linux-kernel - Re: [PATCH v2 17/20] linux/array_size.h: Add __is

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Date:   Sun, 21 Nov 2021 14:22:35 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Alejandro Colomar <alx.manpages@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Kees Cook <keescook@...omium.org>,
        Joe Perches <joe@...ches.com>
Subject: Re: [PATCH v2 17/20] linux/array_size.h: Add __is_array(a) to help readability

On Sat, Nov 20, 2021 at 2:01 PM Alejandro Colomar
<alx.manpages@...il.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