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

On 08/13/2014 07:34 PM, Alexei Starovoitov wrote:

On Wed, Aug 13, 2014 at 2:17 AM, Daniel Borkmann [off-list ref] wrote:

quoted

On 08/13/2014 09:57 AM, Alexei Starovoitov wrote:

quoted

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-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>

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.