Re: [dpdk-dev] [PATCH] hash: fix gcc 10 maybe-uninitialized warning

[Kevin Traynor <ktraynor@redhat.com>]

On 15/05/2020 20:06, Wang, Yipeng1 wrote:
>> -----Original Message-----
>> From: Kevin Traynor <ktraynor@redhat.com>
>> Sent: Friday, May 15, 2020 7:28 AM
>> To: dev@dpdk.org; Wang, Yipeng1 <yipeng1.wang@intel.com>; Gobriel,
>> Sameh <sameh.gobriel@intel.com>; Richardson, Bruce
>> <bruce.richardson@intel.com>
>> Cc: honnappa.nagarahalli@arm.com; Yigit, Ferruh <ferruh.yigit@intel.com>;
>> david.marchand@redhat.com; Kevin Traynor <ktraynor@redhat.com>;
>> stable@dpdk.org
>> Subject: [PATCH] hash: fix gcc 10 maybe-uninitialized warning
>>
>> gcc 10.1.1 reports a warning for the ext_bkt_id variable:
>>
>> ../lib/librte_hash/rte_cuckoo_hash.c:
>> In function ‘__rte_hash_add_key_with_hash’:
>> ../lib/librte_hash/rte_cuckoo_hash.c:1104:29:
>> warning: ‘ext_bkt_id’ may be used uninitialized in this function [-Wmaybe-
>> uninitialized]
>>  1104 |  (h->buckets_ext[ext_bkt_id - 1]).sig_current[0] = short_sig;
>>       |                  ~~~~~~~~~~~^~~
>>
>> The return value of rte_ring_sc_dequeue_elem() is already checked, but
>> also initialize ext_bkt_id to zero (invalid value) and check that it also
>> overwritten.
>>
>> Fixes: fbfe568103b0 ("hash: use 32-bit elements rings to save memory")
>> Cc: stable@dpdk.org
>>
>> Signed-off-by: Kevin Traynor <ktraynor@redhat.com>
>> ---
>>  lib/librte_hash/rte_cuckoo_hash.c | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/lib/librte_hash/rte_cuckoo_hash.c
>> b/lib/librte_hash/rte_cuckoo_hash.c
>> index 38767a8a1..90cb99b0e 100644
>> --- a/lib/librte_hash/rte_cuckoo_hash.c
>> +++ b/lib/librte_hash/rte_cuckoo_hash.c
>> @@ -940,6 +940,6 @@ __rte_hash_add_key_with_hash(const struct
>> rte_hash *h, const void *key,
>>  	struct rte_hash_bucket *prim_bkt, *sec_bkt, *cur_bkt;
>>  	struct rte_hash_key *new_k, *keys = h->key_store;
>> +	uint32_t ext_bkt_id = 0;
>>  	uint32_t slot_id;
>> -	uint32_t ext_bkt_id;
>>  	int ret;
>>  	unsigned n_slots;
>> @@ -1096,5 +1096,6 @@ __rte_hash_add_key_with_hash(const struct
>> rte_hash *h, const void *key,
>>  	 */
>>  	if (rte_ring_sc_dequeue_elem(h->free_ext_bkts, &ext_bkt_id,
>> -						sizeof(uint32_t)) != 0) {
>> +						sizeof(uint32_t)) != 0 ||
>> +					ext_bkt_id == 0) {
> [Wang, Yipeng] 
> If convenient, it would be better to make the two lines aligned with same indent...
> 

Hi Yipeng, I had checked the coding style [1] about this and I think
it's correct as 'sizeof..' is a wrap from the first condition so gets a
second tab to indicate that, whereas 'ext_bkt_id..' is the second
condition with no wrap. Fine to change it, if I interpret incorrectly.

[1] third bullet,
http://doc.dpdk.org/guides/contributing/coding_style.html#general

>>  		ret = -ENOSPC;
>>  		goto failure;
>> --
>> 2.21.3
> [Wang, Yipeng] 
> Thanks for the fix. I think It is also better code in general.
> 
> Acked-by: Yipeng Wang <yipeng1.wang@intel.com>
>