Endian/__BYTE_ORDER question

[Joakim Tjernlund]

Adrian Reber <adrian at lisas.de> wrote on 2010/02/11 17:33:29:
>
> On Thu, Feb 11, 2010 at 05:17:37PM +0100, Joakim Tjernlund wrote:
> > I am getting confused about on how to test for Endian in the kernel code. In user
> > space one uses #if __BYTE_ORDER == __LITTLE_ENDIAN or #if __BYTE_ORDER == __BIG_ENDIAN
> >
> > I can see lots of kernel headers using this test too, but it doesn't seem
> > to be an arch specific file #defining __BYTE_ORDER. Instead I find files like:
> >  arch/alpha/math-emu/sfp-util.h
> >  arch/powerpc/include/asm/sfp-machine.h
> >  arch/s390/include/asm/sfp-util.h
> >  arch/sh/math-emu/sfp-util.h
> >
> > How is this supposed to work?
>
> I have no idea how it is actually done in the kernel code... but gcc
> defines it:
>
> gcc -dM -E -x c - <<<'' | grep ENDIAN
> #define __BIG_ENDIAN__ 1
> #define _BIG_ENDIAN 1

That doesn't define __BYTE_ORDER. Try the same gcc command
on a file that #includes <stdlib.h> and you will get both
__BIG_ENDIAN and __LITTLE_ENDIAN

     Jocke