linux/arch/sh/kernel/ftrace.c
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   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
  26static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];
  27
  28static 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 */
  47static unsigned char *ftrace_nop_replace(unsigned long ip)
  48{
  49        __raw_writel(ip + MCOUNT_INSN_SIZE, ftrace_nop);
  50        return ftrace_nop;
  51}
  52
  53static 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 */
  94static atomic_t nmi_running = ATOMIC_INIT(0);
  95static int mod_code_status;             /* holds return value of text write */
  96static void *mod_code_ip;               /* holds the IP to write to */
  97static void *mod_code_newcode;          /* holds the text to write to the IP */
  98
  99static unsigned nmi_wait_count;
 100static atomic_t nmi_update_count = ATOMIC_INIT(0);
 101
 102int 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
 112static 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
 126static 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
 142void 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
 153void ftrace_nmi_exit(void)
 154{
 155        /* Finish all executions before clearing nmi_running */
 156        smp_mb();
 157        atomic_dec(&nmi_running);
 158}
 159
 160static 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
 172static 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
 184static int
 185do_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
 209static 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
 241int 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
 252int 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
 264int 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
 275int __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
 283extern void ftrace_graph_call(void);
 284
 285static 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
 300int 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
 311int 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 */
 340void 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(ftrace_graph_is_dead()))
 348                return;
 349
 350        if (unlikely(atomic_read(&current->tracing_graph_pause)))
 351                return;
 352
 353        /*
 354         * Protect against fault, even if it shouldn't
 355         * happen. This tool is too much intrusive to
 356         * ignore such a protection.
 357         */
 358        __asm__ __volatile__(
 359                "1:                                             \n\t"
 360                "mov.l          @%2, %0                         \n\t"
 361                "2:                                             \n\t"
 362                "mov.l          %3, @%2                         \n\t"
 363                "mov            #0, %1                          \n\t"
 364                "3:                                             \n\t"
 365                ".section .fixup, \"ax\"                        \n\t"
 366                "4:                                             \n\t"
 367                "mov.l          5f, %0                          \n\t"
 368                "jmp            @%0                             \n\t"
 369                " mov           #1, %1                          \n\t"
 370                ".balign 4                                      \n\t"
 371                "5:     .long 3b                                \n\t"
 372                ".previous                                      \n\t"
 373                ".section __ex_table,\"a\"                      \n\t"
 374                ".long 1b, 4b                                   \n\t"
 375                ".long 2b, 4b                                   \n\t"
 376                ".previous                                      \n\t"
 377                : "=&r" (old), "=r" (faulted)
 378                : "r" (parent), "r" (return_hooker)
 379        );
 380
 381        if (unlikely(faulted)) {
 382                ftrace_graph_stop();
 383                WARN_ON(1);
 384                return;
 385        }
 386
 387        err = ftrace_push_return_trace(old, self_addr, &trace.depth, 0);
 388        if (err == -EBUSY) {
 389                __raw_writel(old, parent);
 390                return;
 391        }
 392
 393        trace.func = self_addr;
 394
 395        /* Only trace if the calling function expects to */
 396        if (!ftrace_graph_entry(&trace)) {
 397                current->curr_ret_stack--;
 398                __raw_writel(old, parent);
 399        }
 400}
 401#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 402