UAPI: fix endianness conditionals in linux/aio_abi.h

In the UAPI header files, __BIG_ENDIAN and __LITTLE_ENDIAN must be
compared against __BYTE_ORDER in preprocessor conditionals where these are
exposed to userspace (that is they're not inside __KERNEL__ conditionals).

However, in the main kernel the norm is to check for
"defined(__XXX_ENDIAN)" rather than comparing against __BYTE_ORDER and
this has incorrectly leaked into the userspace headers.

The definition of PADDED() in linux/aio_abi.h is wrong in this way.  Note
that userspace will likely interpret this and thus the order of fields in
struct iocb incorrectly as the little-endian variant on big-endian
machines - depending on header inclusion order.

[!!!] NOTE [!!!]  This patch may adversely change the userspace API.  It might
be better to fix the ordering of aio_key and aio_reserved1 in struct iocb.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Benjamin LaHaise <bcrl@kvack.org>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/uapi/linux/aio_abi.h

@@ -62,9 +62,9 @@ struct io_event {
 	__s64		res2;		/* secondary result */
 };
 
-#if defined(__LITTLE_ENDIAN)
+#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
 #define PADDED(x,y)	x, y
-#elif defined(__BIG_ENDIAN)
+#elif defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
 #define PADDED(x,y)	y, x
 #else
 #error edit for your odd byteorder.