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

[Rong Chen <rong.a.chen@intel.com>]

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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