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From:   Matthew Wilcox <willy@infradead.org>
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Subject: Re: [hnaz-mm:master 272/379] lib/vsprintf.c:991:13: warning:
 variable 'modbuildid' set but not used
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 <20220301102448.ff9bf910213d705842a2dd45@linux-foundation.org>
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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.