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bpf: verifier: remove dead code

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Instead of overwriting dead code with jmp -1 instructions
remove it completely for root.  Adjust verifier state and
line info appropriately.

v2:
 - adjust func_info (Alexei);
 - make sure first instruction retains line info (Alexei).
v4: (Yonghong)
 - remove unnecessary if (!insn to remove) checks;
 - always keep last line info if first live instruction lacks one.
v5: (Martin Lau)
 - improve and clarify comments.

Signed-off-by: Jakub Kicinski <jakub.kicinski@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 22:45:20 -08:00 • committed by Alexei Starovoitov
parent e2ae4ca266
commit 52875a04f4
3 changed files with 186 additions and 3 deletions
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12
kernel/bpf/core.c
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@ -462,6 +462,18 @@ struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
return prog_adj;
}
int bpf_remove_insns(struct bpf_prog *prog, u32 off, u32 cnt)
{
/* Branch offsets can't overflow when program is shrinking, no need
* to call bpf_adj_branches(..., true) here
*/
memmove(prog->insnsi + off, prog->insnsi + off + cnt,
sizeof(struct bpf_insn) * (prog->len - off - cnt));
prog->len -= cnt;
return WARN_ON_ONCE(bpf_adj_branches(prog, off, off + cnt, off, false));
}
void bpf_prog_kallsyms_del_subprogs(struct bpf_prog *fp)
{
int i;