Re: [RFC PATCH v3 bpf-next 2/5] bpf/verifier: rewrite subprog boundary detection

Alexei Starovoitov
2018-04-17T23:48:30Z

On Fri, Apr 06, 2018 at 06:13:59PM +0100, Edward Cree wrote:
> By storing a subprogno in each insn's aux data, we avoid the need to keep
> the list of subprog starts sorted or bsearch() it in find_subprog().
> Also, get rid of the weird one-based indexing of subprog numbers.
>
> Signed-off-by: Edward Cree <ecree@solarflare.com>
> ---
> include/linux/bpf_verifier.h | 3 +-
> kernel/bpf/verifier.c | 284 ++++++++++++++++++++++++++-----------------
> 2 files changed, 177 insertions(+), 110 deletions(-)
>
> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> index 8f70dc181e23..17990dd56e65 100644
> --- a/include/linux/bpf_verifier.h
> +++ b/include/linux/bpf_verifier.h
> @@ -146,6 +146,7 @@ struct bpf_insn_aux_data {
> s32 call_imm; /* saved imm field of call insn */
> };
> int ctx_field_size; /* the ctx field size for load insn, maybe 0 */
> + u16 subprogno; /* subprog in which this insn resides */
> bool seen; /* this insn was processed by the verifier */
> };

as I was saying before this is no go.
subprogno is meaningless in the hierarchy of: prog -> func -> bb -> insn
Soon bpf will have libraries and this field would need to become
a pointer back to bb or func structure creating unnecessary circular dependency.