Re: [PATCH v10 2/9] tracing/probes: Support dumping fetcharg program for debugging dynamic events

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

Sashiko made a good comment:

> commit ce5985c5ce46daa952ae907992e02e403e601c04
> Author: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> tracing/probes: Support dumping fetcharg program for debugging dynamic events
> This commit introduces a new configuration option
> CONFIG_PROBE_EVENTS_DUMP_FETCHARG to debug dynamic events. When enabled, it
> appends commented lines containing the fetch instructions to dynamic events in
> tracefs files. This helps in verifying the compiled fetch instructions for
> each probe argument.
> > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> > index a8420e6abb56a..cfa807d8e760f 100644
> > --- a/kernel/trace/trace_kprobe.c
> > +++ b/kernel/trace/trace_kprobe.c
> > @@ -1320,6 +1320,8 @@ static int trace_kprobe_show(struct seq_file *m, struct dyn_event *ev)
> >  		seq_printf(m, " %s=%s", tk->tp.args[i].name, tk->tp.args[i].comm);
> >  	seq_putc(m, '\n');
> >  
> > +	trace_probe_dump_args(m, &tk->tp);
> > +
> Does enabling CONFIG_PROBE_EVENTS_DUMP_FETCHARG break in-tree userspace tools
> that parse kprobe_events?
> For example, perf probe reads the kprobe_events file directly. It passes
> the unexpected # lines to parse_probe_trace_command() in
> tools/perf/util/probe-file.c:__probe_file__get_namelist(), which returns
> -EINVAL and immediately aborts the event listing process.
> Similarly, the ftrace2bconf script does not ignore # lines when reading
> kprobe_events, which leads it to mistakenly emit invalid bootconfig syntax
> in tools/bootconfig/scripts/ftrace2bconf.sh:kprobe_event_options()
> (e.g. ftrace.event.kprobes.#.probes += ...).

Yeah, those tools needs to be updated. Anyway, the tools which reads the
files in tracefs should skip the lines started with #, Those are comment
lines. (e.g. trace file, hist file, etc.)

Thanks,

-- 
Masami Hiramatsu