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

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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: Xining Xu <mac.xxn@outlook.com>
Tested-by: Barry Song <v-songbaohua@oppo.com>
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Acked-by: Joe 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Xining Xu 2024-05-07 15:27:57 +12:00 committed by Andrew Morton
parent 6813216bbd
commit b1be5844c1
2 changed files with 20 additions and 0 deletions
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14
Documentation/dev-tools/checkpatch.rst
View File

@ -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

6
scripts/checkpatch.pl
View File

@ -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