[dpdk-dev] [PATCH] app/testpmd: fix IP checksum calculation

[George Prekas]

On 12/3/2020 10:08 AM, Stephen Hemminger wrote:
> On Thu, 3 Dec 2020 07:59:54 -0600
> George Prekas <prekageo at amazon.com> wrote:
>
>> Insert a compiler barrier to make sure that the IP checksum calculation
>> happens after setting all the fields of the IP header.
>>
>> Signed-off-by: George Prekas <prekageo at amazon.com>
> I don't think this is necessary. All other OS's don't have to do this.
> The CPU is going to maintain proper memory order.

Hi Stephen,

This is not a CPU or OS issue. This is a compiler issue. The compiler is 
free to reorder statements if it does not detect dependencies between 
them. Without this compiler barrier, the calculated IP checksum is wrong.