libsanitizer/sanitizer_common/sanitizer_symbolizer_posix_libcdep.cc

   1 //===-- sanitizer_symbolizer_posix_libcdep.cc -----------------------------===//
   2 //
   3 // This file is distributed under the University of Illinois Open Source
   4 // License. See LICENSE.TXT for details.
   5 //
   6 //===----------------------------------------------------------------------===//
   7 //
   8 // This file is shared between AddressSanitizer and ThreadSanitizer
   9 // run-time libraries.
  10 // POSIX-specific implementation of symbolizer parts.
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "sanitizer_platform.h"
  14 #if SANITIZER_POSIX
  15 #include "sanitizer_allocator_internal.h"
  16 #include "sanitizer_common.h"
  17 #include "sanitizer_flags.h"
  18 #include "sanitizer_internal_defs.h"
  19 #include "sanitizer_linux.h"
  20 #include "sanitizer_placement_new.h"
  21 #include "sanitizer_procmaps.h"
  22 #include "sanitizer_symbolizer.h"
  23 #include "sanitizer_symbolizer_libbacktrace.h"
  24
  25 #include <errno.h>
  26 #include <stdlib.h>
  27 #include <sys/wait.h>
  28 #include <unistd.h>
  29
  30 // C++ demangling function, as required by Itanium C++ ABI. This is weak,
  31 // because we do not require a C++ ABI library to be linked to a program
  32 // using sanitizers; if it's not present, we'll just use the mangled name.
  33 namespace __cxxabiv1 {
  34   extern "C" SANITIZER_WEAK_ATTRIBUTE
  35   char *__cxa_demangle(const char *mangled, char *buffer,
  36                                   size_t *length, int *status);
  37 }
  38
  39 namespace __sanitizer {
  40
  41 // Attempts to demangle the name via __cxa_demangle from __cxxabiv1.
  42 static const char *DemangleCXXABI(const char *name) {
  43   // FIXME: __cxa_demangle aggressively insists on allocating memory.
  44   // There's not much we can do about that, short of providing our
  45   // own demangler (libc++abi's implementation could be adapted so that
  46   // it does not allocate). For now, we just call it anyway, and we leak
  47   // the returned value.
  48   if (__cxxabiv1::__cxa_demangle)
  49     if (const char *demangled_name =
  50           __cxxabiv1::__cxa_demangle(name, 0, 0, 0))
  51       return demangled_name;
  52
  53   return name;
  54 }
  55
  56 // Extracts the prefix of "str" that consists of any characters not
  57 // present in "delims" string, and copies this prefix to "result", allocating
  58 // space for it.
  59 // Returns a pointer to "str" after skipping extracted prefix and first
  60 // delimiter char.
  61 static const char *ExtractToken(const char *str, const char *delims,
  62                                 char **result) {
  63   uptr prefix_len = internal_strcspn(str, delims);
  64   *result = (char*)InternalAlloc(prefix_len + 1);
  65   internal_memcpy(*result, str, prefix_len);
  66   (*result)[prefix_len] = '\0';
  67   const char *prefix_end = str + prefix_len;
  68   if (*prefix_end != '\0') prefix_end++;
  69   return prefix_end;
  70 }
  71
  72 // Same as ExtractToken, but converts extracted token to integer.
  73 static const char *ExtractInt(const char *str, const char *delims,
  74                               int *result) {
  75   char *buff;
  76   const char *ret = ExtractToken(str, delims, &buff);
  77   if (buff != 0) {
  78     *result = (int)internal_atoll(buff);
  79   }
  80   InternalFree(buff);
  81   return ret;
  82 }
  83
  84 static const char *ExtractUptr(const char *str, const char *delims,
  85                                uptr *result) {
  86   char *buff;
  87   const char *ret = ExtractToken(str, delims, &buff);
  88   if (buff != 0) {
  89     *result = (uptr)internal_atoll(buff);
  90   }
  91   InternalFree(buff);
  92   return ret;
  93 }
  94
  95 class ExternalSymbolizerInterface {
  96  public:
  97   // Can't declare pure virtual functions in sanitizer runtimes:
  98   // __cxa_pure_virtual might be unavailable.
  99   virtual char *SendCommand(bool is_data, const char *module_name,
 100                             uptr module_offset) {
 101     UNIMPLEMENTED();
 102   }
 103 };
 104
 105 // SymbolizerProcess encapsulates communication between the tool and
 106 // external symbolizer program, running in a different subprocess.
 107 // SymbolizerProcess may not be used from two threads simultaneously.
 108 class SymbolizerProcess : public ExternalSymbolizerInterface {
 109  public:
 110   explicit SymbolizerProcess(const char *path)
 111       : path_(path),
 112         input_fd_(kInvalidFd),
 113         output_fd_(kInvalidFd),
 114         times_restarted_(0),
 115         failed_to_start_(false),
 116         reported_invalid_path_(false) {
 117     CHECK(path_);
 118     CHECK_NE(path_[0], '\0');
 119   }
 120
 121   char *SendCommand(bool is_data, const char *module_name, uptr module_offset) {
 122     for (; times_restarted_ < kMaxTimesRestarted; times_restarted_++) {
 123       // Start or restart symbolizer if we failed to send command to it.
 124       if (char *res = SendCommandImpl(is_data, module_name, module_offset))
 125         return res;
 126       Restart();
 127     }
 128     if (!failed_to_start_) {
 129       Report("WARNING: Failed to use and restart external symbolizer!\n");
 130       failed_to_start_ = true;
 131     }
 132     return 0;
 133   }
 134
 135  private:
 136   bool Restart() {
 137     if (input_fd_ != kInvalidFd)
 138       internal_close(input_fd_);
 139     if (output_fd_ != kInvalidFd)
 140       internal_close(output_fd_);
 141     return StartSymbolizerSubprocess();
 142   }
 143
 144   char *SendCommandImpl(bool is_data, const char *module_name,
 145                         uptr module_offset) {
 146     if (input_fd_ == kInvalidFd || output_fd_ == kInvalidFd)
 147       return 0;
 148     CHECK(module_name);
 149     if (!RenderInputCommand(buffer_, kBufferSize, is_data, module_name,
 150                             module_offset))
 151       return 0;
 152     if (!writeToSymbolizer(buffer_, internal_strlen(buffer_)))
 153       return 0;
 154     if (!readFromSymbolizer(buffer_, kBufferSize))
 155       return 0;
 156     return buffer_;
 157   }
 158
 159   bool readFromSymbolizer(char *buffer, uptr max_length) {
 160     if (max_length == 0)
 161       return true;
 162     uptr read_len = 0;
 163     while (true) {
 164       uptr just_read = internal_read(input_fd_, buffer + read_len,
 165                                      max_length - read_len - 1);
 166       // We can't read 0 bytes, as we don't expect external symbolizer to close
 167       // its stdout.
 168       if (just_read == 0 || just_read == (uptr)-1) {
 169         Report("WARNING: Can't read from symbolizer at fd %d\n", input_fd_);
 170         return false;
 171       }
 172       read_len += just_read;
 173       if (ReachedEndOfOutput(buffer, read_len))
 174         break;
 175     }
 176     buffer[read_len] = '\0';
 177     return true;
 178   }
 179
 180   bool writeToSymbolizer(const char *buffer, uptr length) {
 181     if (length == 0)
 182       return true;
 183     uptr write_len = internal_write(output_fd_, buffer, length);
 184     if (write_len == 0 || write_len == (uptr)-1) {
 185       Report("WARNING: Can't write to symbolizer at fd %d\n", output_fd_);
 186       return false;
 187     }
 188     return true;
 189   }
 190
 191   bool StartSymbolizerSubprocess() {
 192     if (!FileExists(path_)) {
 193       if (!reported_invalid_path_) {
 194         Report("WARNING: invalid path to external symbolizer!\n");
 195         reported_invalid_path_ = true;
 196       }
 197       return false;
 198     }
 199
 200     int *infd = NULL;
 201     int *outfd = NULL;
 202     // The client program may close its stdin and/or stdout and/or stderr
 203     // thus allowing socketpair to reuse file descriptors 0, 1 or 2.
 204     // In this case the communication between the forked processes may be
 205     // broken if either the parent or the child tries to close or duplicate
 206     // these descriptors. The loop below produces two pairs of file
 207     // descriptors, each greater than 2 (stderr).
 208     int sock_pair[5][2];
 209     for (int i = 0; i < 5; i++) {
 210       if (pipe(sock_pair[i]) == -1) {
 211         for (int j = 0; j < i; j++) {
 212           internal_close(sock_pair[j][0]);
 213           internal_close(sock_pair[j][1]);
 214         }
 215         Report("WARNING: Can't create a socket pair to start "
 216                "external symbolizer (errno: %d)\n", errno);
 217         return false;
 218       } else if (sock_pair[i][0] > 2 && sock_pair[i][1] > 2) {
 219         if (infd == NULL) {
 220           infd = sock_pair[i];
 221         } else {
 222           outfd = sock_pair[i];
 223           for (int j = 0; j < i; j++) {
 224             if (sock_pair[j] == infd) continue;
 225             internal_close(sock_pair[j][0]);
 226             internal_close(sock_pair[j][1]);
 227           }
 228           break;
 229         }
 230       }
 231     }
 232     CHECK(infd);
 233     CHECK(outfd);
 234
 235     // Real fork() may call user callbacks registered with pthread_atfork().
 236     int pid = internal_fork();
 237     if (pid == -1) {
 238       // Fork() failed.
 239       internal_close(infd[0]);
 240       internal_close(infd[1]);
 241       internal_close(outfd[0]);
 242       internal_close(outfd[1]);
 243       Report("WARNING: failed to fork external symbolizer "
 244              " (errno: %d)\n", errno);
 245       return false;
 246     } else if (pid == 0) {
 247       // Child subprocess.
 248       internal_close(STDOUT_FILENO);
 249       internal_close(STDIN_FILENO);
 250       internal_dup2(outfd[0], STDIN_FILENO);
 251       internal_dup2(infd[1], STDOUT_FILENO);
 252       internal_close(outfd[0]);
 253       internal_close(outfd[1]);
 254       internal_close(infd[0]);
 255       internal_close(infd[1]);
 256       for (int fd = sysconf(_SC_OPEN_MAX); fd > 2; fd--)
 257         internal_close(fd);
 258       ExecuteWithDefaultArgs(path_);
 259       internal__exit(1);
 260     }
 261
 262     // Continue execution in parent process.
 263     internal_close(outfd[0]);
 264     internal_close(infd[1]);
 265     input_fd_ = infd[0];
 266     output_fd_ = outfd[1];
 267
 268     // Check that symbolizer subprocess started successfully.
 269     int pid_status;
 270     SleepForMillis(kSymbolizerStartupTimeMillis);
 271     int exited_pid = waitpid(pid, &pid_status, WNOHANG);
 272     if (exited_pid != 0) {
 273       // Either waitpid failed, or child has already exited.
 274       Report("WARNING: external symbolizer didn't start up correctly!\n");
 275       return false;
 276     }
 277
 278     return true;
 279   }
 280
 281   virtual bool RenderInputCommand(char *buffer, uptr max_length, bool is_data,
 282                                   const char *module_name,
 283                                   uptr module_offset) const {
 284     UNIMPLEMENTED();
 285   }
 286
 287   virtual bool ReachedEndOfOutput(const char *buffer, uptr length) const {
 288     UNIMPLEMENTED();
 289   }
 290
 291   virtual void ExecuteWithDefaultArgs(const char *path_to_binary) const {
 292     UNIMPLEMENTED();
 293   }
 294
 295   const char *path_;
 296   int input_fd_;
 297   int output_fd_;
 298
 299   static const uptr kBufferSize = 16 * 1024;
 300   char buffer_[kBufferSize];
 301
 302   static const uptr kMaxTimesRestarted = 5;
 303   static const int kSymbolizerStartupTimeMillis = 10;
 304   uptr times_restarted_;
 305   bool failed_to_start_;
 306   bool reported_invalid_path_;
 307 };
 308
 309 // For now we assume the following protocol:
 310 // For each request of the form
 311 //   <module_name> <module_offset>
 312 // passed to STDIN, external symbolizer prints to STDOUT response:
 313 //   <function_name>
 314 //   <file_name>:<line_number>:<column_number>
 315 //   <function_name>
 316 //   <file_name>:<line_number>:<column_number>
 317 //   ...
 318 //   <empty line>
 319 class LLVMSymbolizerProcess : public SymbolizerProcess {
 320  public:
 321   explicit LLVMSymbolizerProcess(const char *path) : SymbolizerProcess(path) {}
 322
 323  private:
 324   bool RenderInputCommand(char *buffer, uptr max_length, bool is_data,
 325                           const char *module_name, uptr module_offset) const {
 326     internal_snprintf(buffer, max_length, "%s\"%s\" 0x%zx\n",
 327                       is_data ? "DATA " : "", module_name, module_offset);
 328     return true;
 329   }
 330
 331   bool ReachedEndOfOutput(const char *buffer, uptr length) const {
 332     // Empty line marks the end of llvm-symbolizer output.
 333     return length >= 2 && buffer[length - 1] == '\n' &&
 334            buffer[length - 2] == '\n';
 335   }
 336
 337   void ExecuteWithDefaultArgs(const char *path_to_binary) const {
 338 #if defined(__x86_64__)
 339     const char* const kSymbolizerArch = "--default-arch=x86_64";
 340 #elif defined(__i386__)
 341     const char* const kSymbolizerArch = "--default-arch=i386";
 342 #elif defined(__powerpc64__)
 343     const char* const kSymbolizerArch = "--default-arch=powerpc64";
 344 #else
 345     const char* const kSymbolizerArch = "--default-arch=unknown";
 346 #endif
 347     execl(path_to_binary, path_to_binary, kSymbolizerArch, (char *)0);
 348   }
 349 };
 350
 351 class Addr2LineProcess : public SymbolizerProcess {
 352  public:
 353   Addr2LineProcess(const char *path, const char *module_name)
 354       : SymbolizerProcess(path), module_name_(internal_strdup(module_name)) {}
 355
 356   const char *module_name() const { return module_name_; }
 357
 358  private:
 359   bool RenderInputCommand(char *buffer, uptr max_length, bool is_data,
 360                           const char *module_name, uptr module_offset) const {
 361     if (is_data)
 362       return false;
 363     CHECK_EQ(0, internal_strcmp(module_name, module_name_));
 364     internal_snprintf(buffer, max_length, "0x%zx\n", module_offset);
 365     return true;
 366   }
 367
 368   bool ReachedEndOfOutput(const char *buffer, uptr length) const {
 369     // Output should consist of two lines.
 370     int num_lines = 0;
 371     for (uptr i = 0; i < length; ++i) {
 372       if (buffer[i] == '\n')
 373         num_lines++;
 374       if (num_lines >= 2)
 375         return true;
 376     }
 377     return false;
 378   }
 379
 380   void ExecuteWithDefaultArgs(const char *path_to_binary) const {
 381     execl(path_to_binary, path_to_binary, "-Cfe", module_name_, (char *)0);
 382   }
 383
 384   const char *module_name_;  // Owned, leaked.
 385 };
 386
 387 class Addr2LinePool : public ExternalSymbolizerInterface {
 388  public:
 389   explicit Addr2LinePool(const char *addr2line_path,
 390                          LowLevelAllocator *allocator)
 391       : addr2line_path_(addr2line_path), allocator_(allocator),
 392         addr2line_pool_(16) {}
 393
 394   char *SendCommand(bool is_data, const char *module_name, uptr module_offset) {
 395     if (is_data)
 396       return 0;
 397     Addr2LineProcess *addr2line = 0;
 398     for (uptr i = 0; i < addr2line_pool_.size(); ++i) {
 399       if (0 ==
 400           internal_strcmp(module_name, addr2line_pool_[i]->module_name())) {
 401         addr2line = addr2line_pool_[i];
 402         break;
 403       }
 404     }
 405     if (!addr2line) {
 406       addr2line =
 407           new(*allocator_) Addr2LineProcess(addr2line_path_, module_name);
 408       addr2line_pool_.push_back(addr2line);
 409     }
 410     return addr2line->SendCommand(is_data, module_name, module_offset);
 411   }
 412
 413  private:
 414   const char *addr2line_path_;
 415   LowLevelAllocator *allocator_;
 416   InternalMmapVector<Addr2LineProcess*> addr2line_pool_;
 417 };
 418
 419 #if SANITIZER_SUPPORTS_WEAK_HOOKS
 420 extern "C" {
 421 SANITIZER_INTERFACE_ATTRIBUTE SANITIZER_WEAK_ATTRIBUTE
 422 bool __sanitizer_symbolize_code(const char *ModuleName, u64 ModuleOffset,
 423                                 char *Buffer, int MaxLength);
 424 SANITIZER_INTERFACE_ATTRIBUTE SANITIZER_WEAK_ATTRIBUTE
 425 bool __sanitizer_symbolize_data(const char *ModuleName, u64 ModuleOffset,
 426                                 char *Buffer, int MaxLength);
 427 SANITIZER_INTERFACE_ATTRIBUTE SANITIZER_WEAK_ATTRIBUTE
 428 void __sanitizer_symbolize_flush();
 429 SANITIZER_INTERFACE_ATTRIBUTE SANITIZER_WEAK_ATTRIBUTE
 430 int __sanitizer_symbolize_demangle(const char *Name, char *Buffer,
 431                                    int MaxLength);
 432 }  // extern "C"
 433
 434 class InternalSymbolizer {
 435  public:
 436   typedef bool (*SanitizerSymbolizeFn)(const char*, u64, char*, int);
 437
 438   static InternalSymbolizer *get(LowLevelAllocator *alloc) {
 439     if (__sanitizer_symbolize_code != 0 &&
 440         __sanitizer_symbolize_data != 0) {
 441       return new(*alloc) InternalSymbolizer();
 442     }
 443     return 0;
 444   }
 445
 446   char *SendCommand(bool is_data, const char *module_name, uptr module_offset) {
 447     SanitizerSymbolizeFn symbolize_fn = is_data ? __sanitizer_symbolize_data
 448                                                 : __sanitizer_symbolize_code;
 449     if (symbolize_fn(module_name, module_offset, buffer_, kBufferSize))
 450       return buffer_;
 451     return 0;
 452   }
 453
 454   void Flush() {
 455     if (__sanitizer_symbolize_flush)
 456       __sanitizer_symbolize_flush();
 457   }
 458
 459   const char *Demangle(const char *name) {
 460     if (__sanitizer_symbolize_demangle) {
 461       for (uptr res_length = 1024;
 462            res_length <= InternalSizeClassMap::kMaxSize;) {
 463         char *res_buff = static_cast<char*>(InternalAlloc(res_length));
 464         uptr req_length =
 465             __sanitizer_symbolize_demangle(name, res_buff, res_length);
 466         if (req_length > res_length) {
 467           res_length = req_length + 1;
 468           InternalFree(res_buff);
 469           continue;
 470         }
 471         return res_buff;
 472       }
 473     }
 474     return name;
 475   }
 476
 477  private:
 478   InternalSymbolizer() { }
 479
 480   static const int kBufferSize = 16 * 1024;
 481   static const int kMaxDemangledNameSize = 1024;
 482   char buffer_[kBufferSize];
 483 };
 484 #else  // SANITIZER_SUPPORTS_WEAK_HOOKS
 485
 486 class InternalSymbolizer {
 487  public:
 488   static InternalSymbolizer *get(LowLevelAllocator *alloc) { return 0; }
 489   char *SendCommand(bool is_data, const char *module_name, uptr module_offset) {
 490     return 0;
 491   }
 492   void Flush() { }
 493   const char *Demangle(const char *name) { return name; }
 494 };
 495
 496 #endif  // SANITIZER_SUPPORTS_WEAK_HOOKS
 497
 498 class POSIXSymbolizer : public Symbolizer {
 499  public:
 500   POSIXSymbolizer(ExternalSymbolizerInterface *external_symbolizer,
 501                   InternalSymbolizer *internal_symbolizer,
 502                   LibbacktraceSymbolizer *libbacktrace_symbolizer)
 503       : Symbolizer(),
 504         external_symbolizer_(external_symbolizer),
 505         internal_symbolizer_(internal_symbolizer),
 506         libbacktrace_symbolizer_(libbacktrace_symbolizer) {}
 507
 508   uptr SymbolizePC(uptr addr, AddressInfo *frames, uptr max_frames) {
 509     BlockingMutexLock l(&mu_);
 510     if (max_frames == 0)
 511       return 0;
 512     const char *module_name;
 513     uptr module_offset;
 514     if (!FindModuleNameAndOffsetForAddress(addr, &module_name, &module_offset))
 515       return 0;
 516     // First, try to use libbacktrace symbolizer (if it's available).
 517     if (libbacktrace_symbolizer_ != 0) {
 518       mu_.CheckLocked();
 519       uptr res = libbacktrace_symbolizer_->SymbolizeCode(
 520           addr, frames, max_frames, module_name, module_offset);
 521       if (res > 0)
 522         return res;
 523     }
 524     const char *str = SendCommand(false, module_name, module_offset);
 525     if (str == 0) {
 526       // Symbolizer was not initialized or failed. Fill only data
 527       // about module name and offset.
 528       AddressInfo *info = &frames[0];
 529       info->Clear();
 530       info->FillAddressAndModuleInfo(addr, module_name, module_offset);
 531       return 1;
 532     }
 533     uptr frame_id = 0;
 534     for (frame_id = 0; frame_id < max_frames; frame_id++) {
 535       AddressInfo *info = &frames[frame_id];
 536       char *function_name = 0;
 537       str = ExtractToken(str, "\n", &function_name);
 538       CHECK(function_name);
 539       if (function_name[0] == '\0') {
 540         // There are no more frames.
 541         break;
 542       }
 543       info->Clear();
 544       info->FillAddressAndModuleInfo(addr, module_name, module_offset);
 545       info->function = function_name;
 546       // Parse <file>:<line>:<column> buffer.
 547       char *file_line_info = 0;
 548       str = ExtractToken(str, "\n", &file_line_info);
 549       CHECK(file_line_info);
 550       const char *line_info = ExtractToken(file_line_info, ":", &info->file);
 551       line_info = ExtractInt(line_info, ":", &info->line);
 552       line_info = ExtractInt(line_info, "", &info->column);
 553       InternalFree(file_line_info);
 554
 555       // Functions and filenames can be "??", in which case we write 0
 556       // to address info to mark that names are unknown.
 557       if (0 == internal_strcmp(info->function, "??")) {
 558         InternalFree(info->function);
 559         info->function = 0;
 560       }
 561       if (0 == internal_strcmp(info->file, "??")) {
 562         InternalFree(info->file);
 563         info->file = 0;
 564       }
 565     }
 566     if (frame_id == 0) {
 567       // Make sure we return at least one frame.
 568       AddressInfo *info = &frames[0];
 569       info->Clear();
 570       info->FillAddressAndModuleInfo(addr, module_name, module_offset);
 571       frame_id = 1;
 572     }
 573     return frame_id;
 574   }
 575
 576   bool SymbolizeData(uptr addr, DataInfo *info) {
 577     BlockingMutexLock l(&mu_);
 578     LoadedModule *module = FindModuleForAddress(addr);
 579     if (module == 0)
 580       return false;
 581     const char *module_name = module->full_name();
 582     uptr module_offset = addr - module->base_address();
 583     internal_memset(info, 0, sizeof(*info));
 584     info->address = addr;
 585     info->module = internal_strdup(module_name);
 586     info->module_offset = module_offset;
 587     // First, try to use libbacktrace symbolizer (if it's available).
 588     if (libbacktrace_symbolizer_ != 0) {
 589       mu_.CheckLocked();
 590       if (libbacktrace_symbolizer_->SymbolizeData(info))
 591         return true;
 592     }
 593     const char *str = SendCommand(true, module_name, module_offset);
 594     if (str == 0)
 595       return true;
 596     str = ExtractToken(str, "\n", &info->name);
 597     str = ExtractUptr(str, " ", &info->start);
 598     str = ExtractUptr(str, "\n", &info->size);
 599     info->start += module->base_address();
 600     return true;
 601   }
 602
 603   bool GetModuleNameAndOffsetForPC(uptr pc, const char **module_name,
 604                                    uptr *module_address) {
 605     BlockingMutexLock l(&mu_);
 606     return FindModuleNameAndOffsetForAddress(pc, module_name, module_address);
 607   }
 608
 609   bool CanReturnFileLineInfo() {
 610     return internal_symbolizer_ != 0 || external_symbolizer_ != 0 ||
 611            libbacktrace_symbolizer_ != 0;
 612   }
 613
 614   void Flush() {
 615     BlockingMutexLock l(&mu_);
 616     if (internal_symbolizer_ != 0) {
 617       SymbolizerScope sym_scope(this);
 618       internal_symbolizer_->Flush();
 619     }
 620   }
 621
 622   const char *Demangle(const char *name) {
 623     BlockingMutexLock l(&mu_);
 624     // Run hooks even if we don't use internal symbolizer, as cxxabi
 625     // demangle may call system functions.
 626     SymbolizerScope sym_scope(this);
 627     // Try to use libbacktrace demangler (if available).
 628     if (libbacktrace_symbolizer_ != 0) {
 629       if (const char *demangled = libbacktrace_symbolizer_->Demangle(name))
 630         return demangled;
 631     }
 632     if (internal_symbolizer_ != 0)
 633       return internal_symbolizer_->Demangle(name);
 634     return DemangleCXXABI(name);
 635   }
 636
 637   void PrepareForSandboxing() {
 638 #if SANITIZER_LINUX && !SANITIZER_ANDROID
 639     BlockingMutexLock l(&mu_);
 640     // Cache /proc/self/exe on Linux.
 641     CacheBinaryName();
 642 #endif
 643   }
 644
 645  private:
 646   char *SendCommand(bool is_data, const char *module_name, uptr module_offset) {
 647     mu_.CheckLocked();
 648     // First, try to use internal symbolizer.
 649     if (internal_symbolizer_) {
 650       SymbolizerScope sym_scope(this);
 651       return internal_symbolizer_->SendCommand(is_data, module_name,
 652                                                module_offset);
 653     }
 654     // Otherwise, fall back to external symbolizer.
 655     if (external_symbolizer_) {
 656       SymbolizerScope sym_scope(this);
 657       return external_symbolizer_->SendCommand(is_data, module_name,
 658                                                module_offset);
 659     }
 660     return 0;
 661   }
 662
 663   LoadedModule *FindModuleForAddress(uptr address) {
 664     mu_.CheckLocked();
 665     bool modules_were_reloaded = false;
 666     if (modules_ == 0 || !modules_fresh_) {
 667       modules_ = (LoadedModule*)(symbolizer_allocator_.Allocate(
 668           kMaxNumberOfModuleContexts * sizeof(LoadedModule)));
 669       CHECK(modules_);
 670       n_modules_ = GetListOfModules(modules_, kMaxNumberOfModuleContexts,
 671                                     /* filter */ 0);
 672       CHECK_GT(n_modules_, 0);
 673       CHECK_LT(n_modules_, kMaxNumberOfModuleContexts);
 674       modules_fresh_ = true;
 675       modules_were_reloaded = true;
 676     }
 677     for (uptr i = 0; i < n_modules_; i++) {
 678       if (modules_[i].containsAddress(address)) {
 679         return &modules_[i];
 680       }
 681     }
 682     // Reload the modules and look up again, if we haven't tried it yet.
 683     if (!modules_were_reloaded) {
 684       // FIXME: set modules_fresh_ from dlopen()/dlclose() interceptors.
 685       // It's too aggressive to reload the list of modules each time we fail
 686       // to find a module for a given address.
 687       modules_fresh_ = false;
 688       return FindModuleForAddress(address);
 689     }
 690     return 0;
 691   }
 692
 693   bool FindModuleNameAndOffsetForAddress(uptr address, const char **module_name,
 694                                          uptr *module_offset) {
 695     mu_.CheckLocked();
 696     LoadedModule *module = FindModuleForAddress(address);
 697     if (module == 0)
 698       return false;
 699     *module_name = module->full_name();
 700     *module_offset = address - module->base_address();
 701     return true;
 702   }
 703
 704   // 16K loaded modules should be enough for everyone.
 705   static const uptr kMaxNumberOfModuleContexts = 1 << 14;
 706   LoadedModule *modules_;  // Array of module descriptions is leaked.
 707   uptr n_modules_;
 708   // If stale, need to reload the modules before looking up addresses.
 709   bool modules_fresh_;
 710   BlockingMutex mu_;
 711
 712   ExternalSymbolizerInterface *external_symbolizer_;  // Leaked.
 713   InternalSymbolizer *const internal_symbolizer_;     // Leaked.
 714   LibbacktraceSymbolizer *libbacktrace_symbolizer_;   // Leaked.
 715 };
 716
 717 Symbolizer *Symbolizer::PlatformInit() {
 718   if (!common_flags()->symbolize) {
 719     return new(symbolizer_allocator_) POSIXSymbolizer(0, 0, 0);
 720   }
 721   InternalSymbolizer* internal_symbolizer =
 722       InternalSymbolizer::get(&symbolizer_allocator_);
 723   ExternalSymbolizerInterface *external_symbolizer = 0;
 724   LibbacktraceSymbolizer *libbacktrace_symbolizer = 0;
 725
 726   if (!internal_symbolizer) {
 727     libbacktrace_symbolizer =
 728         LibbacktraceSymbolizer::get(&symbolizer_allocator_);
 729     if (!libbacktrace_symbolizer) {
 730       const char *path_to_external = common_flags()->external_symbolizer_path;
 731       if (path_to_external && path_to_external[0] == '\0') {
 732         // External symbolizer is explicitly disabled. Do nothing.
 733       } else {
 734         // Find path to llvm-symbolizer if it's not provided.
 735         if (!path_to_external)
 736           path_to_external = FindPathToBinary("llvm-symbolizer");
 737         if (path_to_external) {
 738           external_symbolizer = new(symbolizer_allocator_)
 739               LLVMSymbolizerProcess(path_to_external);
 740         } else if (common_flags()->allow_addr2line) {
 741           // If llvm-symbolizer is not found, try to use addr2line.
 742           if (const char *addr2line_path = FindPathToBinary("addr2line")) {
 743             external_symbolizer = new(symbolizer_allocator_)
 744                 Addr2LinePool(addr2line_path, &symbolizer_allocator_);
 745           }
 746         }
 747       }
 748     }
 749   }
 750
 751   return new(symbolizer_allocator_) POSIXSymbolizer(
 752       external_symbolizer, internal_symbolizer, libbacktrace_symbolizer);
 753 }
 754
 755 }  // namespace __sanitizer
 756
 757 #endif  // SANITIZER_POSIX