arch/arm/kernel/ftrace.c

   1 /*
   2  * Dynamic function tracing support.
   3  *
   4  * Copyright (C) 2008 Abhishek Sagar <sagar.abhishek@gmail.com>
   5  * Copyright (C) 2010 Rabin Vincent <rabin@rab.in>
   6  *
   7  * For licencing details, see COPYING.
   8  *
   9  * Defines low-level handling of mcount calls when the kernel
  10  * is compiled with the -pg flag. When using dynamic ftrace, the
  11  * mcount call-sites get patched with NOP till they are enabled.
  12  * All code mutation routines here are called under stop_machine().
  13  */
  14
  15 #include <linux/ftrace.h>
  16 #include <linux/module.h>
  17 #include <linux/uaccess.h>
  18
  19 #include <asm/cacheflush.h>
  20 #include <asm/opcodes.h>
  21 #include <asm/ftrace.h>
  22
  23 #include "insn.h"
  24
  25 #ifdef CONFIG_THUMB2_KERNEL
  26 #define NOP             0xf85deb04      /* pop.w {lr} */
  27 #else
  28 #define NOP             0xe8bd4000      /* pop {lr} */
  29 #endif
  30
  31 #ifdef CONFIG_DYNAMIC_FTRACE
  32 #ifdef CONFIG_OLD_MCOUNT
  33 #define OLD_MCOUNT_ADDR ((unsigned long) mcount)
  34 #define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
  35
  36 #define OLD_NOP         0xe1a00000      /* mov r0, r0 */
  37
  38 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
  39 {
  40         return rec->arch.old_mcount ? OLD_NOP : NOP;
  41 }
  42
  43 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
  44 {
  45         if (!rec->arch.old_mcount)
  46                 return addr;
  47
  48         if (addr == MCOUNT_ADDR)
  49                 addr = OLD_MCOUNT_ADDR;
  50         else if (addr == FTRACE_ADDR)
  51                 addr = OLD_FTRACE_ADDR;
  52
  53         return addr;
  54 }
  55 #else
  56 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
  57 {
  58         return NOP;
  59 }
  60
  61 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
  62 {
  63         return addr;
  64 }
  65 #endif
  66
  67 int ftrace_arch_code_modify_prepare(void)
  68 {
  69         set_kernel_text_rw();
  70         set_all_modules_text_rw();
  71         return 0;
  72 }
  73
  74 int ftrace_arch_code_modify_post_process(void)
  75 {
  76         set_all_modules_text_ro();
  77         set_kernel_text_ro();
  78         return 0;
  79 }
  80
  81 static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
  82 {
  83         return arm_gen_branch_link(pc, addr);
  84 }
  85
  86 static int ftrace_modify_code(unsigned long pc, unsigned long old,
  87                               unsigned long new, bool validate)
  88 {
  89         unsigned long replaced;
  90
  91         if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
  92                 old = __opcode_to_mem_thumb32(old);
  93                 new = __opcode_to_mem_thumb32(new);
  94         } else {
  95                 old = __opcode_to_mem_arm(old);
  96                 new = __opcode_to_mem_arm(new);
  97         }
  98
  99         if (validate) {
 100                 if (probe_kernel_read(&replaced, (void *)pc, MCOUNT_INSN_SIZE))
 101                         return -EFAULT;
 102
 103                 if (replaced != old)
 104                         return -EINVAL;
 105         }
 106
 107         if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
 108                 return -EPERM;
 109
 110         flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
 111
 112         return 0;
 113 }
 114
 115 int ftrace_update_ftrace_func(ftrace_func_t func)
 116 {
 117         unsigned long pc;
 118         unsigned long new;
 119         int ret;
 120
 121         pc = (unsigned long)&ftrace_call;
 122         new = ftrace_call_replace(pc, (unsigned long)func);
 123
 124         ret = ftrace_modify_code(pc, 0, new, false);
 125
 126 #ifdef CONFIG_OLD_MCOUNT
 127         if (!ret) {
 128                 pc = (unsigned long)&ftrace_call_old;
 129                 new = ftrace_call_replace(pc, (unsigned long)func);
 130
 131                 ret = ftrace_modify_code(pc, 0, new, false);
 132         }
 133 #endif
 134
 135         return ret;
 136 }
 137
 138 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 139 {
 140         unsigned long new, old;
 141         unsigned long ip = rec->ip;
 142
 143         old = ftrace_nop_replace(rec);
 144         new = ftrace_call_replace(ip, adjust_address(rec, addr));
 145
 146         return ftrace_modify_code(rec->ip, old, new, true);
 147 }
 148
 149 int ftrace_make_nop(struct module *mod,
 150                     struct dyn_ftrace *rec, unsigned long addr)
 151 {
 152         unsigned long ip = rec->ip;
 153         unsigned long old;
 154         unsigned long new;
 155         int ret;
 156
 157         old = ftrace_call_replace(ip, adjust_address(rec, addr));
 158         new = ftrace_nop_replace(rec);
 159         ret = ftrace_modify_code(ip, old, new, true);
 160
 161 #ifdef CONFIG_OLD_MCOUNT
 162         if (ret == -EINVAL && addr == MCOUNT_ADDR) {
 163                 rec->arch.old_mcount = true;
 164
 165                 old = ftrace_call_replace(ip, adjust_address(rec, addr));
 166                 new = ftrace_nop_replace(rec);
 167                 ret = ftrace_modify_code(ip, old, new, true);
 168         }
 169 #endif
 170
 171         return ret;
 172 }
 173
 174 int __init ftrace_dyn_arch_init(void)
 175 {
 176         return 0;
 177 }
 178 #endif /* CONFIG_DYNAMIC_FTRACE */
 179
 180 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 181 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
 182                            unsigned long frame_pointer)
 183 {
 184         unsigned long return_hooker = (unsigned long) &return_to_handler;
 185         struct ftrace_graph_ent trace;
 186         unsigned long old;
 187         int err;
 188
 189         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 190                 return;
 191
 192         old = *parent;
 193         *parent = return_hooker;
 194
 195         trace.func = self_addr;
 196         trace.depth = current->curr_ret_stack + 1;
 197
 198         /* Only trace if the calling function expects to */
 199         if (!ftrace_graph_entry(&trace)) {
 200                 *parent = old;
 201                 return;
 202         }
 203
 204         err = ftrace_push_return_trace(old, self_addr, &trace.depth,
 205                                        frame_pointer);
 206         if (err == -EBUSY) {
 207                 *parent = old;
 208                 return;
 209         }
 210 }
 211
 212 #ifdef CONFIG_DYNAMIC_FTRACE
 213 extern unsigned long ftrace_graph_call;
 214 extern unsigned long ftrace_graph_call_old;
 215 extern void ftrace_graph_caller_old(void);
 216
 217 static int __ftrace_modify_caller(unsigned long *callsite,
 218                                   void (*func) (void), bool enable)
 219 {
 220         unsigned long caller_fn = (unsigned long) func;
 221         unsigned long pc = (unsigned long) callsite;
 222         unsigned long branch = arm_gen_branch(pc, caller_fn);
 223         unsigned long nop = 0xe1a00000; /* mov r0, r0 */
 224         unsigned long old = enable ? nop : branch;
 225         unsigned long new = enable ? branch : nop;
 226
 227         return ftrace_modify_code(pc, old, new, true);
 228 }
 229
 230 static int ftrace_modify_graph_caller(bool enable)
 231 {
 232         int ret;
 233
 234         ret = __ftrace_modify_caller(&ftrace_graph_call,
 235                                      ftrace_graph_caller,
 236                                      enable);
 237
 238 #ifdef CONFIG_OLD_MCOUNT
 239         if (!ret)
 240                 ret = __ftrace_modify_caller(&ftrace_graph_call_old,
 241                                              ftrace_graph_caller_old,
 242                                              enable);
 243 #endif
 244
 245         return ret;
 246 }
 247
 248 int ftrace_enable_ftrace_graph_caller(void)
 249 {
 250         return ftrace_modify_graph_caller(true);
 251 }
 252
 253 int ftrace_disable_ftrace_graph_caller(void)
 254 {
 255         return ftrace_modify_graph_caller(false);
 256 }
 257 #endif /* CONFIG_DYNAMIC_FTRACE */
 258 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */