perf probe: Check the orphaned -x option

To avoid probing in unintended binary, the orphaned -x option must be
checked and warned.

Without this patch, following command sets up the probe in the kernel.

-----
# perf probe -a strcpy -x ./perf
Added new event:
probe:strcpy (on strcpy)

You can now use it in all perf tools, such as:

perf record -e probe:strcpy -aR sleep 1
-----

But in this case, it seems that the user may want to probe in the perf
binary. With this patch, perf-probe correctly handles the orphaned -x.

-----
# perf probe -a strcpy -x ./perf
Error: -x/-m must follow the probe definitions.
...
-----

Reported-by: Jiri Olsa <[e-mail]>
Acked-by: Jiri Olsa <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Masami Hiramatsu <[e-mail]>
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-probe.c

···
 	bool mod_events;
 	bool uprobes;
 	bool quiet;
+	bool target_used;
 	int nevents;
 	struct perf_probe_event events[MAX_PROBES];
 	struct strlist *dellist;
···
 		pev->target = strdup(params.target);
 		if (!pev->target)
 			return -ENOMEM;
+		params.target_used = true;
 	}
 
 	/* Parse a perf-probe command into event */
···
 		params.target = strdup(ptr);
 		if (!params.target)
 			return -ENOMEM;
+		params.target_used = false;
 
 		found = 1;
 		buf = ptr + (strlen(ptr) - 3);
···
 		}
 		free(params.target);
 		params.target = tmp;
+		params.target_used = false;
 		ret = 0;
 	}
 
···
 	}
 
 	if (params.nevents) {
+		/* Ensure the last given target is used */
+		if (params.target && !params.target_used) {
+			pr_warning("  Error: -x/-m must follow the probe definitions.\n");
+			usage_with_options(probe_usage, options);
+		}
+
 		ret = add_perf_probe_events(params.events, params.nevents,
 					    params.max_probe_points,
 					    params.force_add);