RE: [PATCH 05/10] vla: allow side effects for sizeof argument

["Agovic, Sanimir" <sanimir.agovic@intel.com>]

Thanks for your review.

I avoid to re-send the complete patch series, thus see my 
alternative proposal below. Once I receive more feedback
I will re-publish my patch series including this fix if 
applicable.

Meanwhile you can track our latest development efforts on
http://intel-gdb.github.io/ branch vla-c99.

 -Sanimir

    vla: allow side effects for subscripts in the sizeof operator

    C99 requires the sizeof operator to be evaluated at runtime to retrieve
    the size of the vla, reflect this behavior in gdb.

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

    (gdb) p sizeof(vla[0])

    yields N.

    2013-10-18  Sanimir Agovic  <sanimir.agovic@intel.com>
                Keven Boell  <keven.boell@intel.com>

        * eval.c (evaluate_subexp_for_sizeof): Allow side effects for
        subscripts in the sizeof operator.

    Change-Id: I945e8a259e850cc0470faa742a0d2191122ef37b

diff --git a/gdb/eval.c b/gdb/eval.c
index ab3cb95..255ea09 100644
--- a/gdb/eval.c
+++ b/gdb/eval.c
@@ -3054,6 +3054,13 @@ evaluate_subexp_for_sizeof (struct expression *exp, int *pos)
       return
        value_from_longest (size_type, (LONGEST) TYPE_LENGTH (type));

+    case BINOP_SUBSCRIPT:
+      /* In case of a variable length array we need to evaluate the subscript
+        with side effects to correcly infere the size.  */
+      val = evaluate_subexp (NULL_TYPE, exp, pos, EVAL_NORMAL);
+      return value_from_longest (size_type,
+                                (LONGEST) TYPE_LENGTH (value_type (val)));
+
     default:
       val = evaluate_subexp (NULL_TYPE, exp, pos, EVAL_AVOID_SIDE_EFFECTS);
       return value_from_longest (size_type,

> -----Original Message-----
> From: Tom Tromey [mailto:tromey@redhat.com]
> Sent: Thursday, October 24, 2013 09:55 PM
> To: Agovic, Sanimir
> Cc: gdb-patches@sourceware.org
> Subject: Re: [PATCH 05/10] vla: allow side effects for sizeof argument
> 
> >>>>> "Sanimir" == Sanimir Agovic <sanimir.agovic@intel.com> writes:
> 
> Sanimir> C99 requires the sizeof operator to be evaluated at runtime to compute
> Sanimir> the size of the vla, reflect this behavior in gdb.
> 
> Sanimir> -      val = evaluate_subexp (NULL_TYPE, exp, pos, EVAL_AVOID_SIDE_EFFECTS);
> Sanimir> +      val = evaluate_subexp (NULL_TYPE, exp, pos, EVAL_NORMAL);
> 
> I think this will do the wrong thing for cases like (assuming "int x"):
> 
>     (gdb) print sizeof (x++)
> 
> I think some other approach will be needed for this patch.
> 
> Tom
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