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

Steven Rostedt
2021-06-04T20:48:42Z

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