Re: [Qemu-devel] [PATCH 3/4] s390-ccw.img: Fix compile warning in s390 ccw virtio code

[Alexander Graf <agraf@suse.de>]

On 04/23/2013 01:23 PM, Christian Borntraeger wrote:
> Lets fix this gcc warning:
>
> virtio.c: In function ‘vring_send_buf’:
> virtio.c:125:35: error: operation on ‘vr->next_idx’ may be undefined
> [-Werror=sequence-point]
>
> Signed-off-by: Christian Borntraeger<borntraeger@de.ibm.com>
> ---
>   pc-bios/s390-ccw/virtio.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/pc-bios/s390-ccw/virtio.c b/pc-bios/s390-ccw/virtio.c
> index 79e2941..1968fc6 100644
> --- a/pc-bios/s390-ccw/virtio.c
> +++ b/pc-bios/s390-ccw/virtio.c
> @@ -122,7 +122,9 @@ static void vring_send_buf(struct vring *vr, void *p, int len, int flags)
>       vr->desc[vr->next_idx].addr = (ulong)p;
>       vr->desc[vr->next_idx].len = len;
>       vr->desc[vr->next_idx].flags = flags&  ~VRING_HIDDEN_IS_CHAIN;
> -    vr->desc[vr->next_idx].next = ++vr->next_idx;
> +    vr->desc[vr->next_idx].next = vr->next_idx;
> +    vr->desc[vr->next_idx].next++;
> +    vr->next_idx++;

Hrm. This looks a lot more complicated than it needs to. Why is gcc 
emitting a warning here? Maybe it only wants braces. Please try whether

.next = ++(vr->next_id);

works for you.


Alex