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