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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>
This commit is contained in:
Jakub Kicinski 2019-01-22 22:45:21 -08:00 committed by Alexei Starovoitov
parent 52875a04f4
commit a1b14abc00
1 changed files with 23 additions and 0 deletions
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23
kernel/bpf/verifier.c
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@ -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);