linux-kernel - [PATCH v6 2/2] scripts: checkpatch: check unused parameters for function-like macro

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Date: Thu,  4 Apr 2024 11:42:54 +1300
From: Barry Song <21cnbao@...il.com>
To: akpm@...ux-foundation.org,
	linux-doc@...r.kernel.org,
	workflows@...r.kernel.org
Cc: apw@...onical.com,
	broonie@...nel.org,
	chenhuacai@...ngson.cn,
	chris@...kel.net,
	corbet@....net,
	dwaipayanray1@...il.com,
	herbert@...dor.apana.org.au,
	joe@...ches.com,
	linux-kernel@...r.kernel.org,
	linux@...ck-us.net,
	lukas.bulwahn@...il.com,
	mac.xxn@...look.com,
	sfr@...b.auug.org.au,
	v-songbaohua@...o.com,
	Max Filippov <jcmvbkbc@...il.com>,
	Jeff Johnson <quic_jjohnson@...cinc.com>,
	Charlemagne Lasse <charlemagnelasse@...il.com>
Subject: [PATCH v6 2/2] scripts: checkpatch: check unused parameters for function-like macro

From: Xining Xu <mac.xxn@...look.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.

 WARNING: Argument 'a' is not used in function-like macro
 #21: FILE: mm/init-mm.c:20:
 +#define test(a) do { } while (0)

 total: 0 errors, 1 warnings, 8 lines checked

Signed-off-by: Xining Xu <mac.xxn@...look.com>
Tested-by: Barry Song <v-songbaohua@...o.com>
Signed-off-by: Barry Song <v-songbaohua@...o.com>
Cc: Chris Zankel <chris@...kel.net>
Cc: Huacai Chen <chenhuacai@...ngson.cn>
Cc: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Guenter Roeck <linux@...ck-us.net>
Cc: Stephen Rothwell <sfr@...b.auug.org.au>
Cc: Mark Brown <broonie@...nel.org>
Cc: Andy Whitcroft <apw@...onical.com>
Cc: Dwaipayan Ray <dwaipayanray1@...il.com>
Cc: Joe Perches <joe@...ches.com>
Cc: Jonathan Corbet <corbet@....net>
Cc: Lukas Bulwahn <lukas.bulwahn@...il.com>
Cc: Max Filippov <jcmvbkbc@...il.com>
Cc: Jeff Johnson <quic_jjohnson@...cinc.com>
Cc: Charlemagne Lasse <charlemagnelasse@...il.com>
---
 Documentation/dev-tools/checkpatch.rst | 14 ++++++++++++++
 scripts/checkpatch.pl                  |  6 ++++++
 2 files changed, 20 insertions(+)

diff --git a/Documentation/dev-tools/checkpatch.rst b/Documentation/dev-tools/checkpatch.rst
index 127968995847..a9fac978a525 100644
--- a/Documentation/dev-tools/checkpatch.rst
+++ b/Documentation/dev-tools/checkpatch.rst
@@ -906,6 +906,20 @@ Macros, Attributes and Symbols
 
     See: https://lore.kernel.org/lkml/1399671106.2912.21.camel@joe-AO725/
 
+  **MACRO_ARG_UNUSED**
+    If function-like macros do not utilize a parameter, it might result
+    in a build warning. We advocate for utilizing static inline functions
+    to replace such macros.
+    For example, for a macro such as the one below::
+
+      #define test(a) do { } while (0)
+
+    there would be a warning like below::
+
+      WARNING: Argument 'a' is not used in function-like macro.
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl
+
   **SINGLE_STATEMENT_DO_WHILE_MACRO**
     For the multi-statement macros, it is necessary to use the do-while
     loop to avoid unpredictable code paths. The do-while loop helps to
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 9c4c4a61bc83..9895d7e38a9f 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6040,6 +6040,12 @@ sub process {
 					CHK("MACRO_ARG_PRECEDENCE",
 					    "Macro argument '$arg' may be better as '($arg)' to avoid precedence issues\n" . "$herectx");
 				}
+
+# check if this is an unused argument
+				if ($define_stmt !~ /\b$arg\b/) {
+					WARN("MACRO_ARG_UNUSED",
+						"Argument '$arg' is not used in function-like macro\n" . "$herectx");
+				}
 			}
 
 # check for macros with flow control, but without ## concatenation
-- 
2.34.1