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

[John Ogness]

On 2022-03-01, Matthew Wilcox <willy@xxxxxxxxxxxxx> 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.

AFAICT it is not possible to use the gnu_printf format attribute for
this because the va_list to check is a field within the passed in struct
pointer @va_fmt.

John Ogness