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/uaccess.h>
  17 #include <linux/module.h>
  18 #include <linux/stop_machine.h>
  19
  20 #include <asm/cacheflush.h>
  21 #include <asm/opcodes.h>
  22 #include <asm/ftrace.h>
  23 #include <asm/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
  33 static int __ftrace_modify_code(void *data)
  34 {
  35         int *command = data;
  36
  37         set_kernel_text_rw();
  38         ftrace_modify_all_code(*command);
  39         set_kernel_text_ro();
  40
  41         return 0;
  42 }
  43
  44 void arch_ftrace_update_code(int command)
  45 {
  46         stop_machine(__ftrace_modify_code, &command, NULL);
  47 }
  48
  49 #ifdef CONFIG_OLD_MCOUNT
  50 #define OLD_MCOUNT_ADDR ((unsigned long) mcount)
  51 #define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
  52
  53 #define OLD_NOP         0xe1a00000      /* mov r0, r0 */
  54
  55 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
  56 {
  57         return rec->arch.old_mcount ? OLD_NOP : NOP;
  58 }
  59
  60 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
  61 {
  62         if (!rec->arch.old_mcount)
  63                 return addr;
  64
  65         if (addr == MCOUNT_ADDR)
  66                 addr = OLD_MCOUNT_ADDR;
  67         else if (addr == FTRACE_ADDR)
  68                 addr = OLD_FTRACE_ADDR;
  69
  70         return addr;
  71 }
  72 #else
  73 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
  74 {
  75         return NOP;
  76 }
  77
  78 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
  79 {
  80         return addr;
  81 }
  82 #endif
  83
  84 int ftrace_arch_code_modify_prepare(void)
  85 {
  86         set_all_modules_text_rw();
  87         return 0;
  88 }
  89
  90 int ftrace_arch_code_modify_post_process(void)
  91 {
  92         set_all_modules_text_ro();
  93         /* Make sure any TLB misses during machine stop are cleared. */
  94         flush_tlb_all();
  95         return 0;
  96 }
  97
  98 static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr,
  99                                          bool warn)
 100 {
 101         return arm_gen_branch_link(pc, addr, warn);
 102 }
 103
 104 static int ftrace_modify_code(unsigned long pc, unsigned long old,
 105                               unsigned long new, bool validate)
 106 {
 107         unsigned long replaced;
 108
 109         if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
 110                 old = __opcode_to_mem_thumb32(old);
 111                 new = __opcode_to_mem_thumb32(new);
 112         } else {
 113                 old = __opcode_to_mem_arm(old);
 114                 new = __opcode_to_mem_arm(new);
 115         }
 116
 117         if (validate) {
 118                 if (probe_kernel_read(&replaced, (void *)pc, MCOUNT_INSN_SIZE))
 119                         return -EFAULT;
 120
 121                 if (replaced != old)
 122                         return -EINVAL;
 123         }
 124
 125         if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
 126                 return -EPERM;
 127
 128         flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
 129
 130         return 0;
 131 }
 132
 133 int ftrace_update_ftrace_func(ftrace_func_t func)
 134 {
 135         unsigned long pc;
 136         unsigned long new;
 137         int ret;
 138
 139         pc = (unsigned long)&ftrace_call;
 140         new = ftrace_call_replace(pc, (unsigned long)func, true);
 141
 142         ret = ftrace_modify_code(pc, 0, new, false);
 143
 144 #ifdef CONFIG_OLD_MCOUNT
 145         if (!ret) {
 146                 pc = (unsigned long)&ftrace_call_old;
 147                 new = ftrace_call_replace(pc, (unsigned long)func, true);
 148
 149                 ret = ftrace_modify_code(pc, 0, new, false);
 150         }
 151 #endif
 152
 153         return ret;
 154 }
 155
 156 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 157 {
 158         unsigned long new, old;
 159         unsigned long ip = rec->ip;
 160         unsigned long aaddr = adjust_address(rec, addr);
 161         struct module *mod = NULL;
 162
 163 #ifdef CONFIG_ARM_MODULE_PLTS
 164         mod = rec->arch.mod;
 165 #endif
 166
 167         old = ftrace_nop_replace(rec);
 168         new = ftrace_call_replace(ip, aaddr, !mod);
 169 #ifdef CONFIG_ARM_MODULE_PLTS
 170         if (!new && mod) {
 171                 aaddr = get_module_plt(mod, ip, aaddr);
 172                 new = ftrace_call_replace(ip, aaddr, true);
 173         }
 174 #endif
 175
 176         return ftrace_modify_code(rec->ip, old, new, true);
 177 }
 178
 179 int ftrace_make_nop(struct module *mod,
 180                     struct dyn_ftrace *rec, unsigned long addr)
 181 {
 182         unsigned long aaddr = adjust_address(rec, addr);
 183         unsigned long ip = rec->ip;
 184         unsigned long old;
 185         unsigned long new;
 186         int ret;
 187
 188 #ifdef CONFIG_ARM_MODULE_PLTS
 189         /* mod is only supplied during module loading */
 190         if (!mod)
 191                 mod = rec->arch.mod;
 192         else
 193                 rec->arch.mod = mod;
 194 #endif
 195
 196         old = ftrace_call_replace(ip, aaddr,
 197                                   !IS_ENABLED(CONFIG_ARM_MODULE_PLTS) || !mod);
 198 #ifdef CONFIG_ARM_MODULE_PLTS
 199         if (!old && mod) {
 200                 aaddr = get_module_plt(mod, ip, aaddr);
 201                 old = ftrace_call_replace(ip, aaddr, true);
 202         }
 203 #endif
 204
 205         new = ftrace_nop_replace(rec);
 206         ret = ftrace_modify_code(ip, old, new, true);
 207
 208 #ifdef CONFIG_OLD_MCOUNT
 209         if (ret == -EINVAL && addr == MCOUNT_ADDR) {
 210                 rec->arch.old_mcount = true;
 211
 212                 old = ftrace_call_replace(ip, adjust_address(rec, addr),
 213                                           !IS_ENABLED(CONFIG_ARM_MODULE_PLTS) || !mod);
 214                 new = ftrace_nop_replace(rec);
 215                 ret = ftrace_modify_code(ip, old, new, true);
 216         }
 217 #endif
 218
 219         return ret;
 220 }
 221
 222 int __init ftrace_dyn_arch_init(void)
 223 {
 224         return 0;
 225 }
 226 #endif /* CONFIG_DYNAMIC_FTRACE */
 227
 228 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 229 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
 230                            unsigned long frame_pointer)
 231 {
 232         unsigned long return_hooker = (unsigned long) &return_to_handler;
 233         struct ftrace_graph_ent trace;
 234         unsigned long old;
 235         int err;
 236
 237         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 238                 return;
 239
 240         old = *parent;
 241         *parent = return_hooker;
 242
 243         trace.func = self_addr;
 244         trace.depth = current->curr_ret_stack + 1;
 245
 246         /* Only trace if the calling function expects to */
 247         if (!ftrace_graph_entry(&trace)) {
 248                 *parent = old;
 249                 return;
 250         }
 251
 252         err = ftrace_push_return_trace(old, self_addr, &trace.depth,
 253                                        frame_pointer, NULL);
 254         if (err == -EBUSY) {
 255                 *parent = old;
 256                 return;
 257         }
 258 }
 259
 260 #ifdef CONFIG_DYNAMIC_FTRACE
 261 extern unsigned long ftrace_graph_call;
 262 extern unsigned long ftrace_graph_call_old;
 263 extern void ftrace_graph_caller_old(void);
 264
 265 static int __ftrace_modify_caller(unsigned long *callsite,
 266                                   void (*func) (void), bool enable)
 267 {
 268         unsigned long caller_fn = (unsigned long) func;
 269         unsigned long pc = (unsigned long) callsite;
 270         unsigned long branch = arm_gen_branch(pc, caller_fn);
 271         unsigned long nop = 0xe1a00000; /* mov r0, r0 */
 272         unsigned long old = enable ? nop : branch;
 273         unsigned long new = enable ? branch : nop;
 274
 275         return ftrace_modify_code(pc, old, new, true);
 276 }
 277
 278 static int ftrace_modify_graph_caller(bool enable)
 279 {
 280         int ret;
 281
 282         ret = __ftrace_modify_caller(&ftrace_graph_call,
 283                                      ftrace_graph_caller,
 284                                      enable);
 285
 286 #ifdef CONFIG_OLD_MCOUNT
 287         if (!ret)
 288                 ret = __ftrace_modify_caller(&ftrace_graph_call_old,
 289                                              ftrace_graph_caller_old,
 290                                              enable);
 291 #endif
 292
 293         return ret;
 294 }
 295
 296 int ftrace_enable_ftrace_graph_caller(void)
 297 {
 298         return ftrace_modify_graph_caller(true);
 299 }
 300
 301 int ftrace_disable_ftrace_graph_caller(void)
 302 {
 303         return ftrace_modify_graph_caller(false);
 304 }
 305 #endif /* CONFIG_DYNAMIC_FTRACE */
 306 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */