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

[kernel test robot <lkp@intel.com>]

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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);
     ^~~~~~~~~
   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

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