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

Rong Chen
2021-06-07T05:50:00Z

On 6/5/21 4:48 AM, Steven Rostedt wrote:
> 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
>

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@lists.01.org
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