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

["Wang, Yipeng1" <yipeng1.wang@intel.com>]

> -----Original Message-----
> From: Kevin Traynor <ktraynor@redhat.com>
> Sent: Friday, May 15, 2020 12:18 PM
> To: Wang, Yipeng1 <yipeng1.wang@intel.com>; dev@dpdk.org; 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; stable@dpdk.org
> Subject: Re: [PATCH] hash: fix gcc 10 maybe-uninitialized warning
> 
> 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
[Wang, Yipeng] I see your point now. Thanks for explaining and I think it makes sense to distinguish these two.
I guess it just came from my own aesthetic preference.
and I don’t have the best coding style : )

> 
> >>  		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>
> >