On Fri, Mar 27, 2026 at 8:45 AM Takeru Hayasaka [off-list ref] wrote:

Understood. I was a bit surprised to read that this area ended up taking
months of follow-up work....

One thing I am still trying to understand is what the preferred
debuggability/observability direction would be for existing
tailcall-heavy BPF/XDP deployments.

Tail calls are already used in practice as a program decomposition
mechanism, especially in XDP pipelines, and that leaves tail-called leaf
programs harder to observe today.

If fentry on tail-called programs is not something you'd want upstream,
is there another direction you would recommend for improving
observability/debuggability of such existing deployments?

You don't need fentry to debug.
perf works just fine on all bpf progs whether tailcall or not.

Also pls don't top post.