linux-kernel - Re: [COMPAT] Add compat

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Message-Id: <200709290138.24562.arnd@arndb.de>
Date:	Sat, 29 Sep 2007 01:38:23 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Kyle McMartin <kyle@...artin.ca>
Cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	Kyle McMartin <kyle@...artin.ca>
Subject: Re: [COMPAT] Add compat_merge64 helper

On Saturday 29 September 2007, you wrote:
> +static inline u64 compat_merge64(u32 left, u32 right)
> +{
> +#if defined(__BIG_ENDIAN)
> +       return ((u64)left << 32) | right;
> +#else /* defined (__LITTLE_ENDIAN) */
> +       return ((u64)right << 32) | left;
> +#endif
> +}

Looks good, if we can guarantee that

1. Byte order matches the order in which 64 bit arguments are split
   in system call conventions on all platforms.
2. Every user of compat_merge64() includes asm/byteorder.h

Both should be easy to prove, but I'm not convinced until someone
actually does it.

	Arnd <><
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