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Date: Mon, 3 Mar 2014 11:05:01 +0100
From: Hagen Paul Pfeifer <hagen@jauu.net>
To: Daniel Borkmann <dborkman@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>,
        "David S. Miller" <davem@davemloft.net>,
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Subject: Re: [PATCH v3 net-next 1/1] bpf32->bpf64 mapper and bpf64 interpreter
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* 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