1 files changed, 11 insertions, 0 deletions
diff --git a/eval_intern.h b/eval_intern.h
index 190ef9195c..596d45ac82 100644
--- a/eval_intern.h
+++ b/eval_intern.h
@@ -91,9 +91,20 @@ extern int select_large_fdset(int, fd_set *, fd_set *, fd_set *, struct timeval
       rb_fiber_start(); \
   } while (0)
 
+/*
+  ensure tag to be accessible, `buf' is at the beginning.
+  the end is `prev' which is written in TH_PUSH_TAG().
+*/
+#if defined(__GNUC__) && __GNUC__ >= 4
+/* suppress -Wstrict-aliasing, and should be inlined */
+# define ENSURE_TAG_WRITABLE(tag) MEMZERO((tag).buf, int, 1)
+#else
+# define ENSURE_TAG_WRITABLE(tag) (*(volatile int *)(tag).buf = 0)
+#endif
 #define TH_PUSH_TAG(th) do { \
   rb_thread_t * const _th = (th); \
   struct rb_vm_tag _tag; \
+  ENSURE_TAG_WRITABLE(_tag); \
   _tag.tag = 0; \
   _tag.prev = _th->tag; \
   _th->tag = &_tag;