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samples/kprobes/kretprobe_example.c
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// SPDX-License-Identifier: GPL-2.0-only |
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/* * 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> * |
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* If no func_name is specified, kernel_clone is instrumented |
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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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* * 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> |
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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); 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; } |
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NOKPROBE_SYMBOL(entry_handler); |
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/* * 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) { |
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unsigned long retval = regs_return_value(regs); |
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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)); |
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pr_info("%s returned %lu and took %lld ns to execute ", |
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func_name, retval, (long long)delta); return 0; } |
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NOKPROBE_SYMBOL(ret_handler); |
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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) { |
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pr_err("register_kretprobe failed, returned %d ", ret); |
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return -1; } |
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pr_info("Planted return probe at %s: %p ", |
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my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr); return 0; } static void __exit kretprobe_exit(void) { unregister_kretprobe(&my_kretprobe); |
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pr_info("kretprobe at %p unregistered ", 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 ", |
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my_kretprobe.nmissed, my_kretprobe.kp.symbol_name); } module_init(kretprobe_init) module_exit(kretprobe_exit) MODULE_LICENSE("GPL"); |