From: Eric Dumazet <eric.dumazet@gmail.com>
To: David Miller <davem@davemloft.net>
Cc: dborkman@redhat.com, netdev@vger.kernel.org
Subject: Re: [PATCH net-next 0/8] Add complementary BPF conditional jump instructions
Date: Mon, 31 Dec 2012 19:29:02 -0800 [thread overview]
Message-ID: <1357010942.21409.8948.camel@edumazet-glaptop> (raw)
In-Reply-To: <20121231.143715.1238174487756359071.davem@davemloft.net>
On Mon, 2012-12-31 at 14:37 -0800, David Miller wrote:
> Whilst I agree that adding NE jumps adds great value and closes a
> serious gap, the rest can be synthesized by simply swapping the
> arguments and using a comparison that does already exist.
>
> Why isn't that sufficient?
I am afraid none of these patches is needed at all.
Swapping the jt/jf is plainly enough for the user land compiler.
libcap seems to do it already
# tcpdump -i lo 'len!=0 && ip6' -d
(000) ld #pktlen
(001) jeq #0x0 jt 5 jf 2
(002) ldh [12]
(003) jeq #0x86dd jt 4 jf 5
(004) ret #96
(005) ret #0
# tcpdump -i lo 'len==0 && ip6' -d
(000) ld #pktlen
(001) jeq #0x0 jt 2 jf 5
(002) ldh [12]
(003) jeq #0x86dd jt 4 jf 5
(004) ret #96
(005) ret #0
next prev parent reply other threads:[~2013-01-01 3:29 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-31 13:59 [PATCH net-next 0/8] Add complementary BPF conditional jump instructions Daniel Borkmann
2012-12-31 13:59 ` [PATCH net-next 1/8] net: bpf: add lt,le jump operations to bpf machine Daniel Borkmann
2012-12-31 13:59 ` [PATCH net-next 2/8] x86: bpf_jit_comp: add JMP instructions for BPF JIT Daniel Borkmann
2012-12-31 13:59 ` [PATCH net-next 3/8] sparc: " Daniel Borkmann
2012-12-31 13:59 ` [PATCH net-next 4/8] PPC: " Daniel Borkmann
2012-12-31 13:59 ` [PATCH net-next 5/8] net: bpf: add neq jump operations to bpf machine Daniel Borkmann
2013-01-01 3:25 ` Eric Dumazet
2012-12-31 13:59 ` [PATCH net-next 7/8] sparc: bpf_jit_comp: add JMP_NEQ instructions for BPF JIT Daniel Borkmann
2012-12-31 13:59 ` [PATCH net-next 8/8] PPC: " Daniel Borkmann
2012-12-31 17:00 ` [PATCH net-next 6/8] x86: " Daniel Borkmann
2012-12-31 22:37 ` [PATCH net-next 0/8] Add complementary BPF conditional jump instructions David Miller
2013-01-01 3:29 ` Eric Dumazet [this message]
2013-01-01 5:18 ` David Miller
2013-01-02 10:47 ` Daniel Borkmann
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