selftests/ftrace: Add a testcase for many kprobe events

Add a testcase to test kprobes via ftrace interface
with many concurrent kprobe events.

This tries to add many kprobe events (up to 256) on
kernel functions. To avoid making ftrace-based
kprobes (kprobes on fentry), it skips first N bytes
(on x86 N=5, on ppc or arm N=4) of function entry.
After that, it enables all those events, disable it,
and remove it.

Since the unoptimization buffer reclaiming will
be delayed, after removing events, it will wait
enough time.

Link: http://lkml.kernel.org/r/149577388470.11702.11832460851769204511.stgit@devboxSigned-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

tools/testing/selftests/ftrace/test.d/kprobe/multiple_kprobes.tc

+#!/bin/sh
+# description: Register/unregister many kprobe events
+
+# ftrace fentry skip size depends on the machine architecture.
+# Currently HAVE_KPROBES_ON_FTRACE defined on x86 and powerpc
+case `uname -m` in
+  x86_64|i[3456]86) OFFS=5;;
+  ppc*) OFFS=4;;
+  *) OFFS=0;;
+esac
+
+echo "Setup up to 256 kprobes"
+grep t /proc/kallsyms | cut -f3 -d" " | grep -v .*\\..* | \
+head -n 256 | while read i; do echo p ${i}+${OFFS} ; done > kprobe_events ||:
+
+echo 1 > events/kprobes/enable
+echo 0 > events/kprobes/enable
+echo > kprobe_events
+echo "Waiting for unoptimizing & freeing"
+sleep 5
+echo "Done"