ftrace/samples: Add multi direct interface test module

Adding simple module that uses multi direct interface:

  register_ftrace_direct_multi
  unregister_ftrace_direct_multi

The init function registers trampoline for 2 functions,
and exit function unregisters them.

Link: https://lkml.kernel.org/r/20211008091336.33616-9-jolsa@kernel.org

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

samples/ftrace/Makefile

@@ -3,6 +3,7 @@
 obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct.o
 obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct-too.o
 obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct-modify.o
+obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct-multi.o
 
 CFLAGS_sample-trace-array.o := -I$(src)
 obj-$(CONFIG_SAMPLE_TRACE_ARRAY) += sample-trace-array.o

samples/ftrace/ftrace-direct-multi.c

@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/module.h>
+
+#include <linux/mm.h> /* for handle_mm_fault() */
+#include <linux/ftrace.h>
+#include <linux/sched/stat.h>
+
+void my_direct_func(unsigned long ip)
+{
+	trace_printk("ip %lx\n", ip);
+}
+
+extern void my_tramp(void *);
+
+asm (
+"	.pushsection    .text, \"ax\", @progbits\n"
+"	.type		my_tramp, @function\n"
+"	.globl		my_tramp\n"
+"   my_tramp:"
+"	pushq %rbp\n"
+"	movq %rsp, %rbp\n"
+"	pushq %rdi\n"
+"	movq 8(%rbp), %rdi\n"
+"	call my_direct_func\n"
+"	popq %rdi\n"
+"	leave\n"
+"	ret\n"
+"	.size		my_tramp, .-my_tramp\n"
+"	.popsection\n"
+);
+
+static struct ftrace_ops direct;
+
+static int __init ftrace_direct_multi_init(void)
+{
+	ftrace_set_filter_ip(&direct, (unsigned long) wake_up_process, 0, 0);
+	ftrace_set_filter_ip(&direct, (unsigned long) schedule, 0, 0);
+
+	return register_ftrace_direct_multi(&direct, (unsigned long) my_tramp);
+}
+
+static void __exit ftrace_direct_multi_exit(void)
+{
+	unregister_ftrace_direct_multi(&direct, (unsigned long) my_tramp);
+}
+
+module_init(ftrace_direct_multi_init);
+module_exit(ftrace_direct_multi_exit);
+
+MODULE_AUTHOR("Jiri Olsa");
+MODULE_DESCRIPTION("Example use case of using register_ftrace_direct_multi()");
+MODULE_LICENSE("GPL");