[PATCH v4 2/2] scripts: checkpatch: check unused parameters for function-like macro

[Barry Song <21cnbao@gmail.com>]

From: Xining Xu <mac.xxn@outlook.com>

If function-like macros do not utilize a parameter, it might result in a
build warning.  In our coding style guidelines, we advocate for utilizing
static inline functions to replace such macros.  This patch verifies
compliance with the new rule.

For a macro such as the one below,

 #define test(a) do { } while (0)

The test result is as follows.

 ERROR: Parameter 'a' is not used in function-like macro, please use static
 inline instead
 #21: FILE: mm/init-mm.c:20:
 +#define test(a) do { } while (0)

 total: 1 errors, 0 warnings, 8 lines checked

Signed-off-by: Xining Xu <mac.xxn@outlook.com>
Tested-by: Barry Song <v-songbaohua@oppo.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: Huacai Chen <chenhuacai@loongson.cn>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Mark Brown <broonie@kernel.org>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Dwaipayan Ray <dwaipayanray1@gmail.com>
Cc: Joe Perches <joe@perches.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
---
 scripts/checkpatch.pl | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 9c4c4a61bc83..bcb886014d60 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6109,6 +6109,36 @@ sub process {
 				WARN("TRAILING_SEMICOLON",
 				     "macros should not use a trailing semicolon\n" . "$herectx");
 			}
+
+			# match "\s*" rather than "\s+" after the balanced parens, as macro definition with arguments
+			# is not required to have whitespace after arguments
+			if ($dstat =~ /^\+\s*#\s*define\s+$Ident$balanced_parens\s*(\S+.*)(\/[\/*].*)?/) {
+				my $params = $1 || "";
+				my $body = $2 || "";
+
+			    # get the individual params
+				$params =~ tr/()//d;
+				# remove leading and trailing whitespace
+				$params =~ s/^\s+|\s+$//g;
+
+				$ctx =~ s/\n*$//;
+				my $cnt = statement_rawlines($ctx);
+				my $herectx = get_stat_here($linenr, $cnt, $here);
+
+				if ($params ne "") {
+					my @paramList = split /,\s*/, $params;
+					foreach my $param(@paramList) {
+						if ($param =~ /\.\.\.$/) {
+							# if the param name ends with "...", skip the check
+							next;
+						}
+						if ($body !~ /\b$param\b/) {
+							WARN("UNUSED_PARAM_IN_MACRO",
+								"Parameter '$param' is not used in function-like macro\n" . "$herectx");
+						}
+					}
+				}
+			}
 		}
 
 # check for redundant bracing round if etc
-- 
2.34.1