solana_rbpf::ebpf
pub const ST_DW_REG: u8 = BPF_STX | BPF_MEM | BPF_DW; // 123u8
BPF opcode: stxdw [dst + off], src /// (dst + offset) as u64 = src.
stxdw [dst + off], src
(dst + offset) as u64 = src