[RFC bpf-next 7/8] bpf: migrate insn remove to list patching infra

[Jiong Wang <jiong.wang@netronome.com>]

This patch migrate dead code remove pass to new list patching
infrastructure.

Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
---
 kernel/bpf/verifier.c | 59 +++++++++++++++++----------------------------------
 1 file changed, 19 insertions(+), 40 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 58d6bbe..abe11fd 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -8500,49 +8500,30 @@ verifier_linearize_list_insn(struct bpf_verifier_env *env,
 	return ret_env;
 }
 
-static int opt_remove_dead_code(struct bpf_verifier_env *env)
+static int opt_remove_useless_code(struct bpf_verifier_env *env)
 {
-	struct bpf_insn_aux_data *aux_data = env->insn_aux_data;
-	int insn_cnt = env->prog->len;
-	int i, err;
-
-	for (i = 0; i < insn_cnt; i++) {
-		int j;
-
-		j = 0;
-		while (i + j < insn_cnt && !aux_data[i + j].seen)
-			j++;
-		if (!j)
-			continue;
-
-		err = verifier_remove_insns(env, i, j);
-		if (err)
-			return err;
-		insn_cnt = env->prog->len;
-	}
-
-	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;
+	struct bpf_insn_aux_data *auxs = env->insn_aux_data;
+	const struct bpf_insn nop =
+		BPF_JMP_IMM(BPF_JA, 0, 0, 0);
+	struct bpf_list_insn *list, *elem;
+	int ret = 0;
 
-	for (i = 0; i < insn_cnt; i++) {
-		if (memcmp(&insn[i], &ja, sizeof(ja)))
+	list = bpf_create_list_insn(env->prog);
+	if (IS_ERR(list))
+		return PTR_ERR(list);
+	for (elem = list; elem; elem = elem->next) {
+		if (auxs[elem->orig_idx - 1].seen &&
+		    memcmp(&elem->insn, &nop, sizeof(nop)))
 			continue;
 
-		err = verifier_remove_insns(env, i, 1);
-		if (err)
-			return err;
-		insn_cnt--;
-		i--;
+		elem->flag |= LIST_INSN_FLAG_REMOVED;
 	}
 
-	return 0;
+	env = verifier_linearize_list_insn(env, list);
+	if (IS_ERR(env))
+		ret = PTR_ERR(env);
+	bpf_destroy_list_insn(list);
+	return ret;
 }
 
 static int opt_subreg_zext_lo32_rnd_hi32(struct bpf_verifier_env *env,
@@ -9488,9 +9469,7 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr,
 		if (ret == 0)
 			opt_hard_wire_dead_code_branches(env);
 		if (ret == 0)
-			ret = opt_remove_dead_code(env);
-		if (ret == 0)
-			ret = opt_remove_nops(env);
+			ret = opt_remove_useless_code(env);
 	} else {
 		if (ret == 0)
 			sanitize_dead_code(env);
-- 
2.7.4