[Qemu-devel] [PULL v2 11/31] virtio-scsi: Fix build with gcc 9

[Paolo Bonzini <pbonzini@redhat.com>]

From: Greg Kurz <groug@kaod.org>

Build fails with gcc 9:

  CC      ppc64-softmmu/hw/scsi/virtio-scsi.o
hw/scsi/virtio-scsi.c: In function ‘virtio_scsi_do_tmf’:
hw/scsi/virtio-scsi.c:265:39: error: taking address of packed member of ‘struct virtio_scsi_ctrl_tmf_req’ may result in an unaligned pointer value [-Werror=address-of-packed-member]
  265 |     virtio_tswap32s(VIRTIO_DEVICE(s), &req->req.tmf.subtype);
      |                                       ^~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

All the fields in struct virtio_scsi_ctrl_tmf_req are naturally aligned,
so we could in theory drop QEMU_PACKED. Unfortunately, the header file
is imported from linux which already has the packed attribute. Trying to
fix that in the update-linux-headers.sh script is likely to produce
ugliness. Turn the call to virtio_tswap32s() into an assignment instead.

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <155137678223.44753.5438092367451176318.stgit@bahia.lan>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/scsi/virtio-scsi.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index ce99d28..839f120 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -262,7 +262,13 @@ static int virtio_scsi_do_tmf(VirtIOSCSI *s, VirtIOSCSIReq *req)
     /* Here VIRTIO_SCSI_S_OK means "FUNCTION COMPLETE".  */
     req->resp.tmf.response = VIRTIO_SCSI_S_OK;
 
-    virtio_tswap32s(VIRTIO_DEVICE(s), &req->req.tmf.subtype);
+    /*
+     * req->req.tmf has the QEMU_PACKED attribute. Don't use virtio_tswap32s()
+     * to avoid compiler errors.
+     */
+    req->req.tmf.subtype =
+        virtio_tswap32(VIRTIO_DEVICE(s), req->req.tmf.subtype);
+
     switch (req->req.tmf.subtype) {
     case VIRTIO_SCSI_T_TMF_ABORT_TASK:
     case VIRTIO_SCSI_T_TMF_QUERY_TASK:
-- 
1.8.3.1