From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56911) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XHHDY-0003mU-Ji for qemu-devel@nongnu.org; Tue, 12 Aug 2014 14:54:53 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XHHDO-00079c-18 for qemu-devel@nongnu.org; Tue, 12 Aug 2014 14:54:44 -0400 From: Tom Musta Date: Tue, 12 Aug 2014 13:53:34 -0500 Message-Id: <1407869623-11185-4-git-send-email-tommusta@gmail.com> In-Reply-To: <1407869623-11185-1-git-send-email-tommusta@gmail.com> References: <1407869623-11185-1-git-send-email-tommusta@gmail.com> Subject: [Qemu-devel] [V2 PATCH 03/12] linux-user: Properly Handle semun Structure In Cross-Endian Situations List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org, qemu-ppc@nongnu.org Cc: peter.maydell@linaro.org, riku.voipio@linaro.org, agraf@suse.de, Tom Musta 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 value passed to semctl is an 8 byte (abi_long) value and thus does not have the 4-byte val field in the correct location. In order to rectify this, the other half of the union must be accessed. This is achieved in code by performing a byte swap on the entire 8 byte union, followed by a 4-byte swap of the first half. Also, eliminate an extraneous (dead) line of code that sets target_su.val in the IPC_SET/IPC_GET case. Signed-off-by: Tom Musta --- V2: Reworked per comments from Peter. linux-user/syscall.c | 13 +++++++++++-- 1 files changed, 11 insertions(+), 2 deletions(-) diff --git a/linux-user/syscall.c b/linux-user/syscall.c index 229c482..bee1f4e 100644 --- a/linux-user/syscall.c +++ b/linux-user/syscall.c @@ -2647,9 +2647,18 @@ static inline abi_long do_semctl(int semid, int semnum, int cmd, switch( cmd ) { case GETVAL: case SETVAL: - arg.val = tswap32(target_su.val); + /* 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 8-byte structure is byteswapped, followed by + * a swap of the 4 byte val field. In other cases, the data is + * already in proper host byte order. */ + if (sizeof(target_su.val) != (sizeof(target_su.buf))) { + target_su.buf = tswapal(target_su.buf); + arg.val = tswap32(target_su.val); + } else { + arg.val = 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