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

[Daniel Borkmann <dborkman@redhat.com>]

On 08/13/2014 07:34 PM, Alexei Starovoitov wrote:
> On Wed, Aug 13, 2014 at 2:17 AM, Daniel Borkmann <dborkman@redhat.com> wrote:
>> 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.
>
> ok. As you saw the full explanation is long, so I opted for 'it_does_this'
> commit log. In the next rev will add more reasons to this log. Sure.

Great, thanks.