arch/sh/kernel/ftrace.c

   1 /*
   2  * Copyright (C) 2008 Matt Fleming <matt@console-pimps.org>
   3  * Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org>
   4  *
   5  * Code for replacing ftrace calls with jumps.
   6  *
   7  * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
   8  *
   9  * Thanks goes to Ingo Molnar, for suggesting the idea.
  10  * Mathieu Desnoyers, for suggesting postponing the modifications.
  11  * Arjan van de Ven, for keeping me straight, and explaining to me
  12  * the dangers of modifying code on the run.
  13  */
  14 #include <linux/uaccess.h>
  15 #include <linux/ftrace.h>
  16 #include <linux/string.h>
  17 #include <linux/init.h>
  18 #include <linux/io.h>
  19 #include <linux/kernel.h>
  20 #include <asm/ftrace.h>
  21 #include <asm/cacheflush.h>
  22 #include <asm/unistd.h>
  23 #include <trace/syscall.h>
  24
  25 #ifdef CONFIG_DYNAMIC_FTRACE
  26 static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];
  27
  28 static unsigned char ftrace_nop[4];
  29 /*
  30  * If we're trying to nop out a call to a function, we instead
  31  * place a call to the address after the memory table.
  32  *
  33  * 8c011060 <a>:
  34  * 8c011060:       02 d1           mov.l   8c01106c <a+0xc>,r1
  35  * 8c011062:       22 4f           sts.l   pr,@-r15
  36  * 8c011064:       02 c7           mova    8c011070 <a+0x10>,r0
  37  * 8c011066:       2b 41           jmp     @r1
  38  * 8c011068:       2a 40           lds     r0,pr
  39  * 8c01106a:       09 00           nop
  40  * 8c01106c:       68 24           .word 0x2468     <--- ip
  41  * 8c01106e:       1d 8c           .word 0x8c1d
  42  * 8c011070:       26 4f           lds.l   @r15+,pr <--- ip + MCOUNT_INSN_SIZE
  43  *
  44  * We write 0x8c011070 to 0x8c01106c so that on entry to a() we branch
  45  * past the _mcount call and continue executing code like normal.
  46  */
  47 static unsigned char *ftrace_nop_replace(unsigned long ip)
  48 {
  49         __raw_writel(ip + MCOUNT_INSN_SIZE, ftrace_nop);
  50         return ftrace_nop;
  51 }
  52
  53 static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
  54 {
  55         /* Place the address in the memory table. */
  56         __raw_writel(addr, ftrace_replaced_code);
  57
  58         /*
  59          * No locking needed, this must be called via kstop_machine
  60          * which in essence is like running on a uniprocessor machine.
  61          */
  62         return ftrace_replaced_code;
  63 }
  64
  65 /*
  66  * Modifying code must take extra care. On an SMP machine, if
  67  * the code being modified is also being executed on another CPU
  68  * that CPU will have undefined results and possibly take a GPF.
  69  * We use kstop_machine to stop other CPUS from exectuing code.
  70  * But this does not stop NMIs from happening. We still need
  71  * to protect against that. We separate out the modification of
  72  * the code to take care of this.
  73  *
  74  * Two buffers are added: An IP buffer and a "code" buffer.
  75  *
  76  * 1) Put the instruction pointer into the IP buffer
  77  *    and the new code into the "code" buffer.
  78  * 2) Wait for any running NMIs to finish and set a flag that says
  79  *    we are modifying code, it is done in an atomic operation.
  80  * 3) Write the code
  81  * 4) clear the flag.
  82  * 5) Wait for any running NMIs to finish.
  83  *
  84  * If an NMI is executed, the first thing it does is to call
  85  * "ftrace_nmi_enter". This will check if the flag is set to write
  86  * and if it is, it will write what is in the IP and "code" buffers.
  87  *
  88  * The trick is, it does not matter if everyone is writing the same
  89  * content to the code location. Also, if a CPU is executing code
  90  * it is OK to write to that code location if the contents being written
  91  * are the same as what exists.
  92  */
  93 #define MOD_CODE_WRITE_FLAG (1 << 31)   /* set when NMI should do the write */
  94 static atomic_t nmi_running = ATOMIC_INIT(0);
  95 static int mod_code_status;             /* holds return value of text write */
  96 static void *mod_code_ip;               /* holds the IP to write to */
  97 static void *mod_code_newcode;          /* holds the text to write to the IP */
  98
  99 static unsigned nmi_wait_count;
 100 static atomic_t nmi_update_count = ATOMIC_INIT(0);
 101
 102 int ftrace_arch_read_dyn_info(char *buf, int size)
 103 {
 104         int r;
 105
 106         r = snprintf(buf, size, "%u %u",
 107                      nmi_wait_count,
 108                      atomic_read(&nmi_update_count));
 109         return r;
 110 }
 111
 112 static void clear_mod_flag(void)
 113 {
 114         int old = atomic_read(&nmi_running);
 115
 116         for (;;) {
 117                 int new = old & ~MOD_CODE_WRITE_FLAG;
 118
 119                 if (old == new)
 120                         break;
 121
 122                 old = atomic_cmpxchg(&nmi_running, old, new);
 123         }
 124 }
 125
 126 static void ftrace_mod_code(void)
 127 {
 128         /*
 129          * Yes, more than one CPU process can be writing to mod_code_status.
 130          *    (and the code itself)
 131          * But if one were to fail, then they all should, and if one were
 132          * to succeed, then they all should.
 133          */
 134         mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode,
 135                                              MCOUNT_INSN_SIZE);
 136
 137         /* if we fail, then kill any new writers */
 138         if (mod_code_status)
 139                 clear_mod_flag();
 140 }
 141
 142 void ftrace_nmi_enter(void)
 143 {
 144         if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
 145                 smp_rmb();
 146                 ftrace_mod_code();
 147                 atomic_inc(&nmi_update_count);
 148         }
 149         /* Must have previous changes seen before executions */
 150         smp_mb();
 151 }
 152
 153 void ftrace_nmi_exit(void)
 154 {
 155         /* Finish all executions before clearing nmi_running */
 156         smp_mb();
 157         atomic_dec(&nmi_running);
 158 }
 159
 160 static void wait_for_nmi_and_set_mod_flag(void)
 161 {
 162         if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG))
 163                 return;
 164
 165         do {
 166                 cpu_relax();
 167         } while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG));
 168
 169         nmi_wait_count++;
 170 }
 171
 172 static void wait_for_nmi(void)
 173 {
 174         if (!atomic_read(&nmi_running))
 175                 return;
 176
 177         do {
 178                 cpu_relax();
 179         } while (atomic_read(&nmi_running));
 180
 181         nmi_wait_count++;
 182 }
 183
 184 static int
 185 do_ftrace_mod_code(unsigned long ip, void *new_code)
 186 {
 187         mod_code_ip = (void *)ip;
 188         mod_code_newcode = new_code;
 189
 190         /* The buffers need to be visible before we let NMIs write them */
 191         smp_mb();
 192
 193         wait_for_nmi_and_set_mod_flag();
 194
 195         /* Make sure all running NMIs have finished before we write the code */
 196         smp_mb();
 197
 198         ftrace_mod_code();
 199
 200         /* Make sure the write happens before clearing the bit */
 201         smp_mb();
 202
 203         clear_mod_flag();
 204         wait_for_nmi();
 205
 206         return mod_code_status;
 207 }
 208
 209 static int ftrace_modify_code(unsigned long ip, unsigned char *old_code,
 210                        unsigned char *new_code)
 211 {
 212         unsigned char replaced[MCOUNT_INSN_SIZE];
 213
 214         /*
 215          * Note: Due to modules and __init, code can
 216          *  disappear and change, we need to protect against faulting
 217          *  as well as code changing. We do this by using the
 218          *  probe_kernel_* functions.
 219          *
 220          * No real locking needed, this code is run through
 221          * kstop_machine, or before SMP starts.
 222          */
 223
 224         /* read the text we want to modify */
 225         if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
 226                 return -EFAULT;
 227
 228         /* Make sure it is what we expect it to be */
 229         if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
 230                 return -EINVAL;
 231
 232         /* replace the text with the new text */
 233         if (do_ftrace_mod_code(ip, new_code))
 234                 return -EPERM;
 235
 236         flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);
 237
 238         return 0;
 239 }
 240
 241 int ftrace_update_ftrace_func(ftrace_func_t func)
 242 {
 243         unsigned long ip = (unsigned long)(&ftrace_call) + MCOUNT_INSN_OFFSET;
 244         unsigned char old[MCOUNT_INSN_SIZE], *new;
 245
 246         memcpy(old, (unsigned char *)ip, MCOUNT_INSN_SIZE);
 247         new = ftrace_call_replace(ip, (unsigned long)func);
 248
 249         return ftrace_modify_code(ip, old, new);
 250 }
 251
 252 int ftrace_make_nop(struct module *mod,
 253                     struct dyn_ftrace *rec, unsigned long addr)
 254 {
 255         unsigned char *new, *old;
 256         unsigned long ip = rec->ip;
 257
 258         old = ftrace_call_replace(ip, addr);
 259         new = ftrace_nop_replace(ip);
 260
 261         return ftrace_modify_code(rec->ip, old, new);
 262 }
 263
 264 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 265 {
 266         unsigned char *new, *old;
 267         unsigned long ip = rec->ip;
 268
 269         old = ftrace_nop_replace(ip);
 270         new = ftrace_call_replace(ip, addr);
 271
 272         return ftrace_modify_code(rec->ip, old, new);
 273 }
 274
 275 int __init ftrace_dyn_arch_init(void)
 276 {
 277         return 0;
 278 }
 279 #endif /* CONFIG_DYNAMIC_FTRACE */
 280
 281 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 282 #ifdef CONFIG_DYNAMIC_FTRACE
 283 extern void ftrace_graph_call(void);
 284
 285 static int ftrace_mod(unsigned long ip, unsigned long old_addr,
 286                       unsigned long new_addr)
 287 {
 288         unsigned char code[MCOUNT_INSN_SIZE];
 289
 290         if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE))
 291                 return -EFAULT;
 292
 293         if (old_addr != __raw_readl((unsigned long *)code))
 294                 return -EINVAL;
 295
 296         __raw_writel(new_addr, ip);
 297         return 0;
 298 }
 299
 300 int ftrace_enable_ftrace_graph_caller(void)
 301 {
 302         unsigned long ip, old_addr, new_addr;
 303
 304         ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
 305         old_addr = (unsigned long)(&skip_trace);
 306         new_addr = (unsigned long)(&ftrace_graph_caller);
 307
 308         return ftrace_mod(ip, old_addr, new_addr);
 309 }
 310
 311 int ftrace_disable_ftrace_graph_caller(void)
 312 {
 313         unsigned long ip, old_addr, new_addr;
 314
 315         ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
 316         old_addr = (unsigned long)(&ftrace_graph_caller);
 317         new_addr = (unsigned long)(&skip_trace);
 318
 319         return ftrace_mod(ip, old_addr, new_addr);
 320 }
 321 #endif /* CONFIG_DYNAMIC_FTRACE */
 322
 323 /*
 324  * Hook the return address and push it in the stack of return addrs
 325  * in the current thread info.
 326  *
 327  * This is the main routine for the function graph tracer. The function
 328  * graph tracer essentially works like this:
 329  *
 330  * parent is the stack address containing self_addr's return address.
 331  * We pull the real return address out of parent and store it in
 332  * current's ret_stack. Then, we replace the return address on the stack
 333  * with the address of return_to_handler. self_addr is the function that
 334  * called mcount.
 335  *
 336  * When self_addr returns, it will jump to return_to_handler which calls
 337  * ftrace_return_to_handler. ftrace_return_to_handler will pull the real
 338  * return address off of current's ret_stack and jump to it.
 339  */
 340 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
 341 {
 342         unsigned long old;
 343         int faulted, err;
 344         struct ftrace_graph_ent trace;
 345         unsigned long return_hooker = (unsigned long)&return_to_handler;
 346
 347         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 348                 return;
 349
 350         /*
 351          * Protect against fault, even if it shouldn't
 352          * happen. This tool is too much intrusive to
 353          * ignore such a protection.
 354          */
 355         __asm__ __volatile__(
 356                 "1:                                             \n\t"
 357                 "mov.l          @%2, %0                         \n\t"
 358                 "2:                                             \n\t"
 359                 "mov.l          %3, @%2                         \n\t"
 360                 "mov            #0, %1                          \n\t"
 361                 "3:                                             \n\t"
 362                 ".section .fixup, \"ax\"                        \n\t"
 363                 "4:                                             \n\t"
 364                 "mov.l          5f, %0                          \n\t"
 365                 "jmp            @%0                             \n\t"
 366                 " mov           #1, %1                          \n\t"
 367                 ".balign 4                                      \n\t"
 368                 "5:     .long 3b                                \n\t"
 369                 ".previous                                      \n\t"
 370                 ".section __ex_table,\"a\"                      \n\t"
 371                 ".long 1b, 4b                                   \n\t"
 372                 ".long 2b, 4b                                   \n\t"
 373                 ".previous                                      \n\t"
 374                 : "=&r" (old), "=r" (faulted)
 375                 : "r" (parent), "r" (return_hooker)
 376         );
 377
 378         if (unlikely(faulted)) {
 379                 ftrace_graph_stop();
 380                 WARN_ON(1);
 381                 return;
 382         }
 383
 384         err = ftrace_push_return_trace(old, self_addr, &trace.depth, 0);
 385         if (err == -EBUSY) {
 386                 __raw_writel(old, parent);
 387                 return;
 388         }
 389
 390         trace.func = self_addr;
 391
 392         /* Only trace if the calling function expects to */
 393         if (!ftrace_graph_entry(&trace)) {
 394                 current->curr_ret_stack--;
 395                 __raw_writel(old, parent);
 396         }
 397 }
 398 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */