static int bpf_unclone_prologue(struct bpf_insn *insn_buf, bool direct_write,
				const struct bpf_prog *prog, int drop_verdict)
{
	struct bpf_insn *insn = insn_buf;

	if (!direct_write)
		return 0;

	/* if (!skb->cloned)
	 *       goto start;
	 *
	 * (Fast-path, otherwise approximation that we might be
	 *  a clone, do the rest in helper.)
	 */
	*insn++ = BPF_LDX_MEM(BPF_B, BPF_REG_6, BPF_REG_1, CLONED_OFFSET());
	*insn++ = BPF_ALU32_IMM(BPF_AND, BPF_REG_6, CLONED_MASK);
	*insn++ = BPF_JMP_IMM(BPF_JEQ, BPF_REG_6, 0, 7);

	/* ret = bpf_skb_pull_data(skb, 0); */
	*insn++ = BPF_MOV64_REG(BPF_REG_6, BPF_REG_1);
	*insn++ = BPF_ALU64_REG(BPF_XOR, BPF_REG_2, BPF_REG_2);
	*insn++ = BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
			       BPF_FUNC_skb_pull_data);
	/* if (!ret)
	 *      goto restore;
	 * return TC_ACT_SHOT;
	 */
	*insn++ = BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2);
	*insn++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_0, drop_verdict);
	*insn++ = BPF_EXIT_INSN();

	/* restore: */
	*insn++ = BPF_MOV64_REG(BPF_REG_1, BPF_REG_6);
	/* start: */
	*insn++ = prog->insnsi[0];

	return insn - insn_buf;
}
Unknown