Add AOT support for the EntryPoint property for UnmanagedCallersOnly. (…

…#44809)

* Change mono_reflection_create_custom_attr_data_args_noalloc () so it returns the beginning of the metadata string so its length can be computed.

* Add AOT support for the EntryPoint property for UnmanagedCallersOnly.

Fixes #44803.

* Update src/mono/mono/mini/driver.c

Co-authored-by: Aleksey Kliger (λgeek) <akliger@gmail.com>

Co-authored-by: Aleksey Kliger (λgeek) <akliger@gmail.com>

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

@@ -374,7 +374,9 @@ load_cattr_value (MonoImage *image, MonoType *t, MonoObject **out_obj, const cha
 		g_error ("generic valutype %s not handled in custom attr value decoding", m_class_get_name (t->data.klass));
 		break;
 
-	case MONO_TYPE_STRING:
+	case MONO_TYPE_STRING: {
+		const char *start = p;
+
 		if (!bcheck_blob (p, 0, boundp, error))
 			return NULL;
 MONO_DISABLE_WARNING (4310) // cast truncates constant value
@@ -389,7 +391,7 @@ MONO_RESTORE_WARNING
 			return NULL;
 		*end = p + slen;
 		if (!out_obj)
-			return (void*)p;
+			return (void*)start;
 		// https://bugzilla.xamarin.com/show_bug.cgi?id=60848
 		// Custom attribute strings are encoded as wtf-8 instead of utf-8.
 		// If we decode using utf-8 like the spec says, we will silently fail
@@ -398,6 +400,7 @@ MONO_RESTORE_WARNING
 		// See https://simonsapin.github.io/wtf-8/ for a description of wtf-8.
 		*out_obj = (MonoObject*)mono_string_new_wtf8_len_checked (mono_domain_get (), p, slen, error);
 		return NULL;
+	}
 	case MONO_TYPE_CLASS: {
 		MonoType *type = load_cattr_type (image, t, TRUE, p, boundp, end, error, &slen);
 		if (out_obj) {
@@ -1204,7 +1207,9 @@ mono_reflection_create_custom_attr_data_args (MonoImage *image, MonoMethod *meth
  * mono_reflection_create_custom_attr_data_args_noalloc:
  *
  * Same as mono_reflection_create_custom_attr_data_args but allocate no managed objects, return values
- * using C arrays. Only usable for cattrs with primitive/type arguments.
+ * using C arrays. Only usable for cattrs with primitive/type/string arguments.
+ * For types, a MonoType* is returned.
+ * For strings, the address in the metadata blob is returned.
  * TYPED_ARGS, NAMED_ARGS, and NAMED_ARG_INFO should be freed using g_free ().
  */
 void

src/mono/mono/mini/aot-compiler.c

@@ -5060,10 +5060,42 @@ MONO_RESTORE_WARNING
 				if (cattr->attrs [j].ctor && mono_is_corlib_image (m_class_get_image (cattr->attrs [j].ctor->klass)) && !strcmp (m_class_get_name (cattr->attrs [j].ctor->klass), "UnmanagedCallersOnlyAttribute"))
 					break;
 			if (j < cattr->num_attrs) {
-				MonoMethod *wrapper = mono_marshal_get_managed_wrapper (method, NULL, 0, error);
+				MonoCustomAttrEntry *e = &cattr->attrs [j];
+				const char *named;
+				int slen;
+				char *export_name = NULL;
+				MonoMethod *wrapper;
+
+				if (!(method->flags & METHOD_ATTRIBUTE_STATIC)) {
+					g_warning ("AOT restriction: Method '%s' must be static since it is decorated with [UnmanagedCallers].",
+						mono_method_full_name (method, TRUE));
+					exit (1);
+				}
+
+				gpointer *typed_args = NULL;
+				gpointer *named_args = NULL;
+				CattrNamedArg *named_arg_info = NULL;
+				int num_named_args = 0;
+				mono_reflection_create_custom_attr_data_args_noalloc (acfg->image, e->ctor, e->data, e->data_size, &typed_args, &named_args, &num_named_args, &named_arg_info, error);
+				mono_error_assert_ok (error);
+				for (j = 0; j < num_named_args; ++j) {
+					if (named_arg_info [j].field && !strcmp (named_arg_info [j].field->name, "EntryPoint")) {
+						named = named_args [j];
+						slen = mono_metadata_decode_value (named, &named);
+						export_name = (char *)g_malloc (slen + 1);
+						memcpy (export_name, named, slen);
+						export_name [slen] = 0;
+					}
+				}
+				g_free (named_args);
+				g_free (named_arg_info);
+
+				wrapper = mono_marshal_get_managed_wrapper (method, NULL, 0, error);
 				mono_error_assert_ok (error);
 
 				add_method (acfg, wrapper);
+				if (export_name)
+					g_hash_table_insert (acfg->export_names, wrapper, export_name);
 			}
 #endif
 

src/mono/mono/mini/driver.c

@@ -452,7 +452,9 @@ method_should_be_regression_tested (MonoMethod *method, gboolean interp)
 		if (!is_ok (error))
 			continue;
 
-		char *utf8_str = (char*)(void*)typed_args[0]; //this points into image memory that is constant
+		const char *arg = (const char*)typed_args [0];
+		mono_metadata_decode_value (arg, &arg);
+		char *utf8_str = (char*)arg; //this points into image memory that is constant
 		g_free (typed_args);
 		g_free (named_args);
 		g_free (arginfo);
@@ -3352,4 +3354,3 @@ mono_parse_env_options (int *ref_argc, char **ref_argv [])
 	fprintf (stderr, "%s", ret);
 	exit (1);
 }
-