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
  18 #include <asm/cacheflush.h>
  19 #include <asm/ftrace.h>
  20
  21 #ifdef CONFIG_THUMB2_KERNEL
  22 #define NOP             0xeb04f85d      /* pop.w {lr} */
  23 #else
  24 #define NOP             0xe8bd4000      /* pop {lr} */
  25 #endif
  26
  27 #ifdef CONFIG_DYNAMIC_FTRACE
  28 #ifdef CONFIG_OLD_MCOUNT
  29 #define OLD_MCOUNT_ADDR ((unsigned long) mcount)
  30 #define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
  31
  32 #define OLD_NOP         0xe1a00000      /* mov r0, r0 */
  33
  34 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
  35 {
  36         return rec->arch.old_mcount ? OLD_NOP : NOP;
  37 }
  38
  39 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
  40 {
  41         if (!rec->arch.old_mcount)
  42                 return addr;
  43
  44         if (addr == MCOUNT_ADDR)
  45                 addr = OLD_MCOUNT_ADDR;
  46         else if (addr == FTRACE_ADDR)
  47                 addr = OLD_FTRACE_ADDR;
  48
  49         return addr;
  50 }
  51 #else
  52 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
  53 {
  54         return NOP;
  55 }
  56
  57 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
  58 {
  59         return addr;
  60 }
  61 #endif
  62
  63 #ifdef CONFIG_THUMB2_KERNEL
  64 static unsigned long ftrace_gen_branch(unsigned long pc, unsigned long addr,
  65                                        bool link)
  66 {
  67         unsigned long s, j1, j2, i1, i2, imm10, imm11;
  68         unsigned long first, second;
  69         long offset;
  70
  71         offset = (long)addr - (long)(pc + 4);
  72         if (offset < -16777216 || offset > 16777214) {
  73                 WARN_ON_ONCE(1);
  74                 return 0;
  75         }
  76
  77         s       = (offset >> 24) & 0x1;
  78         i1      = (offset >> 23) & 0x1;
  79         i2      = (offset >> 22) & 0x1;
  80         imm10   = (offset >> 12) & 0x3ff;
  81         imm11   = (offset >>  1) & 0x7ff;
  82
  83         j1 = (!i1) ^ s;
  84         j2 = (!i2) ^ s;
  85
  86         first = 0xf000 | (s << 10) | imm10;
  87         second = 0x9000 | (j1 << 13) | (j2 << 11) | imm11;
  88         if (link)
  89                 second |= 1 << 14;
  90
  91         return (second << 16) | first;
  92 }
  93 #else
  94 static unsigned long ftrace_gen_branch(unsigned long pc, unsigned long addr,
  95                                        bool link)
  96 {
  97         unsigned long opcode = 0xea000000;
  98         long offset;
  99
 100         if (link)
 101                 opcode |= 1 << 24;
 102
 103         offset = (long)addr - (long)(pc + 8);
 104         if (unlikely(offset < -33554432 || offset > 33554428)) {
 105                 /* Can't generate branches that far (from ARM ARM). Ftrace
 106                  * doesn't generate branches outside of kernel text.
 107                  */
 108                 WARN_ON_ONCE(1);
 109                 return 0;
 110         }
 111
 112         offset = (offset >> 2) & 0x00ffffff;
 113
 114         return opcode | offset;
 115 }
 116 #endif
 117
 118 static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
 119 {
 120         return ftrace_gen_branch(pc, addr, true);
 121 }
 122
 123 static int ftrace_modify_code(unsigned long pc, unsigned long old,
 124                               unsigned long new)
 125 {
 126         unsigned long replaced;
 127
 128         if (probe_kernel_read(&replaced, (void *)pc, MCOUNT_INSN_SIZE))
 129                 return -EFAULT;
 130
 131         if (replaced != old)
 132                 return -EINVAL;
 133
 134         if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
 135                 return -EPERM;
 136
 137         flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
 138
 139         return 0;
 140 }
 141
 142 int ftrace_update_ftrace_func(ftrace_func_t func)
 143 {
 144         unsigned long pc, old;
 145         unsigned long new;
 146         int ret;
 147
 148         pc = (unsigned long)&ftrace_call;
 149         memcpy(&old, &ftrace_call, MCOUNT_INSN_SIZE);
 150         new = ftrace_call_replace(pc, (unsigned long)func);
 151
 152         ret = ftrace_modify_code(pc, old, new);
 153
 154 #ifdef CONFIG_OLD_MCOUNT
 155         if (!ret) {
 156                 pc = (unsigned long)&ftrace_call_old;
 157                 memcpy(&old, &ftrace_call_old, MCOUNT_INSN_SIZE);
 158                 new = ftrace_call_replace(pc, (unsigned long)func);
 159
 160                 ret = ftrace_modify_code(pc, old, new);
 161         }
 162 #endif
 163
 164         return ret;
 165 }
 166
 167 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 168 {
 169         unsigned long new, old;
 170         unsigned long ip = rec->ip;
 171
 172         old = ftrace_nop_replace(rec);
 173         new = ftrace_call_replace(ip, adjust_address(rec, addr));
 174
 175         return ftrace_modify_code(rec->ip, old, new);
 176 }
 177
 178 int ftrace_make_nop(struct module *mod,
 179                     struct dyn_ftrace *rec, unsigned long addr)
 180 {
 181         unsigned long ip = rec->ip;
 182         unsigned long old;
 183         unsigned long new;
 184         int ret;
 185
 186         old = ftrace_call_replace(ip, adjust_address(rec, addr));
 187         new = ftrace_nop_replace(rec);
 188         ret = ftrace_modify_code(ip, old, new);
 189
 190 #ifdef CONFIG_OLD_MCOUNT
 191         if (ret == -EINVAL && addr == MCOUNT_ADDR) {
 192                 rec->arch.old_mcount = true;
 193
 194                 old = ftrace_call_replace(ip, adjust_address(rec, addr));
 195                 new = ftrace_nop_replace(rec);
 196                 ret = ftrace_modify_code(ip, old, new);
 197         }
 198 #endif
 199
 200         return ret;
 201 }
 202
 203 int __init ftrace_dyn_arch_init(void *data)
 204 {
 205         *(unsigned long *)data = 0;
 206
 207         return 0;
 208 }
 209 #endif /* CONFIG_DYNAMIC_FTRACE */
 210
 211 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 212 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
 213                            unsigned long frame_pointer)
 214 {
 215         unsigned long return_hooker = (unsigned long) &return_to_handler;
 216         struct ftrace_graph_ent trace;
 217         unsigned long old;
 218         int err;
 219
 220         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 221                 return;
 222
 223         old = *parent;
 224         *parent = return_hooker;
 225
 226         err = ftrace_push_return_trace(old, self_addr, &trace.depth,
 227                                        frame_pointer);
 228         if (err == -EBUSY) {
 229                 *parent = old;
 230                 return;
 231         }
 232
 233         trace.func = self_addr;
 234
 235         /* Only trace if the calling function expects to */
 236         if (!ftrace_graph_entry(&trace)) {
 237                 current->curr_ret_stack--;
 238                 *parent = old;
 239         }
 240 }
 241
 242 #ifdef CONFIG_DYNAMIC_FTRACE
 243 extern unsigned long ftrace_graph_call;
 244 extern unsigned long ftrace_graph_call_old;
 245 extern void ftrace_graph_caller_old(void);
 246
 247 static int __ftrace_modify_caller(unsigned long *callsite,
 248                                   void (*func) (void), bool enable)
 249 {
 250         unsigned long caller_fn = (unsigned long) func;
 251         unsigned long pc = (unsigned long) callsite;
 252         unsigned long branch = ftrace_gen_branch(pc, caller_fn, false);
 253         unsigned long nop = 0xe1a00000; /* mov r0, r0 */
 254         unsigned long old = enable ? nop : branch;
 255         unsigned long new = enable ? branch : nop;
 256
 257         return ftrace_modify_code(pc, old, new);
 258 }
 259
 260 static int ftrace_modify_graph_caller(bool enable)
 261 {
 262         int ret;
 263
 264         ret = __ftrace_modify_caller(&ftrace_graph_call,
 265                                      ftrace_graph_caller,
 266                                      enable);
 267
 268 #ifdef CONFIG_OLD_MCOUNT
 269         if (!ret)
 270                 ret = __ftrace_modify_caller(&ftrace_graph_call_old,
 271                                              ftrace_graph_caller_old,
 272                                              enable);
 273 #endif
 274
 275         return ret;
 276 }
 277
 278 int ftrace_enable_ftrace_graph_caller(void)
 279 {
 280         return ftrace_modify_graph_caller(true);
 281 }
 282
 283 int ftrace_disable_ftrace_graph_caller(void)
 284 {
 285         return ftrace_modify_graph_caller(false);
 286 }
 287 #endif /* CONFIG_DYNAMIC_FTRACE */
 288 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */