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

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Date: Mon, 01 Apr 2024 18:39:16 -0700
From: Joe Perches <joe@...ches.com>
To: Mac Xu <mac.xxn@...look.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