From: Daniel Borkmann <dborkman@redhat.com>
To: Alexei Starovoitov <ast@plumgrid.com>
Cc: Chema Gonzalez <chema@google.com>,
"David S. Miller" <davem@davemloft.net>,
Ingo Molnar <mingo@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Eric Dumazet <edumazet@google.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Arnaldo Carvalho de Melo <acme@infradead.org>,
Jiri Olsa <jolsa@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Andrew Morton <akpm@linux-foundation.org>,
Kees Cook <keescook@chromium.org>,
Network Development <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 net-next 0/2] split BPF out of core networking
Date: Tue, 24 Jun 2014 10:33:15 +0200 [thread overview]
Message-ID: <53A937CB.7040309@redhat.com> (raw)
In-Reply-To: <CAMEtUuwV3y4G5+kLQNXojn4vrLmub4JVf1RyZoRoNNnX8U_yJA@mail.gmail.com>
On 06/23/2014 11:57 PM, Alexei Starovoitov wrote:
> On Fri, Jun 20, 2014 at 9:44 AM, Chema Gonzalez <chema@google.com> wrote:
...
>>>> - nop: I'd like to have a nop. Do I know why? Nope.
>>> nope. Let's not add unnecessary instructions.
>> A valid nop is a useful instruction: padding, filling up arrays of
>> sock_filter_int correctly (as in lib/test_bpf.c, where we're currently
>> using a "ld #0", which loads zero to register A), and other use cases
>> (see http://en.wikipedia.org/wiki/NOP ).
>
> especially I don't like to add 'nop' instruction.
> code==0 to mean 'ld #0' is one of classic BPF ugliness.
I think it was probably unintended to be able to have unreachable
code e.g. filled with 'nops' where both jt, jf just jump over it,
but that quirk we cannot change anymore in the classic checker
and have to carry onwards.
> We're not filling up arrays with nops in lib/test_bpf.c
> Zero is invalid opcode in eBPF and should stay so, since it's
> an easy check for humans like me who are looking at eBPF in hex.
next prev parent reply other threads:[~2014-06-24 8:33 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-02 7:01 [PATCH v2 net-next 0/2] split BPF out of core networking Alexei Starovoitov
2014-06-02 7:01 ` [PATCH v2 net-next 1/2] net: filter: split filter.c into two files Alexei Starovoitov
2014-06-02 7:01 ` [PATCH v2 net-next 2/2] net: filter: split BPF out of core networking Alexei Starovoitov
2014-06-02 8:57 ` [PATCH v2 net-next 0/2] " Daniel Borkmann
2014-06-02 15:41 ` Alexei Starovoitov
2014-06-02 17:04 ` Daniel Borkmann
2014-06-02 19:02 ` Alexei Starovoitov
2014-06-03 8:56 ` Daniel Borkmann
2014-06-03 15:44 ` Alexei Starovoitov
2014-06-03 20:35 ` Daniel Borkmann
2014-06-03 20:58 ` Alexei Starovoitov
2014-06-03 21:40 ` Chema Gonzalez
2014-06-04 0:38 ` Alexei Starovoitov
2014-06-20 16:44 ` Chema Gonzalez
2014-06-23 9:18 ` David Laight
2014-06-23 21:57 ` Alexei Starovoitov
2014-06-24 8:33 ` Daniel Borkmann [this message]
2014-06-02 13:15 ` Jonathan Corbet
2014-06-02 13:24 ` Steven Rostedt
2014-06-02 14:16 ` Arnaldo Carvalho de Melo
2014-06-02 14:57 ` Alexei Starovoitov
2014-06-03 18:16 ` Ingo Molnar
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