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

[Rong Chen]

On 6/5/21 4:48 AM, Steven Rostedt wrote:
> On Fri, 4 Jun 2021 19:12:03 +0800
> kernel test robot <lkp@xxxxxxxxx> 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@xxxxxxxxx>
> >
> > 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

Hi Steve,

Thanks for the feedback, we'll ignore the commit to avoid new reports 
for this warning.

Best Regards,
Rong Chen

> >     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@xxxxxxxxxxxx
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