On Wed, 7 Jul 2021 12:20:57 +0200 Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > On Wed, Jul 07, 2021 at 07:15:10PM +0900, Masami Hiramatsu wrote: > > > I actually don't want to keep this feature because no one use it. > > (only systemtap needs it?) > > Yeah, you mentioned systemtap, but since that's out-of-tree I don't > care. Their problem. > > > 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. > > When would you do the alloc? When installing the retprobe, but that > might be inside the allocator, which means you can't call the allocator > etc.. :-) Yes, so the user may need to allocate a pool right before register_kretprobe(). (whether per-kretprobe or per-task or global pool, that is user's choice.) > > If we look at struct ftrace_ret_stack, it has a few fixed function > fields. The calltime one is all that is needed for the kretprobe > example code. kretprobe consumes 3 fields, a pointer to 'struct kretprobe' (which stores callee function address in 'kretprobe::kp.addr'), a return address and a frame pointer (*). * note that this frame pointer might be used for fixing up the stack trace, but the fixup method depends on the architecture. Thank you, -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
