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 #define MAX_SYMBOL_LEN 64 18 static char symbol[MAX_SYMBOL_LEN] = "_do_fork"; 19 module_param_string(symbol, symbol, sizeof(symbol), 0644); 20 21 /* For each probe you need to allocate a kprobe structure */ 22 static struct kprobe kp = { 23 .symbol_name = symbol, 24 }; 25 26 /* kprobe pre_handler: called just before the probed instruction is executed */ 27 static int handler_pre(struct kprobe *p, struct pt_regs *regs) 28 { 29 #ifdef CONFIG_X86 30 printk(KERN_INFO "<%s> pre_handler: p->addr = 0x%p, ip = %lx," 31 " flags = 0x%lx\n", 32 p->symbol_name, p->addr, regs->ip, regs->flags); 33 #endif 34 #ifdef CONFIG_PPC 35 printk(KERN_INFO "<%s> pre_handler: p->addr = 0x%p, nip = 0x%lx," 36 " msr = 0x%lx\n", 37 p->symbol_name, p->addr, regs->nip, regs->msr); 38 #endif 39 #ifdef CONFIG_MIPS 40 printk(KERN_INFO "<%s> pre_handler: p->addr = 0x%p, epc = 0x%lx," 41 " status = 0x%lx\n", 42 p->symbol_name, p->addr, regs->cp0_epc, regs->cp0_status); 43 #endif 44 #ifdef CONFIG_TILEGX 45 printk(KERN_INFO "<%s> pre_handler: p->addr = 0x%p, pc = 0x%lx," 46 " ex1 = 0x%lx\n", 47 p->symbol_name, p->addr, regs->pc, regs->ex1); 48 #endif 49 50 /* A dump_stack() here will give a stack backtrace */ 51 return 0; 52 } 53 54 /* kprobe post_handler: called after the probed instruction is executed */ 55 static void handler_post(struct kprobe *p, struct pt_regs *regs, 56 unsigned long flags) 57 { 58 #ifdef CONFIG_X86 59 printk(KERN_INFO "<%s> post_handler: p->addr = 0x%p, flags = 0x%lx\n", 60 p->symbol_name, p->addr, regs->flags); 61 #endif 62 #ifdef CONFIG_PPC 63 printk(KERN_INFO "<%s> post_handler: p->addr = 0x%p, msr = 0x%lx\n", 64 p->symbol_name, p->addr, regs->msr); 65 #endif 66 #ifdef CONFIG_MIPS 67 printk(KERN_INFO "<%s> post_handler: p->addr = 0x%p, status = 0x%lx\n", 68 p->symbol_name, p->addr, regs->cp0_status); 69 #endif 70 #ifdef CONFIG_TILEGX 71 printk(KERN_INFO "<%s> post_handler: p->addr = 0x%p, ex1 = 0x%lx\n", 72 p->symbol_name, p->addr, regs->ex1); 73 #endif 74 } 75 76 /* 77 * fault_handler: this is called if an exception is generated for any 78 * instruction within the pre- or post-handler, or when Kprobes 79 * single-steps the probed instruction. 80 */ 81 static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr) 82 { 83 printk(KERN_INFO "fault_handler: p->addr = 0x%p, trap #%dn", 84 p->addr, trapnr); 85 /* Return 0 because we don't handle the fault. */ 86 return 0; 87 } 88 89 static int __init kprobe_init(void) 90 { 91 int ret; 92 kp.pre_handler = handler_pre; 93 kp.post_handler = handler_post; 94 kp.fault_handler = handler_fault; 95 96 ret = register_kprobe(&kp); 97 if (ret < 0) { 98 printk(KERN_INFO "register_kprobe failed, returned %d\n", ret); 99 return ret; 100 } 101 printk(KERN_INFO "Planted kprobe at %p\n", kp.addr); 102 return 0; 103 } 104 105 static void __exit kprobe_exit(void) 106 { 107 unregister_kprobe(&kp); 108 printk(KERN_INFO "kprobe at %p unregistered\n", kp.addr); 109 } 110 111 module_init(kprobe_init) 112 module_exit(kprobe_exit) 113 MODULE_LICENSE("GPL"); 114