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Re: [Qemu-devel] [PATCH] virtio-scsi: Fix build with gcc 9
From: |
Peter Maydell |
Subject: |
Re: [Qemu-devel] [PATCH] virtio-scsi: Fix build with gcc 9 |
Date: |
Thu, 28 Feb 2019 18:31:34 +0000 |
On Thu, 28 Feb 2019 at 17:59, Greg Kurz <address@hidden> wrote:
>
> 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 <address@hidden>
> ---
> 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 ce99d288b035..839f1202567d 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:
Reviewed-by: Peter Maydell <address@hidden>
I haven't generally bothered to add comments about packed
structs when I've switched away from the *s versions of byteswap
functions, but it doesn't hurt.
We should consider just replacing the other dozen uses
of virtio_tswap*s() with the non-s versions and dropping the
s functions entirely...
thanks
-- PMM