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

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Message-ID:
 <MN0PR20MB47170F8BDF17A5B9914AC610F33E2@MN0PR20MB4717.namprd20.prod.outlook.com>
Date: Tue, 2 Apr 2024 15:05:51 +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 Tue, 2024-04-02 at 00:16 +0000, Mac Xu wrote:
> > > 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.
> 
> Hi again Xining.
> 
> Thanks.
> 
> That looks good but it doesn't match the script output
> which doesn't use ", please use static inline instead."
> (and I believe the script should not output that too)
> 
> Another good thing would be to add a line like:
> 
>         See: https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl
> 
> For example, from: checkpatch.rst
> 
>   **ALLOC_SIZEOF_STRUCT**
>     The allocation style is bad.  In general for family of
>     allocation functions using sizeof() to get memory size,
>     constructs like::
> 
>       p = alloc(sizeof(struct foo), ...)
> 
>     should be::
> 
>       p = alloc(sizeof(*p), ...)
> 
>     See: https://www.kernel.org/doc/html/latest/process/coding-style.html#allocating-memory
> 
> 

Hi again Joe,

Thanks again for the detailed comments.

Here's the code (which keeps unchanged):
+# 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 updated document, which drops the ", please use static inline instead" from the
warning message, and adds a link at the end of this document block:
+
+  **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: Parameter 'a' is not used in function-like macro.
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl


Regards,
Xining.