Linux内核调试方法总结之Kprobes
Kprobes
【用途】【参考kernel/Documentation/kprobes.txt帮助文档】
Kprobes是一个轻量级内核调试工具，同时又是其他一些更高级的内核调试工具(如perf和systemtap)的基础，在Linux 4.0内核版本中，eBPF特性也寄生于kprobe之上。
【原理】
Kprobes的主要作用是在指定函数调用前后添加自定义函数，从而实现动态探测点的功能。
Kprobes有两种使用方法：1）模块加载；2)通过debugfs操作。
【接口说明】【参考kernel/sample/kprobes】
关键结构体
#include <linux/kprobes.h>
struct kprobe {
kprobe_opcode_t *addr; /* Location of the probe point */
const char *symbol_name; /* Allow user to indicate symbol name of the probe point */
kprobe_pre_handler_t pre_handler; /* Called before addr is executed */
kprobe_pre_handler_t post_handler; /* Called after addr is executed */
kprobe_pre_handler_t fault_handler; /* Called if executing addr caused a fault */
};
注册kprobes探测点
int register_kprobe(struct kprobe *p);
注销kprobes探测点
void unregister_kprobe(struct kprobe *p);
【实例】
/*
* NOTE: This example is works on x86 and powerpc.
* Here's a sample kernel module showing the use of kprobes to dump a
* stack trace and selected registers when do_fork() is called.
* * For more information on theory of operation of kprobes, see
* Documentation/kprobes.txt
* * You will see the trace data in /var/log/messages and on the console
* whenever do_fork() is invoked to create a new process.
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/kprobes.h>
/* For each probe you need to allocate a kprobe structure */
static struct kprobe kp = {
.symbol_name = "do_fork",
};
/* kprobe pre_handler: called just before the probed instruction is executed */
static int handler_pre(struct kprobe *p, struct pt_regs *regs) {
#ifdef CONFIG_X86
printk(KERN_INFO "pre_handler: p->addr = 0x%p, ip = %lx," " flags = 0x%lx\r\n", p->addr, regs->ip, regs->flags);
#endif
#ifdef CONFIG_PPC
printk(KERN_INFO "pre_handler: p->addr = 0x%p, nip = 0x%lx," " msr = 0x%lx\r\n", p->addr, regs->nip, regs->msr);
#endif
#ifdef CONFIG_MIPS
printk(KERN_INFO "pre_handler: p->addr = 0x%p, epc = 0x%lx," " status = 0x%lx\r\n", p->addr, regs->cp0_epc, regs->cp0_status);
#endif
/* A dump_stack() here will give a stack backtrace */
return 0;
}
/* kprobe post_handler: called after the probed instruction is executed */
static void handler_post(struct kprobe *p, struct pt_regs *regs, unsigned long flags) {
#ifdef CONFIG_X86
printk(KERN_INFO "post_handler: p->addr = 0x%p, flags = 0x%lx\r\n", p->addr, regs->flags);
#endif
#ifdef CONFIG_PPC
printk(KERN_INFO "post_handler: p->addr = 0x%p, msr = 0x%lx\r\n", p->addr, regs->msr);
#endif
#ifdef CONFIG_MIPS
printk(KERN_INFO "post_handler: p->addr = 0x%p, status = 0x%lx\r\n", p->addr, regs->cp0_status);
#endif
}
/*
* fault_handler: this is called if an exception is generated for any
* instruction within the pre- or post-handler, or when Kprobes
* single-steps the probed instruction.
*/
static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr) {
printk(KERN_INFO "fault_handler: p->addr = 0x%p, trap #%dn", p->addr, trapnr);
/* Return 0 because we don't handle the fault. */
return 0;
}
static int __init kprobe_init(void) {
int ret;
kp.pre_handler = handler_pre;
kp.post_handler = handler_post;
kp.fault_handler = handler_fault;
ret = register_kprobe(&kp);
if (ret < 0) {
printk(KERN_INFO "register_kprobe failed, returned %d\r\n", ret);
return ret;
}
printk(KERN_INFO "Planted kprobe at %p\r\n", kp.addr);
return 0;
}
static void __exit kprobe_exit(void) {
unregister_kprobe(&kp);
printk(KERN_INFO "kprobe at %p unregistered\r\n", kp.addr);
}
module_init(kprobe_init) module_exit(kprobe_exit) MODULE_LICENSE("GPL");
