[Mono] UnsafeAccessorAttribute non-generic support for field (#88626)

* Detect an UnsafeAccessorAttribute for method with interpreter

* Change field to property

* Get Kind from typed_args

* define MonoUnsafeAccessorKind enum

* Add the frontend for JIT

* Add mono_marshal_get_unsafe_accessor_wrapper and WRAPPER_SUBTYPE_UNSAFE_ACCESSOR

And the associated AOT compiler/runtime and marshaling caching boilerplate.

* [interp] get the unsafe accessor wrapper

* fix: skip visibility in unsafe accessor wrappers

that is the whole point of them

* fix: decode the length and copy the name from UnsafeAccessorAttribute

The name has a length as a prefix and doesn not have a null terminator

* [mini] compile wrapper

* [aot] Emit unsafe accessor wrappers to the AOT image

* Add the method to emit wrapper for field

* Fix typo

* Remove assertion for interpreter

* Fix format and replace assertion with proper exception

* Free the memory and throw proper NotImplementedException

* Enable StaticField and Field tests

Co-authored-by: Aleksey Kliger <[email protected]>
Co-authored-by: Aaron Robinson <[email protected]>

src/mono/mono/metadata/CMakeLists.txt

@@ -171,6 +171,8 @@ set(metadata_common_sources
     abi-details.h
     abi.c
     memory-manager.c
+    unsafe-accessor.h
+    unsafe-accessor.c
     icall-table.h
     ${icall_table_sources})
 

src/mono/mono/metadata/class-internals.h

@@ -1421,6 +1421,9 @@ mono_method_has_no_body (MonoMethod *method);
 MONO_COMPONENT_API MonoMethodHeader*
 mono_method_get_header_internal (MonoMethod *method, MonoError *error);
 
+gboolean
+mono_method_metadata_has_header (MonoMethod *method);
+
 MONO_COMPONENT_API void
 mono_method_get_param_names_internal (MonoMethod *method, const char **names);
 

src/mono/mono/metadata/custom-attrs.c

@@ -50,6 +50,7 @@ static gboolean type_is_reference (MonoType *type);
 static GENERATE_GET_CLASS_WITH_CACHE (custom_attribute_typed_argument, "System.Reflection", "CustomAttributeTypedArgument");
 static GENERATE_GET_CLASS_WITH_CACHE (custom_attribute_named_argument, "System.Reflection", "CustomAttributeNamedArgument");
 static GENERATE_TRY_GET_CLASS_WITH_CACHE (customattribute_data, "System.Reflection", "RuntimeCustomAttributeData");
+static GENERATE_TRY_GET_CLASS_WITH_CACHE (unsafe_accessor_attribute, "System.Runtime.CompilerServices", "UnsafeAccessorAttribute");
 
 static MonoCustomAttrInfo*
 mono_custom_attrs_from_builders_handle (MonoImage *alloc_img, MonoImage *image, MonoArrayHandle cattrs, gboolean respect_cattr_visibility);
@@ -2056,6 +2057,62 @@ mono_custom_attrs_from_method_checked (MonoMethod *method, MonoError *error)
 	return mono_custom_attrs_from_index_checked (m_class_get_image (method->klass), idx, FALSE, error);
 }
 
+gboolean
+mono_method_get_unsafe_accessor_attr_data (MonoMethod *method, int *accessor_kind, char **member_name, MonoError *error)
+{
+	MonoCustomAttrInfo *cinfo = mono_custom_attrs_from_method_checked (method, error);
+
+	if (!cinfo)
+		return FALSE;
+
+	MonoClass *unsafeAccessor = mono_class_try_get_unsafe_accessor_attribute_class ();
+	MonoCustomAttrEntry *attr = NULL;
+
+	for (int idx = 0; idx < cinfo->num_attrs; ++idx) {
+		MonoClass *ctor_class = cinfo->attrs [idx].ctor->klass;
+		if (ctor_class == unsafeAccessor) {
+			attr = &cinfo->attrs [idx];
+			break;
+		}
+	}
+
+	if (!attr){
+		if (!cinfo->cached)
+			mono_custom_attrs_free(cinfo);
+		return FALSE;
+	}
+
+	MonoDecodeCustomAttr *decoded_args = mono_reflection_create_custom_attr_data_args_noalloc (m_class_get_image (attr->ctor->klass), attr->ctor, attr->data, attr->data_size, error);
+
+	if (!is_ok (error)) {
+		mono_error_cleanup (error);
+		mono_reflection_free_custom_attr_data_args_noalloc (decoded_args);
+		if (!cinfo->cached)
+			mono_custom_attrs_free(cinfo);
+		return FALSE;
+	}
+
+	g_assert (decoded_args->typed_args_num == 1);
+	*accessor_kind =  *(int*)decoded_args->typed_args [0]->value.primitive;
+
+	for (int i = 0; i < decoded_args->named_args_num; ++i) {
+		if (decoded_args->named_args_info [i].prop && !strcmp (decoded_args->named_args_info [i].prop->name, "Name")) {
+			const char *ptr = (const char*)decoded_args->named_args [i]->value.primitive;
+			uint32_t len = mono_metadata_decode_value (ptr, &ptr);
+			char *name = m_method_alloc0 (method, len + 1);
+			memcpy (name, ptr, len);
+			name[len] = 0;
+			*member_name = (char*)name;
+		}
+	}
+
+	mono_reflection_free_custom_attr_data_args_noalloc (decoded_args);
+	if (!cinfo->cached)
+		mono_custom_attrs_free(cinfo);
+
+	return TRUE;
+}
+
 /**
  * mono_custom_attrs_from_class:
  */

src/mono/mono/metadata/loader-internals.h

@@ -88,6 +88,7 @@ typedef struct {
 	GHashTable *cominterop_invoke_cache;
 	GHashTable *cominterop_wrapper_cache; /* LOCKING: marshal lock */
 	GHashTable *thunk_invoke_cache;
+	GHashTable *unsafe_accessor_cache;
 } MonoWrapperCaches;
 
 /* Lock-free allocator */

src/mono/mono/metadata/loader.c

@@ -2076,8 +2076,8 @@ mono_method_get_header_internal (MonoMethod *method, MonoError *error)
 	g_assert (mono_metadata_token_table (method->token) == MONO_TABLE_METHOD);
 	idx = mono_metadata_token_index (method->token);
 
-        if (G_UNLIKELY (img->has_updates))
-                loc = mono_metadata_update_get_updated_method_rva (img, idx);
+	if (G_UNLIKELY (img->has_updates))
+		loc = mono_metadata_update_get_updated_method_rva (img, idx);
 
 	if (!loc) {
 		rva = mono_metadata_decode_row_col (&img->tables [MONO_TABLE_METHOD], idx - 1, MONO_METHOD_RVA);
@@ -2100,6 +2100,44 @@ mono_method_get_header_internal (MonoMethod *method, MonoError *error)
 	return mono_metadata_parse_mh_full (img, container, (const char *)loc, error);
 }
 
+gboolean
+mono_method_metadata_has_header (MonoMethod *method)
+{
+	int idx;
+	guint32 rva;
+	MonoImage* img;
+	gpointer loc = NULL;
+
+	img = m_class_get_image (method->klass);
+
+	if (mono_method_has_no_body (method)) {
+		return FALSE;
+	}
+
+	if (method->is_inflated) {
+		MonoMethodInflated *imethod = (MonoMethodInflated *) method;
+		return mono_method_metadata_has_header (imethod->declaring);
+	}
+
+	if (method->wrapper_type != MONO_WRAPPER_NONE || method->sre_method) {
+		MonoMethodWrapper *mw = (MonoMethodWrapper *)method;
+		return mw->header != NULL;
+	}
+
+	g_assert (mono_metadata_token_table (method->token) == MONO_TABLE_METHOD);
+	idx = mono_metadata_token_index (method->token);
+
+	if (G_UNLIKELY (img->has_updates))
+		loc = mono_metadata_update_get_updated_method_rva (img, idx);
+
+	if (!loc) {
+		rva = mono_metadata_decode_row_col (&img->tables [MONO_TABLE_METHOD], idx - 1, MONO_METHOD_RVA);
+		loc = mono_image_rva_map (img, rva);
+	}
+
+	return loc != NULL;
+}
+
 MonoMethodHeader*
 mono_method_get_header_checked (MonoMethod *method, MonoError *error)
 // Public function that must initialize MonoError for compatibility.

src/mono/mono/metadata/marshal-lightweight.c

@@ -39,6 +39,7 @@
 #include "mono/metadata/handle.h"
 #include "mono/metadata/custom-attrs-internals.h"
 #include "mono/metadata/icall-internals.h"
+#include "mono/metadata/unsafe-accessor.h"
 #include "mono/utils/mono-tls.h"
 #include "mono/utils/mono-memory-model.h"
 #include "mono/utils/atomic.h"
@@ -2319,6 +2320,79 @@ emit_array_accessor_wrapper_ilgen (MonoMethodBuilder *mb, MonoMethod *method, Mo
 	mono_mb_emit_byte (mb, CEE_RET);
 }
 
+static void
+emit_unsafe_accessor_field_wrapper (MonoMethodBuilder *mb, MonoMethod *accessor_method, MonoMethodSignature *sig, MonoGenericContext *ctx, MonoUnsafeAccessorKind kind, const char *member_name)
+{
+	// Field access requires a single argument for target type and a return type.
+	g_assert (kind == MONO_UNSAFE_ACCESSOR_FIELD || kind == MONO_UNSAFE_ACCESSOR_STATIC_FIELD);
+	g_assert (member_name != NULL);
+
+	MonoType *target_type = sig->params[0]; // params[0] is the field's parent
+	MonoType *ret_type = sig->ret;
+	if (sig->param_count != 1 || target_type == NULL || sig->ret->type == MONO_TYPE_VOID) {
+		mono_mb_emit_exception_full (mb, "System", "BadImageFormatException", "Invalid usage of UnsafeAccessorAttribute.");
+		return;
+	}
+
+	MonoClass *target_class = mono_class_from_mono_type_internal (target_type);
+	gboolean target_byref = m_type_is_byref (target_type);
+	gboolean target_valuetype = m_class_is_valuetype (target_class);
+	gboolean ret_byref = m_type_is_byref (ret_type);
+	if (!ret_byref || (kind == MONO_UNSAFE_ACCESSOR_FIELD && target_valuetype && !target_byref)) {
+		mono_mb_emit_exception_full (mb, "System", "BadImageFormatException", "Invalid usage of UnsafeAccessorAttribute.");
+		return;
+	}
+
+	MonoClassField *target_field = mono_class_get_field_from_name_full (target_class, member_name, NULL);
+	if (target_field == NULL || !mono_metadata_type_equal_full (target_field->type, m_class_get_byval_arg (mono_class_from_mono_type_internal (ret_type)), TRUE)) {
+		mono_mb_emit_exception_full (mb, "System", "MissingFieldException", 
+			g_strdup_printf("No '%s' in '%s'. Or the type of '%s' doesn't match", member_name, m_class_get_name (target_class), member_name));
+		return;
+	}
+	gboolean is_field_static = !!(target_field->type->attrs & FIELD_ATTRIBUTE_STATIC);
+	if ((kind == MONO_UNSAFE_ACCESSOR_FIELD && is_field_static) || (kind == MONO_UNSAFE_ACCESSOR_STATIC_FIELD && !is_field_static)) {
+		mono_mb_emit_exception_full (mb, "System", "MissingFieldException", g_strdup_printf("UnsafeAccessorKind does not match expected static modifier on field '%s' in '%s'", member_name, m_class_get_name (target_class)));
+		return;
+	}
+
+	if (kind == MONO_UNSAFE_ACCESSOR_FIELD)
+		mono_mb_emit_ldarg (mb, 0);
+	mono_mb_emit_op (mb, kind == MONO_UNSAFE_ACCESSOR_FIELD ? CEE_LDFLDA : CEE_LDSFLDA, target_field);
+	mono_mb_emit_byte (mb, CEE_RET);
+}
+
+static void
+emit_unsafe_accessor_wrapper_ilgen (MonoMethodBuilder *mb, MonoMethod *accessor_method, MonoMethodSignature *sig, MonoGenericContext *ctx, MonoUnsafeAccessorKind kind, const char *member_name)
+{
+	if (accessor_method->is_generic) {
+		mono_mb_emit_exception_full (mb, "System", "NotImplementedException", "UnsafeAccessor_Generics");
+		return;
+	}
+
+	if (!m_method_is_static (accessor_method)) {
+		mono_mb_emit_exception_full (mb, "System", "BadImageFormatException", "UnsafeAccessor_NonStatic");
+		return;
+	}
+
+	switch (kind) {
+	case MONO_UNSAFE_ACCESSOR_FIELD:
+	case MONO_UNSAFE_ACCESSOR_STATIC_FIELD:
+		emit_unsafe_accessor_field_wrapper (mb, accessor_method, sig, ctx, kind, member_name);
+		return;
+	case MONO_UNSAFE_ACCESSOR_CTOR:
+		// TODO
+		mono_mb_emit_exception_full (mb, "System", "NotImplementedException", "UnsafeAccessor");
+		return;
+	case MONO_UNSAFE_ACCESSOR_METHOD:
+	case MONO_UNSAFE_ACCESSOR_STATIC_METHOD:
+		// TODO
+		mono_mb_emit_exception_full (mb, "System", "NotImplementedException", "UnsafeAccessor");
+		return;
+	default:
+		g_assert_not_reached(); // some unknown wrapper kind
+	}
+}
+
 static void
 emit_generic_array_helper_ilgen (MonoMethodBuilder *mb, MonoMethod *method, MonoMethodSignature *csig)
 {
@@ -3158,6 +3232,7 @@ mono_marshal_lightweight_init (void)
 	cb.emit_synchronized_wrapper = emit_synchronized_wrapper_ilgen;
 	cb.emit_unbox_wrapper = emit_unbox_wrapper_ilgen;
 	cb.emit_array_accessor_wrapper = emit_array_accessor_wrapper_ilgen;
+	cb.emit_unsafe_accessor_wrapper = emit_unsafe_accessor_wrapper_ilgen;
 	cb.emit_generic_array_helper = emit_generic_array_helper_ilgen;
 	cb.emit_thunk_invoke_wrapper = emit_thunk_invoke_wrapper_ilgen;
 	cb.emit_create_string_hack = emit_create_string_hack_ilgen;

src/mono/mono/metadata/marshal.c

@@ -5094,6 +5094,96 @@ mono_marshal_get_array_accessor_wrapper (MonoMethod *method)
 	return res;
 }
 
+/*
+ * mono_marshal_get_unsafe_accessor_wrapper:
+ *
+ *   Return a wrapper for an extern [UnsafeAccessor] method that accesses a member of some class.
+ *
+ *   member_name can be NULL in which case the name of the member is the same as the name of the accessor method
+ *
+ *   If the kind is Field or StaticField the accessor_method must have a signature like:
+ *       ref FieldType AccessorMethod (TargetClassOrStruct @this);
+ *   or
+ *       ref FieldType AccessorMethod (ref TargetStruct @this);
+ *
+ *   If the kind is Method or StaticMethod, the accessor_method must have a signature like:
+ *       ReturnType AccessorMethod (TargetClassOrStruct @this[, FirstArg arg1[, SecondArg arg2[, ...]]])
+ *
+ *   where the member method is
+ *
+ *       class TargetClassOrStruct {
+ *           ReturnType MemberName ([FirstArg arg1[, SecondArg arg2[, ...]]]);
+ *       }
+ *
+ *
+ *  or
+ *       ReturnType AccessorMethod (ref TargetStruct @this[, FirstArg arg1[, SecondArg arg2[, ...]]])
+ *
+ *   where the member method is
+ *
+ *       struct TargetStruct {
+ *           ReturnType MemberName ([FirstArg arg1[, SecondArg arg2[, ...]]]);
+ *       }
+ *
+ *
+ *  If the kind is Constructor, the accessor_method must have a signature like:
+ *       TargetClass AccessorMethod ([FirstArg arg1[, SecondArg arg2[, ...]]]);
+ */
+MonoMethod *
+mono_marshal_get_unsafe_accessor_wrapper (MonoMethod *accessor_method, MonoUnsafeAccessorKind kind, const char *member_name)
+{
+	MonoMethodSignature *sig;
+	MonoMethodBuilder *mb;
+	MonoMethod *res;
+	GHashTable *cache;
+	MonoGenericContext *ctx = NULL;
+	MonoMethod *orig_method = NULL;
+	WrapperInfo *info;
+
+	if (member_name == NULL)
+		member_name = accessor_method->name;
+
+	/*
+	 * Check cache
+	 */
+	if (ctx) {
+		cache = NULL;
+		g_assert_not_reached ();
+	} else {
+		cache = get_cache (&mono_method_get_wrapper_cache (accessor_method)->unsafe_accessor_cache, mono_aligned_addr_hash, NULL);
+		if ((res = mono_marshal_find_in_cache (cache, accessor_method)))
+			return res;
+	}
+
+	sig = mono_metadata_signature_dup_full (get_method_image (accessor_method), mono_method_signature_internal (accessor_method));
+	sig->pinvoke = 0;
+
+	mb = mono_mb_new (accessor_method->klass, accessor_method->name, MONO_WRAPPER_OTHER);
+
+	get_marshal_cb ()->mb_skip_visibility (mb);
+
+	get_marshal_cb ()->emit_unsafe_accessor_wrapper (mb, accessor_method, sig, ctx, kind, member_name);
+
+	info = mono_wrapper_info_create (mb, WRAPPER_SUBTYPE_UNSAFE_ACCESSOR);
+	info->d.unsafe_accessor.method = accessor_method;
+	info->d.unsafe_accessor.kind = kind;
+	info->d.unsafe_accessor.member_name = member_name;
+
+	if (ctx) {
+		MonoMethod *def;
+		def = mono_mb_create_and_cache_full (cache, accessor_method, mb, sig, sig->param_count + 16, info, NULL);
+		res = cache_generic_wrapper (cache, orig_method, def, ctx, orig_method);
+	} else {
+		res = mono_mb_create_and_cache_full (cache, accessor_method, mb, sig, sig->param_count + 16, info, NULL);
+	}
+	mono_mb_free (mb);
+
+	// TODO: remove before merging
+	mono_method_print_code (res);
+
+	return res;
+}
+
 #ifdef HOST_WIN32
 
 static void*
@@ -6398,4 +6488,5 @@ mono_wrapper_caches_free (MonoWrapperCaches *cache)
 	free_hash (cache->cominterop_invoke_cache);
 	free_hash (cache->cominterop_wrapper_cache);
 	free_hash (cache->thunk_invoke_cache);
+	free_hash (cache->unsafe_accessor_cache);
 }