[PATCH] ring: compilation fix with GCC-12

[Konstantin Ananyev]

06/08/2022 19:35, Honnappa Nagarahalli пишет:
> <snip>
> 
>>
>> GCC 12 raises the following warning:
>>
>> In function '__rte_ring_dequeue_elems_128',
>>      inlined from '__rte_ring_dequeue_elems' at
>> 		../lib/ring/rte_ring_elem_pvt.h:262:3,
>>      inlined from '__rte_ring_do_hts_dequeue_elem' at
>> 		../lib/ring/rte_ring_hts_elem_pvt.h:237:3,
>>      inlined from 'rte_ring_mc_hts_dequeue_bulk_elem' at
>> 		../lib/ring/rte_ring_hts.h:83:9,
>>      inlined from 'rte_ring_dequeue_bulk_elem' at
>> 		../lib/ring/rte_ring_elem.h:391:10,
>>      inlined from 'rte_ring_dequeue_elem' at
>> 		../lib/ring/rte_ring_elem.h:476:9,
>>      inlined from 'rte_ring_dequeue' at
>> 		../lib/ring/rte_ring.h:463:9,
>>      inlined from 'rxa_intr_ring_dequeue' at
>> 		../lib/eventdev/rte_event_eth_rx_adapter.c:1196:10:
>> ../lib/ring/rte_ring_elem_pvt.h:234:25: error: 'memcpy' writing
>> 	32 bytes into a region of size 8 overflows the destination
>> 	[-Werror=stringop-overflow=]
>>    234 |    memcpy((void *)(obj + i), (void *)(ring + idx), 32);
>>        |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> Replacing memcpy with rte_memcpy fixes the GCC-12 compilation issue.
> Any reason why this replacement fixes the problem?
> Do you have any performance numbers with this change?
> 
>> Also it would be better to change to rte_memcpy as the function is called in
>> fastpath.
> On Arm platforms, memcpy in the later versions has the best performance.

I agree with Honnappa, it is better to keep memcpy() here.
Actually what is strange - why it ends up in 
__rte_ring_dequeue_elems_128() at all?
Inside rxa_intr_ring_dequeue() we clearly doing: rte_ring_dequeue(),
which should boil down to ___rte_ring_dequeue_elems_64().
it should go to __rte_ring_dequeue_elems_128() at all.

Another q - is this warning happens only on arm platforms?

> 
>>
>> Bugzilla ID: 1062
>> Fixes: 1fc73390bcf5 ("ring: refactor exported headers")
>> Cc: stable at dpdk.org
>>
>> Signed-off-by: Amit Prakash Shukla <amitprakashs at marvell.com>
>> ---
>>   lib/ring/rte_ring_elem_pvt.h | 18 ++++++++++--------
>>   1 file changed, 10 insertions(+), 8 deletions(-)
>>
>> diff --git a/lib/ring/rte_ring_elem_pvt.h b/lib/ring/rte_ring_elem_pvt.h index
>> 83788c56e6..3d85b13333 100644
>> --- a/lib/ring/rte_ring_elem_pvt.h
>> +++ b/lib/ring/rte_ring_elem_pvt.h
>> @@ -10,6 +10,8 @@
>>   #ifndef _RTE_RING_ELEM_PVT_H_
>>   #define _RTE_RING_ELEM_PVT_H_
>>
>> +#include <rte_memcpy.h>
>> +
>>   static __rte_always_inline void
>>   __rte_ring_enqueue_elems_32(struct rte_ring *r, const uint32_t size,
>>   		uint32_t idx, const void *obj_table, uint32_t n) @@ -97,20
>> +99,20 @@ __rte_ring_enqueue_elems_128(struct rte_ring *r, uint32_t
>> prod_head,
>>   	const rte_int128_t *obj = (const rte_int128_t *)obj_table;
>>   	if (likely(idx + n <= size)) {
>>   		for (i = 0; i < (n & ~0x1); i += 2, idx += 2)
>> -			memcpy((void *)(ring + idx),
>> +			rte_memcpy((void *)(ring + idx),
>>   				(const void *)(obj + i), 32);
>>   		switch (n & 0x1) {
>>   		case 1:
>> -			memcpy((void *)(ring + idx),
>> +			rte_memcpy((void *)(ring + idx),
>>   				(const void *)(obj + i), 16);
>>   		}
>>   	} else {
>>   		for (i = 0; idx < size; i++, idx++)
>> -			memcpy((void *)(ring + idx),
>> +			rte_memcpy((void *)(ring + idx),
>>   				(const void *)(obj + i), 16);
>>   		/* Start at the beginning */
>>   		for (idx = 0; i < n; i++, idx++)
>> -			memcpy((void *)(ring + idx),
>> +			rte_memcpy((void *)(ring + idx),
>>   				(const void *)(obj + i), 16);
>>   	}
>>   }
>> @@ -231,17 +233,17 @@ __rte_ring_dequeue_elems_128(struct rte_ring *r,
>> uint32_t prod_head,
>>   	rte_int128_t *obj = (rte_int128_t *)obj_table;
>>   	if (likely(idx + n <= size)) {
>>   		for (i = 0; i < (n & ~0x1); i += 2, idx += 2)
>> -			memcpy((void *)(obj + i), (void *)(ring + idx), 32);
>> +			rte_memcpy((void *)(obj + i), (void *)(ring + idx), 32);
>>   		switch (n & 0x1) {
>>   		case 1:
>> -			memcpy((void *)(obj + i), (void *)(ring + idx), 16);
>> +			rte_memcpy((void *)(obj + i), (void *)(ring + idx), 16);
>>   		}
>>   	} else {
>>   		for (i = 0; idx < size; i++, idx++)
>> -			memcpy((void *)(obj + i), (void *)(ring + idx), 16);
>> +			rte_memcpy((void *)(obj + i), (void *)(ring + idx), 16);
>>   		/* Start at the beginning */
>>   		for (idx = 0; i < n; i++, idx++)
>> -			memcpy((void *)(obj + i), (void *)(ring + idx), 16);
>> +			rte_memcpy((void *)(obj + i), (void *)(ring + idx), 16);
>>   	}
>>   }
>>
>> --
>> 2.25.1
>