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Subject: Re: [PATCH v5 2/2] scripts: checkpatch: check unused parameters for
 function-like macro
From: Joe Perches <joe@perches.com>
To: Mac Xu <mac.xxn@outlook.com>, Barry Song <21cnbao@gmail.com>, 
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Date: Mon, 01 Apr 2024 18:39:16 -0700
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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@outlook.com>
> > >=20
> > > If function-like macros do not utilize a parameter, it might result i=
n a
> > > build warning.  In our coding style guidelines, we advocate for utili=
zing
> > > static inline functions to replace such macros.  This patch verifies
> > > compliance with the new rule.
> > >=20
> > > For a macro such as the one below,
> > >=20
> > > =A0#define test(a) do { } while (0)
> > >=20
> > > The test result is as follows.
> > >=20
> > > =A0ERROR: Parameter 'a' is not used in function-like macro, please us=
e static
> > > =A0inline instead
> > > =A0#21: FILE: mm/init-mm.c:20:
> > > =A0+#define test(a) do { } while (0)
> >=20
> > This is no longer true.
> > Please update the ERROR->WARN and message as below
> >=20
> > Ideally, this would have an update to
> > Documentation/dev-tools/checkpatch.rst
> >=20
> > to describe the new --verbose message type
>=20
> Hi Joe,
>=20
> Thank you for the comments, here's the code:
>=20
> +# 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");
> +}
>=20
> and here's the document for it which is inserted into the "Macros, Attrib=
utes 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 function=
s
> +    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.
>=20
> Please let me know if the document needs further re-wording to make it he=
lpful 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#macr=
os-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 =3D alloc(sizeof(struct foo), ...)

    should be::

      p =3D alloc(sizeof(*p), ...)

    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#a=
llocating-memory