On Wed, May 22, 2024 at 11:42 PM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> From: Alexei Starovoitov <ast@xxxxxxxxxx>
>
> v1->v2:
> - Replaced copy precision logic with faster and more accurate alternative.
> See find_precision().
...
> +static void find_precise_reg(struct bpf_reg_state *cur_reg)
> +{
> + struct bpf_reg_state *reg;
> +
> + reg = cur_reg->parent;
> + while (reg && reg->type == SCALAR_VALUE) {
> + /*
> + * propagate_liveness() might not have happened for this states yet.
> + * Intermediate reg missing LIVE_READ mark is not an issue.
> + */
> + if (reg->precise && (reg->live & REG_LIVE_READ)) {
> + cur_reg->precise = true;
> + break;
> + }
> + reg = reg->parent;
> + }
> +}
> +
> +static void find_precision(struct bpf_verifier_state *cur_state)
> +{
> + struct bpf_func_state *state;
> + struct bpf_reg_state *reg;
> +
> + if (!get_loop_entry(cur_state))
> + return;
> + bpf_for_each_reg_in_vstate(cur_state, state, reg, ({
> + if (reg->type != SCALAR_VALUE || reg->precise)
> + continue;
> + find_precise_reg(reg);
> + }));
> +}
This turned out to be an ok idea for a good case and
horrible idea when loop doesn't converge, since walking parentage
chain is very expensive when loop is reaching million of iterations.
There will be a v3 with fixes.
pw-bot: cr
