linux-kernel - Re: [PATCH RFC v4 net-next 01/26] net: filter: add "load 64-bit immediate" eBPF instruction

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Message-ID: <53EBD5B3.10200@zytor.com>
Date:	Wed, 13 Aug 2014 14:16:35 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Alexei Starovoitov <ast@...mgrid.com>,
	Andy Lutomirski <luto@...capital.net>
CC:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Chema Gonzalez <chema@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Linux API <linux-api@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v4 net-next 01/26] net: filter: add "load 64-bit immediate"
 eBPF instruction

On 08/13/2014 02:02 PM, Alexei Starovoitov wrote:
> On Wed, Aug 13, 2014 at 11:35 AM, Andy Lutomirski <luto@...capital.net> wrote:
>>
>> The compiler can still think of it as a single insn, though, but some
>> future compiler might not.
> 
> I think that would be very dangerous.
> compiler (user space) and kernel interpreter must have the same
> understanding of ISA.
> 

Only at the point of the interface layer.  The compiler can treat it as
a single instruction internally, the JIT can do peephole optimization,
but as long as the instruction stream at the boundary matches the
official ISA spec everything is fine.

	-hpa

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