On Fri, Mar 27, 2026 at 8:12 AM Takeru Hayasaka <[email protected]> wrote: > > Hi Alexei > > Thanks, and Sorry, I sent an older changelog from while I was still > iterating on this, and it described the issue incorrectly. > > My changelog made this sound like an IBT/non-IBT-specific issue, but > that was wrong. On current kernels, fentry on tail-called programs is > not supported in either case. Only the regular fentry patch site is > patched; there is no tail-call landing patching in either case, so > disabling IBT does not make it work. > > What this series was trying to do was add support for fentry on > tail-called x86 programs. The non-IBT part was only about a bug in my > initial implementation of that support, not the underlying motivation. > > The motivation is observability of existing tailcall-heavy BPF/XDP > programs, where tail-called leaf programs are currently a blind spot for > fentry-based debugging.
I get that, but I'd rather not open this can of worms. We had enough headaches when tailcalls, fentry, subprogs are combined. Like this set: https://lore.kernel.org/all/[email protected]/ and the followups.
