Avoid gcc stringop-overflow warning for intended overflow in smashtest

* tests/smash_test.c (q): New global variable (volatile).
* tests/smash_test.c (main): Clear q if i is 3000 or 6000; set q to
the address of the modified byte if i is 5678; add comment.

1 files changed, 13 insertions, 2 deletions

diff --git a/tests/smash_test.c b/tests/smash_test.c
index 4ba7be04..9aab02de 100644
--- a/tests/smash_test.c
+++ b/tests/smash_test.c
@@ -13,6 +13,8 @@
 
 char * A[COUNT];
 
+char * volatile q;
+
 int main(void)
 {
   int i;
@@ -23,8 +25,17 @@ int main(void)
   for (i = 0; i < COUNT; ++i) {
      A[i] = p = (char*)GC_MALLOC(SIZE);
 
-     if (i%3000 == 0) GC_gcollect();
-     if (i%5678 == 0 && p != 0) p[SIZE + i/2000] = 42;
+     if (i%3000 == 0) {
+        q = NULL;
+        GC_gcollect();
+     } else if (i%5678 == 0 && p != 0) {
+        /* Write a byte past the end of the allocated object    */
+        /* but not beyond the last word of the object's memory. */
+        /* A volatile intermediate pointer variable is used to  */
+        /* avoid a compiler complain of out-of-bounds access.   */
+        q = &p[(SIZE + i/2000) /* 42 */];
+        *q = 42;
+     }
   }
   return 0;
 }