Fixed ivar offset checking to take account for alignment.

init.c

@@ -756,21 +756,37 @@ __objc_compute_ivar_offsets (Class class)
     }
   else
     {
-      if (class->ivars != 0)
+      if (NULL == class->ivars)
         {
+          return;
+        }
       Class super = class_superclass_of_class(class);
       int start = class->ivars->ivar_list[0].ivar_offset;
-          /* Quick and dirty test */
-          if (Nil != super && start != super->instance_size)
+      /* Quick and dirty test.  If the first ivar comes straight after the last
+       * class, then it's fine. */
+      if (Nil == super || start == super->instance_size)
         {
+          return;
+        }
+      /* Find the last superclass with at least one ivar. */
       while (NULL == super->ivars) 
         {
           super = class_superclass_of_class(super);
         }
       struct objc_ivar *ivar = 
         &super->ivars->ivar_list[super->ivars->ivar_count-1];
-              if (start != (ivar->ivar_offset + objc_sizeof_type(ivar->ivar_type)))
+      if (start == (ivar->ivar_offset + objc_sizeof_type(ivar->ivar_type)))
+        {
+          return;
+        }
+      /* The classes don't line up, but don't panic; check that the
+       * difference is not just padding for alignment */
+      int align = objc_alignof_type(class->ivars->ivar_list[0].ivar_type);
+      if (start > ivar->ivar_offset && 
+          start - ivar->ivar_offset < align)
         {
+          return;
+        }
       /* Panic if this class has an instance variable that overlaps the
        * superclass. */
       fprintf(stderr, 
@@ -787,9 +803,6 @@ __objc_compute_ivar_offsets (Class class)
       abort();
     }
 }
-        }
-    }
-}
 
 static void
 objc_send_load (void)