Re: [PATCH] checkpatch: Detect '%#' or '%0#' in printf-style format strings

[Dov Murik <dovmurik@linux.vnet.ibm.com>]

On 14/09/2020 9:55, Philippe Mathieu-Daudé wrote:
> +qemu-perl team
> 
> On 9/14/20 8:01 AM, Dov Murik wrote:
>> According to the coding style document, we should use literal '0x' prefix
>> instead of printf's '#' flag (which appears as '%#' or '%0#' in the format
>> string).  Add a checkpatch rule to enforce that.
>>
>> Note that checkpatch already had a similar rule for trace-events files.
>>
>> Example usage:
>>
>>    $ scripts/checkpatch.pl --file chardev/baum.c
>>    ...
>>    ERROR: Don't use '#' flag of printf format ('%#') in format strings, use '0x' prefix instead
>>    #366: FILE: chardev/baum.c:366:
>>    +            DPRINTF("Broken packet %#2x, tossing\n", req); \
>>    ...
>>    ERROR: Don't use '#' flag of printf format ('%#') in format strings, use '0x' prefix instead
>>    #472: FILE: chardev/baum.c:472:
>>    +        DPRINTF("unrecognized request %0#2x\n", req);
>>    ...
>>
>> Signed-off-by: Dov Murik <dovmurik@linux.vnet.ibm.com>
>> ---
>>   scripts/checkpatch.pl | 12 ++++++++++++
>>   1 file changed, 12 insertions(+)
>>
>> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
>> index bd3faa154c..6ec2a9f6a1 100755
>> --- a/scripts/checkpatch.pl
>> +++ b/scripts/checkpatch.pl
>> @@ -2891,6 +2891,18 @@ sub process {
>>   			}
>>   		}
>>   
>> +# check for %# or %0# in printf-style format strings
>> +		while ($line =~ /(?:^|")([X\t]*)(?:"|$)/g) {
>> +			my $string = substr($rawline, $-[1], $+[1] - $-[1]);
>> +			$string =~ s/%%/__/g;
>> +			if ($string =~ /(?<!%)%0?#/) {
>> +				ERROR("Don't use '#' flag of printf format " .
>> +				      "('%#') in format strings, use '0x' " .
>> +				      "prefix instead\n" . $herecurr);
>> +				last;
>> +			}
>> +		}
>> +
>>   # QEMU specific tests
>>   		if ($rawline =~ /\b(?:Qemu|QEmu)\b/) {
>>   			ERROR("use QEMU instead of Qemu or QEmu\n" . $herecurr);
>>
> 
> Thank you for this patch!
> 
> What about folding it in the same block?
> 

That makes sense, except that 'last' statement which will escape the 
loop if one of the bad patterns is found.

Maybe we can just drop 'last' from both if-then blocks?  We'll get 
multiple alerts if bad patterns are used more than once in the same 
line, which sounds OK to me.


> -- >8 --
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -2880,15 +2880,22 @@ sub process {
>                                  $herecurr);
>                  }
> 
> -# check for %L{u,d,i} in strings
> +# format strings checks
>                  my $string;
>                  while ($line =~ /(?:^|")([X\t]*)(?:"|$)/g) {
>                          $string = substr($rawline, $-[1], $+[1] - $-[1]);
>                          $string =~ s/%%/__/g;
> +                       # check for %L{u,d,i} in strings
>                          if ($string =~ /(?<!%)%L[udi]/) {
>                                  ERROR("\%Ld/%Lu are not-standard C, use
> %lld/%llu\n" . $herecurr);
>                                  last;
>                          }
> +                       if ($string =~ /(?<!%)%0?#/) {
> +                               ERROR("Don't use '#' flag of printf
> format " .
> +                                     "('%#') in format strings, use
> '0x' " .
> +                                     "prefix instead\n" . $herecurr);
> +                               last;
> +                       }
>                  }
> 
>   # QEMU specific tests
> ---
>