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108 lines
3.0 KiB
108 lines
3.0 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* kretprobe_example.c |
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* |
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* Here's a sample kernel module showing the use of return probes to |
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* report the return value and total time taken for probed function |
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* to run. |
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* |
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* usage: insmod kretprobe_example.ko func=<func_name> |
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* |
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* If no func_name is specified, kernel_clone is instrumented |
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* |
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* For more information on theory of operation of kretprobes, see |
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* Documentation/trace/kprobes.rst |
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* |
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* Build and insert the kernel module as done in the kprobe example. |
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* You will see the trace data in /var/log/messages and on the console |
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* whenever the probed function returns. (Some messages may be suppressed |
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* if syslogd is configured to eliminate duplicate messages.) |
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*/ |
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#include <linux/kernel.h> |
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#include <linux/module.h> |
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#include <linux/kprobes.h> |
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#include <linux/ktime.h> |
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#include <linux/limits.h> |
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#include <linux/sched.h> |
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static char func_name[NAME_MAX] = "kernel_clone"; |
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module_param_string(func, func_name, NAME_MAX, S_IRUGO); |
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MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the" |
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" function's execution time"); |
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/* per-instance private data */ |
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struct my_data { |
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ktime_t entry_stamp; |
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}; |
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/* Here we use the entry_hanlder to timestamp function entry */ |
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static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs) |
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{ |
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struct my_data *data; |
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if (!current->mm) |
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return 1; /* Skip kernel threads */ |
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data = (struct my_data *)ri->data; |
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data->entry_stamp = ktime_get(); |
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return 0; |
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} |
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NOKPROBE_SYMBOL(entry_handler); |
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/* |
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* Return-probe handler: Log the return value and duration. Duration may turn |
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* out to be zero consistently, depending upon the granularity of time |
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* accounting on the platform. |
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*/ |
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static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs) |
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{ |
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unsigned long retval = regs_return_value(regs); |
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struct my_data *data = (struct my_data *)ri->data; |
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s64 delta; |
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ktime_t now; |
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now = ktime_get(); |
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delta = ktime_to_ns(ktime_sub(now, data->entry_stamp)); |
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pr_info("%s returned %lu and took %lld ns to execute\n", |
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func_name, retval, (long long)delta); |
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return 0; |
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} |
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NOKPROBE_SYMBOL(ret_handler); |
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static struct kretprobe my_kretprobe = { |
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.handler = ret_handler, |
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.entry_handler = entry_handler, |
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.data_size = sizeof(struct my_data), |
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/* Probe up to 20 instances concurrently. */ |
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.maxactive = 20, |
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}; |
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static int __init kretprobe_init(void) |
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{ |
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int ret; |
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my_kretprobe.kp.symbol_name = func_name; |
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ret = register_kretprobe(&my_kretprobe); |
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if (ret < 0) { |
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pr_err("register_kretprobe failed, returned %d\n", ret); |
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return -1; |
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} |
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pr_info("Planted return probe at %s: %p\n", |
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my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr); |
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return 0; |
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} |
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static void __exit kretprobe_exit(void) |
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{ |
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unregister_kretprobe(&my_kretprobe); |
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pr_info("kretprobe at %p unregistered\n", my_kretprobe.kp.addr); |
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/* nmissed > 0 suggests that maxactive was set too low. */ |
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pr_info("Missed probing %d instances of %s\n", |
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my_kretprobe.nmissed, my_kretprobe.kp.symbol_name); |
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} |
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module_init(kretprobe_init) |
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module_exit(kretprobe_exit) |
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MODULE_LICENSE("GPL");
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