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/opcodes.h>
  20 #include <asm/ftrace.h>
  21
  22 #include "insn.h"
  23
  24 #ifdef CONFIG_THUMB2_KERNEL
  25 #define NOP             0xf85deb04      /* pop.w {lr} */
  26 #else
  27 #define NOP             0xe8bd4000      /* pop {lr} */
  28 #endif
  29
  30 #ifdef CONFIG_DYNAMIC_FTRACE
  31 #ifdef CONFIG_OLD_MCOUNT
  32 #define OLD_MCOUNT_ADDR ((unsigned long) mcount)
  33 #define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
  34
  35 #define OLD_NOP         0xe1a00000      /* mov r0, r0 */
  36
  37 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
  38 {
  39         return rec->arch.old_mcount ? OLD_NOP : NOP;
  40 }
  41
  42 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
  43 {
  44         if (!rec->arch.old_mcount)
  45                 return addr;
  46
  47         if (addr == MCOUNT_ADDR)
  48                 addr = OLD_MCOUNT_ADDR;
  49         else if (addr == FTRACE_ADDR)
  50                 addr = OLD_FTRACE_ADDR;
  51
  52         return addr;
  53 }
  54 #else
  55 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
  56 {
  57         return NOP;
  58 }
  59
  60 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
  61 {
  62         return addr;
  63 }
  64 #endif
  65
  66 static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
  67 {
  68         return arm_gen_branch_link(pc, addr);
  69 }
  70
  71 static int ftrace_modify_code(unsigned long pc, unsigned long old,
  72                               unsigned long new, bool validate)
  73 {
  74         unsigned long replaced;
  75
  76         if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
  77                 old = __opcode_to_mem_thumb32(old);
  78                 new = __opcode_to_mem_thumb32(new);
  79         } else {
  80                 old = __opcode_to_mem_arm(old);
  81                 new = __opcode_to_mem_arm(new);
  82         }
  83
  84         if (validate) {
  85                 if (probe_kernel_read(&replaced, (void *)pc, MCOUNT_INSN_SIZE))
  86                         return -EFAULT;
  87
  88                 if (replaced != old)
  89                         return -EINVAL;
  90         }
  91
  92         if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
  93                 return -EPERM;
  94
  95         flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
  96
  97         return 0;
  98 }
  99
 100 int ftrace_update_ftrace_func(ftrace_func_t func)
 101 {
 102         unsigned long pc;
 103         unsigned long new;
 104         int ret;
 105
 106         pc = (unsigned long)&ftrace_call;
 107         new = ftrace_call_replace(pc, (unsigned long)func);
 108
 109         ret = ftrace_modify_code(pc, 0, new, false);
 110
 111 #ifdef CONFIG_OLD_MCOUNT
 112         if (!ret) {
 113                 pc = (unsigned long)&ftrace_call_old;
 114                 new = ftrace_call_replace(pc, (unsigned long)func);
 115
 116                 ret = ftrace_modify_code(pc, 0, new, false);
 117         }
 118 #endif
 119
 120         return ret;
 121 }
 122
 123 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 124 {
 125         unsigned long new, old;
 126         unsigned long ip = rec->ip;
 127
 128         old = ftrace_nop_replace(rec);
 129         new = ftrace_call_replace(ip, adjust_address(rec, addr));
 130
 131         return ftrace_modify_code(rec->ip, old, new, true);
 132 }
 133
 134 int ftrace_make_nop(struct module *mod,
 135                     struct dyn_ftrace *rec, unsigned long addr)
 136 {
 137         unsigned long ip = rec->ip;
 138         unsigned long old;
 139         unsigned long new;
 140         int ret;
 141
 142         old = ftrace_call_replace(ip, adjust_address(rec, addr));
 143         new = ftrace_nop_replace(rec);
 144         ret = ftrace_modify_code(ip, old, new, true);
 145
 146 #ifdef CONFIG_OLD_MCOUNT
 147         if (ret == -EINVAL && addr == MCOUNT_ADDR) {
 148                 rec->arch.old_mcount = true;
 149
 150                 old = ftrace_call_replace(ip, adjust_address(rec, addr));
 151                 new = ftrace_nop_replace(rec);
 152                 ret = ftrace_modify_code(ip, old, new, true);
 153         }
 154 #endif
 155
 156         return ret;
 157 }
 158
 159 int __init ftrace_dyn_arch_init(void)
 160 {
 161         return 0;
 162 }
 163 #endif /* CONFIG_DYNAMIC_FTRACE */
 164
 165 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 166 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
 167                            unsigned long frame_pointer)
 168 {
 169         unsigned long return_hooker = (unsigned long) &return_to_handler;
 170         struct ftrace_graph_ent trace;
 171         unsigned long old;
 172         int err;
 173
 174         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 175                 return;
 176
 177         old = *parent;
 178         *parent = return_hooker;
 179
 180         trace.func = self_addr;
 181         trace.depth = current->curr_ret_stack + 1;
 182
 183         /* Only trace if the calling function expects to */
 184         if (!ftrace_graph_entry(&trace)) {
 185                 *parent = old;
 186                 return;
 187         }
 188
 189         err = ftrace_push_return_trace(old, self_addr, &trace.depth,
 190                                        frame_pointer);
 191         if (err == -EBUSY) {
 192                 *parent = old;
 193                 return;
 194         }
 195 }
 196
 197 #ifdef CONFIG_DYNAMIC_FTRACE
 198 extern unsigned long ftrace_graph_call;
 199 extern unsigned long ftrace_graph_call_old;
 200 extern void ftrace_graph_caller_old(void);
 201
 202 static int __ftrace_modify_caller(unsigned long *callsite,
 203                                   void (*func) (void), bool enable)
 204 {
 205         unsigned long caller_fn = (unsigned long) func;
 206         unsigned long pc = (unsigned long) callsite;
 207         unsigned long branch = arm_gen_branch(pc, caller_fn);
 208         unsigned long nop = 0xe1a00000; /* mov r0, r0 */
 209         unsigned long old = enable ? nop : branch;
 210         unsigned long new = enable ? branch : nop;
 211
 212         return ftrace_modify_code(pc, old, new, true);
 213 }
 214
 215 static int ftrace_modify_graph_caller(bool enable)
 216 {
 217         int ret;
 218
 219         ret = __ftrace_modify_caller(&ftrace_graph_call,
 220                                      ftrace_graph_caller,
 221                                      enable);
 222
 223 #ifdef CONFIG_OLD_MCOUNT
 224         if (!ret)
 225                 ret = __ftrace_modify_caller(&ftrace_graph_call_old,
 226                                              ftrace_graph_caller_old,
 227                                              enable);
 228 #endif
 229
 230         return ret;
 231 }
 232
 233 int ftrace_enable_ftrace_graph_caller(void)
 234 {
 235         return ftrace_modify_graph_caller(true);
 236 }
 237
 238 int ftrace_disable_ftrace_graph_caller(void)
 239 {
 240         return ftrace_modify_graph_caller(false);
 241 }
 242 #endif /* CONFIG_DYNAMIC_FTRACE */
 243 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */