Commit b1be5844 authored by Xining Xu's avatar Xining Xu Committed by Andrew Morton
Browse files

scripts: checkpatch: check unused parameters for function-like macro 

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

Link: https://lkml.kernel.org/r/20240507032757.146386-3-21cnbao@gmail.com


Signed-off-by: default avatarXining Xu <mac.xxn@outlook.com>
Tested-by: default avatarBarry Song <v-songbaohua@oppo.com>
Signed-off-by: default avatarBarry Song <v-songbaohua@oppo.com>
Acked-by: default avatarJoe Perches <joe@perches.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: Jonathan Corbet <corbet@lwn.net>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Jeff Johnson <quic_jjohnson@quicinc.com>
Cc: Charlemagne Lasse <charlemagnelasse@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 6813216b

Documentation/dev-tools/checkpatch.rst

+14 −0
Original line number Diff line number Diff line
@@ -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

scripts/checkpatch.pl

+6 −0
Original line number Diff line number Diff line
@@ -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