linux-kernel - Re: [PATCH] byteorder: force in-place endian conversion to always evaluate args

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Message-Id: <1217009975.5971.21.camel@brick>
Date:	Fri, 25 Jul 2008 11:19:35 -0700
From:	Harvey Harrison <harvey.harrison@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] byteorder: force in-place endian conversion to always
	evaluate args

On Fri, 2008-07-25 at 14:14 -0400, H. Peter Anvin wrote:
> Harvey Harrison wrote:
> > David Miller reported breakage in ide when the in-place byteorder helpers
> > were used as the macros do not always evaluate their args which led to
> > an infinite loop.
> > 
> > Just make them functions to ensure they always do so.
> 
> > -#define __cpu_to_be64s(x) do {} while (0)
> 
> For what it's worth, the way to write a macro like this:
> 
> #define __cpu_to_be64s(x) ((void)(x))

If you've looked at the byteorder rework I've done in -mm, these get
unified in a single include/linux/byteorder.h and look like:

static inline void __le16_to_cpus(__u16 *p)
{
#ifdef __BIG_ENDIAN
	__swab16s(p);
#endif
}

static inline void __be16_to_cpus(__u16 *p)
{
#ifdef __LITTLE_ENDIAN
	__swab16s(p);
#endif
}

...etc.

As you can now rely on __BIG/__LITTLE_ENDIAN being set reliably.

Harvey

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