Re: [dpdk-dev] [PATCH] net: fix checksum on big endian CPUs

["Morten Brørup" <mb@smartsharesystems.com>]

> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Hongzhi Guo
> Sent: Friday, July 10, 2020 1:43 PM
> 
> With current code, the checksum of odd-length buffers is wrong on
> big endian CPUs: the last byte is not properly summed to the
> accumulator.
> 
> Fix this by left-shifting the remaining byte by 8. For instance,
> if the last byte is 0x42, we should add 0x4200 to the accumulator
> on big endian CPUs.
> 
> This change is similar to what is suggested in Errata 3133 of
> RFC 1071.
> 
> Fixes: 6006818cfb26("net: new checksum functions")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Hongzhi Guo <guohongzhi1@huawei.com>
> ---
> v2:
> * Explain the logic in the commit log
> * Fixed commit title
> ---
> ---
>  lib/librte_net/rte_ip.h | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/librte_net/rte_ip.h b/lib/librte_net/rte_ip.h
> index 292f63fd7..4fb0e314a 100644
> --- a/lib/librte_net/rte_ip.h
> +++ b/lib/librte_net/rte_ip.h
> @@ -139,8 +139,11 @@ __rte_raw_cksum(const void *buf, size_t len,
> uint32_t sum)
>  	}
> 
>  	/* if length is in odd bytes */
> -	if (len == 1)
> -		sum += *((const uint8_t *)u16_buf);
> +	if (len == 1) {
> +		uint16_t left = 0;
> +		*(uint8_t *)&left = *(const uint8_t *)u16_buf;
> +		sum += left;
> +	}
> 
>  	return sum;
>  }
> --
> 2.21.0.windows.1
> 

This is correct for both big and little endian CPUs.

Reviewed-by: Morten Brørup <mb@smartsharesystems.com>