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From: David Laight <David.Laight@ACULAB.COM>
To: "'Alexei Starovoitov'" <ast@plumgrid.com>,
        "David S. Miller" <davem@davemloft.net>
CC: Ingo Molnar <mingo@kernel.org>,
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Subject: RE: [PATCH RFC v4 net-next 00/26] BPF syscall, maps, verifier,
 samples, llvm
Thread-Topic: [PATCH RFC v4 net-next 00/26] BPF syscall, maps, verifier,
 samples, llvm
Thread-Index: AQHPts7ddeWWduZ1mkyrLBQLyib/7JvOOEfw
Date: Wed, 13 Aug 2014 08:52:30 +0000
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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.

	David