linux-kernel - Re: [Intel-gfx] [PATCH v9 2/8] util_macros: Add exact_type macro to catch type mis-match while compiling

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Message-ID: <f9cc9317-044d-4f7e-a37c-a06df7262077@intel.com>
Date:   Thu, 25 Aug 2022 17:04:26 +0900
From:   Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>
To:     <bgolaszewski@...libre.com>
CC:     <intel-gfx@...ts.freedesktop.org>,
        <thomas.hellstrom@...ux.intel.com>, <keescook@...omium.org>,
        <jani.nikula@...el.com>, <linux-kernel@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>, <chris@...is-wilson.co.uk>,
        <airlied@...ux.ie>, <andrzej.hajda@...el.com>,
        <matthew.auld@...el.com>, <daniel@...ll.ch>, <mchehab@...nel.org>,
        <nirmoy.das@...el.com>, <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [Intel-gfx] [PATCH v9 2/8] util_macros: Add exact_type macro to
 catch type mis-match while compiling

Hi Bartosz Golaszewski,

would you mind taking a look at this patch?

Thanks,
G.G.

On 8/24/22 5:45 PM, Gwan-gyeong Mun wrote:
> It adds exact_type and exactly_pgoff_t macro to catch type mis-match while
> compiling. The existing typecheck() macro outputs build warnings, but the
> newly added exact_type() macro uses the BUILD_BUG_ON() macro to generate
> a build break when the types are different and can be used to detect
> explicit build errors.
> 
> v6: Move macro addition location so that it can be used by other than drm
>      subsystem (Jani, Mauro, Andi)
> 
> Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>
> Cc: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
> Cc: Matthew Auld <matthew.auld@...el.com>
> Cc: Nirmoy Das <nirmoy.das@...el.com>
> Cc: Jani Nikula <jani.nikula@...el.com>
> Cc: Andi Shyti <andi.shyti@...ux.intel.com>
> Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
> ---
>   include/linux/util_macros.h | 25 +++++++++++++++++++++++++
>   1 file changed, 25 insertions(+)
> 
> diff --git a/include/linux/util_macros.h b/include/linux/util_macros.h
> index 72299f261b25..b6624b275257 100644
> --- a/include/linux/util_macros.h
> +++ b/include/linux/util_macros.h
> @@ -2,6 +2,9 @@
>   #ifndef _LINUX_HELPER_MACROS_H_
>   #define _LINUX_HELPER_MACROS_H_
>   
> +#include <linux/types.h>
> +#include <linux/bug.h>
> +
>   #define __find_closest(x, a, as, op)					\
>   ({									\
>   	typeof(as) __fc_i, __fc_as = (as) - 1;				\
> @@ -38,4 +41,26 @@
>    */
>   #define find_closest_descending(x, a, as) __find_closest(x, a, as, >=)
>   
> +/**
> + * exact_type - break compile if source type and destination value's type are
> + * not the same
> + * @T: Source type
> + * @n: Destination value
> + *
> + * It is a helper macro for a poor man's -Wconversion: only allow variables of
> + * an exact type. It determines whether the source type and destination value's
> + * type are the same while compiling, and it breaks compile if two types are
> + * not the same
> + */
> +#define exact_type(T, n) \
> +	BUILD_BUG_ON(!__builtin_constant_p(n) && !__builtin_types_compatible_p(T, typeof(n)))
> +
> +/**
> + * exactly_pgoff_t - helper to check if the type of a value is pgoff_t
> + * @n: value to compare pgoff_t type
> + *
> + * It breaks compile if the argument value's type is not pgoff_t type.
> + */
> +#define exactly_pgoff_t(n) exact_type(pgoff_t, n)
> +
>   #endif