On Tue, Aug 27, 2024 at 5:48 AM Leon Hwang <leon.hwang@xxxxxxxxx> wrote:
>
> > I wonder if disallowing to freplace programs when
> > replacement.tail_call_reachable != replaced.tail_call_reachable
> > would be a better option?
> >
>
> This idea is wonderful.
>
> We can disallow attaching tail_call_reachable freplace prog to
> not-tail_call_reachable bpf prog. So, the following 3 cases are allowed.
>
> 1. attach tail_call_reachable freplace prog to tail_call_reachable bpf prog.
> 2. attach not-tail_call_reachable freplace prog to tail_call_reachable
> bpf prog.
> 3. attach not-tail_call_reachable freplace prog to
> not-tail_call_reachable bpf prog.
I think it's fine to disable freplace and tail_call combination altogether.
And speaking of the patch. The following:
- if (tail_call_reachable) {
-
LOAD_TAIL_CALL_CNT_PTR(bpf_prog->aux->stack_depth);
- ip += 7;
- }
+ LOAD_TAIL_CALL_CNT_PTR(bpf_prog->aux->stack_depth);
+ ip += 7;
Is too high of a penalty for every call for freplace+tail_call combo.
So disable it in the verifier.
pw-bot: cr
