solana_rbpf::ebpf
pub const ST_H_REG: u8 = BPF_STX | BPF_MEM | BPF_H; // 0_x6bu8
BPF opcode: stxh [dst + off], src /// (dst + offset) as u16 = src.
stxh [dst + off], src
(dst + offset) as u16 = src