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authorJakub Kicinski <jakub.kicinski@netronome.com>2019-01-22 22:45:21 -0800
committerAlexei Starovoitov <ast@kernel.org>2019-01-23 17:35:32 -0800
commita1b14abc009d9c13be355dbd4a4c4d47816ad3db (patch)
tree755c19bcbbdbc875252133b72d706f23ffbb06b6 /kernel/bpf
parent52875a04f4b26e7ef30a288ea096f7cfec0e93cd (diff)
downloadlinux-a1b14abc009d9c13be355dbd4a4c4d47816ad3db.tar.bz2
bpf: verifier: remove unconditional branches by 0
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>
Diffstat (limited to 'kernel/bpf')
-rw-r--r--kernel/bpf/verifier.c23
1 files changed, 23 insertions, 0 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 099b2541f87f..f39bca188a5c 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -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);