linux-kernel - Re: [PATCH v5 2/2] scripts: checkpatch: check unused parameters for function-like macro

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Date: Tue, 2 Apr 2024 00:16:40 +0000
From: Mac Xu <mac.xxn@...look.com>
To: Joe Perches <joe@...ches.com>, Barry Song <21cnbao@...il.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"workflows@...r.kernel.org" <workflows@...r.kernel.org>
CC: "apw@...onical.com" <apw@...onical.com>, "broonie@...nel.org"
	<broonie@...nel.org>, "chenhuacai@...ngson.cn" <chenhuacai@...ngson.cn>,
	"chris@...kel.net" <chris@...kel.net>, "corbet@....net" <corbet@....net>,
	"dwaipayanray1@...il.com" <dwaipayanray1@...il.com>,
	"herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux@...ck-us.net" <linux@...ck-us.net>, "lukas.bulwahn@...il.com"
	<lukas.bulwahn@...il.com>, "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
	"v-songbaohua@...o.com" <v-songbaohua@...o.com>, Max Filippov
	<jcmvbkbc@...il.com>, Jeff Johnson <quic_jjohnson@...cinc.com>, Charlemagne
 Lasse <charlemagnelasse@...il.com>
Subject: Re: [PATCH v5 2/2] scripts: checkpatch: check unused parameters for
 function-like macro


> On Mon, 2024-04-01 at 14:21 +1300, Barry Song wrote:
> > 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.
> >
> >  ERROR: Parameter 'a' is not used in function-like macro, please use static
> >  inline instead
> >  #21: FILE: mm/init-mm.c:20:
> >  +#define test(a) do { } while (0)
> 
> This is no longer true.
> Please update the ERROR->WARN and message as below
> 
> Ideally, this would have an update to
> Documentation/dev-tools/checkpatch.rst
> 
> to describe the new --verbose message type

Hi Joe,

Thank you for the comments, here's the code:

+# 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");
+}

and here's the document for it which is inserted into the "Macros, Attributes and
Symbols" section of checkpatch.rst starting from line 909:
+
+  **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 as below::
+
+      #define test(a) do { } while (0)
+
+    there would be a warning as below::
+
+      WARNING: Parameter 'a' is not used in function-like macro, please use
+      static inline instead.

Please let me know if the document needs further re-wording to make it helpful enough
to the readers.

Thanks,
Xining