[Linux-kernel-mentees] [PATCH v2] checkpatch: Fix the usage of capture group ( ... )

Mrinal Pandey mrinalmni at gmail.com
Tue Jul 14 03:23:52 UTC 2020

The usage of "capture group (...)" in the immediate condition after `&&`
results in `$1` being uninitialized. This issues a warning "Use of
uninitialized value $1 in regexp compilation at ./scripts/checkpatch.pl
line 2638".

I noticed this bug while running checkpatch on the set of commits from
v5.7 to v5.8-rc1 of the kernel on the commits with a diff content in
their commit message.

This bug was introduced in the script by commit e518e9a59ec3
("checkpatch: emit an error when there's a diff in a changelog"). It has
been in the script since then.

The author intended to store the match made by capture group in variable
`$1`. This should have contained the name of the file as `[\w/]+` matched.
However, this couldn't be accomplished due to usage of capture group and
`$1` in the same regular expression.

Fix this by placing the capture group in the condition before `&&`.
Thus, `$1` can be initialized to the text that capture group matches
thereby setting it to the desired and required value.

Reviewed-by: Lukas Bulwahn <lukas.bulwahn at gmail.com>
Tested-by: Lukas Bulwahn <lukas.bulwahn at gmail.com>
Signed-off-by: Mrinal Pandey <mrinalmni at gmail.com>
Changes since v1:
Add Reviewed-by and Tested-by tag

 scripts/checkpatch.pl | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 4c820607540b..e73e998d582a 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2636,8 +2636,8 @@ sub process {
 # Check if the commit log has what seems like a diff which can confuse patch
 		if ($in_commit_log && !$commit_log_has_diff &&
-		    (($line =~ m@^\s+diff\b.*a/[\w/]+@ &&
-		      $line =~ m@^\s+diff\b.*a/([\w/]+)\s+b/$1\b@) ||
+		    (($line =~ m@^\s+diff\b.*a/([\w/]+)@ &&
+		      $line =~ m@^\s+diff\b.*a/[\w/]+\s+b/$1\b@) ||
 		     $line =~ m@^\s*(?:\-\-\-\s+a/|\+\+\+\s+b/)@ ||
 		     $line =~ m/^\s*\@\@ \-\d+,\d+ \+\d+,\d+ \@\@/)) {

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