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 #include <asm/set_memory.h>
  25
  26 #ifdef CONFIG_THUMB2_KERNEL
  27 #define NOP             0xf85deb04      /* pop.w {lr} */
  28 #else
  29 #define NOP             0xe8bd4000      /* pop {lr} */
  30 #endif
  31
  32 #ifdef CONFIG_DYNAMIC_FTRACE
  33
  34 static int __ftrace_modify_code(void *data)
  35 {
  36         int *command = data;
  37
  38         set_kernel_text_rw();
  39         ftrace_modify_all_code(*command);
  40         set_kernel_text_ro();
  41
  42         return 0;
  43 }
  44
  45 void arch_ftrace_update_code(int command)
  46 {
  47         stop_machine(__ftrace_modify_code, &command, NULL);
  48 }
  49
  50 #ifdef CONFIG_OLD_MCOUNT
  51 #define OLD_MCOUNT_ADDR ((unsigned long) mcount)
  52 #define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
  53
  54 #define OLD_NOP         0xe1a00000      /* mov r0, r0 */
  55
  56 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
  57 {
  58         return rec->arch.old_mcount ? OLD_NOP : NOP;
  59 }
  60
  61 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
  62 {
  63         if (!rec->arch.old_mcount)
  64                 return addr;
  65
  66         if (addr == MCOUNT_ADDR)
  67                 addr = OLD_MCOUNT_ADDR;
  68         else if (addr == FTRACE_ADDR)
  69                 addr = OLD_FTRACE_ADDR;
  70
  71         return addr;
  72 }
  73 #else
  74 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
  75 {
  76         return NOP;
  77 }
  78
  79 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
  80 {
  81         return addr;
  82 }
  83 #endif
  84
  85 int ftrace_arch_code_modify_prepare(void)
  86 {
  87         set_all_modules_text_rw();
  88         return 0;
  89 }
  90
  91 int ftrace_arch_code_modify_post_process(void)
  92 {
  93         set_all_modules_text_ro();
  94         /* Make sure any TLB misses during machine stop are cleared. */
  95         flush_tlb_all();
  96         return 0;
  97 }
  98
  99 static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
 100 {
 101         return arm_gen_branch_link(pc, addr);
 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);
 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);
 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
 161         old = ftrace_nop_replace(rec);
 162         new = ftrace_call_replace(ip, adjust_address(rec, addr));
 163
 164         return ftrace_modify_code(rec->ip, old, new, true);
 165 }
 166
 167 int ftrace_make_nop(struct module *mod,
 168                     struct dyn_ftrace *rec, unsigned long addr)
 169 {
 170         unsigned long ip = rec->ip;
 171         unsigned long old;
 172         unsigned long new;
 173         int ret;
 174
 175         old = ftrace_call_replace(ip, adjust_address(rec, addr));
 176         new = ftrace_nop_replace(rec);
 177         ret = ftrace_modify_code(ip, old, new, true);
 178
 179 #ifdef CONFIG_OLD_MCOUNT
 180         if (ret == -EINVAL && addr == MCOUNT_ADDR) {
 181                 rec->arch.old_mcount = true;
 182
 183                 old = ftrace_call_replace(ip, adjust_address(rec, addr));
 184                 new = ftrace_nop_replace(rec);
 185                 ret = ftrace_modify_code(ip, old, new, true);
 186         }
 187 #endif
 188
 189         return ret;
 190 }
 191
 192 int __init ftrace_dyn_arch_init(void)
 193 {
 194         return 0;
 195 }
 196 #endif /* CONFIG_DYNAMIC_FTRACE */
 197
 198 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 199 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
 200                            unsigned long frame_pointer)
 201 {
 202         unsigned long return_hooker = (unsigned long) &return_to_handler;
 203         struct ftrace_graph_ent trace;
 204         unsigned long old;
 205         int err;
 206
 207         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 208                 return;
 209
 210         old = *parent;
 211         *parent = return_hooker;
 212
 213         trace.func = self_addr;
 214         trace.depth = current->curr_ret_stack + 1;
 215
 216         /* Only trace if the calling function expects to */
 217         if (!ftrace_graph_entry(&trace)) {
 218                 *parent = old;
 219                 return;
 220         }
 221
 222         err = ftrace_push_return_trace(old, self_addr, &trace.depth,
 223                                        frame_pointer, NULL);
 224         if (err == -EBUSY) {
 225                 *parent = old;
 226                 return;
 227         }
 228 }
 229
 230 #ifdef CONFIG_DYNAMIC_FTRACE
 231 extern unsigned long ftrace_graph_call;
 232 extern unsigned long ftrace_graph_call_old;
 233 extern void ftrace_graph_caller_old(void);
 234
 235 static int __ftrace_modify_caller(unsigned long *callsite,
 236                                   void (*func) (void), bool enable)
 237 {
 238         unsigned long caller_fn = (unsigned long) func;
 239         unsigned long pc = (unsigned long) callsite;
 240         unsigned long branch = arm_gen_branch(pc, caller_fn);
 241         unsigned long nop = 0xe1a00000; /* mov r0, r0 */
 242         unsigned long old = enable ? nop : branch;
 243         unsigned long new = enable ? branch : nop;
 244
 245         return ftrace_modify_code(pc, old, new, true);
 246 }
 247
 248 static int ftrace_modify_graph_caller(bool enable)
 249 {
 250         int ret;
 251
 252         ret = __ftrace_modify_caller(&ftrace_graph_call,
 253                                      ftrace_graph_caller,
 254                                      enable);
 255
 256 #ifdef CONFIG_OLD_MCOUNT
 257         if (!ret)
 258                 ret = __ftrace_modify_caller(&ftrace_graph_call_old,
 259                                              ftrace_graph_caller_old,
 260                                              enable);
 261 #endif
 262
 263         return ret;
 264 }
 265
 266 int ftrace_enable_ftrace_graph_caller(void)
 267 {
 268         return ftrace_modify_graph_caller(true);
 269 }
 270
 271 int ftrace_disable_ftrace_graph_caller(void)
 272 {
 273         return ftrace_modify_graph_caller(false);
 274 }
 275 #endif /* CONFIG_DYNAMIC_FTRACE */
 276 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */