samples/kprobes: Add __kprobes and NOKPROBE_SYMBOL() for handlers.

Add __kprobes and NOKPROBE_SYMBOL() for sample kprobe handlers.
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200505134059.878578033@linutronix.de

samples/kprobes/kprobe_example.c

@@ -25,7 +25,7 @@ static struct kprobe kp = {
 };
 
 /* kprobe pre_handler: called just before the probed instruction is executed */
-static int handler_pre(struct kprobe *p, struct pt_regs *regs)
+static int __kprobes handler_pre(struct kprobe *p, struct pt_regs *regs)
 {
 #ifdef CONFIG_X86
 	pr_info("<%s> pre_handler: p->addr = 0x%p, ip = %lx, flags = 0x%lx\n",
@@ -54,7 +54,7 @@ static int handler_pre(struct kprobe *p, struct pt_regs *regs)
 }
 
 /* kprobe post_handler: called after the probed instruction is executed */
-static void handler_post(struct kprobe *p, struct pt_regs *regs,
+static void __kprobes handler_post(struct kprobe *p, struct pt_regs *regs,
 				unsigned long flags)
 {
 #ifdef CONFIG_X86
@@ -90,6 +90,8 @@ static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
 	/* Return 0 because we don't handle the fault. */
 	return 0;
 }
+/* NOKPROBE_SYMBOL() is also available */
+NOKPROBE_SYMBOL(handler_fault);
 
 static int __init kprobe_init(void)
 {

samples/kprobes/kretprobe_example.c

@@ -48,6 +48,7 @@ static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
 	data->entry_stamp = ktime_get();
 	return 0;
 }
+NOKPROBE_SYMBOL(entry_handler);
 
 /*
  * Return-probe handler: Log the return value and duration. Duration may turn
@@ -67,6 +68,7 @@ static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
 			func_name, retval, (long long)delta);
 	return 0;
 }
+NOKPROBE_SYMBOL(ret_handler);
 
 static struct kretprobe my_kretprobe = {
 	.handler		= ret_handler,