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Date: Wed, 13 Aug 2014 11:17:37 +0200
From: Daniel Borkmann <dborkman@redhat.com>
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To: Alexei Starovoitov <ast@plumgrid.com>
CC: "David S. Miller" <davem@davemloft.net>, Ingo Molnar <mingo@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>, linux-api@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC v4 net-next 01/26] net: filter: add "load 64-bit immediate"
 eBPF instruction
References: <1407916658-8731-1-git-send-email-ast@plumgrid.com> <1407916658-8731-2-git-send-email-ast@plumgrid.com>
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On 08/13/2014 09:57 AM, Alexei Starovoitov wrote:
> add BPF_LD_IMM64 instruction to load 64-bit immediate value into register.
> All previous instructions were 8-byte. This is first 16-byte instruction.
> Two consecutive 'struct bpf_insn' blocks are interpreted as single instruction:
> insn[0/1].code = BPF_LD | BPF_DW | BPF_IMM
> insn[0/1].dst_reg = destination register
> insn[0].imm = lower 32-bit
> insn[1].imm = upper 32-bit
>
> Classic BPF has similar instruction: BPF_LD | BPF_W | BPF_IMM
> which loads 32-bit immediate value into a register.
>
> x64 JITs it as single 'movabsq %rax, imm64'
> arm64 may JIT as sequence of four 'movk x0, #imm16, lsl #shift' insn
>
> Note that old eBPF programs are binary compatible with new interpreter.
>
> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>

For follow-ups on this series, can you put the actual motivation
for this change from the cover letter into this commit log as it
otherwise doesn't say anything clearly why it is needed. Code and
test case looks good to me.