Re: [RFC PATCH bpf-next 3/3] bpf, arm64: Optimize ADD,SUB,JMP BPF_K using arm64 add/sub immediates

[Daniel Borkmann <daniel@iogearbox.net>]

On 5/7/20 3:05 AM, Luke Nelson wrote:
> The current code for BPF_{ADD,SUB} BPF_K loads the BPF immediate to a
> temporary register before performing the addition/subtraction. Similarly,
> BPF_JMP BPF_K cases load the immediate to a temporary register before
> comparison.
> 
> This patch introduces optimizations that use arm64 immediate add, sub,
> cmn, or cmp instructions when the BPF immediate fits. If the immediate
> does not fit, it falls back to using a temporary register.
> 
> Example of generated code for BPF_ALU64_IMM(BPF_ADD, R0, 2):
> 
> without optimization:
> 
>    24: mov x10, #0x2
>    28: add x7, x7, x10
> 
> with optimization:
> 
>    24: add x7, x7, #0x2
> 
> The code could use A64_{ADD,SUB}_I directly and check if it returns
> AARCH64_BREAK_FAULT, similar to how logical immediates are handled.
> However, aarch64_insn_gen_add_sub_imm from insn.c prints error messages
> when the immediate does not fit, and it's simpler to check if the
> immediate fits ahead of time.
> 
> Co-developed-by: Xi Wang <xi.wang@gmail.com>
> Signed-off-by: Xi Wang <xi.wang@gmail.com>
> Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>

Same here:

Acked-by: Daniel Borkmann <daniel@iogearbox.net>

Thanks!