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

[Mrinal Pandey <mrinalmni@gmail.com>]

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On 20/07/12 09:18AM, Lukas Bulwahn wrote:
> On Sun, Jul 12, 2020 at 7:18 AM Mrinal Pandey <mrinalmni@gmail.com> wrote:
> 
> > On Sun, Jul 12, 2020 at 12:44 AM Lukas Bulwahn <lukas.bulwahn@gmail.com>
> > wrote:
> >
> >>
> >>
> >> On Sat, Jul 11, 2020 at 5:44 PM Mrinal Pandey <mrinalmni@gmail.com>
> >> wrote:
> >>
> >>> The usage of "capture group (...)" in the immediate condition after `&&`
> >>> results in `$1` being uninitialized. This eventually crashes the script.
> >>>
> >>>
> >> It does not really crash it, right? It just emits a warning.
> >>
> >
> > Sir,
> >
> > Yes. I will modify the line accordingly.
> >
> >>
> >>
> >>> Fix this by placing the capture group in the condition before `&&`.
> >>> Thus, `$1` can be initialized to the text it matches thereby setting it
> >>> to the desired and required value.
> >>>
> >>>
> >> Maybe you can look when this bug was introduced?
> >>
> >
> > The bug was first introduced with the commit `e518e9a59ec3` when the block
> > was
> > added to the script. It has been like that since then.
> > Should I add this detail too in the commit message?
> >
> 
> Yes, please do.
> 
> Commits are referred to with its hash shortened to 12 characters and the
> commit message header in the following format:
> 
> Commit e518e9a59ec3 ("checkpatch: emit an error when there's a diff in a
> changelog")
> 
> 
> Further note:
> - can you also explain what the author intended to do?
> - can you describe in one sentence how you discovered this bug?
> - use checkpatch.pl on your own patch.
> 
> Please rework the commit message and resend to this list, Shuah and me.
> 
> I think if that patch is then okay, we have a quick look and then you can
> send it out to the general list.
>
Sir,

Please let me know if the commit message could be further improved or
this is what you seek.
I ran my patch through checkpatch and it says that the patch has no
obvious style problems.
I hope I wasn't supposed to include patch version history on this patch,
please correct me if I am wrong.

Thank you.
> 
> Lukas
> 
> >

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. The warning was thrown on the commits
which had 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 RegEx.

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

Signed-off-by: Mrinal Pandey <mrinalmni@gmail.com>
---
 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+ \@\@/)) {
 			ERROR("DIFF_IN_COMMIT_MSG",
-- 
2.25.1


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