Re: [PATCH v2] vhost: fix build

[zhoumin <zhoumin@loongson.cn>]

Hi Chenbo,


On Mon, 26 Sep 2022, 10:57, Xia, Chenbo wrote:
> Hi Min,
>
>> -----Original Message-----
>> From: Min Zhou <zhoumin@loongson.cn>
>> Sent: Monday, August 29, 2022 4:29 PM
>> To: david.marchand@redhat.com; maxime.coquelin@redhat.com; Xia, Chenbo
>> <chenbo.xia@intel.com>; zhoumin@loongson.cn
>> Cc: dev@dpdk.org; maobibo@loongson.cn
>> Subject: [PATCH v2] vhost: fix build
>>
>> On CentOS 8 or Debian 10.4 systems using gcc 12.1 to cross
>> compile DPDK, gcc shows a following warning which will cause
>> build to fail when build is run with -werror:
>>
>> In function 'mbuf_to_desc',
>>      inlined from 'vhost_enqueue_async_packed'
>> at ../lib/vhost/virtio_net.c:1826:6,
>>      inlined from 'virtio_dev_rx_async_packed'
>> at ../lib/vhost/virtio_net.c:1840:6,
>>      inlined from 'virtio_dev_rx_async_submit_packed.constprop'
>> at ../lib/vhost/virtio_net.c:1900:7:
>> ../lib/vhost/virtio_net.c:1161:35: error: 'buf_vec[0].buf_len' may be used
>> uninitialized [-Werror=maybe-uninitialized]
>>   1161 |         buf_len = buf_vec[vec_idx].buf_len;
>>        |                   ~~~~~~~~~~~~~~~~^~~~~~~~
>> ../lib/vhost/virtio_net.c: In function
>> 'virtio_dev_rx_async_submit_packed.constprop':
>> ../lib/vhost/virtio_net.c:1838:27: note: 'buf_vec' declared here
>>   1838 |         struct buf_vector buf_vec[BUF_VECTOR_MAX];
>>        |                           ^~~~~~~
>> cc1: all warnings being treated as errors
>>
>> Actually, there are eight places to see the same codes in the file
>> lib/vhost/virtio_net.c, and all these `buf_vec` arraies are
>> initialized by sub-function calls under various conditions.
>>
>> Although It's hard to understand why gcc just emits warning at one
>> of the eight places, adding validity checks for array length is
>> reasonable and can also fix the warning.
>>
>> Signed-off-by: David Marchand <david.marchand@redhat.com>
>> Signed-off-by: Min Zhou <zhoumin@loongson.cn>
>> ---
>>   lib/vhost/virtio_net.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
> Just want you to know that your patch is still pending because by accident
> your fix is almost the same as a previous patch that fixes a real issue but
> that patch is still in progress:
>
> http://patchwork.dpdk.org/project/dpdk/patch/20220802004938.23670-2-cfontana@suse.de/
>
> Thanks,
> Chenbo

Thanks for your helpful reply.
I think I can drop this patch if the patch you mentioned above could be 
accepted.

Thanks,
Min Zhou
>> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
>> index 35fa4670fd..99233f1759 100644
>> --- a/lib/vhost/virtio_net.c
>> +++ b/lib/vhost/virtio_net.c
>> @@ -1153,7 +1153,7 @@ mbuf_to_desc(struct virtio_net *dev, struct
>> vhost_virtqueue *vq,
>>   	struct virtio_net_hdr_mrg_rxbuf tmp_hdr, *hdr = NULL;
>>   	struct vhost_async *async = vq->async;
>>
>> -	if (unlikely(m == NULL))
>> +	if (unlikely(m == NULL || nr_vec == 0))
>>   		return -1;
>>
>>   	buf_addr = buf_vec[vec_idx].buf_addr;
>> @@ -2673,6 +2673,9 @@ desc_to_mbuf(struct virtio_net *dev, struct
>> vhost_virtqueue *vq,
>>   	struct vhost_async *async = vq->async;
>>   	struct async_inflight_info *pkts_info;
>>
>> +	if (unlikely(nr_vec == 0))
>> +		return -1;
>> +
>>   	buf_addr = buf_vec[vec_idx].buf_addr;
>>   	buf_iova = buf_vec[vec_idx].buf_iova;
>>   	buf_len = buf_vec[vec_idx].buf_len;
>> --
>> 2.31.1