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