linux-kernel - Re: [PATCH v3 net-next 1/1] bpf32->bpf64 mapper and bpf64 interpreter

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Date:	Mon, 3 Mar 2014 11:05:01 +0100
From:	Hagen Paul Pfeifer <hagen@...u.net>
To:	Daniel Borkmann <dborkman@...hat.com>
Cc:	Alexei Starovoitov <ast@...mgrid.com>,
	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Tom Zanussi <tom.zanussi@...ux.intel.com>,
	Jovi Zhangwei <jovi.zhangwei@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Pekka Enberg <penberg@....fi>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Jesse Gross <jesse@...ira.com>
Subject: Re: [PATCH v3 net-next 1/1] bpf32->bpf64 mapper and bpf64 interpreter

* Daniel Borkmann | 2014-03-01 01:30:00 [+0100]:

>>>as in 'struct bpf_insn' the immediate value is 32 bit, so for 64 bit
>>>comparisons, you'd still need to load to immediate values, right?
>>
>>there is no insn that use 64-bit immediate, since 64-bit immediates
>>are extremely rare. grep x86-64 asm code for movabsq will return very few.
>>llvm or gcc can easily construct any constant by combination of mov,
>>shifts and ors.
>>bpf64 comparisons are all 64-bit right now. So far I didn't see a need to do
>>32-bit comparison, since old bpf is all unsigned, mapping 32->64 of
>>Jxx is painless.
>
>Hm, fair enough, I was just thinking for comparisons of IPv6 addresses
>when we do socket filtering. On the other hand, old and new insns are
>both 64 bit wide and can be used though the same api then.

What about the long term idea to support JITed nftables? A 128 bit immediate
is required - maybe the biggest requirement for nftable support.

Hagen
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