linux-kernel - Re: [PATCH 00/12] treewide: Fix GENMASK misuses

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Message-ID: <0306bec0ec270b01b09441da3200252396abed27.camel@perches.com>
Date:   Sun, 28 Jul 2019 16:45:22 -0700
From:   Joe Perches <joe@...ches.com>
To:     Rikard Falkeborn <rikard.falkeborn@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     johannes@...solutions.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/12] treewide: Fix GENMASK misuses

On Sat, 2019-07-27 at 21:54 +0200, Rikard Falkeborn wrote:
> Trimming CC-list.
> 
> > It'd can't be done as it's used in declarations
> > and included in asm files and it uses the UL()
> > macro.
> 
> Can the BUILD_BUG_ON_ZERO() macro be used instead? It works in
> declarations. I don't know if it works in asm-files, but the below
> changes builds an x86-64 allyesconfig without problems (after the rest
> of this series have been applied.

Maybe, fine by me if it works.

Perhaps you should submit this and let the build-bot
verify it.



> /Rikard
> 
> ---
>  include/linux/bits.h | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/bits.h b/include/linux/bits.h
> index 669d69441a62..52e747d27f87 100644
> --- a/include/linux/bits.h
> +++ b/include/linux/bits.h
> @@ -2,6 +2,7 @@
>  #ifndef __LINUX_BITS_H
>  #define __LINUX_BITS_H
>  
> +#include <linux/build_bug.h>
>  #include <linux/const.h>
>  #include <asm/bitsperlong.h>
>  
> @@ -19,11 +20,15 @@
>   * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.
>   */
>  #define GENMASK(h, l) \
> +	(BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
> +		__is_constexpr(h) && __is_constexpr(l), (l) > (h), 0)) + \
>  	(((~UL(0)) - (UL(1) << (l)) + 1) & \
> -	 (~UL(0) >> (BITS_PER_LONG - 1 - (h))))
> +	 (~UL(0) >> (BITS_PER_LONG - 1 - (h)))))
>  
>  #define GENMASK_ULL(h, l) \
> +	(BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
> +		__is_constexpr(h) && __is_constexpr(l), (l) > (h), 0)) + \
>  	(((~ULL(0)) - (ULL(1) << (l)) + 1) & \
> -	 (~ULL(0) >> (BITS_PER_LONG_LONG - 1 - (h))))
> +	 (~ULL(0) >> (BITS_PER_LONG_LONG - 1 - (h)))))
>  
>  #endif	/* __LINUX_BITS_H */