Re: kernel/trace/trace.c:3634:2: warning: function might be possible candidate for 'gnu_printf' format attribute

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 4 Jun 2021 19:12:03 +0800
kernel test robot <lkp@intel.com> wrote:

> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   f88cd3fb9df228e5ce4e13ec3dbad671ddb2146e
> commit: 9a6944fee68e25084130386c608c5ac8db487581 tracing: Add a verifier to check string pointers for trace events
> date:   3 months ago
> config: x86_64-rhel (attached as .config)
> compiler: gcc-6 (Ubuntu 6.4.0-17ubuntu1) 6.4.0 20180424
> reproduce (this is a W=1 build):
>         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9a6944fee68e25084130386c608c5ac8db487581
>         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>         git fetch --no-tags linus master
>         git checkout 9a6944fee68e25084130386c608c5ac8db487581
>         # save the attached .config to linux build tree
>         make W=1 ARCH=x86_64 
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
> 
> All warnings (new ones prefixed by >>):
> 
>    kernel/trace/trace.c: In function 'test_can_verify_check':
> >> kernel/trace/trace.c:3634:2: warning: function might be possible candidate for 'gnu_printf' format attribute [-Wsuggest-attribute=format]  
>      vsnprintf(buf, 16, "%d", ap);
>      ^~~~~~~~~

"test_can_verify_check" is not a generic function that needs a printf
format check. This is a bogus warning. Please remove it as being an issue.

-- Steve



>    kernel/trace/trace.c: In function 'trace_check_vprintf':
>    kernel/trace/trace.c:3717:3: warning: function might be possible candidate for 'gnu_printf' format attribute [-Wsuggest-attribute=format]
>       trace_seq_vprintf(&iter->seq, iter->fmt, ap);
>       ^~~~~~~~~~~~~~~~~
>    kernel/trace/trace.c:3756:3: warning: function might be possible candidate for 'gnu_printf' format attribute [-Wsuggest-attribute=format]
>       trace_seq_vprintf(&iter->seq, p, ap);
>       ^~~~~~~~~~~~~~~~~
> 
> 
> vim +/gnu_printf +3634 kernel/trace/trace.c
> 
>   3617	
>   3618	static int test_can_verify_check(const char *fmt, ...)
>   3619	{
>   3620		char buf[16];
>   3621		va_list ap;
>   3622		int ret;
>   3623	
>   3624		/*
>   3625		 * The verifier is dependent on vsnprintf() modifies the va_list
>   3626		 * passed to it, where it is sent as a reference. Some architectures
>   3627		 * (like x86_32) passes it by value, which means that vsnprintf()
>   3628		 * does not modify the va_list passed to it, and the verifier
>   3629		 * would then need to be able to understand all the values that
>   3630		 * vsnprintf can use. If it is passed by value, then the verifier
>   3631		 * is disabled.
>   3632		 */
>   3633		va_start(ap, fmt);
> > 3634		vsnprintf(buf, 16, "%d", ap);  
>   3635		ret = va_arg(ap, int);
>   3636		va_end(ap);
>   3637	
>   3638		return ret;
>   3639	}
>   3640	
> 
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org