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

[Daniel Borkmann]

On 08/13/2014 07:34 PM, Alexei Starovoitov wrote:
> On Wed, Aug 13, 2014 at 2:17 AM, Daniel Borkmann <dborkman@xxxxxxxxxx> 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@xxxxxxxxxxxx>
> >
> >
> > 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.
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