1 /* 2 * Copyright (C) 2008 Matt Fleming <mjf@gentoo.org> 3 * Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org> 4 * 5 * Code for replacing ftrace calls with jumps. 6 * 7 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com> 8 * 9 * Thanks goes to Ingo Molnar, for suggesting the idea. 10 * Mathieu Desnoyers, for suggesting postponing the modifications. 11 * Arjan van de Ven, for keeping me straight, and explaining to me 12 * the dangers of modifying code on the run. 13 */ 14 #include <linux/uaccess.h> 15 #include <linux/ftrace.h> 16 #include <linux/string.h> 17 #include <linux/init.h> 18 #include <linux/io.h> 19 #include <asm/ftrace.h> 20 #include <asm/cacheflush.h> 21 22 static unsigned char ftrace_nop[] = { 23 0x09, 0x00, /* nop */ 24 0x09, 0x00, /* nop */ 25 }; 26 27 static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE]; 28 29 unsigned char *ftrace_nop_replace(void) 30 { 31 return ftrace_nop; 32 } 33 34 static int is_sh_nop(unsigned char *ip) 35 { 36 return strncmp(ip, ftrace_nop, sizeof(ftrace_nop)); 37 } 38 39 unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr) 40 { 41 /* Place the address in the memory table. */ 42 if (addr == CALLER_ADDR) 43 __raw_writel(addr + MCOUNT_INSN_OFFSET, ftrace_replaced_code); 44 else 45 __raw_writel(addr, ftrace_replaced_code); 46 47 /* 48 * No locking needed, this must be called via kstop_machine 49 * which in essence is like running on a uniprocessor machine. 50 */ 51 return ftrace_replaced_code; 52 } 53 54 int ftrace_modify_code(unsigned long ip, unsigned char *old_code, 55 unsigned char *new_code) 56 { 57 unsigned char replaced[MCOUNT_INSN_SIZE]; 58 59 /* 60 * Note: Due to modules and __init, code can 61 * disappear and change, we need to protect against faulting 62 * as well as code changing. We do this by using the 63 * probe_kernel_* functions. 64 * 65 * No real locking needed, this code is run through 66 * kstop_machine, or before SMP starts. 67 */ 68 69 /* 70 * If we're trying to nop out a call to a function, we instead 71 * place a call to the address after the memory table. 72 */ 73 if (is_sh_nop(new_code) == 0) 74 __raw_writel(ip + MCOUNT_INSN_SIZE, (unsigned long)new_code); 75 76 /* read the text we want to modify */ 77 if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE)) 78 return -EFAULT; 79 80 /* Make sure it is what we expect it to be */ 81 if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0) 82 return -EINVAL; 83 84 /* replace the text with the new text */ 85 if (probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE)) 86 return -EPERM; 87 88 flush_icache_range(ip, ip + MCOUNT_INSN_SIZE); 89 90 return 0; 91 } 92 93 int ftrace_update_ftrace_func(ftrace_func_t func) 94 { 95 unsigned long ip = (unsigned long)(&ftrace_call); 96 unsigned char old[MCOUNT_INSN_SIZE], *new; 97 98 memcpy(old, (unsigned char *)(ip + MCOUNT_INSN_OFFSET), MCOUNT_INSN_SIZE); 99 new = ftrace_call_replace(ip, (unsigned long)func); 100 101 return ftrace_modify_code(ip + MCOUNT_INSN_OFFSET, old, new); 102 } 103 104 int ftrace_make_nop(struct module *mod, 105 struct dyn_ftrace *rec, unsigned long addr) 106 { 107 unsigned char *new, *old; 108 unsigned long ip = rec->ip; 109 110 old = ftrace_call_replace(ip, addr); 111 new = ftrace_nop_replace(); 112 113 return ftrace_modify_code(rec->ip, old, new); 114 } 115 116 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) 117 { 118 unsigned char *new, *old; 119 unsigned long ip = rec->ip; 120 121 old = ftrace_nop_replace(); 122 new = ftrace_call_replace(ip, addr); 123 124 return ftrace_modify_code(rec->ip, old, new); 125 } 126 127 int __init ftrace_dyn_arch_init(void *data) 128 { 129 /* The return code is retured via data */ 130 __raw_writel(0, (unsigned long)data); 131 132 return 0; 133 } 134