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Subject[PATCH 05/10] ftrace: Add sample module that uses register_ftrace_direct()
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

Add a sample module that shows a simple use case for
regsiter_ftrace_direct(), and how to use it.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
samples/Kconfig | 7 ++++++
samples/Makefile | 1 +
samples/ftrace/Makefile | 3 +++
samples/ftrace/ftrace-direct.c | 45 ++++++++++++++++++++++++++++++++++
4 files changed, 56 insertions(+)
create mode 100644 samples/ftrace/Makefile
create mode 100644 samples/ftrace/ftrace-direct.c

diff --git a/samples/Kconfig b/samples/Kconfig
index c8dacb4dda80..6481b1f7705d 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -19,6 +19,13 @@ config SAMPLE_TRACE_PRINTK
This builds a module that calls trace_printk() and can be used to
test various trace_printk() calls from a module.

+config SAMPLE_FTRACE_DIRECT
+ tristate "Build register_ftrace_direct() example"
+ depends on DYNAMIC_FTRACE_WITH_DIRECT_CALLS && m
+ help
+ This builds an ftrace direct function example
+ that hooks to wake_up_process and prints the parameters.
+
config SAMPLE_KOBJECT
tristate "Build kobject examples"
help
diff --git a/samples/Makefile b/samples/Makefile
index 7d6e4ca28d69..cd496d633370 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -17,6 +17,7 @@ obj-$(CONFIG_SAMPLE_RPMSG_CLIENT) += rpmsg/
subdir-$(CONFIG_SAMPLE_SECCOMP) += seccomp
obj-$(CONFIG_SAMPLE_TRACE_EVENTS) += trace_events/
obj-$(CONFIG_SAMPLE_TRACE_PRINTK) += trace_printk/
+obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace/
obj-$(CONFIG_VIDEO_PCI_SKELETON) += v4l/
obj-y += vfio-mdev/
subdir-$(CONFIG_SAMPLE_VFS) += vfs
diff --git a/samples/ftrace/Makefile b/samples/ftrace/Makefile
new file mode 100644
index 000000000000..3718ab39eba3
--- /dev/null
+++ b/samples/ftrace/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct.o
diff --git a/samples/ftrace/ftrace-direct.c b/samples/ftrace/ftrace-direct.c
new file mode 100644
index 000000000000..1483f067b000
--- /dev/null
+++ b/samples/ftrace/ftrace-direct.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/module.h>
+
+#include <linux/sched.h> /* for wake_up_process() */
+#include <linux/ftrace.h>
+
+void my_direct_func(struct task_struct *p)
+{
+ trace_printk("wakeing up %s-%d\n", p->comm, p->pid);
+}
+
+extern void my_tramp(void *);
+
+asm (
+" .pushsection .text, \"ax\", @progbits\n"
+" my_tramp:"
+" pushq %rbp\n"
+" movq %rsp, %rbp\n"
+" pushq %rdi\n"
+" call my_direct_func\n"
+" popq %rdi\n"
+" leave\n"
+" ret\n"
+" .popsection\n"
+);
+
+
+static int __init ftrace_direct_init(void)
+{
+ return register_ftrace_direct((unsigned long)wake_up_process,
+ (unsigned long)my_tramp);
+}
+
+static void __exit ftrace_direct_exit(void)
+{
+ unregister_ftrace_direct((unsigned long)wake_up_process,
+ (unsigned long)my_tramp);
+}
+
+module_init(ftrace_direct_init);
+module_exit(ftrace_direct_exit);
+
+MODULE_AUTHOR("Steven Rostedt");
+MODULE_DESCRIPTION("Example use case of using register_ftrace_direct()");
+MODULE_LICENSE("GPL");
--
2.23.0

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