[PATCH] panic: suppress gnu_printf warning

[Manuel López-Ibáñez]

On 07/01/2024 19:21, Andrew Morton wrote:
> On Sun,  7 Jan 2024 17:16:41 +0800 Baoquan He <bhe@redhat.com> wrote:
>
>> with GCC 13.2.1 and W=1, there's compiling warning like this:
>>
>> kernel/panic.c: In function ?__warn?:
>> kernel/panic.c:676:17: warning: function ?__warn? might be a candidate for ?gnu_printf? format attribute [-Wsuggest-attribute=format]
>>    676 |                 vprintk(args->fmt, args->args);
>>        |                 ^~~~~~~
>>
>> The normal __printf(x,y) adding can't fix it. So add workaround which
>> disables -Wsuggest-attribute=format to mute it.
>>
>> ...
>>
>> --- a/kernel/panic.c
>> +++ b/kernel/panic.c
>> @@ -666,8 +666,13 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
>>   		pr_warn("WARNING: CPU: %d PID: %d at %pS\n",
>>   			raw_smp_processor_id(), current->pid, caller);
>>   
>> +#pragma GCC diagnostic push
>> +#ifndef __clang__
>> +#pragma GCC diagnostic ignored "-Wsuggest-attribute=format"
>> +#endif
>>   	if (args)
>>   		vprintk(args->fmt, args->args);
>> +#pragma GCC diagnostic pop
>>   
>>   	print_modules();
> __warn() clearly isn't such a candidate.  I'm suspecting that gcc's
> implementation of this warning is pretty crude.  Is it a new thing in
> gcc-13.2?

I suspect the warning is about vprintk(), which does seem a printf-like 
function but something (early inlining?) may be messing up the context and GCC 
warns about __warn(). This may be bug: 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=28492

If vprintk() already has the format attribute, then the messed up function name 
may be confusing GCC into warning again about it.

Best wishes,

Manuel.