Re: [dpdk-dev] [PATCH v2 1/2] net/avp: fix gcc 10 maybe-uninitialized warning

[Kevin Traynor <ktraynor@redhat.com>]

On 12/03/2020 14:31, Ferruh Yigit wrote:
> On 3/12/2020 2:18 PM, Kevin Traynor wrote:
>> On 12/03/2020 13:25, Ferruh Yigit wrote:
>>> On 3/11/2020 11:32 AM, Kevin Traynor wrote:
>>>> gcc 10.0.1 reports:
>>>>
>>>> ../drivers/net/avp/avp_ethdev.c: In function ‘avp_xmit_scattered_pkts’:
>>>> ../drivers/net/avp/avp_ethdev.c:1791:24:
>>>> warning: ‘avp_bufs[count]’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>>>>  1791 |   tx_bufs[i] = avp_bufs[count];
>>>>       |                ~~~~~~~~^~~~~~~
>>>> ../drivers/net/avp/avp_ethdev.c:1791:24:
>>>> warning: ‘avp_bufs[count]’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>>>>
>>>> Fix by intializing the array.
>>>>
>>>> Fixes: 295abce2d25b ("net/avp: add packet transmit functions")
>>>> Cc: stable@dpdk.org
>>>>
>>>> Signed-off-by: Kevin Traynor <ktraynor@redhat.com>
>>>> ---
>>>> v2: no change
>>>>
>>>> note, commit log violates line length but I didn't want to split warning msg.
>>>>
>>>> Cc: allain.legacy@windriver.com
>>>> Cc: Steven Webster <steven.webster@windriver.com>
>>>> Cc: Matt Peters <matt.peters@windriver.com>
>>>> ---
>>>>  drivers/net/avp/avp_ethdev.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/net/avp/avp_ethdev.c b/drivers/net/avp/avp_ethdev.c
>>>> index cd747b6be..1abe96ce5 100644
>>>> --- a/drivers/net/avp/avp_ethdev.c
>>>> +++ b/drivers/net/avp/avp_ethdev.c
>>>> @@ -1695,5 +1695,5 @@ avp_xmit_scattered_pkts(void *tx_queue,
>>>>  {
>>>>  	struct rte_avp_desc *avp_bufs[(AVP_MAX_TX_BURST *
>>>> -				       RTE_AVP_MAX_MBUF_SEGMENTS)];
>>>> +				       RTE_AVP_MAX_MBUF_SEGMENTS)] = {};
>>>>  	struct avp_queue *txq = (struct avp_queue *)tx_queue;
>>>>  	struct rte_avp_desc *tx_bufs[AVP_MAX_TX_BURST];
>>>>
>>>
>>> Isn't this a false positive, can there be any case 'avp_bufs[]' used
>>> uninitialized? Or am I missing something.
>>>
>>
>> I presume it's because it's not being initialized in the fn and there is
>> some paths in fn's it's passed to that don't initialize it. Of course in
>> practice with "normal" values this might not happen.
> 
> 'avp_fifo_get(alloc_q, (void **)&avp_bufs, segments);' initializes it, and I am
> not just talking about 'normal' case, I don't see any case that 'avp_bufs[]'
> used uninitialized, can you see any?
> 

Well, it's initialization there is dependent on not hitting the first
return and the loop executing.

>>
>>> If this is false positive, does it worth to report to issue to gcc?
>>>
>>
>