Merge pull request #10355 from BrzVlad/fix-sgen-string

[sgen] Fix string size inconsistency between alloc/scan

This could lead to crashes when having strings with size at the LOS boundary.

#10309



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mono/metadata/object-internals.h

@@ -153,6 +153,8 @@ struct _MonoString {
 	mono_unichar2 chars [MONO_ZERO_LEN_ARRAY];
 };
 
+#define MONO_SIZEOF_MONO_STRING (MONO_STRUCT_OFFSET (MonoString, chars))
+
 #define mono_object_class(obj) (((MonoObject*)(obj))->vtable->klass)
 #define mono_object_domain(obj) (((MonoObject*)(obj))->vtable->domain)
 

mono/metadata/object.c

@@ -6997,7 +6997,7 @@ mono_object_get_size (MonoObject* o)
 
 	MonoClass* klass = mono_object_class (o);
 	if (klass == mono_defaults.string_class) {
-		return sizeof (MonoString) + 2 * mono_string_length ((MonoString*) o) + 2;
+		return MONO_SIZEOF_MONO_STRING + 2 * mono_string_length ((MonoString*) o) + 2;
 	} else if (o->vtable->rank) {
 		MonoArray *array = (MonoArray*)o;
 		size_t size = MONO_SIZEOF_MONO_ARRAY + mono_array_element_size (klass) * mono_array_length (array);
@@ -7240,7 +7240,7 @@ mono_string_get_pinned (MonoString *str, MonoError *error)
 		return str;
 	int size;
 	MonoString *news;
-	size = sizeof (MonoString) + 2 * (mono_string_length (str) + 1);
+	size = MONO_SIZEOF_MONO_STRING + 2 * (mono_string_length (str) + 1);
 	news = (MonoString *)mono_gc_alloc_pinned_obj (((MonoObject*)str)->vtable, size);
 	if (news) {
 		memcpy (mono_string_chars (news), mono_string_chars (str), mono_string_length (str) * 2);

mono/metadata/sgen-client-mono.h

@@ -115,7 +115,7 @@ sgen_client_slow_object_get_size (GCVTable vtable, GCObject* o)
 	 * mono_array_length_fast not using the object's vtable.
 	 */
 	if (klass == mono_defaults.string_class) {
-		return G_STRUCT_OFFSET (MonoString, chars) + 2 * mono_string_length_fast ((MonoString*) o) + 2;
+		return MONO_SIZEOF_MONO_STRING + 2 * mono_string_length_fast ((MonoString*) o) + 2;
 	} else if (m_class_get_rank (klass)) {
 		return sgen_mono_array_size (vtable, (MonoArray*)o, NULL, 0);
 	} else {