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

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Message-ID: <778f1ccf1945f79c317dd0a4d2a90d3855770713.camel@perches.com>
Date: Wed, 24 Jul 2024 20:40:23 -0700
From: Joe Perches <joe@...ches.com>
To: Julian Sun <sunjunchao2870@...il.com>
Cc: linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, 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 Wed, 2024-07-24 at 22:09 -0400, Julian Sun wrote:
> Joe Perches <joe@...ches.com> 于2024年7月24日周三 09:30写道：
> > 
> > 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
> Yeah, I noticted the test. The difference between checkpatch and
> macro_checker is that checkpatch only checks the patch files, instead
> of the entire source files, which results in the inability to check
> all macros in source files.

Another possibility:

$ git ls-files -- '*.[ch]' | \
  xargs ./scripts/checkpatch -f --terse --no-summary --types=MACRO_ARG_UNUSED

Though I agree the addition of a test for "do {} while (0)" and
no content would be also be useful for unused macro args tests.
---
 scripts/checkpatch.pl | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 39032224d504f..285d29b3e9010 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6060,7 +6060,9 @@ sub process {
 				}
 
 # check if this is an unused argument
-				if ($define_stmt !~ /\b$arg\b/) {
+				if ($define_stmt !~ /\b$arg\b/ &&
+				    $define_stmt !~ /^$/ &&
+				    $define_stmt !~ /^do\s*\{\s*\}\s*while\s*\(\s*0\s*\)$/) {
 					WARN("MACRO_ARG_UNUSED",
 					     "Argument '$arg' is not used in function-like macro\n" . "$herectx");
 				}