netdev - Re: [PATCH net-next] bpf/verifier: improve disassembly of BPF

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Date:   Tue, 26 Sep 2017 15:37:12 +0100
From:   Edward Cree <ecree@...arflare.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>
CC:     Y Song <ys114321@...il.com>, David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Jiong Wang <jiong.wang@...ronome.com>,
        "Jakub Kicinski" <jakub.kicinski@...ronome.com>
Subject: Re: [PATCH net-next] bpf/verifier: improve disassembly of BPF_END
 instructions

On 26/09/17 02:33, Alexei Starovoitov wrote:
> On Mon, Sep 25, 2017 at 11:44:02PM +0200, Daniel Borkmann wrote:
>> But above cast to be16 also doesn't seem quite C-like in terms
>> of what we're actually doing... 3rd option would be my personal
>> preference even if it doesn't look C-like, but otoh we also have
>> 'call' etc which is neither.

<snip>

> In that sense (be16) cast is pretty much self explanatory.
> So I'd like to continue bikesheding in hopes to convince you
> to accept either 1 or 2 above ;)
I agree with Daniel.  3rd option `r1 = be16 r1` is best, as it's an
 actual ALU operation, not just a cast.  And since it looks like we're
 drifting vaguely near a consensus on that (even if Alexei still isn't
 convinced ;-) I'll spin v2 patches with that and `r1 = (u32) -r1`, so
 we have something concrete to argue about...

-Ed