virtio-scsi: Fix build with gcc 9

[Qemu-devel] [PATCH] virtio-scsi: Fix build with gcc 9

Posted by Greg Kurz 6 years, 8 months ago

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>
---
 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:

Re: [Qemu-devel] [PATCH] virtio-scsi: Fix build with gcc 9

Posted by Peter Maydell 6 years, 8 months ago

On Thu, 28 Feb 2019 at 17:59, Greg Kurz <groug@kaod.org> 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 <groug@kaod.org>
> ---
>  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 <peter.maydell@linaro.org>

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

Re: [Qemu-devel] [PATCH] virtio-scsi: Fix build with gcc 9

Posted by Paolo Bonzini 6 years, 8 months ago

On 28/02/19 19:31, Peter Maydell wrote:
> On Thu, 28 Feb 2019 at 17:59, Greg Kurz <groug@kaod.org> 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 <groug@kaod.org>
>> ---
>>  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 <peter.maydell@linaro.org>
> 
> 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...

Applied, thanks.

Paolo