Re: [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: sta...@dpdk.org

Signed-off-by: Amit Prakash Shukla <amitpraka...@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