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

kernel test robot
2021-06-04T11:12:27Z

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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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