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

[Teun Burgers]

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.

The second part is the (temporary) addition of an assertion in optics.c. 
There
is an array bound violation here detect by compiling with array bound 
checking enabled.
The assertion is triggered  in owl.tst for test 3 when running gnugo 
--mode gtp < owl.tst.

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  2004-06-21 14:38:23.000000000 +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;
 }
@@ -3779,7 +3779,14 @@
    * 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 = 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;