x86: kprobes: add kprobes smoke tests that run on boot

Here is a quick and naive smoke test for kprobes. This is intended to
just verify if some unrelated change broke the *probes subsystem. It is
self contained, architecture agnostic and isn't of any great use by itself.

This needs to be built in the kernel and runs a basic set of tests to
verify if kprobes, jprobes and kretprobes run fine on the kernel. In case
of an error, it'll print out a message with a "BUG" prefix.

This is a start; we intend to add more tests to this bucket over time.

Thanks to Jim Keniston and Masami Hiramatsu for comments and suggestions.

Tested on x86 (32/64) and powerpc.

Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/kprobes.c

@@ -824,6 +824,8 @@ static int __init init_kprobes(void)
 	if (!err)
 		err = register_die_notifier(&kprobe_exceptions_nb);
 
+	if (!err)
+		init_test_probes();
 	return err;
 }