linux-kernel - Re: about __BITS_PER

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Message-Id: <201104111724.57607.arnd@arndb.de>
Date:	Mon, 11 Apr 2011 17:24:57 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	"Guan Xuetao" <gxt@...c.pku.edu.cn>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: about __BITS_PER_LONG

On Monday 11 April 2011, Guan Xuetao wrote:
> --- a/include/asm-generic/bitsperlong.h
> +++ b/include/asm-generic/bitsperlong.h
> @@ -9,7 +9,11 @@
>   * to decide it, but rather check a compiler provided macro.
>   */
>  #ifndef __BITS_PER_LONG
> -#define __BITS_PER_LONG 32
> +#   ifdef CONFIG_64BIT
> +#      define __BITS_PER_LONG 64
> +#   else
> +#      define __BITS_PER_LONG 32
> +#   endif /* CONFIG_64BIT */
>  #endif
>  

Unfortunately, this does not work, because the __BITS_PER_LONG definition is meant
for user space. You have to make this depend on a preprocessor macro that
is provided by the compiler based on the command line switches (e.g. -m64) that
a use could pass to the compiler.

In user space, the CONFIG_* symbols are meaningless.

	Arnd
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