Re: [RFC PATCH bpf-next] RV32G eBPF JIT

From: Luke Nelson
Date: Tue Jun 25 2019 - 16:26:35 EST

On Mon, Jun 24, 2019 at 9:45 AM Jiong Wang <> wrote:
> Looks to me 32-bit optimization is not enabled.
> If you define bpf_jit_needs_zext to return true
> bool bpf_jit_needs_zext(void)
> {
> return true;
> }
> Then you don't need to zero high 32-bit when writing 32-bit sub-register
> and you just need to implement the explicit zero extension insn which is a
> special variant of BPF_MOV. This can save quite a few instructions. RV64
> and arches like arm has implemented this, please search
> "aux->verifier_zext".
> And there is a doc for this optimization:

Thanks for the pointer. I'll add this optimization before sending out
an updated version of the patch.

â Luke