Re: [PATCH] vsprintf: Drop unused assignment of fmt.state

From: Petr Mladek
Date: Mon Feb 10 2025 - 08:10:04 EST


On Thu 2025-02-06 17:32:32, Andy Shevchenko wrote:
> On Thu, Feb 06, 2025 at 01:25:07AM +0800, I Hsin Cheng wrote:
> > Remove unused assignment of "fmt.state", in both cases the value of
> > "fmt.state" will be overwritten by either "FORMAT_STATE_PRECISION" or
> > "FORMAT_STATE_NUM", the value "FORMAT_STATE_NONE" isn't going to be used
> > after the assignment.
>
> ...
>
> > struct fmt format_decode(struct fmt fmt, struct printf_spec *spec)
>
> > spec->field_width = -spec->field_width;
> > spec->flags |= LEFT;
> > }
> > - fmt.state = FORMAT_STATE_NONE;
> > +
> > goto precision;
> > }
> >
>
> While both are kinda redundant, this is not obvious what's stated in the commit
> message. Yes, `goto qualifier;` is straightforward, but not `goto precision;`.
> Which makes me think that these assignments can make code robust against
> potential future changes to allow to catch up the wrong code paths.

I fully agree with Andy here.

That said, I see the following right below the two conditions modified
in this patch:

/* By default */
fmt.state = FORMAT_STATE_NONE;

A good solution would be to move it up. It will be then obvious
that we could remove these two initializations. I mean
to do the following:

--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2563,13 +2563,15 @@ struct fmt format_decode(struct fmt fmt, struct printf_spec *spec)
const char *start = fmt.str;
char flag;

+ /* By default */
+ fmt.state = FORMAT_STATE_NONE;
+
/* we finished early by reading the field width */
if (unlikely(fmt.state == FORMAT_STATE_WIDTH)) {
if (spec->field_width < 0) {
spec->field_width = -spec->field_width;
spec->flags |= LEFT;
}
- fmt.state = FORMAT_STATE_NONE;
goto precision;
}

@@ -2578,13 +2580,9 @@ struct fmt format_decode(struct fmt fmt, struct printf_spec *spec)
if (spec->precision < 0)
spec->precision = 0;

- fmt.state = FORMAT_STATE_NONE;
goto qualifier;
}

- /* By default */
- fmt.state = FORMAT_STATE_NONE;
-
for (; *fmt.str ; fmt.str++) {
if (*fmt.str == '%')
break;


Best Regards,
Petr