Hi Steve, On Mon, 26 Nov 2018 11:32:15 -0500 Steven Rostedt <rost...@goodmis.org> wrote:
> On Mon, 26 Nov 2018 18:21:12 +0900 > Masami Hiramatsu <mhira...@kernel.org> wrote: > > > > > Note, if another fgraph_ops is registered in the same location, its > > > retfunc may be called that was set by a previous fgraph_ops. This > > > is not a regression because that's what can happen today if you unregister > > > a callback from the current function_graph tracer and register another > > > one. If this is an issue, there are ways to solve it. > > > > Yeah, I need the solution, maybe an API to get correct return address? :) > > One way to solve this is to also have a counter array that gets updated > every time the index array gets updated. And save the counter to the > shadow stack index as well. This way, we only call the return if the > counter on the stack matches what's in the counter on the counter array > for the index. Hmm, but we already know the current stack "header" entry when calling handlers, don't we? I thought we just calcurate out from curr_ret_stack. > > By the way, are there any way to hold a private data on each ret_stack > > entry? > > Since kretprobe supports "entry data" passed from entry_handler to > > return handler, we have to store the data or data-instance on the ret_stack. > > > > This feature is used by systemtap to save the function entry data, like > > function parameters etc., so that return handler analyzes the parameters > > with return value. > > Yes, I remember you telling me about this at plumbers, and while I was > writing this code I had that in mind. It wouldn't be too hard to > implement, I just left it off for now. I also left it off because I > have some questions about what exactly is needed. What size do you > require to be stored. Especially if we want to keep the shadow stack > smaller. I was going to find a way to implement some of the data that > is already stored via the ret_stack with this instead, and make the > ret_stack entry smaller. Should we allow just sizeof(long)*3? or just > let user choose any size and if they run out of stack, then too bad. We > just wont let it crash. I need only sizeof(unsigned long). If the kretprobe user requires more, it will be fall back to current method -- get an "instance" and store its address to the entry :-) Thank you, -- Masami Hiramatsu <mhira...@kernel.org>
