[Linux-kernel-mentees] [PATCH v2] checkpatch: fix false positives in REPEATED_WORD warning

[Aditya]

On 22/10/20 8:20 pm, Aditya Srivastava wrote:
> Presence of hexadecimal address or symbol results in false warning
> message by checkpatch.pl.
> 
> For example, running checkpatch on commit b8ad540dd4e4 ("mptcp: fix
> memory leak in mptcp_subflow_create_socket()") results in warning:
> 
> WARNING:REPEATED_WORD: Possible repeated word: 'ff'
>     00 00 00 00 00 00 00 00 00 2f 30 0a 81 88 ff ff  ........./0.....
> 
> Similarly, the presence of list command output in commit results in
> an unnecessary warning.
> 
> For example, running checkpatch on commit 899e5ffbf246 ("perf record:
> Introduce --switch-output-event") gives:
> 
> WARNING:REPEATED_WORD: Possible repeated word: 'root'
>   dr-xr-x---. 12 root root    4096 Apr 27 17:46 ..
> 
> Here, it reports 'ff' and 'root to be repeated, but it is in fact part
> of some address or code, where it has to be repeated.
> 
> In these cases, the intent of the warning to find stylistic issues in
> commit messages is not met and the warning is just completely wrong in
> this case.
> 
> To avoid these warnings, add additional regex check for the
> directory permission pattern and avoid checking the line for this
> class of warning. Similarly, to avoid hex pattern, check if the word
> consists of hex symbols and skip this warning if, it forms a pattern
> of repeating sequence or contains more special character after pattern
> than non hex characters.
> 
> A quick evaluation on v5.6..v5.8 showed that this fix reduces
> REPEATED_WORD warnings from 2797 to 907.
> 
> A quick manual check found all cases are related to hex output or
> list command outputs in commit messages.
> 
> Signed-off-by: Aditya Srivastava <yashsri421 at gmail.com>
> ---
>  scripts/checkpatch.pl | 33 ++++++++++++++++++++++++++++++++-
>  1 file changed, 32 insertions(+), 1 deletion(-)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 9b9ffd876e8a..0f57e99ed670 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -3051,7 +3051,10 @@ sub process {
>  		}
>  
>  # check for repeated words separated by a single space
> -		if ($rawline =~ /^\+/ || $in_commit_log) {
> +# avoid false positive from list command eg, '-rw-r--r-- 1 root root'
> +		if (($rawline =~ /^\+/ || $in_commit_log) &&
> +		$rawline !~ /[bcCdDlMnpPs\?-][rwxsStT-]{9}/) {
> +			my @hex_seq = $rawline =~ /\b[0-9a-f]{2,} \b/g;
>  			while ($rawline =~ /\b($word_pattern) (?=($word_pattern))/g) {
>  
>  				my $first = $1;
> @@ -3065,6 +3068,34 @@ sub process {
>  				next if ($first ne $second);
>  				next if ($first eq 'long');
>  
> +				# avoid repeating hex occurrences like 'ff ff fe 09 ...'
> +				if ($first =~ /\b[0-9a-f]{2,}/) {
> +					# if such sequence occurs more than 4, it is most probably part of some of code
> +					next if ((scalar @hex_seq)>4);
> +
> +					# for hex occurrences which are less than 4
> +					# get first hex word in the line
> +					if ($rawline =~ /\b[0-9a-f]{2,} /) {
> +						my $post_hex_seq = $';
> +
> +						# set suffieciently high default values to avoid ignoring or counting in absence of another
> +						my $non_hex_char_pos = 1000;
> +						my $special_chars_pos = 500;
> +
> +						if ($post_hex_seq =~ /[g-z]+/) {
> +							# first non hex character in post_hex_seq
> +							$non_hex_char_pos = $-[0];
> +						}
> +						if($post_hex_seq =~ /[^a-zA-Z0-9]{2,}/) {
> +							# first occurrence of 2 or more special chars
> +							$special_chars_pos = $-[0];
> +						}
> +
> +						# as such occurrences are not common, it is more likely to be a part of some code
> +						next if ($special_chars_pos<$non_hex_char_pos);
> +					}
> +				}
> +
>  				if (WARN("REPEATED_WORD",
>  					 "Possible repeated word: '$first'\n" . $herecurr) &&
>  				    $fix) {
> 

I have also generated some reports showing impact caused by the changes:

Hex variations causing warning previously:
https://github.com/AdityaSrivast/kernel-tasks/blob/master/Task3/hex_variations.txt

Change in warnings and errors:
https://github.com/AdityaSrivast/kernel-tasks/blob/master/Task3/relative_summary/summary_relative.txt

Warnings which are dropped:
https://github.com/AdityaSrivast/kernel-tasks/blob/master/Task3/relative_summary/dropped_warnings/summary.txt

Thanks
Aditya