Re: [PATCH] eal: fix unaligned loads/stores in rte_memcpy_aligned

[Luc Pelletier <lucp.at.work@gmail.com>]

Hi,

This patch can be abandoned. As indicated in another thread
(http://mails.dpdk.org/archives/dev/2022-February/234889.html), there
is no requirement/desire to make this change.

Thanks.

Le sam. 15 janv. 2022 à 14:39, Luc Pelletier <lucp.at.work@gmail.com> a écrit :
>
> Calls to rte_memcpy_aligned could result in unaligned loads/stores for
> 1 < n < 16. This is undefined behavior according to the C standard,
> and it gets flagged by the clang undefined behavior sanitizer.
>
> rte_memcpy_aligned is called with aligned src and dst addresses. When
> n is odd, the code would copy a single byte first, increment src/dst,
> then, depending on the value of n, would cast src/dst to a qword, dword
> or word pointer. This results in an unaligned load/store. Reversing the
> order of the casts & copies (ie. copying a qword first, dword second,
> etc.) fixes the issue.
>
> Fixes: d35cc1fe6a7a ("eal/x86: revert select optimized memcpy at run-time")
> Cc: Xiaoyun Li <xiaoyun.li@intel.com>
> Cc: stable@dpdk.org
>
> Signed-off-by: Luc Pelletier <lucp.at.work@gmail.com>
> ---
>  lib/eal/x86/include/rte_memcpy.h | 24 ++++++++++++------------
>  1 file changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/lib/eal/x86/include/rte_memcpy.h b/lib/eal/x86/include/rte_memcpy.h
> index 1b6c6e585f..a4eb1316b6 100644
> --- a/lib/eal/x86/include/rte_memcpy.h
> +++ b/lib/eal/x86/include/rte_memcpy.h
> @@ -818,25 +818,25 @@ rte_memcpy_aligned(void *dst, const void *src, size_t n)
>  {
>         void *ret = dst;
>
> -       /* Copy size <= 16 bytes */
> +       /* Copy size < 16 bytes */
>         if (n < 16) {
> -               if (n & 0x01) {
> -                       *(uint8_t *)dst = *(const uint8_t *)src;
> -                       src = (const uint8_t *)src + 1;
> -                       dst = (uint8_t *)dst + 1;
> -               }
> -               if (n & 0x02) {
> -                       *(uint16_t *)dst = *(const uint16_t *)src;
> -                       src = (const uint16_t *)src + 1;
> -                       dst = (uint16_t *)dst + 1;
> +               if (n & 0x08) {
> +                       *(uint64_t *)dst = *(const uint64_t *)src;
> +                       src = (const uint64_t *)src + 1;
> +                       dst = (uint64_t *)dst + 1;
>                 }
>                 if (n & 0x04) {
>                         *(uint32_t *)dst = *(const uint32_t *)src;
>                         src = (const uint32_t *)src + 1;
>                         dst = (uint32_t *)dst + 1;
>                 }
> -               if (n & 0x08)
> -                       *(uint64_t *)dst = *(const uint64_t *)src;
> +               if (n & 0x02) {
> +                       *(uint16_t *)dst = *(const uint16_t *)src;
> +                       src = (const uint16_t *)src + 1;
> +                       dst = (uint16_t *)dst + 1;
> +               }
> +               if (n & 0x01)
> +                       *(uint8_t *)dst = *(const uint8_t *)src;
>
>                 return ret;
>         }
> --
> 2.25.1
>