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
  19 #include <asm/cacheflush.h>
  20 #include <asm/opcodes.h>
  21 #include <asm/ftrace.h>
  22
  23 #include "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 unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
  39 {
  40         return rec->arch.old_mcount ? OLD_NOP : NOP;
  41 }
  42
  43 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
  44 {
  45         if (!rec->arch.old_mcount)
  46                 return addr;
  47
  48         if (addr == MCOUNT_ADDR)
  49                 addr = OLD_MCOUNT_ADDR;
  50         else if (addr == FTRACE_ADDR)
  51                 addr = OLD_FTRACE_ADDR;
  52
  53         return addr;
  54 }
  55 #else
  56 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
  57 {
  58         return NOP;
  59 }
  60
  61 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
  62 {
  63         return addr;
  64 }
  65 #endif
  66
  67 int ftrace_arch_code_modify_prepare(void)
  68 {
  69         set_all_modules_text_rw();
  70         return 0;
  71 }
  72
  73 int ftrace_arch_code_modify_post_process(void)
  74 {
  75         set_all_modules_text_ro();
  76         return 0;
  77 }
  78
  79 static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
  80 {
  81         return arm_gen_branch_link(pc, addr);
  82 }
  83
  84 static int ftrace_modify_code(unsigned long pc, unsigned long old,
  85                               unsigned long new, bool validate)
  86 {
  87         unsigned long replaced;
  88
  89         if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
  90                 old = __opcode_to_mem_thumb32(old);
  91                 new = __opcode_to_mem_thumb32(new);
  92         } else {
  93                 old = __opcode_to_mem_arm(old);
  94                 new = __opcode_to_mem_arm(new);
  95         }
  96
  97         if (validate) {
  98                 if (probe_kernel_read(&replaced, (void *)pc, MCOUNT_INSN_SIZE))
  99                         return -EFAULT;
 100
 101                 if (replaced != old)
 102                         return -EINVAL;
 103         }
 104
 105         if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
 106                 return -EPERM;
 107
 108         flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
 109
 110         return 0;
 111 }
 112
 113 int ftrace_update_ftrace_func(ftrace_func_t func)
 114 {
 115         unsigned long pc;
 116         unsigned long new;
 117         int ret;
 118
 119         pc = (unsigned long)&ftrace_call;
 120         new = ftrace_call_replace(pc, (unsigned long)func);
 121
 122         ret = ftrace_modify_code(pc, 0, new, false);
 123
 124 #ifdef CONFIG_OLD_MCOUNT
 125         if (!ret) {
 126                 pc = (unsigned long)&ftrace_call_old;
 127                 new = ftrace_call_replace(pc, (unsigned long)func);
 128
 129                 ret = ftrace_modify_code(pc, 0, new, false);
 130         }
 131 #endif
 132
 133         return ret;
 134 }
 135
 136 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 137 {
 138         unsigned long new, old;
 139         unsigned long ip = rec->ip;
 140
 141         old = ftrace_nop_replace(rec);
 142         new = ftrace_call_replace(ip, adjust_address(rec, addr));
 143
 144         return ftrace_modify_code(rec->ip, old, new, true);
 145 }
 146
 147 int ftrace_make_nop(struct module *mod,
 148                     struct dyn_ftrace *rec, unsigned long addr)
 149 {
 150         unsigned long ip = rec->ip;
 151         unsigned long old;
 152         unsigned long new;
 153         int ret;
 154
 155         old = ftrace_call_replace(ip, adjust_address(rec, addr));
 156         new = ftrace_nop_replace(rec);
 157         ret = ftrace_modify_code(ip, old, new, true);
 158
 159 #ifdef CONFIG_OLD_MCOUNT
 160         if (ret == -EINVAL && addr == MCOUNT_ADDR) {
 161                 rec->arch.old_mcount = true;
 162
 163                 old = ftrace_call_replace(ip, adjust_address(rec, addr));
 164                 new = ftrace_nop_replace(rec);
 165                 ret = ftrace_modify_code(ip, old, new, true);
 166         }
 167 #endif
 168
 169         return ret;
 170 }
 171
 172 int __init ftrace_dyn_arch_init(void)
 173 {
 174         return 0;
 175 }
 176 #endif /* CONFIG_DYNAMIC_FTRACE */
 177
 178 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 179 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
 180                            unsigned long frame_pointer)
 181 {
 182         unsigned long return_hooker = (unsigned long) &return_to_handler;
 183         struct ftrace_graph_ent trace;
 184         unsigned long old;
 185         int err;
 186
 187         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 188                 return;
 189
 190         old = *parent;
 191         *parent = return_hooker;
 192
 193         trace.func = self_addr;
 194         trace.depth = current->curr_ret_stack + 1;
 195
 196         /* Only trace if the calling function expects to */
 197         if (!ftrace_graph_entry(&trace)) {
 198                 *parent = old;
 199                 return;
 200         }
 201
 202         err = ftrace_push_return_trace(old, self_addr, &trace.depth,
 203                                        frame_pointer);
 204         if (err == -EBUSY) {
 205                 *parent = old;
 206                 return;
 207         }
 208 }
 209
 210 #ifdef CONFIG_DYNAMIC_FTRACE
 211 extern unsigned long ftrace_graph_call;
 212 extern unsigned long ftrace_graph_call_old;
 213 extern void ftrace_graph_caller_old(void);
 214
 215 static int __ftrace_modify_caller(unsigned long *callsite,
 216                                   void (*func) (void), bool enable)
 217 {
 218         unsigned long caller_fn = (unsigned long) func;
 219         unsigned long pc = (unsigned long) callsite;
 220         unsigned long branch = arm_gen_branch(pc, caller_fn);
 221         unsigned long nop = 0xe1a00000; /* mov r0, r0 */
 222         unsigned long old = enable ? nop : branch;
 223         unsigned long new = enable ? branch : nop;
 224
 225         return ftrace_modify_code(pc, old, new, true);
 226 }
 227
 228 static int ftrace_modify_graph_caller(bool enable)
 229 {
 230         int ret;
 231
 232         ret = __ftrace_modify_caller(&ftrace_graph_call,
 233                                      ftrace_graph_caller,
 234                                      enable);
 235
 236 #ifdef CONFIG_OLD_MCOUNT
 237         if (!ret)
 238                 ret = __ftrace_modify_caller(&ftrace_graph_call_old,
 239                                              ftrace_graph_caller_old,
 240                                              enable);
 241 #endif
 242
 243         return ret;
 244 }
 245
 246 int ftrace_enable_ftrace_graph_caller(void)
 247 {
 248         return ftrace_modify_graph_caller(true);
 249 }
 250
 251 int ftrace_disable_ftrace_graph_caller(void)
 252 {
 253         return ftrace_modify_graph_caller(false);
 254 }
 255 #endif /* CONFIG_DYNAMIC_FTRACE */
 256 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */