Separately allocate class_serial on 32-bit systems

On 32-bit systems, VWA causes class_serial to not be aligned (it only
guarantees 4 byte alignment but class_serial is 8 bytes and requires 8
byte alignment). This commit uses a hack to allocate class_serial
through malloc. Once VWA allocates with 8 byte alignment in the future,
we will revert this commit.

3 files changed, 16 insertions, 2 deletions

diff --git a/class.c b/class.c
index 1281a243ab..9739aadc73 100644
--- a/class.c
+++ b/class.c
@@ -208,6 +208,9 @@ class_alloc(VALUE flags, VALUE klass)
 
 #if USE_RVARGC
     memset(RCLASS_EXT(obj), 0, sizeof(rb_classext_t));
+# if SIZEOF_SERIAL_T != SIZEOF_VALUE
+    RCLASS(obj)->class_serial_ptr = ZALLOC(rb_serial_t);
+# endif
 #else
     obj->ptr = ZALLOC(rb_classext_t);
 #endif
diff --git a/gc.c b/gc.c
index 02f3e0bbb4..aca15ad426 100644
--- a/gc.c
+++ b/gc.c
@@ -3132,6 +3132,10 @@ obj_free(rb_objspace_t *objspace, VALUE obj)
         rb_class_remove_subclass_head(obj);
 	rb_class_remove_from_module_subclasses(obj);
 	rb_class_remove_from_super_subclasses(obj);
+#if SIZEOF_SERIAL_T != SIZEOF_VALUE && USE_RVARGC
+        xfree(RCLASS(obj)->class_serial_ptr);
+#endif
+
 #if !USE_RVARGC
 	if (RCLASS_EXT(obj))
             xfree(RCLASS_EXT(obj));
diff --git a/internal/class.h b/internal/class.h
index 9edc821701..8942f80c9b 100644
--- a/internal/class.h
+++ b/internal/class.h
@@ -55,7 +55,7 @@ struct rb_classext_struct {
      * included. Hopefully that makes sense.
      */
     struct rb_subclass_entry *module_subclass_entry;
-#if SIZEOF_SERIAL_T != SIZEOF_VALUE /* otherwise class_serial is in struct RClass */
+#if SIZEOF_SERIAL_T != SIZEOF_VALUE && !USE_RVARGC /* otherwise class_serial is in struct RClass */
     rb_serial_t class_serial;
 #endif
     const VALUE origin_;
@@ -76,6 +76,9 @@ struct RClass {
 #else
     /* Class serial does not fit into struct RClass. Place m_tbl instead. */
     struct rb_id_table *m_tbl;
+# if USE_RVARGC
+    rb_serial_t *class_serial_ptr;
+# endif
 #endif
 };
 
@@ -103,7 +106,11 @@ typedef struct rb_classext_struct rb_classext_t;
 #if SIZEOF_SERIAL_T == SIZEOF_VALUE
 # define RCLASS_SERIAL(c) (RCLASS(c)->class_serial)
 #else
-# define RCLASS_SERIAL(c) (RCLASS_EXT(c)->class_serial)
+# if USE_RVARGC
+#  define RCLASS_SERIAL(c) (*RCLASS(c)->class_serial_ptr)
+# else
+#  define RCLASS_SERIAL(c) (RCLASS_EXT(c)->class_serial)
+# endif
 #endif
 #define RCLASS_INCLUDER(c) (RCLASS_EXT(c)->includer)
 #define RCLASS_SUBCLASS_ENTRY(c) (RCLASS_EXT(c)->subclass_entry)