MIME-Version: 1.0
References: <20211119113644.1600-1-alx.manpages@gmail.com> <20211120130104.185699-1-alx.manpages@gmail.com>
 <20211120130104.185699-19-alx.manpages@gmail.com>
In-Reply-To: <20211120130104.185699-19-alx.manpages@gmail.com>
From:   Arnd Bergmann <arnd@arndb.de>
Date:   Sun, 21 Nov 2021 14:22:35 +0100
Message-ID: <CAK8P3a13pWLNdE6-BP8GEtSait66=V+Wo7GPWP-FkyXMHP5tPQ@mail.gmail.com>
Subject: Re: [PATCH v2 17/20] linux/array_size.h: Add __is_array(a) to help readability
To:     Alejandro Colomar <alx.manpages@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Kees Cook <keescook@chromium.org>,
        Joe Perches <joe@perches.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Sat, Nov 20, 2021 at 2:01 PM Alejandro Colomar
<alx.manpages@gmail.com> wrote:
>
>  /* &a[0] degrades to a pointer: a different type from an array */
> -#define __must_be_array(a)  __must_be(!__same_type((a), &(a)[0]))
> +#define __is_array(a)  (!__same_type((a), &(a)[0]))
> +
> +#define __must_be_array(a)  __must_be(__is_array(a))

I'd go the other way here if you want to improve this, and open-code it
to avoid nested macros. That produces more readable error messages
with recent compilers that try to unwind each macro one at a time.

      Arnd