BPF_REG_ARG4
*insn++ = BPF_MOV64_IMM(BPF_REG_ARG4, offset);
*insn++ = BPF_MOV64_REG(BPF_REG_ARG4, BPF_REG_X);
*insn++ = BPF_ALU64_IMM(BPF_ADD, BPF_REG_ARG4, offset);