On Wed, 7 Jul 2021 19:45:30 +0900 Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: > 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. Yeah, maybe it is not hard to update. > > > > > 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 (*). Oops, I forgot to add "void *data" for storing user data. Thank you, -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
