linux-kernel - Re: [PATCH] scripts: add macro_checker script to check unused parameters in macros

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Message-ID: <7a1be8c1f49fc6356a0a79591af3c3de8d4675ec.camel@perches.com>
Date: Wed, 24 Jul 2024 06:30:29 -0700
From: Joe Perches <joe@...ches.com>
To: Julian Sun <sunjunchao2870@...il.com>, linux-wireless@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Cc: jack@...e.cz, brauner@...nel.org, viro@...iv.linux.org.uk, 
 masahiroy@...nel.org, akpm@...ux-foundation.org, n.schier@....de,
 ojeda@...nel.org,  djwong@...nel.org, kvalo@...nel.org
Subject: Re: [PATCH] scripts: add macro_checker script to check unused
 parameters in macros

On Tue, 2024-07-23 at 05:11 -0400, Julian Sun wrote:
> Hi,
> 
> Recently, I saw a patch[1] on the ext4 mailing list regarding
> the correction of a macro definition error. Jan mentioned
> that "The bug in the macro is a really nasty trap...".
> Because existing compilers are unable to detect
> unused parameters in macro definitions. This inspired me
> to write a script to check for unused parameters in
> macro definitions and to run it.
> 

checkpatch has a similar test:

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

$ git log --format=email -1 b1be5844c1a0124a49a30a20a189d0a53aa10578
>From b1be5844c1a0124a49a30a20a189d0a53aa10578 Mon Sep 17 00:00:00 2001
From: Xining Xu <mac.xxn@...look.com>
Date: Tue, 7 May 2024 15:27:57 +1200
Subject: [PATCH] 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