linux-kernel - Re: [PATCH v1 1/3] lib/vsprintf: Replace hidden BUILD_BUG_ON() with static

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Date:   Fri, 31 Jul 2020 18:48:45 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v1 1/3] lib/vsprintf: Replace hidden BUILD_BUG_ON() with static_assert()

On Fri, Jul 31, 2020 at 5:40 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Fri, 31 Jul 2020 15:31:43 +0300
> Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
>
> > First of all, there is no compile time check for the SMALL
> > to be ' ' (0x20, i.e. space). Second, for ZEROPAD the check
> > is hidden in the code.
> >
> > For better maintenance replace BUILD_BUG_ON() with static_assert()
> > for ZEROPAD and move it closer to the definition. While at it,
> > introduce check for SMALL.
> >
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > ---
> >  lib/vsprintf.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > index 31a674dd2674..8a8ac7ce0289 100644
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -381,6 +381,9 @@ int num_to_str(char *buf, int size, unsigned long long num, unsigned int width)
> >  #define SMALL        32              /* use lowercase in hex (must be 32 == 0x20) */
> >  #define SPECIAL      64              /* prefix hex with "0x", octal with "0" */
> >
> > +static_assert(ZEROPAD + ' ' == '0');
>
> I would have it match the comment above:
>
> static_assert(ZEROPAD == ('0' - ' '));

Okay, makes sense.
Will do in v2.

> But other than that:
>
> Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

Thanks!

>
> -- Steve
>
> > +static_assert(SMALL == ' ');
> > +
> >  enum format_type {
> >       FORMAT_TYPE_NONE, /* Just a string part */
> >       FORMAT_TYPE_WIDTH,
> > @@ -507,7 +510,7 @@ char *number(char *buf, char *end, unsigned long long num,
> >       /* zero or space padding */
> >       if (!(spec.flags & LEFT)) {
> >               char c = ' ' + (spec.flags & ZEROPAD);
> > -             BUILD_BUG_ON(' ' + ZEROPAD != '0');
> > +
> >               while (--field_width >= 0) {
> >                       if (buf < end)
> >                               *buf = c;
>


-- 
With Best Regards,
Andy Shevchenko