Re: [PATCH bpf v1 2/2] selftests/bpf: Add raw_tp tests for PTR_MAYBE_NULL marking

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2024-12-04 at 21:48 +0100, Kumar Kartikeya Dwivedi wrote:

[...[

(A) ----.
        |
        v
> > > What this will do in both cases::
> > > First, avoid walking states when off != 0, and reset id.
> > > If off == 0, go inside mark_ptr_or_null_reg and walk all regs, and
> > > remove marks for those with off != 0.

(B) ----.
        |
        v
> > That's getting intrusive.
> > How about we reset id=0 in adjust_ptr_min_max_vals()
> > right after we suppressed "null-check it first" message for raw_tp-s.
> > 
> > That will address the issue as well, right?
> 
> Yes (minor detail, it needs to be reset to a new id, otherwise we have
> warn on maybe_null set but !reg->id, but the idea is the same).
> Let's see what Eduard thinks and then I can give it a go.

Sorry for delay.

I like what Kumar is proposing in (A) because it could be generalized:
there is no real harm in doing 'r2 = r1; r2 += 8; r1 != 0; ...'
and what Kumar suggests could be used to lift the "null-check it first ..."
restriction.

However, as far as I understand, the plan is to fix this by generating
two entry tracepoint states: one with parameter as null, another with
parameter not-null (all combinations for every parameter).
If that is the plan, what Alexei suggests in (B) is simpler.