linux-kernel - [PATCH 2/4] UAPI: Fix endianness conditionals in linux/acct.h

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Date:	Wed, 06 Mar 2013 20:47:43 +0000
From:	David Howells <dhowells@...hat.com>
To:	torvalds@...ux-foundation.org
Cc:	linux-arch@...r.kernel.org, sfr@...b.auug.org.au,
	Joakim.Tjernlund@...nsmode.se, arnd@...db.de,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: [PATCH 2/4] UAPI: Fix endianness conditionals in linux/acct.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 ACCT_BYTEORDER in linux/acct.h is wrong in this way.  Note
that userspace will likely interpret this incorrectly as the big-endian variant
on little-endian machines - depending on header inclusion order.

[!!!] NOTE [!!!]  This patch may adversely change the userspace API.  It might
be better to fix the value of ACCT_BYTEORDER.

Signed-off-by: David Howells <dhowells@...hat.com>
---

 include/uapi/linux/acct.h |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/acct.h b/include/uapi/linux/acct.h
index 11b6ca3..df2f9a0 100644
--- a/include/uapi/linux/acct.h
+++ b/include/uapi/linux/acct.h
@@ -107,10 +107,12 @@ struct acct_v3
 #define ACORE		0x08	/* ... dumped core */
 #define AXSIG		0x10	/* ... was killed by a signal */

-#ifdef __BIG_ENDIAN
+#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
 #define ACCT_BYTEORDER	0x80	/* accounting file is big endian */
-#else
+#elif defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
 #define ACCT_BYTEORDER	0x00	/* accounting file is little endian */
+#else
+#error unspecified endianness
 #endif

 #ifndef __KERNEL__

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