netdev - Re: more test

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Message-Id: <20170426.222339.1486764869366311464.davem@davemloft.net>
Date:   Wed, 26 Apr 2017 22:23:39 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     ast@...com
Cc:     daniel@...earbox.net, netdev@...r.kernel.org
Subject: Re: more test_progs...

From: Alexei Starovoitov <ast@...com>
Date: Wed, 26 Apr 2017 16:49:35 -0700

> It's only needed for test_pkt_access.c test,
> since it's being fancy and doing iph->ihl * 4.

It is going to be a common idiom in anything looking at
transport headers, no?

> Also such tcp->urg_ptr access into packed struct is more efficient
> after JITing then sparc's own load_half_unaligned in asm, since it's
> done inline and doesn't need a call.
> 
> Note that such tcphdr workaround is not necessary for more
> real programs: test_l4lb.c and test_xdp.c, since they do:
> if (iph->ihl != 5)
>    return drop;

Hmmm...

> Does sparc64 have some special instructions like that?

Unfortunately not.

I think we need to seriously consider tracking "Pointer
incremented by power of 2 N" and stuff like that.

I know it's not easy, but it is necessary.

Having stuff like the packed thing above is just a completely
unnecessary detail to expose to users writing these programs.