ftrace: Add sample module that uses register_ftrace_direct()

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>

diff --git a/samples/Kconfig b/samples/Kconfig
index c8dacb4dda80c0d44548e81391bd4a65f276048b..65b5967dac0c0f08baf1cc0030fd483749d2b8b7 100644 (file)
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -19,6 +19,14 @@ 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
+       depends on X86_64 # has x86_64 inlined asm
+       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 7d6e4ca28d696ac539f1e690eee8d36c8635f917..cd496d633370173179994ef6093eb48997cb3d32 100644 (file)
--- 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 (file)
index 0000000..3718ab3
--- /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 (file)
index 0000000..1483f06
--- /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");