Re: [PATCH] [RFC] #define __BYTE_ORDER

[Joakim Tjernlund]

geert.uytterhoeven@xxxxxxxxx wrote on 2010/03/24 19:37:36:
>
> On Wed, Mar 24, 2010 at 19:21, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > On Wed, 17 Mar 2010 19:10:55 +0100
> > Joakim Tjernlund <Joakim.Tjernlund@xxxxxxxxxxxx> 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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