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
  24 #include "insn.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 #ifdef CONFIG_OLD_MCOUNT
  34 #define OLD_MCOUNT_ADDR ((unsigned long) mcount)
  35 #define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
  36
  37 #define OLD_NOP         0xe1a00000      /* mov r0, r0 */
  38
  39 static int __ftrace_modify_code(void *data)
  40 {
  41         int *command = data;
  42
  43         set_kernel_text_rw();
  44         ftrace_modify_all_code(*command);
  45         set_kernel_text_ro();
  46
  47         return 0;
  48 }
  49
  50 void arch_ftrace_update_code(int command)
  51 {
  52         stop_machine(__ftrace_modify_code, &command, NULL);
  53 }
  54
  55 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
  56 {
  57         return rec->arch.old_mcount ? OLD_NOP : NOP;
  58 }
  59
  60 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
  61 {
  62         if (!rec->arch.old_mcount)
  63                 return addr;
  64
  65         if (addr == MCOUNT_ADDR)
  66                 addr = OLD_MCOUNT_ADDR;
  67         else if (addr == FTRACE_ADDR)
  68                 addr = OLD_FTRACE_ADDR;
  69
  70         return addr;
  71 }
  72 #else
  73 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
  74 {
  75         return NOP;
  76 }
  77
  78 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
  79 {
  80         return addr;
  81 }
  82 #endif
  83
  84 int ftrace_arch_code_modify_prepare(void)
  85 {
  86         set_all_modules_text_rw();
  87         return 0;
  88 }
  89
  90 int ftrace_arch_code_modify_post_process(void)
  91 {
  92         set_all_modules_text_ro();
  93         /* Make sure any TLB misses during machine stop are cleared. */
  94         flush_tlb_all();
  95         return 0;
  96 }
  97
  98 static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
  99 {
 100         return arm_gen_branch_link(pc, addr);
 101 }
 102
 103 static int ftrace_modify_code(unsigned long pc, unsigned long old,
 104                               unsigned long new, bool validate)
 105 {
 106         unsigned long replaced;
 107
 108         if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
 109                 old = __opcode_to_mem_thumb32(old);
 110                 new = __opcode_to_mem_thumb32(new);
 111         } else {
 112                 old = __opcode_to_mem_arm(old);
 113                 new = __opcode_to_mem_arm(new);
 114         }
 115
 116         if (validate) {
 117                 if (probe_kernel_read(&replaced, (void *)pc, MCOUNT_INSN_SIZE))
 118                         return -EFAULT;
 119
 120                 if (replaced != old)
 121                         return -EINVAL;
 122         }
 123
 124         if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
 125                 return -EPERM;
 126
 127         flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
 128
 129         return 0;
 130 }
 131
 132 int ftrace_update_ftrace_func(ftrace_func_t func)
 133 {
 134         unsigned long pc;
 135         unsigned long new;
 136         int ret;
 137
 138         pc = (unsigned long)&ftrace_call;
 139         new = ftrace_call_replace(pc, (unsigned long)func);
 140
 141         ret = ftrace_modify_code(pc, 0, new, false);
 142
 143 #ifdef CONFIG_OLD_MCOUNT
 144         if (!ret) {
 145                 pc = (unsigned long)&ftrace_call_old;
 146                 new = ftrace_call_replace(pc, (unsigned long)func);
 147
 148                 ret = ftrace_modify_code(pc, 0, new, false);
 149         }
 150 #endif
 151
 152         return ret;
 153 }
 154
 155 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 156 {
 157         unsigned long new, old;
 158         unsigned long ip = rec->ip;
 159
 160         old = ftrace_nop_replace(rec);
 161         new = ftrace_call_replace(ip, adjust_address(rec, addr));
 162
 163         return ftrace_modify_code(rec->ip, old, new, true);
 164 }
 165
 166 int ftrace_make_nop(struct module *mod,
 167                     struct dyn_ftrace *rec, unsigned long addr)
 168 {
 169         unsigned long ip = rec->ip;
 170         unsigned long old;
 171         unsigned long new;
 172         int ret;
 173
 174         old = ftrace_call_replace(ip, adjust_address(rec, addr));
 175         new = ftrace_nop_replace(rec);
 176         ret = ftrace_modify_code(ip, old, new, true);
 177
 178 #ifdef CONFIG_OLD_MCOUNT
 179         if (ret == -EINVAL && addr == MCOUNT_ADDR) {
 180                 rec->arch.old_mcount = true;
 181
 182                 old = ftrace_call_replace(ip, adjust_address(rec, addr));
 183                 new = ftrace_nop_replace(rec);
 184                 ret = ftrace_modify_code(ip, old, new, true);
 185         }
 186 #endif
 187
 188         return ret;
 189 }
 190
 191 int __init ftrace_dyn_arch_init(void)
 192 {
 193         return 0;
 194 }
 195 #endif /* CONFIG_DYNAMIC_FTRACE */
 196
 197 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 198 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
 199                            unsigned long frame_pointer)
 200 {
 201         unsigned long return_hooker = (unsigned long) &return_to_handler;
 202         struct ftrace_graph_ent trace;
 203         unsigned long old;
 204         int err;
 205
 206         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 207                 return;
 208
 209         old = *parent;
 210         *parent = return_hooker;
 211
 212         trace.func = self_addr;
 213         trace.depth = current->curr_ret_stack + 1;
 214
 215         /* Only trace if the calling function expects to */
 216         if (!ftrace_graph_entry(&trace)) {
 217                 *parent = old;
 218                 return;
 219         }
 220
 221         err = ftrace_push_return_trace(old, self_addr, &trace.depth,
 222                                        frame_pointer);
 223         if (err == -EBUSY) {
 224                 *parent = old;
 225                 return;
 226         }
 227 }
 228
 229 #ifdef CONFIG_DYNAMIC_FTRACE
 230 extern unsigned long ftrace_graph_call;
 231 extern unsigned long ftrace_graph_call_old;
 232 extern void ftrace_graph_caller_old(void);
 233
 234 static int __ftrace_modify_caller(unsigned long *callsite,
 235                                   void (*func) (void), bool enable)
 236 {
 237         unsigned long caller_fn = (unsigned long) func;
 238         unsigned long pc = (unsigned long) callsite;
 239         unsigned long branch = arm_gen_branch(pc, caller_fn);
 240         unsigned long nop = 0xe1a00000; /* mov r0, r0 */
 241         unsigned long old = enable ? nop : branch;
 242         unsigned long new = enable ? branch : nop;
 243
 244         return ftrace_modify_code(pc, old, new, true);
 245 }
 246
 247 static int ftrace_modify_graph_caller(bool enable)
 248 {
 249         int ret;
 250
 251         ret = __ftrace_modify_caller(&ftrace_graph_call,
 252                                      ftrace_graph_caller,
 253                                      enable);
 254
 255 #ifdef CONFIG_OLD_MCOUNT
 256         if (!ret)
 257                 ret = __ftrace_modify_caller(&ftrace_graph_call_old,
 258                                              ftrace_graph_caller_old,
 259                                              enable);
 260 #endif
 261
 262         return ret;
 263 }
 264
 265 int ftrace_enable_ftrace_graph_caller(void)
 266 {
 267         return ftrace_modify_graph_caller(true);
 268 }
 269
 270 int ftrace_disable_ftrace_graph_caller(void)
 271 {
 272         return ftrace_modify_graph_caller(false);
 273 }
 274 #endif /* CONFIG_DYNAMIC_FTRACE */
 275 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */