linux-kernel - Re: [PATCH] Documentation: coding-style: ask function-like macros to evaluate parameters

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Date: Wed, 20 Mar 2024 08:49:19 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Barry Song <21cnbao@...il.com>
Cc: Stephen Rothwell <sfr@...b.auug.org.au>, corbet@....net,
 workflows@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, Barry Song <v-songbaohua@...o.com>, Chris
 Zankel <chris@...kel.net>, Huacai Chen <chenhuacai@...ngson.cn>, Herbert Xu
 <herbert@...dor.apana.org.au>, Guenter Roeck <linux@...ck-us.net>, Max
 Filippov <jcmvbkbc@...il.com>
Subject: Re: [PATCH] Documentation: coding-style: ask function-like macros
 to evaluate parameters

On Wed, 20 Mar 2024 16:24:30 +1300 Barry Song <21cnbao@...il.com> wrote:

> Hi Stephen,
> Thanks for reviewing.
> 
> On Wed, Mar 20, 2024 at 2:42 PM Stephen Rothwell <sfr@...b.auug.org.au> wrote:
> >
> > Hi Barry,
> >
> > On Wed, 20 Mar 2024 13:16:56 +1300 Barry Song <21cnbao@...il.com> wrote:
> > >
> > > diff --git a/Documentation/process/coding-style.rst b/Documentation/process/coding-style.rst
> > > index 9c7cf7347394..8065747fddff 100644
> > > --- a/Documentation/process/coding-style.rst
> > > +++ b/Documentation/process/coding-style.rst
> > > @@ -827,6 +827,13 @@ Macros with multiple statements should be enclosed in a do - while block:
> > >                               do_this(b, c);          \
> > >               } while (0)
> > >
> > > +Function-like macros should evaluate their parameters, for unused parameters,
> > > +cast them to void:
> > > +
> > > +.. code-block:: c
> > > +
> > > +     #define macrofun(a) do { (void) (a); } while (0)
> > > +
> >
> > Maybe add some comment about using a static inline function for these
> > simple versions instead, if at all possible, (it is suggested just
> > above this section) since that will still type check arguments.
> 
> right, what about adding the below section together with the above (void) cast?
> 
> +Another approach could involve utilizing a static inline function to replace
> +the macro.:
> +
> +.. code-block:: c
> +
> +       static inline void fun(struct foo *foo)
> +       {
> +       }
> +

Stronger than that please.  Just tell people not to use macros in such
situations.  Always code it in C.