[EXT] Re: [PATCH] ring: compilation fix with GCC-12

[Amit Prakash Shukla]

> -----Original Message-----
> From: Amit Prakash Shukla <amitprakashs at marvell.com>
> Sent: Tuesday, August 23, 2022 3:08 PM
> To: Konstantin Ananyev <konstantin.v.ananyev at yandex.ru>; Honnappa
> Nagarahalli <Honnappa.Nagarahalli at arm.com>
> Cc: dev at dpdk.org; Jerin Jacob Kollanukkaran <jerinj at marvell.com>;
> stable at dpdk.org; nd <nd at arm.com>
> Subject: RE: [EXT] Re: [PATCH] ring: compilation fix with GCC-12
> 
> Thanks for the feedback. My apologies for delayed reply.
> 
> > -----Original Message-----
> > From: Konstantin Ananyev <konstantin.v.ananyev at yandex.ru>
> > Sent: Sunday, August 7, 2022 5:56 PM
> > To: Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com>; Amit
> Prakash
> > Shukla <amitprakashs at marvell.com>
> > Cc: dev at dpdk.org; Jerin Jacob Kollanukkaran <jerinj at marvell.com>;
> > stable at dpdk.org; nd <nd at arm.com>
> > Subject: [EXT] Re: [PATCH] ring: compilation fix with GCC-12
> >
> > External Email
> >
> > ----------------------------------------------------------------------
> > 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.
> 
> I agree. After having close look and doing few experiments, ideally it should
> not be going to __rte_ring_dequeue_elems_128().
> Sizeof(in call of rte_ring_dequeue_elem) gets evaluated at compile time
> which in this case it is evaluated to 8 bytes so
> __rte_ring_dequeue_elems_128() shall not be in the path. Looks like more
> of a gcc-12 bug.?
> 
> >
> > Another q - is this warning happens only on arm platforms?
> Warning is observed on x86 with build type as debug.
> "meson --werror --buildtype=debug build"
> 
> >
> > >
> > >>
> > >> 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
> > >