bpf: verifier: remove unconditional branches by 0 (a1b14abc) · Commits · 戴 / test

Unconditional branches by 0 instructions are basically noops but they can result from earlier optimizations, e.g. a conditional jumps which would never be taken or a conditional jump around dead code. Remove those branches. v0.2: - s/opt_remove_dead_branches/opt_remove_nops/ (Jiong). Signed-off-by:

Jakub Kicinski <jakub.kicinski@netronome.com> Reviewed-by:

Jiong Wang <jiong.wang@netronome.com> Acked-by:

Yonghong Song <yhs@fb.com> Signed-off-by:

Alexei Starovoitov <ast@kernel.org>

kernel/bpf/verifier.c

+23 −0

Original line number	Diff line number	Diff line
		@@ -6660,6 +6660,27 @@ static int opt_remove_dead_code(struct bpf_verifier_env *env)
		return 0;
		}

		static int opt_remove_nops(struct bpf_verifier_env *env)
		{
		const struct bpf_insn ja = BPF_JMP_IMM(BPF_JA, 0, 0, 0);
		struct bpf_insn *insn = env->prog->insnsi;
		int insn_cnt = env->prog->len;
		int i, err;

		for (i = 0; i < insn_cnt; i++) {
		if (memcmp(&insn[i], &ja, sizeof(ja)))
		continue;

		err = verifier_remove_insns(env, i, 1);
		if (err)
		return err;
		insn_cnt--;
		i--;
		}

		return 0;
		}

		/* convert load instructions that access fields of a context type into a
		* sequence of instructions that access fields of the underlying structure:
		* struct __sk_buff -> struct sk_buff
		@@ -7452,6 +7473,8 @@ skip_full_check:
		opt_hard_wire_dead_code_branches(env);
		if (ret == 0)
		ret = opt_remove_dead_code(env);
		if (ret == 0)
		ret = opt_remove_nops(env);
		} else {
		if (ret == 0)
		sanitize_dead_code(env);

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