Re: [PATCH v2 00/12] tracing/probe: Add multi-probes per event support

Steven Rostedt
2019-07-31T15:25:44Z

On Thu, 20 Jun 2019 00:07:09 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Hello,
>
> This is the 2nd version of multi-probes per event support on ftrace
> and perf-tools.
>
> Previous version is here;
> https://lkml.org/lkml/2019/5/31/573
>
> >From this version, I omitted first 9 patches which has been picked
> to Steve's tree.
> In this version, I've fixed some bugs and hardened some unexpected
> error cases according to Steve's comment.
> Here are changes in this version:
>
> - [1/12] This have below changes.
> - Warn if the primary trace_probe does not exist.
> - Fix enable_trace_kprobe() to not return error if the any probes
> are "gone" state. If all probes have gone or any other error
> reason, the event can not be enabled and return error.
> - Fix trace_probe_enable() to roll back all enabled uprobe if
> any one of uprobe is failed to enable.
> - [7/12] Swap the checking order of filename for avoiding unexpected
> memory access.
>
>
> ====
> For trace-event, we can insert same trace-event on several places
> on the code, and those can record similar information as a same event
> with same format.
>
> This series implements similar feature on probe-event. Since the probe
> event is based on the compiled binary, sometimes we find that the target
> source line is complied into several different addresses, e.g. inlined
> function, unrolled loop, etc. In those cases, it is useful to put a
> same probe-event on different addresses.
>
> With this series, we can append multi probes on one event as below
>
> # echo p:testevent _do_fork r1=%ax r2=%dx > kprobe_events
> # echo p:testevent fork_idle r1=%ax r2=%cx >> kprobe_events
> # kprobe_events
> p:kprobes/testevent _do_fork r1=%ax r2=%dx
> p:kprobes/testevent fork_idle r1=%ax r2=%cx
>
> This means testevent is hit on both of _do_fork and fork_idle.
> As you can see, the appended event must have same number of arguments
> and those must have same 'type' and 'name' as original one. This is like
> a function signature, it checks whether the appending event has the same
> type and name of event arguments and same probe type, but doesn't care
> about the assignment.
>
> So, below appending commands will be rejected.
>
> # echo p:testevent _do_fork r1=%ax r2=%dx > kprobe_events
> # echo p:testevent fork_idle r1=%ax >> kprobe_events
> (No 2nd argument)
> # echo p:testevent fork_idle r1=%ax r2=%ax:x8 >> kprobe_events
> (The type of 2nd argument is different)
>
> If one inlined code has an argument on a register, but another
> inlined code has fixed value (as a result of optimization),
> you can also specify the fixed immediate value, e.g.
>
> # echo p:testevent _do_fork r1=%ax r2=%dx > kprobe_events
> # echo p:testevent fork_idle r1=%ax r2=\1 >> kprobe_events
>
>

Hi Masami,

I applied this patch set to my queue. Nice feature! I'll probably be
testing it a bit more. I wont be pushing it to my repo until v5.3-rc3
comes out, as I'll plan on rebasing my for-next branch on that.

Thanks!

-- Steve