Revert "[Mono] Fix support for nested structs with explicit layout (#61467)"

This reverts commit 64d1276.

Author: agocke

src/mono/mono/metadata/class-init.c

@@ -1864,85 +1864,6 @@ mono_class_is_gparam_with_nonblittable_parent (MonoClass *klass)
 	return parent_class != mono_defaults.object_class;
 }
 
-/**
- * Checks if there are any overlapping object and non-object fields.
- * The alignment of object reference fields is checked elswhere and this function assumes
- * that all references are aligned correctly.
- *
- * \param layout_check A buffer to check which bytes hold object references or values
- * \param klass Checked struct
- * \param field_offsets Offsets of the klass' fields relative to the start of layout_check
- * \param field_count Count of klass fields
- * \param invalid_field_offset When the layout is invalid it will be set to the offset of the field which is invalid
- * 
- * \return True if the layout of the struct is valid, otherwise false.
- */
-static gboolean
-validate_struct_fields_overlaps (guint8 *layout_check, int layout_size, MonoClass *klass, const int *field_offsets, const int field_count, int *invalid_field_offset)
-{
-	MonoClassField *field;
-	MonoType *ftype;
-	int field_offset;
-
-	for (int i = 0; i < field_count && !mono_class_has_failure (klass); i++) {
-		// using mono_class_get_fields_internal isn't appropriate here because it will
-		// try to call mono_class_setup_fields which is what we're doing already
-		field = &m_class_get_fields (klass) [i];
-		field_offset = field_offsets [i];
-
-		if (!field)
-			continue;
-		if (mono_field_is_deleted (field))
-			continue;
-		if (field->type->attrs & FIELD_ATTRIBUTE_STATIC)
-			continue;
-
-		ftype = mono_type_get_underlying_type (field->type);
-		ftype = mono_type_get_basic_type_from_generic (ftype);
-
-		if (mono_type_is_struct (ftype)) {
-			// recursively check the layout of the embedded struct
-			MonoClass *embedded_class = mono_class_from_mono_type_internal (ftype);
-			g_assert (m_class_is_fields_inited (embedded_class));
-
-			const int embedded_fields_count = mono_class_get_field_count (embedded_class);
-			int *embedded_offsets = g_new0 (int, embedded_fields_count);
-			for (int j = 0; j < embedded_fields_count; ++j) {
-				embedded_offsets [j] = field_offset + m_class_get_fields (embedded_class) [j].offset - MONO_ABI_SIZEOF (MonoObject);
-			}
-
-			gboolean is_valid = validate_struct_fields_overlaps (layout_check, layout_size, embedded_class, embedded_offsets, embedded_fields_count, invalid_field_offset);
-			g_free (embedded_offsets);
-
-			if (!is_valid) {
-				// overwrite whatever was in the invalid_field_offset with the offset of the currently checked field
-				// we want to return the outer most invalid field
-				*invalid_field_offset = field_offset;
-				return FALSE;
-			}
-		} else {
-			int align = 0;
-			int size = mono_type_size (field->type, &align);
-			guint8 type = type_has_references (klass, ftype) ? 1 : 2;
-
-			// Mark the bytes used by this fields type based on if it contains references or not.
-			// Make sure there are no overlaps between object and non-object fields.
-			for (int j = 0; j < size; j++) {
-				int checked_byte = field_offset + j;
-				g_assert(checked_byte < layout_size);
-
-				if (layout_check [checked_byte] != 0 && layout_check [checked_byte] != type) {
-					*invalid_field_offset = field_offset;
-					return FALSE;
-				}
-				layout_check [checked_byte] = type;
-			}
-		}
-	}
-
-	return TRUE;
-}
-
 /*
  * mono_class_layout_fields:
  * @class: a class
@@ -2233,12 +2154,29 @@ mono_class_layout_fields (MonoClass *klass, int base_instance_size, int packing_
 		}
 
 		/* check for incorrectly aligned or overlapped by a non-object field */
-		guint8 *layout_check;
+		guint8 *layout_check;	
 		if (has_references) {
 			layout_check = g_new0 (guint8, real_size);
-			int invalid_field_offset;
-			if (!validate_struct_fields_overlaps (layout_check, real_size, klass, field_offsets, top, &invalid_field_offset)) {
-				mono_class_set_type_load_failure (klass, "Could not load type '%s' because it contains an object field at offset %d that is incorrectly aligned or overlapped by a non-object field.", klass->name, invalid_field_offset);
+			for (i = 0; i < top && !mono_class_has_failure (klass); i++) {
+				field = &klass->fields [i];
+				if (!field)
+					continue;
+				if (mono_field_is_deleted (field))
+					continue;
+				if (field->type->attrs & FIELD_ATTRIBUTE_STATIC)
+					continue;
+				int align = 0;
+				int size = mono_type_size (field->type, &align);
+				MonoType *ftype = mono_type_get_underlying_type (field->type);
+				ftype = mono_type_get_basic_type_from_generic (ftype);
+				guint8 type =  type_has_references (klass, ftype) ? 1 : 2;				
+				for (int j = 0; j < size; j++) {
+					if (layout_check [field_offsets [i] + j] != 0 && layout_check [field_offsets [i] + j] != type) {
+						mono_class_set_type_load_failure (klass, "Could not load type '%s' because it contains an object field at offset %d that is incorrectly aligned or overlapped by a non-object field.", klass->name, field->offset);
+						break;
+					}
+					layout_check [field_offsets [i] + j] = type;
+				}
 			}
 			g_free (layout_check);
 		}