ARC_R_0
len = arc_mov_r(buf, ARC_R_0, REG_LO(BPF_REG_0));
len = arc_mov_r(buf, REG_LO(BPF_REG_0), ARC_R_0);
[BPF_REG_1] = {ARC_R_0, ARC_R_1},