[gnugo-devel] Re: patch: malloc(0) and array bound violation

[Teun Burgers]

I wrote:

> The problem with malloc(0) returning 0, leading to assertion failures has not
> been fixed to date. For a message on this subject see e.g.
>
> http://lists.gnu.org/archive/html/gnugo-devel/2004-02/msg00037.html
>
>
> One part of the attached patch (for owl.c) is an update for this problem for 
> 3.5.8.

This patch was buggy. It contained an excess malloc() invocation.
Revised patch attached.

Teun

diff -u tmp/gnugo-3.5.8/engine/optics.c ./gnugo-3.5.8/engine/optics.c
--- tmp/gnugo-3.5.8/engine/optics.c     2004-06-05 18:27:17.000000000 +0200
+++ ./gnugo-3.5.8/engine/optics.c       2004-06-21 14:09:16.000000000 +0200
@@ -1204,8 +1204,10 @@
       vital = black_vital_points;
     for (k = 0; k < best_vp->num_defenses && k < MAX_EYE_ATTACKS; k++)
       vital[pos].defense_points[k] = best_vp->defenses[k];
-    for (k = 0; k < best_vp->num_attacks; k++)
+    for (k = 0; k < best_vp->num_attacks; k++) {
+      ASSERT1(k < MAX_EYE_ATTACKS, pos);
       vital[pos].attack_points[k] = best_vp->attacks[k];
+    }
   }
 
   return 1;
diff -u tmp/gnugo-3.5.8/engine/owl.c ./gnugo-3.5.8/engine/owl.c
--- tmp/gnugo-3.5.8/engine/owl.c        2004-06-05 18:27:17.000000000 +0200
+++ ./gnugo-3.5.8/engine/owl.c  2004-06-23 12:06:52.000000000 +0200
@@ -3545,8 +3545,8 @@
       count_variations = save_count_variations;
     }
 
-    free(list->pattern_list);
-    free(list->pattern_heap);
+    free(list->pattern_list); list->pattern_list = NULL;
+    free(list->pattern_heap); list->pattern_heap = NULL;
   }
   list->counter = -1;
 }
@@ -3778,8 +3778,14 @@
    * but it is easier to allocate more than to count real number of
    * heap elements first.
    */
-  list->pattern_heap = malloc(list->counter * sizeof(*(list->pattern_heap)));
-  gg_assert(list->pattern_heap != NULL);
+  if (list->counter > 0) {
+    list->pattern_heap = (struct matched_pattern_data**)
+               malloc(list->counter * sizeof(struct matched_pattern_data*));
+    gg_assert(list->pattern_heap != NULL);
+  } else {
+    /* free() has defined behaviour for NULL pointer */
+    list->pattern_heap = NULL;
+  }
 
   for (pos = BOARDMIN; pos < BOARDMAX; pos++)
     list->first_pattern_index[pos] = -1;