[Bug exp/26875] Incorrect value printed for address of first element of zero-length array

["vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=26875

--- Comment #3 from Tom de Vries <vries at gcc dot gnu.org> ---
This passes testing:
...
diff --git a/gdb/eval.c b/gdb/eval.c
index 8d0c5747f39..0e8698bd488 100644
--- a/gdb/eval.c
+++ b/gdb/eval.c
@@ -2814,6 +2814,39 @@ evaluate_subexp_for_address (struct expression *exp, int
*pos,


   switch (op)
     {
+    case BINOP_SUBSCRIPT:
+      if (noside != EVAL_SKIP)
+       {
+         /* Skip over the base to get the position of the index.  */
+         int pos_index = *pos + 1;
+         evaluate_subexp (nullptr, exp, &pos_index, EVAL_SKIP);
+
+         /* Check if the index is zero.  Do this without evaluating
+            side effects, such that we can still fall back to default_case. 
*/
+         struct value *index
+           = evaluate_subexp (nullptr, exp, &pos_index,
+                              EVAL_AVOID_SIDE_EFFECTS);
+         if (value_equal (index, value_zero (value_type (index), not_lval)))
+           {
+             /* We're handling op here, skip it.  */
+             (*pos)++;
+
+             /* Evaluate base.  */
+             struct value *base = evaluate_subexp (nullptr, exp, pos, noside);
+
+             /* Evaluate index, for the side-effect, and to return with pos
+                past index.  */
+             evaluate_subexp (nullptr, exp, pos, noside);
+
+             /* Translate &base[0] into (typeof(base[0]) *)base.   */
+             type *element_type = TYPE_TARGET_TYPE (value_type (base));
+             type *return_type = lookup_pointer_type (element_type);
+             return value_cast (return_type, base);
+           }
+       }
+
+      goto default_case;
+
     case UNOP_IND:
       (*pos)++;
       x = evaluate_subexp (nullptr, exp, pos, noside);
...

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