1 /* 2 * NOTE: This example is works on x86 and powerpc. 3 * Here's a sample kernel module showing the use of kprobes to dump a 4 * stack trace and selected registers when do_fork() is called. 5 * 6 * For more information on theory of operation of kprobes, see 7 * Documentation/kprobes.txt 8 * 9 * You will see the trace data in /var/log/messages and on the console 10 * whenever do_fork() is invoked to create a new process. 11 */ 12 13 #include <linux/kernel.h> 14 #include <linux/module.h> 15 #include <linux/kprobes.h> 16 17 /* For each probe you need to allocate a kprobe structure */ 18 static struct kprobe kp = { 19 .symbol_name = "do_fork", 20 }; 21 22 /* kprobe pre_handler: called just before the probed instruction is executed */ 23 static int handler_pre(struct kprobe *p, struct pt_regs *regs) 24 { 25 #ifdef CONFIG_X86 26 printk(KERN_INFO "pre_handler: p->addr = 0x%p, ip = %lx," 27 " flags = 0x%lx\n", 28 p->addr, regs->ip, regs->flags); 29 #endif 30 #ifdef CONFIG_PPC 31 printk(KERN_INFO "pre_handler: p->addr = 0x%p, nip = 0x%lx," 32 " msr = 0x%lx\n", 33 p->addr, regs->nip, regs->msr); 34 #endif 35 36 /* A dump_stack() here will give a stack backtrace */ 37 return 0; 38 } 39 40 /* kprobe post_handler: called after the probed instruction is executed */ 41 static void handler_post(struct kprobe *p, struct pt_regs *regs, 42 unsigned long flags) 43 { 44 #ifdef CONFIG_X86 45 printk(KERN_INFO "post_handler: p->addr = 0x%p, flags = 0x%lx\n", 46 p->addr, regs->flags); 47 #endif 48 #ifdef CONFIG_PPC 49 printk(KERN_INFO "post_handler: p->addr = 0x%p, msr = 0x%lx\n", 50 p->addr, regs->msr); 51 #endif 52 } 53 54 /* 55 * fault_handler: this is called if an exception is generated for any 56 * instruction within the pre- or post-handler, or when Kprobes 57 * single-steps the probed instruction. 58 */ 59 static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr) 60 { 61 printk(KERN_INFO "fault_handler: p->addr = 0x%p, trap #%dn", 62 p->addr, trapnr); 63 /* Return 0 because we don't handle the fault. */ 64 return 0; 65 } 66 67 static int __init kprobe_init(void) 68 { 69 int ret; 70 kp.pre_handler = handler_pre; 71 kp.post_handler = handler_post; 72 kp.fault_handler = handler_fault; 73 74 ret = register_kprobe(&kp); 75 if (ret < 0) { 76 printk(KERN_INFO "register_kprobe failed, returned %d\n", ret); 77 return ret; 78 } 79 printk(KERN_INFO "Planted kprobe at %p\n", kp.addr); 80 return 0; 81 } 82 83 static void __exit kprobe_exit(void) 84 { 85 unregister_kprobe(&kp); 86 printk(KERN_INFO "kprobe at %p unregistered\n", kp.addr); 87 } 88 89 module_init(kprobe_init) 90 module_exit(kprobe_exit) 91 MODULE_LICENSE("GPL"); 92