vla: enable sizeof operator to work with variable length arrays

In C99 the sizeof operator computes the size of a variable length array
at runtime (6.5.3.4 The sizeof operator). This patch reflects the semantic
change in the debugger.

We now are able to get the size of a vla:

1| void foo (size_t n) {
2|   int vla[n];
3| }

(gdb) p sizeof(vla)

yields N * sizeof(int).

gdb/ChangeLog:

	* eval.c (evaluate_subexp_for_sizeof) <OP_VAR_VALUE>: If the type
	passed to sizeof is dynamic evaluate the argument to compute the length.

1 files changed, 7 insertions, 1 deletions

diff --git a/gdb/eval.c b/gdb/eval.c
index c1e47e0..85523cd 100644
--- a/gdb/eval.c
+++ b/gdb/eval.c
@@ -3040,8 +3040,14 @@ evaluate_subexp_for_sizeof (struct expression *exp, int *pos)
       break;
 
     case OP_VAR_VALUE:
-      (*pos) += 4;
       type = SYMBOL_TYPE (exp->elts[pc + 2].symbol);
+      if (is_dynamic_type (type))
+	{
+	  val = evaluate_subexp (NULL_TYPE, exp, pos, EVAL_NORMAL);
+	  type = value_type (val);
+	}
+      else
+	(*pos) += 4;
       break;
 
     default: