Hi Petr,

I love your patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v4.16-rc5 next-20180314]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Petr-Mladek/vsprintf-Prevent-crash-when-dereferencing-invalid-pointers/20180315-214100
config: i386-randconfig-x019-201810 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All errors (new ones prefixed by >>):

   lib/test_printf.c: In function 'plain':
>> lib/test_printf.c:273:8: error: too many arguments to function 'plain_format'
     err = plain_format(ptr);
           ^~~~~~~~~~~~
   lib/test_printf.c:235:1: note: declared here
    plain_format(void)
    ^~~~~~~~~~~~

vim +/plain_format +273 lib/test_printf.c

   256	
   257	/*
   258	 * We can't use test() to test %p because we don't know what output to expect
   259	 * after an address is hashed.
   260	 */
   261	static void __init
   262	plain(void *ptr)
   263	{
   264		int err;
   265	
   266		err = plain_hash(ptr);
   267		if (err) {
   268			pr_warn("plain 'p' does not appear to be hashed\n");
   269			failed_tests++;
   270			return;
   271		}
   272	
 > 273		err = plain_format(ptr);
   274		if (err) {
   275			pr_warn("hashing plain 'p' has unexpected format\n");
   276			failed_tests++;
   277		}
   278	}
   279	

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