linux-kernel - Re: [hnaz-mm:master 272/379] lib/vsprintf.c:991:13: warning: variable 'modbuildid' set but not used

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Date:   Tue, 1 Mar 2022 19:22:46 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     kernel test robot <lkp@...el.com>,
        Maninder Singh <maninder1.s@...sung.com>,
        kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org,
        Johannes Weiner <hannes@...xchg.org>,
        Vaneet Narang <v.narang@...sung.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>
Subject: Re: [hnaz-mm:master 272/379] lib/vsprintf.c:991:13: warning:
 variable 'modbuildid' set but not used

On Tue, Mar 01, 2022 at 10:24:48AM -0800, Andrew Morton wrote:
> >    lib/vsprintf.c: In function 'va_format':
> >    lib/vsprintf.c:1759:9: warning: function 'va_format' might be a candidate for 'gnu_printf' format attribute [-Wsuggest-attribute=format]
> >     1759 |         buf += vsnprintf(buf, end > buf ? end - buf : 0, va_fmt->fmt, va);
> >          |         ^~~
> 
> I wonder what this means.

It means the compiler thinks we might want to add:

__attribute__((format(gnu_printf, x, y))) to the function declaration so it
can type-check the arguments.

'format (ARCHETYPE, STRING-INDEX, FIRST-TO-CHECK)'
     The 'format' attribute specifies that a function takes 'printf',
     'scanf', 'strftime' or 'strfmon' style arguments that should be
     type-checked against a format string.  For example, the
     declaration:

          extern int
          my_printf (void *my_object, const char *my_format, ...)
                __attribute__ ((format (printf, 2, 3)));

     causes the compiler to check the arguments in calls to 'my_printf'
     for consistency with the 'printf' style format string argument
     'my_format'.


I haven't looked into this at all and have no idea if we should.