solana_rbpf::ebpf
pub const LD_W_REG: u8 = BPF_LDX | BPF_MEM | BPF_W; // 0_x61u8
BPF opcode: ldxw dst, [src + off] /// dst = (src + off) as u32.
ldxw dst, [src + off]
dst = (src + off) as u32