linux-kernel - Re: lib/vsprintf.c:1528:9: warning: function 'va_format' might be a candidate for 'gnu

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Message-ID: <6e776c69-12fd-470f-b3ce-dd9f91bacde5@prevas.dk>
Date: Tue, 13 Feb 2024 13:05:29 +0100
From: Rasmus Villemoes <rasmus.villemoes@...vas.dk>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 kernel test robot <lkp@...el.com>
Cc: Petr Mladek <pmladek@...e.com>, oe-kbuild-all@...ts.linux.dev,
 linux-kernel@...r.kernel.org,
 Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: lib/vsprintf.c:1528:9: warning: function 'va_format' might be a
 candidate for 'gnu_printf' format attribute

On 21/01/2024 14.54, Andy Shevchenko wrote:
> On Thu, Jan 11, 2024 at 10:33:09AM +0800, kernel test robot wrote:
>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>> head:   acc657692aed438e9931438f8c923b2b107aebf9
>> commit: 45c3e93d751ea50861c796da3cbfc848fa6ddf55 vsprintf: Factor out %pV handler as va_format()
>> date:   4 years, 9 months ago
> 
> Blast from the past?!
> 
> ..
> 
>>    lib/vsprintf.c: In function 'va_format':
>>>> lib/vsprintf.c:1528:9: warning: function 'va_format' might be a candidate for 'gnu_printf' format attribute [-Wsuggest-attribute=format]
>>     1528 |         buf += vsnprintf(buf, end > buf ? end - buf : 0, va_fmt->fmt, va);
>>          |         ^~~
> 
> This might be still valid, but I have no idea how to properly fix it.
> 

It's a bogus warning, and the fix belongs in the compiler. When
vsnprintf() is called, but neither the format arg nor the va_list arg
are direct arguments to the caller (and the va_list is not built from
actual varargs using va_start()), there's absolutely no way a __printf
attribute could be appropriate.

IDK if we can shut up the test robot by locally disabling the
Wsuggest-attribute with some pragma.

Rasmus