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Re: [patch] Warn on constant value watchpoints
On Mon, Jun 09, 2008 at 08:14:14AM +0200, Jan Kratochvil wrote:
> @@ -5903,7 +5903,27 @@ watch_command_1 (char *arg, int accessfl
> exp_end = arg;
> exp_valid_block = innermost_block;
> mark = value_mark ();
> - fetch_watchpoint_value (exp, &val, NULL, NULL);
> + fetch_watchpoint_value (exp, &val, &val_result, NULL);
> +
> + /* VAL may be unset for unreachable final values. */
> + while (val_result != NULL)
> + {
> + if (VALUE_LVAL (val_result) == lval_memory
> + || VALUE_LVAL (val_result) == lval_register)
> + break;
> + val_result = value_next (val_result);
> + }
val_result is the same as val, except possibly lazy. value_next
(val_result) will always be NULL, won't it? The chain goes the other
way - next from the oldest value (*val_chain argument, or the first
value after the saved mark).
If I'm right it seems like this patch will break "watch a + 1".
Also, I don't know how useful this feature is, but what happens with
"watch foo()"?
> + if (val_result == NULL)
> + {
> + int len;
> +
> + len = exp_end - exp_start;
> + while (len > 0 && isspace (exp_start[len - 1]))
> + len--;
> + error (_("Cannot watch constant value %.*s."), len, exp_start);
> + }
If an intermediate value could not be read, val_result may be NULL.
So this will stop us watching such expressions before they become
readable.
> +If you watch for a change in a numerically entered address you need to
> +dereference it as the address itself is just a constant number which will never
> +change. @value{GDBN} refuses to create a never invokable watchpoint:
never-changing?
--
Daniel Jacobowitz
CodeSourcery