[PATCH v4] checkpatch: add warning for unnecessary use of %h[xudi] and %hh[xudi]

[Dwaipayan Ray <dwaipayanray1@gmail.com>]

Modifiers %h and %hh should never be used.

Commit cbacb5ab0aa0 ("docs: printk-formats: Stop encouraging use
of unnecessary %h[xudi] and %hh[xudi]") specifies that:

"Standard integer promotion is already done and %hx and %hhx is useless
so do not encourage the use of %hh[xudi] or %h[xudi]."

"The "h" and "hh" things should never be used. The only reason for them
being used if you have an "int", but you want to print it out as a
"char" (and honestly, that is a really bad reason, you'd be better off
just using a proper cast to make the code more obvious)."

Add a new check to emit a warning on finding an unneeded use of %h or
%hh modifier.

Also add a fix option to the check.

Link: https://lore.kernel.org/lkml/4910042649a4f3ab22fac93191b8c1fa0a2e17c3.camel@perches.com/

Suggested-by: Joe Perches <joe@perches.com>
Suggested-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Dwaipayan Ray <dwaipayanray1@gmail.com>
---
Changes in v4:
- Change warning type and message
- Use $stat_real and calculate line offset during matches
- fix option now works for any patch line
- # was added to format block to match %#06hh

Changes in v3:
- Change warning message
- Fix regex match to include capture group
- Warn on every unnecesary use of %h on a line
- Add fix option when the format line matches current line

Changes in v2:
- Use $logFunctions instead of the manual list.
- Relocate the check to after logging continuations check.
- Remove perl_version_ok check


 scripts/checkpatch.pl | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 7dc094445d83..3c86ea737e9c 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6027,6 +6027,28 @@ sub process {
 			     "Avoid logging continuation uses where feasible\n" . $herecurr);
 		}
 
+# check for unnecessary use of %h[xudi] and %hh[xudi] in logging functions
+		if (defined $stat &&
+		    $line =~ /\b$logFunctions\s*\(/ &&
+		    index($stat, '"') >= 0) {
+			my $lc = $stat =~ tr@\n@@;
+			$lc = $lc + $linenr;
+			my $stat_real = get_stat_real($linenr, $lc);
+			pos($stat_real) = index($stat_real, '"');
+			while ($stat_real =~ /[^\"%]*(%[\#\d\.\*\-]*(h+)[idux])/g) {
+				my $pspec = $1;
+				my $h = $2;
+				my $lineoff = substr($stat_real, 0, $-[1]) =~ tr@\n@@;
+				if (WARN("UNNECESSARY_MODIFIER",
+					 "Integer promotion: Using '$h' in '$pspec' is unnecessary\n" . "$here\n$stat_real\n") &&
+				    $fix && $fixed[$fixlinenr + $lineoff] =~ /^\+/) {
+					my $nspec = $pspec;
+					$nspec =~ s/h//g;
+					$fixed[$fixlinenr + $lineoff] =~ s/\Q$pspec\E/$nspec/;
+				}
+			}
+		}
+
 # check for mask then right shift without a parentheses
 		if ($perl_version_ok &&
 		    $line =~ /$LvalOrFunc\s*\&\s*($LvalOrFunc)\s*>>/ &&
-- 
2.27.0