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

From: H. Peter Anvin
Date: Wed Aug 13 2014 - 17:17:20 EST

On 08/13/2014 02:02 PM, Alexei Starovoitov wrote:
> On Wed, Aug 13, 2014 at 11:35 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> 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.


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