On Mon, Jul 22, 2024 at 8:27 PM Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > > > We *need to support recursion* is my main point. > > > > Not quite. > > It's not a recursion. The stack collapsed/gone/wiped out before tail_call. > > Only of subprog(), not of handle_tp(). See all those "ENTRY - AFTER" > messages. We do return to all the nested handle_tp() calls and > continue just fine. > > I put the log into [0] for a bit easier visual inspection. > > [0] https://gist.github.com/anakryiko/6ccdfc62188f8ad4991641fb637d954c Argh. So the pathological prog can consume 512*33 of stack. We have to reject it somehow in the verifier or tailor private stack to support it. Then private stack will be a feature and a fix for this issue. But then it would need to preallocate 512*33 per cpu per program. Which is too much. Maybe we can preallocate _aligned_ 512 or 1k per cpu per prog, then adjust r9 before call or tail_call and if r9 is about to cross alignment before tail_call fail the tail call (like tail call cnt was over limit). Hopefully there are better ideas, since it's all quite messy.
