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

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Message-ID: <20170921194426.tnd5xos5irm3gred@ast-mbp>
Date:   Thu, 21 Sep 2017 12:44:28 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Edward Cree <ecree@...arflare.com>, Y Song <ys114321@...il.com>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] bpf/verifier: improve disassembly of BPF_END
 instructions

On Thu, Sep 21, 2017 at 09:29:33PM +0200, Daniel Borkmann wrote:
> On 09/21/2017 06:58 PM, Edward Cree wrote:
> > On 21/09/17 17:40, Y Song wrote:
> > > On Thu, Sep 21, 2017 at 9:24 AM, Edward Cree <ecree@...arflare.com> wrote:
> > > > On 21/09/17 16:52, Alexei Starovoitov wrote:
> > > > > imo
> > > > > (u16) r4 endian be
> > > > > isn't intuitive.
> > > > > Can we come up with some better syntax?
> > > > > Like
> > > > > bswap16be r4
> > > > > bswap32le r4
> > > > Hmm, I don't like these, since bswapbe is a swap on *le* and a nop on be.
> 
> Agree, a bit too much 'swap' semantics in the name that could be
> confusing perhaps, at least the be/le could be missed easily.
> 
> > > > > or
> > > > > 
> > > > > to_be16 r4
> > > > > to_le32 r4
> > > > And the problem here is that it's not just to_be, it's also from_be.
> 
> More intuitive, but agree on the from_be/le. Maybe we should
> just drop the "to_" prefix altogether, and leave the rest as is since
> it's not surrounded by braces, it's also not a cast but rather an op.

'be16 r4' is ambiguous regarding upper bits.

what about my earlier suggestion:
r4 = (be16) (u16) r4
r4 = (le64) (u64) r4

It will be pretty clear what instruction is doing (that upper bits become zero).