUE;
-				add_imt_builder_entry (imt_builder, method, &imt_collisions_bitmap, interface_offset + method_slot_in_interface, slot_num);
-			}
-			interface_offset += mcount;
-		}
-	}
 	for (i = 0; i < MONO_IMT_SIZE; ++i) {
 		/* overwrite the imt slot only if we're building all the entries or if
 		 * we're building this specific one
@@ -1729,7 +1713,7 @@ mono_vtable_build_imt_slot (MonoVTable* vtable, int imt_slot)
 	mono_loader_lock ();
 	/* we change the slot only if it wasn't changed from the generic imt trampoline already */
 	if (!callbacks.imt_entry_inited (vtable, imt_slot))
-		build_imt_slots (vtable->klass, vtable, imt, NULL, imt_slot);
+		build_imt_slots (vtable->klass, vtable, imt, imt_slot);
 	mono_loader_unlock ();
 }
 

src/tests/Loader/classloader/regressions/GitHub_93770/GitHub_93770.cs

@@ -0,0 +1,128 @@
+// 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.Collections.Generic;
+using System.Runtime.CompilerServices;
+using Xunit;
+
+namespace ReproGH93770;
+
+// By default in Mono every class that implements interfaces has 19
+// interface method table slots that are used to dispatch interface
+// calls.  The methods are assigned to slots based on a hash of some
+// metadata.  This test tries to create at least one IMT slot that has
+// a collision by creating an interface with 20 virtual methods.
+//
+// The bug is that if the method also has a non-virtual generic
+// method, the IMT slot with the collision calls the wrong vtable
+// element.
+
+public class ReproGH93770
+{
+    [Fact]
+    public static int TestEntryPoint()
+    {
+        C c = new C();
+        I1 i1 = c;
+        Helper(i1);
+        return 100;
+    }
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static void Helper(I1 i1)
+    {
+    var e = 0;
+    var n = i1.M0();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M1();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M2();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M3();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M4();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M5();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M6();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M7();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M8();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M9();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M10();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M11();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M12();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M13();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M14();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M15();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M16();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M17();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M18();
+    Assert.Equal(e, n);
+    e++;
+    n = i1.M19();
+    Assert.Equal(e, n);
+    e++;
+    }
+}
+
+public interface I1 {
+    public static T Id<T> (T t)=> t;
+
+    public int M0() => 0;
+    public int M1() => 1;
+    public int M2() => 2;
+    public int M3() => 3;
+    public int M4() => 4;
+
+    public int M5() => 5;
+    public int M6() => 6;
+    public int M7() => 7;
+    public int M8() => 8;
+    public int M9() => 9;
+    public int M10() => 10;
+    public int M11() => 11;
+    public int M12() => 12;
+    public int M13() => 13;
+    public int M14() => 14;
+    public int M15() => 15;
+    public int M16() => 16;
+    public int M17() => 17;
+    public int M18() => 18;
+    public int M19() => 19;
+
+}
+
+public class C : I1 {
+
+}
+
+

src/tests/Loader/classloader/regressions/GitHub_93770/GitHub_93770.csproj

@@ -0,0 +1,7 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="GitHub_93770.cs" />
+  </ItemGroup>
+</Project>