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Date:	Wed, 13 Aug 2014 08:52:30 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Alexei Starovoitov' <>,
	"David S. Miller" <>
CC:	Ingo Molnar <>,
	Linus Torvalds <>,
	Andy Lutomirski <>,
	Steven Rostedt <>,
	Daniel Borkmann <>,
	Chema Gonzalez <>,
	Eric Dumazet <>,
	"Peter Zijlstra" <>,
	"H. Peter Anvin" <>,
	"Andrew Morton" <>,
	Kees Cook <>,
	"" <>,
	"" <>,
	"" <>
Subject: RE: [PATCH RFC v4 net-next 00/26] BPF syscall, maps, verifier,
 samples, llvm

From: Of Alexei Starovoitov
> one more RFC...
> Major difference vs previous set is a new 'load 64-bit immediate' eBPF insn.
> Which is first 16-byte instruction. It shows how eBPF ISA can be extended
> while maintaining backward compatibility, but mainly it cleans up eBPF
> program access to maps and improves run-time performance.

Wouldn't it be more sensible to follow the scheme used by a lot of cpus
and add a 'load high' instruction (follow with 'add' or 'or').
It still takes 16 bytes to load a 64bit immediate value, but the instruction
size remains constant.
There is nothing to stop any JIT software detecting the instruction pair.


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