In all the script files, SPDX license identifier is expected on the second
line, the first line being the shebang.

The diff content includes the SPDX licensing information but excludes the
shebang when a change is made to a script file in commit 37f8173dd849
("locking/atomics: Flip fallbacks and  instrumentation") and commit
075c8aa79d54 ("selftests: forwarding: tc_actions.sh: add matchall mirror
test"). In these cases checkpatch issues a false positive warning:
"Misplaced SPDX-License-Identifier tag - use line 1 instead".

I noticed this false positive, while running checkpatch on the set of
commits from v5.7 to v5.8-rc1 of the kernel, on the said commits.
This false positive exists in checkpatch since commit a8da38a9cf0e
("checkpatch: add test for SPDX-License-Identifier on wrong line #")
when the corresponding rule was first added.

Currently, if checkpatch finds a shebang in line 1, it expects the
license identifier in line 2. However, this doesn't work when a shebang
isn't found on the line 1.

Improve this by ensuring the patch to have originated from a script by
checking the extension. However, there are 120 files in the kernel source
that do not have an extension but have a shebang in line 1.

An alternate approach is to check for permissions of the file. There are
53 files in kernel source that have executable flag set but don't have a
shebang in the first line. These files could be patched suitably so that
they don't issue false warnings. Hence, choose this approach.

Reduce SPDX license false warnings on patches by checking the permissions
on the file.

Signed-off-by: Mrinal Pandey <mrinalmni@gmail.com>
---
 scripts/checkpatch.pl | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 4c820607540b..c55595113499 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2368,6 +2368,7 @@ sub process {
 
 	# Trace the real file/line as we go.
 	my $realfile = '';
+	my $realfile_perms = '';
 	my $realline = 0;
 	my $realcnt = 0;
 	my $here = '';
@@ -2555,11 +2556,13 @@ sub process {
 		if ($line =~ /^diff --git.*?(\S+)$/) {
 			$realfile = $1;
 			$realfile =~ s@^([^/]*)/@@ if (!$file);
+			$realfile_perms = `stat -c "%a" $realfile`;
 			$in_commit_log = 0;
 			$found_file = 1;
 		} elsif ($line =~ /^\+\+\+\s+(\S+)/) {
 			$realfile = $1;
 			$realfile =~ s@^([^/]*)/@@ if (!$file);
+			$realfile_perms = `stat -c "%a" $realfile`;
 			$in_commit_log = 0;
 
 			$p1_prefix = $1;
@@ -3166,6 +3169,9 @@ sub process {
 		}
 
 # check for using SPDX license tag at beginning of files
+		if ($realfile_perms =~ /[7531]\d{0,2}/) {
+			$checklicenseline = 2;
+		}
 		if ($realline == $checklicenseline) {
 			if ($rawline =~ /^[ \+]\s*\#\!\s*\//) {
 				$checklicenseline = 2;
-- 
2.25.1