From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:39422)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@redhat.com>) id 1UKPzH-0007Jh-Jh
	for qemu-devel@nongnu.org; Tue, 26 Mar 2013 05:16:14 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <stefanha@redhat.com>) id 1UKPzE-0004zt-MT
	for qemu-devel@nongnu.org; Tue, 26 Mar 2013 05:16:11 -0400
Received: from mx1.redhat.com ([209.132.183.28]:50775)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@redhat.com>) id 1UKPzE-0004zm-EM
	for qemu-devel@nongnu.org; Tue, 26 Mar 2013 05:16:08 -0400
Date: Tue, 26 Mar 2013 10:16:03 +0100
From: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20130326091603.GC17648@stefanha-thinkpad.redhat.com>
References: <1364264646-27542-1-git-send-email-xiawenc@linux.vnet.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <1364264646-27542-1-git-send-email-xiawenc@linux.vnet.ibm.com>
Content-Transfer-Encoding: quoted-printable
Subject: Re: [Qemu-devel] [PATCH] VMXNET3: initialize rx_ridx to eliminate
	compile warning
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
Cc: dmitry@daynix.com, yan@daynix.com, Anthony Liguori <aliguori@us.ibm.com>, qemu-devel@nongnu.org

On Tue, Mar 26, 2013 at 10:24:06AM +0800, Wenchao Xia wrote:
>   Gcc report "hw/vmxnet3.c:972: error: =E2=80=98rx_ridx=E2=80=99 may be=
 used
> uninitialized in this function", so fix it.
>=20
> Signed-off-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
> ---
>  hw/vmxnet3.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>=20
> 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 =3D true;
>      uint32_t rxd_idx;
> -    uint32_t rx_ridx;
> +    uint32_t rx_ridx =3D 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 =3D 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_ri=
dx)) {
            break;
        }

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

>>From now on rx_ridx is initialized.

[...]
        rxcd.rqID =3D 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 %l=
u "
                  "sop %d csum_correct %lu",
                  (unsigned long) rx_ridx,

Used here, fine since we initialized it above.

[...]
    }

Not used outside the while loop.