1 files changed, 106 insertions, 0 deletions

diff --git a/samples/kprobes/kretprobe_example.c b/samples/kprobes/kretprobe_example.c
new file mode 100644
index 000000000000..4e764b317d61
--- /dev/null
+++ b/samples/kprobes/kretprobe_example.c
@@ -0,0 +1,106 @@
+/*
+ * kretprobe_example.c
+ *
+ * Here's a sample kernel module showing the use of return probes to
+ * report the return value and total time taken for probed function
+ * to run.
+ *
+ * usage: insmod kretprobe_example.ko func=<func_name>
+ *
+ * If no func_name is specified, do_fork is instrumented
+ *
+ * For more information on theory of operation of kretprobes, see
+ * Documentation/kprobes.txt
+ *
+ * Build and insert the kernel module as done in the kprobe example.
+ * You will see the trace data in /var/log/messages and on the console
+ * whenever the probed function returns. (Some messages may be suppressed
+ * if syslogd is configured to eliminate duplicate messages.)
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/kprobes.h>
+#include <linux/ktime.h>
+#include <linux/limits.h>
+
+static char func_name[NAME_MAX] = "do_fork";
+module_param_string(func, func_name, NAME_MAX, S_IRUGO);
+MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the"
+                        " function's execution time");
+
+/* per-instance private data */
+struct my_data {
+        ktime_t entry_stamp;
+};
+
+/* Here we use the entry_hanlder to timestamp function entry */
+static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
+{
+        struct my_data *data;
+
+        if (!current->mm)
+                return 1;       /* Skip kernel threads */
+
+        data = (struct my_data *)ri->data;
+        data->entry_stamp = ktime_get();
+        return 0;
+}
+
+/*
+ * Return-probe handler: Log the return value and duration. Duration may turn
+ * out to be zero consistently, depending upon the granularity of time
+ * accounting on the platform.
+ */
+static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
+{
+        int retval = regs_return_value(regs);
+        struct my_data *data = (struct my_data *)ri->data;
+        s64 delta;
+        ktime_t now;
+
+        now = ktime_get();
+        delta = ktime_to_ns(ktime_sub(now, data->entry_stamp));
+        printk(KERN_INFO "%s returned %d and took %lld ns to execute\n",
+                        func_name, retval, (long long)delta);
+        return 0;
+}
+
+static struct kretprobe my_kretprobe = {
+        .handler                = ret_handler,
+        .entry_handler          = entry_handler,
+        .data_size              = sizeof(struct my_data),
+        /* Probe up to 20 instances concurrently. */
+        .maxactive              = 20,
+};
+
+static int __init kretprobe_init(void)
+{
+        int ret;
+
+        my_kretprobe.kp.symbol_name = func_name;
+        ret = register_kretprobe(&my_kretprobe);
+        if (ret < 0) {
+                printk(KERN_INFO "register_kretprobe failed, returned %d\n",
+                                ret);
+                return -1;
+        }
+        printk(KERN_INFO "Planted return probe at %s: %p\n",
+                        my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr);
+        return 0;
+}
+
+static void __exit kretprobe_exit(void)
+{
+        unregister_kretprobe(&my_kretprobe);
+        printk(KERN_INFO "kretprobe at %p unregistered\n",
+                        my_kretprobe.kp.addr);
+
+        /* nmissed > 0 suggests that maxactive was set too low. */
+        printk(KERN_INFO "Missed probing %d instances of %s\n",
+                my_kretprobe.nmissed, my_kretprobe.kp.symbol_name);
+}
+
+module_init(kretprobe_init)
+module_exit(kretprobe_exit)
+MODULE_LICENSE("GPL");