[Qemu-devel] [PATCH 03/12] linux-user: Properly Handle semun Structure In Cross-Endian Situations

From: Tom Musta <tommusta@gmail.com>
To: qemu-devel@nongnu.org, qemu-ppc@nongnu.org
Cc: Tom Musta <tommusta@gmail.com>, riku.voipio@linaro.org, agraf@suse.de
Subject: [Qemu-devel] [PATCH 03/12] linux-user: Properly Handle semun Structure In Cross-Endian Situations
Date: Mon,  4 Aug 2014 11:45:30 -0500	[thread overview]
Message-ID: <1407170739-12237-4-git-send-email-tommusta@gmail.com> (raw)
In-Reply-To: <1407170739-12237-1-git-send-email-tommusta@gmail.com>

The semun union used in the semctl system call contains both an int (val) and
pointers.  In cross-endian situations on 64 bit targets, the target memory
must be byte swapped, otherwise the wrong 32 bits are used for the val
field.

Signed-off-by: Tom Musta <tommusta@gmail.com>

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 229c482..fb03e96 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -2647,9 +2647,14 @@ static inline abi_long do_semctl(int semid, int semnum, int cmd,
     switch( cmd ) {
 	case GETVAL:
 	case SETVAL:
+#if TARGET_ABI_BITS == 64
+            /* In 64 bit cross endian situations, we will erroneously pick up
+             * the wrong half of the union for the "val" element.  To rectify
+             * this, the entire structure is byteswaped. */
+            target_su.buf = tswapal(target_su.buf);
+#endif
             arg.val = tswap32(target_su.val);
             ret = get_errno(semctl(semid, semnum, cmd, arg));
-            target_su.val = tswap32(arg.val);
             break;
 	case GETALL:
 	case SETALL:
-- 
1.7.1
