Re: [Qemu-devel] [PATCH] VMXNET3: initialize rx_ridx to eliminate compile warning

[Stefan Hajnoczi <stefanha@redhat.com>]

On Tue, Mar 26, 2013 at 10:24:06AM +0800, Wenchao Xia wrote:
>   Gcc report "hw/vmxnet3.c:972: error: ‘rx_ridx’ may be used
> uninitialized in this function", so fix it.
> 
> Signed-off-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
> ---
>  hw/vmxnet3.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/hw/vmxnet3.c b/hw/vmxnet3.c
> index 925be80..bdd256e 100644
> --- a/hw/vmxnet3.c
> +++ b/hw/vmxnet3.c
> @@ -969,7 +969,7 @@ vmxnet3_indicate_packet(VMXNET3State *s)
>      struct Vmxnet3_RxDesc rxd;
>      bool is_head = true;
>      uint32_t rxd_idx;
> -    uint32_t rx_ridx;
> +    uint32_t rx_ridx = 0;

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

This seems to be a gcc weakness in some versions.

No warnings here with gcc (GCC) 4.7.2 20121109 (Red Hat 4.7.2-8).

I manually checked the code and there is no path which can use
uninitialized rx_ridx:

static bool
vmxnet3_indicate_packet(VMXNET3State *s)
{
    struct Vmxnet3_RxDesc rxd;
    bool is_head = true;
    uint32_t rxd_idx;
    uint32_t rx_ridx;
[...]
    while (bytes_left > 0) {
[...]
        if (!vmxnet3_get_next_rx_descr(s, is_head, &rxd, &rxd_idx, &rx_ridx)) {
            break;
        }

rx_ridx is assigned by vmxnet3_get_next_rx_descr() unless it returns
false.

>From now on rx_ridx is initialized.

[...]
        rxcd.rqID = RXQ_IDX + rx_ridx * s->rxq_num;

Used here, fine since we initialized it above.

[...]
        VMW_RIPRN("RX Completion descriptor: rxRing: %lu rxIdx %lu len %lu "
                  "sop %d csum_correct %lu",
                  (unsigned long) rx_ridx,

Used here, fine since we initialized it above.

[...]
    }

Not used outside the while loop.