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

[Olivier Matz <olivier.matz@6wind.com>]

On Fri, Jul 10, 2020 at 02:20:08PM +0200, Morten Brørup wrote:
> > 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>

Acked-by: Olivier Matz <olivier.matz@6wind.com>

Thanks!