Re: [RFC 1/8] net/ena: fix warnings related to rte_memcpy and gcc-12

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 8 Jun 2022 14:29:58 +0200
Michał Krawczyk <mk@semihalf.com> wrote:

> wt., 7 cze 2022 o 19:17 Stephen Hemminger <stephen@networkplumber.org>
> napisał(a):
> >
> > Rte_memcpy is not needed for small objects only used on control
> > path. Regular memcpy is as fast or faster and there is more
> > robust since static analysis etc knows what it does.
> >
> > In this driver it was redefining all memcpy as rte_memcpy
> > which is even worse.  
> 
> Hi Stephen,
> 
> I would like to shed some light on why we're redefining all the memcpy
> as rte_memcpy. The ENA HAL is unmodifiable, as it's shared across many
> platforms and we cannot simply adjust it for the DPDK. We can use the
> ena_plat_dpdk.h to change the ena_com (HAL) definitions, and that's
> what we're doing with memcpy. It's being used on the data path for the
> Tx, to copy the bounce buffers. Following the recommendations in [1]
> plus the results from [2], we wanted to make use of the optimized
> memcpy on the ENA's data path as well to reduce the CPU time spent in
> the PMD. I'm worried that removing rte_memcpy from the ena_plat_dpdk.h
> will result in some performance degradation for the ENA data path.
> However I understand your concerns for the control path and I'm ok
> with it.
> 
> [1] https://doc.dpdk.org/guides/prog_guide/writing_efficient_code.html#memory
> [2] https://www.intel.com/content/www/us/en/developer/articles/technical/performance-optimization-of-memcpy-in-dpdk.html
> 
> Thanks,
> Michal
> 


I admit to having little sympathy unfixable for base/ style code.
You could have just replaced memcpy() in their with an abstraction layer
like other drivers.

The full gcc-12 warnings are:

913/2989] Compiling C object drivers/libtmp_rte_net_ena.a.p/net_ena_ena_rss.c.o
In file included from /usr/lib/gcc/x86_64-linux-gnu/12/include/immintrin.h:43,
                 from /usr/lib/gcc/x86_64-linux-gnu/12/include/x86intrin.h:32,
                 from ../lib/eal/x86/include/rte_vect.h:31,
                 from ../lib/eal/x86/include/rte_memcpy.h:17,
                 from ../lib/mempool/rte_mempool.h:46,
                 from ../lib/mbuf/rte_mbuf.h:38,
                 from ../lib/net/rte_ether.h:22,
                 from ../drivers/net/ena/ena_ethdev.h:10,
                 from ../drivers/net/ena/ena_rss.c:6:
In function ‘_mm256_loadu_si256’,
    inlined from ‘rte_mov32’ at ../lib/eal/x86/include/rte_memcpy.h:346:9,
    inlined from ‘rte_mov128’ at ../lib/eal/x86/include/rte_memcpy.h:369:2,
    inlined from ‘rte_memcpy_generic’ at ../lib/eal/x86/include/rte_memcpy.h:445:4,
    inlined from ‘rte_memcpy’ at ../lib/eal/x86/include/rte_memcpy.h:853:10,
    inlined from ‘ena_rss_key_fill’ at ../drivers/net/ena/ena_rss.c:62:2:
/usr/lib/gcc/x86_64-linux-gnu/12/include/avxintrin.h:929:10: warning: array subscript ‘__m256i_u[1]’ is partly outside array bounds of ‘uint8_t[40]’ {aka ‘unsigned char[40]’} [-Warray-bounds]
  929 |   return *__P;
      |          ^~~~
../drivers/net/ena/ena_rss.c: In function ‘ena_rss_key_fill’:
../drivers/net/ena/ena_rss.c:51:24: note: at offset 32 into object ‘default_key’ of size 40
   51 |         static uint8_t default_key[ENA_HASH_KEY_SIZE];
      |                        ^~~~~~~~~~~
In function ‘_mm256_loadu_si256’,
    inlined from ‘rte_mov32’ at ../lib/eal/x86/include/rte_memcpy.h:346:9,
    inlined from ‘rte_mov128’ at ../lib/eal/x86/include/rte_memcpy.h:370:2,
    inlined from ‘rte_memcpy_generic’ at ../lib/eal/x86/include/rte_memcpy.h:445:4,
    inlined from ‘rte_memcpy’ at ../lib/eal/x86/include/rte_memcpy.h:853:10,
    inlined from ‘ena_rss_key_fill’ at ../drivers/net/ena/ena_rss.c:62:2:
/usr/lib/gcc/x86_64-linux-gnu/12/include/avxintrin.h:929:10: warning: array subscript 2 is outside array bounds of ‘uint8_t[40]’ {aka ‘unsigned char[40]’} [-Warray-bounds]
  929 |   return *__P;
      |          ^~~~
../drivers/net/ena/ena_rss.c: In function ‘ena_rss_key_fill’:
../drivers/net/ena/ena_rss.c:51:24: note: at offset 64 into object ‘default_key’ of size 40
   51 |         static uint8_t default_key[ENA_HASH_KEY_SIZE];
      |                        ^~~~~~~~~~~
In function ‘_mm256_loadu_si256’,
    inlined from ‘rte_mov32’ at ../lib/eal/x86/include/rte_memcpy.h:346:9,
    inlined from ‘rte_mov128’ at ../lib/eal/x86/include/rte_memcpy.h:371:2,
    inlined from ‘rte_memcpy_generic’ at ../lib/eal/x86/include/rte_memcpy.h:445:4,
    inlined from ‘rte_memcpy’ at ../lib/eal/x86/include/rte_memcpy.h:853:10,
    inlined from ‘ena_rss_key_fill’ at ../drivers/net/ena/ena_rss.c:62:2:
/usr/lib/gcc/x86_64-linux-gnu/12/include/avxintrin.h:929:10: warning: array subscript 3 is outside array bounds of ‘uint8_t[40]’ {aka ‘unsigned char[40]’} [-Warray-bounds]
  929 |   return *__P;
      |          ^~~~
../drivers/net/ena/ena_rss.c: In function ‘ena_rss_key_fill’:
../drivers/net/ena/ena_rss.c:51:24: note: at offset 96 into object ‘default_key’ of size 40
   51 |         static uint8_t default_key[ENA_HASH_KEY_SIZE];
      |                        ^~~~~~~~~~~
In function ‘_mm256_loadu_si256’,
    inlined from ‘rte_mov32’ at ../lib/eal/x86/include/rte_memcpy.h:346:9,
    inlined from ‘rte_mov64’ at ../lib/eal/x86/include/rte_memcpy.h:358:2,
    inlined from ‘rte_memcpy_generic’ at ../lib/eal/x86/include/rte_memcpy.h:452:4,
    inlined from ‘rte_memcpy’ at ../lib/eal/x86/include/rte_memcpy.h:853:10,
    inlined from ‘ena_rss_key_fill’ at ../drivers/net/ena/ena_rss.c:62:2:
/usr/lib/gcc/x86_64-linux-gnu/12/include/avxintrin.h:929:10: warning: array subscript ‘__m256i_u[1]’ is partly outside array bounds of ‘const void[40]’ [-Warray-bounds]
  929 |   return *__P;
      |          ^~~~
../drivers/net/ena/ena_rss.c: In function ‘ena_rss_key_fill’:
../drivers/net/ena/ena_rss.c:51:24: note: at offset 32 into object ‘default_key’ of size 40
   51 |         static uint8_t default_key[ENA_HASH_KEY_SIZE];
      |                        ^~~~~~~~~~~
../drivers/net/ena/ena_rss.c:51:24: note: at offset [33, 40] into object ‘default_key’ of size 40
../drivers/net/ena/ena_rss.c:51:24: note: at offset 160 into object ‘default_key’ of size 40
../drivers/net/ena/ena_rss.c:51:24: note: at offset 32 into object ‘default_key’ of size 40
In function ‘_mm256_loadu_si256’,
    inlined from ‘rte_mov32’ at ../lib/eal/x86/include/rte_memcpy.h:346:9,
    inlined from ‘rte_memcpy_generic’ at ../lib/eal/x86/include/rte_memcpy.h:457:4,
    inlined from ‘rte_memcpy’ at ../lib/eal/x86/include/rte_memcpy.h:853:10,
    inlined from ‘ena_rss_key_fill’ at ../drivers/net/ena/ena_rss.c:62:2:
/usr/lib/gcc/x86_64-linux-gnu/12/include/avxintrin.h:929:10: warning: array subscript [2, 288230376151711745] is outside array bounds of ‘const void[40]’ [-Warray-bounds]
  929 |   return *__P;
      |          ^~~~
../drivers/net/ena/ena_rss.c: In function ‘ena_rss_key_fill’:
../drivers/net/ena/ena_rss.c:51:24: note: object ‘default_key’ of size 40
   51 |         static uint8_t default_key[ENA_HASH_KEY_SIZE];
      |                        ^~~~~~~~~~~
../drivers/net/ena/ena_rss.c:51:24: note: at offset [1, 40] into object ‘default_key’ of size 40
../drivers/net/ena/ena_rss.c:51:24: note: at offset [128, 192] into object ‘default_key’ of size 40
../drivers/net/ena/ena_rss.c:51:24: note: object ‘default_key’ of size 40
../drivers/net/ena/ena_rss.c:51:24: note: at offset [1, 40] into object ‘default_key’ of size 40
../drivers/net/ena/ena_rss.c:51:24: note: at offset [128, 192] into object ‘default_key’ of size 40
../drivers/net/ena/ena_rss.c:51:24: note: object ‘default_key’ of size 40
In function ‘_mm256_loadu_si256’,
    inlined from ‘rte_mov32’ at ../lib/eal/x86/include/rte_memcpy.h:346:9,
    inlined from ‘rte_memcpy_generic’ at ../lib/eal/x86/include/rte_memcpy.h:458:4,
    inlined from ‘rte_memcpy’ at ../lib/eal/x86/include/rte_memcpy.h:853:10,
    inlined from ‘ena_rss_key_fill’ at ../drivers/net/ena/ena_rss.c:62:2:
/usr/lib/gcc/x86_64-linux-gnu/12/include/avxintrin.h:929:10: warning: array subscript [2, 288230376151711746] is outside array bounds of ‘const void[40]’ [-Warray-bounds]
  929 |   return *__P;
      |          ^~~~
../drivers/net/ena/ena_rss.c: In function ‘ena_rss_key_fill’:
../drivers/net/ena/ena_rss.c:51:24: note: at offset [1, 40] into object ‘default_key’ of size 40
   51 |         static uint8_t default_key[ENA_HASH_KEY_SIZE];
      |                        ^~~~~~~~~~~
../drivers/net/ena/ena_rss.c:51:24: note: at offset [2, 40] into object ‘default_key’ of size 40
../drivers/net/ena/ena_rss.c:51:24: note: at offset [129, 193] into object ‘default_key’ of size 40
../drivers/net/ena/ena_rss.c:51:24: note: at offset [1, 40] into object ‘default_key’ of size 40
../drivers/net/ena/ena_rss.c:51:24: note: at offset [2, 40] into object ‘default_key’ of size 40
../drivers/net/ena/ena_rss.c:51:24: note: at offset [129, 193] into object ‘default_key’ of size 40
../drivers/net/ena/ena_rss.c:51:24: note: at offset [1, 40] into object ‘default_key’ of size 40
In function ‘_mm256_loadu_si256’,
    inlined from ‘rte_mov32’ at ../lib/eal/x86/include/rte_memcpy.h:346:9,
    inlined from ‘rte_memcpy_generic’ at ../lib/eal/x86/include/rte_memcpy.h:438:3,
    inlined from ‘rte_memcpy’ at ../lib/eal/x86/include/rte_memcpy.h:853:10,
    inlined from ‘ena_rss_key_fill’ at ../drivers/net/ena/ena_rss.c:62:2:
/usr/lib/gcc/x86_64-linux-gnu/12/include/avxintrin.h:929:10: warning: array subscript ‘__m256i_u[0]’ is partly outside array bounds of ‘uint8_t[40]’ {aka ‘unsigned char[40]’} [-Warray-bounds]
  929 |   return *__P;
      |          ^~~~
../drivers/net/ena/ena_rss.c: In function ‘ena_rss_key_fill’:
../drivers/net/ena/ena_rss.c:51:24: note: at offset [17, 32] into object ‘default_key’ of size 40
   51 |         static uint8_t default_key[ENA_HASH_KEY_SIZE];
      |                        ^~~~~~~~~~~