On Wed, 7 Jul 2021 10:20:41 +0200 Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > Steve, can you clarify the ftrace side here? Afaict return_to_handler() > > > is similarly affected. > > > > I'm not exactly sure what the issue is. As Masami stated, kretprobe > > uses a ret to return to the calling function, but ftrace uses a jmp. > > I'll have to re-read the ftrace bits, but from the top of my head you > cannot do an indirect jump and preserve all registers at the same time, > so a return stub must use jump from stack aka. ret. > > > kretprobe return tracing is more complex than the function graph return > > tracing is (which is one of the issues I need to overcome to unify > > them), > > I'm not sure it is. IIRC the biggest pain point with kretprobe is that > 'silly' property that the kretprobe_instance are not the same between > kretprobes. Luckily, that's not actually used anywhere, so we can simply > rip that out. I actually don't want to keep this feature because no one use it. (only systemtap needs it?) Anyway, if we keep the idea-level compatibility (not code level), what we need is 'void *data' in the struct kretprobe_instance. User who needs it can allocate their own instance data for their kretprobes when initialising it and sets in their entry handler. Then we can have a simple kretprobe_instance. Thank you, -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
