From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46343) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ebVQ9-0001s5-Hh for qemu-devel@nongnu.org; Tue, 16 Jan 2018 12:53:17 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ebVQ8-0004IC-I2 for qemu-devel@nongnu.org; Tue, 16 Jan 2018 12:53:13 -0500 Received: from mx1.redhat.com ([209.132.183.28]:33110) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ebVQ8-0004HS-9V for qemu-devel@nongnu.org; Tue, 16 Jan 2018 12:53:12 -0500 Date: Tue, 16 Jan 2018 19:53:03 +0200 From: "Michael S. Tsirkin" Message-ID: <1516121887-32738-32-git-send-email-mst@redhat.com> References: <1516121887-32738-1-git-send-email-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1516121887-32738-1-git-send-email-mst@redhat.com> Subject: [Qemu-devel] [PULL v2 31/34] vhost-user: fix misaligned access to payload List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Peter Maydell We currently take a pointer to a misaligned field of a packed structure. clang reports this as a build warning. A fix is to keep payload in a separate structure, and access is it from there using a vectored write. Signed-off-by: Michael S. Tsirkin --- hw/virtio/vhost-user.c | 39 ++++++++++++++++++++++++--------------- 1 file changed, 24 insertions(+), 15 deletions(-) diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c index 6ac3610..7930fd8 100644 --- a/hw/virtio/vhost-user.c +++ b/hw/virtio/vhost-user.c @@ -652,33 +652,34 @@ static void slave_read(void *opaque) { struct vhost_dev *dev = opaque; struct vhost_user *u = dev->opaque; - VhostUserMsg msg = { 0, }; + VhostUserHeader hdr = { 0, }; + VhostUserPayload payload = { 0, }; int size, ret = 0; /* Read header */ - size = read(u->slave_fd, &msg, VHOST_USER_HDR_SIZE); + size = read(u->slave_fd, &hdr, VHOST_USER_HDR_SIZE); if (size != VHOST_USER_HDR_SIZE) { error_report("Failed to read from slave."); goto err; } - if (msg.hdr.size > VHOST_USER_PAYLOAD_SIZE) { + if (hdr.size > VHOST_USER_PAYLOAD_SIZE) { error_report("Failed to read msg header." - " Size %d exceeds the maximum %zu.", msg.hdr.size, + " Size %d exceeds the maximum %zu.", hdr.size, VHOST_USER_PAYLOAD_SIZE); goto err; } /* Read payload */ - size = read(u->slave_fd, &msg.payload, msg.hdr.size); - if (size != msg.hdr.size) { + size = read(u->slave_fd, &payload, hdr.size); + if (size != hdr.size) { error_report("Failed to read payload from slave."); goto err; } - switch (msg.hdr.request) { + switch (hdr.request) { case VHOST_USER_SLAVE_IOTLB_MSG: - ret = vhost_backend_handle_iotlb_msg(dev, &msg.payload.iotlb); + ret = vhost_backend_handle_iotlb_msg(dev, &payload.iotlb); break; case VHOST_USER_SLAVE_CONFIG_CHANGE_MSG : ret = vhost_user_slave_handle_config_change(dev); @@ -692,15 +693,23 @@ static void slave_read(void *opaque) * REPLY_ACK feature handling. Other reply types has to be managed * directly in their request handlers. */ - if (msg.hdr.flags & VHOST_USER_NEED_REPLY_MASK) { - msg.hdr.flags &= ~VHOST_USER_NEED_REPLY_MASK; - msg.hdr.flags |= VHOST_USER_REPLY_MASK; + if (hdr.flags & VHOST_USER_NEED_REPLY_MASK) { + struct iovec iovec[2]; - msg.payload.u64 = !!ret; - msg.hdr.size = sizeof(msg.payload.u64); - size = write(u->slave_fd, &msg, VHOST_USER_HDR_SIZE + msg.hdr.size); - if (size != VHOST_USER_HDR_SIZE + msg.hdr.size) { + hdr.flags &= ~VHOST_USER_NEED_REPLY_MASK; + hdr.flags |= VHOST_USER_REPLY_MASK; + + payload.u64 = !!ret; + hdr.size = sizeof(payload.u64); + + iovec[0].iov_base = &hdr; + iovec[0].iov_len = VHOST_USER_HDR_SIZE; + iovec[1].iov_base = &payload; + iovec[1].iov_len = hdr.size; + + size = writev(u->slave_fd, iovec, ARRAY_SIZE(iovec)); + if (size != VHOST_USER_HDR_SIZE + hdr.size) { error_report("Failed to send msg reply to slave."); goto err; } -- MST