> Sure. The issue is that I need to mark certain frames as "protected" from KeyboardInterrupt, in a way that my signal handler can see when walking the frame stack, so it can decide whether to raise a KeyboardInterrupt immediately or to wait until a safer moment.

OK, I got it, thanks!

> I suspect the way I'm currently munging frames at runtime also annoys PyPy's JIT.

Yes, whenever you touch frames you're disabling the JIT for the call site (and maybe for more call sites up the stack, idk).  So it doesn't matter what you use, `f_func` or `f_locals`, the performance will suffer big time.  Is that acceptable for Trio?