linux-kernel - Re: [PATCH] [RFC] #define __BYTE

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Message-ID: <OFCDA39D22.62EC6456-ONC12576F0.00770DDD-C12576F0.00778EFD@transmode.se>
Date:	Wed, 24 Mar 2010 22:45:53 +0100
From:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	geert.uytterhoeven@...il.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [RFC] #define __BYTE_ORDER

geert.uytterhoeven@...il.com wrote on 2010/03/24 19:37:36:
>
> On Wed, Mar 24, 2010 at 19:21, Andrew Morton <akpm@...ux-foundation.org> wrote:
> > On Wed, 17 Mar 2010 19:10:55 +0100
> > Joakim Tjernlund <Joakim.Tjernlund@...nsmode.se> wrote:
> >
> >> Linux does not define __BYTE_ORDER in its endian header files
> >> which makes some header files bend backwards to get at the
> >> current endian. Lets #define __BYTE_ORDER in big_endian.h/litte_endian.h
> >> to make it easier for header files that are used in user space too.
> >
> > I don't get it.  Why not nuke __BYTE_ORDER altogether and do `#ifdef
> > __LITTLE_ENDIAN' and `#ifdef __BIG_ENDIAN' everywhere?
>
> Because in userspace the convention is that
>   1. _both_ __LITTLE_ENDIAN and __BIG_ENDIAN are defined,
>   2. you have to test for e.g. __BYTE_ORDER == __BIG_ENDIAN.

Precisely, I see that i forgot to mention that in the commit msg.

It is actually worse that that, gcc will only define one of __LITTLE_ENDIAN/__BIG_ENDIAN
so you might be tricked that using just the __LITTLE_ENDIAN/__BIG_ENDIAN defines works.
Then you add some include file such as stdlib.h and it all breaks because now
both __LITTLE_ENDIAN and __BIG_ENDIAN are defined.

 Jocke

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