Re: [PATCH] vhost: fix compilation issue in async path

[David Marchand <david.marchand@redhat.com>]

On Wed, Oct 5, 2022 at 4:49 PM Maxime Coquelin
<maxime.coquelin@redhat.com> wrote:
>
> This patch fixes a compilation issue met with GCC on

GCC 12 (it is worth detailing, since I and Thomas hit the same issue
on some other cross compiling toolchains using GCC 12).

> Loongarch64:

LoongArch64

>
> In function ‘mbuf_to_desc’,
>     inlined from ‘vhost_enqueue_async_packed’ at ../../../dpdk/lib/vhost/virtio_net.c:1822:6,
>     inlined from ‘virtio_dev_rx_async_packed’ at ../../../dpdk/lib/vhost/virtio_net.c:1836:6,
>     inlined from ‘virtio_dev_rx_async_submit_packed’ at ../../../dpdk/lib/vhost/virtio_net.c:1895:7:
> ../../../dpdk/lib/vhost/virtio_net.c:1159:18: error: ‘buf_vec[0].buf_addr’ may be used uninitialized [-Werror=maybe-uninitialized]
>  1159 |         buf_addr = buf_vec[vec_idx].buf_addr;
>       |         ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../../../dpdk/lib/vhost/virtio_net.c: In function ‘virtio_dev_rx_async_submit_packed’:
> ../../../dpdk/lib/vhost/virtio_net.c:1834:27: note: ‘buf_vec’ declared here
>  1834 |         struct buf_vector buf_vec[BUF_VECTOR_MAX];
>       |                           ^~~~~~~
>
> It happens because the compiler assumes that 'size'
> variable in vhost_enqueue_async_packed could wrap to 0 since
> 'size' is uint32_t and pkt->pkt_len too.
>
> In practice, it would never happen since 'pkt->pkt_len' is
> unlikely to be close to UINT32_MAX, but let's just change
> 'size' to uint64_t to make the compiler happy without
> having to add runtime checks.
>
> Fixes: 873e8dad6f49 ("vhost: support packed ring in async datapath")
> Cc: stable@dpdk.org
>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>


-- 
David Marchand