base/debug/stack_trace_posix.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "base/debug/stack_trace.h"
   6
   7 #include <errno.h>
   8 #include <fcntl.h>
   9 #include <signal.h>
  10 #include <stdio.h>
  11 #include <stdlib.h>
  12 #include <sys/param.h>
  13 #include <sys/stat.h>
  14 #include <sys/types.h>
  15 #include <unistd.h>
  16
  17 #include <map>
  18 #include <ostream>
  19 #include <string>
  20 #include <vector>
  21
  22 #if defined(__GLIBCXX__)
  23 #include <cxxabi.h>
  24 #endif
  25 #if !defined(__UCLIBC__)
  26 #include <execinfo.h>
  27 #endif
  28
  29 #if defined(OS_MACOSX)
  30 #include <AvailabilityMacros.h>
  31 #endif
  32
  33 #include "base/basictypes.h"
  34 #include "base/debug/debugger.h"
  35 #include "base/debug/proc_maps_linux.h"
  36 #include "base/logging.h"
  37 #include "base/memory/scoped_ptr.h"
  38 #include "base/memory/singleton.h"
  39 #include "base/numerics/safe_conversions.h"
  40 #include "base/posix/eintr_wrapper.h"
  41 #include "base/strings/string_number_conversions.h"
  42 #include "build/build_config.h"
  43
  44 #if defined(USE_SYMBOLIZE)
  45 #include "base/third_party/symbolize/symbolize.h"
  46 #endif
  47
  48 namespace base {
  49 namespace debug {
  50
  51 namespace {
  52
  53 volatile sig_atomic_t in_signal_handler = 0;
  54
  55 #if !defined(USE_SYMBOLIZE) && defined(__GLIBCXX__)
  56 // The prefix used for mangled symbols, per the Itanium C++ ABI:
  57 // http://www.codesourcery.com/cxx-abi/abi.html#mangling
  58 const char kMangledSymbolPrefix[] = "_Z";
  59
  60 // Characters that can be used for symbols, generated by Ruby:
  61 // (('a'..'z').to_a+('A'..'Z').to_a+('0'..'9').to_a + ['_']).join
  62 const char kSymbolCharacters[] =
  63     "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_";
  64 #endif  // !defined(USE_SYMBOLIZE) && defined(__GLIBCXX__)
  65
  66 #if !defined(USE_SYMBOLIZE)
  67 // Demangles C++ symbols in the given text. Example:
  68 //
  69 // "out/Debug/base_unittests(_ZN10StackTraceC1Ev+0x20) [0x817778c]"
  70 // =>
  71 // "out/Debug/base_unittests(StackTrace::StackTrace()+0x20) [0x817778c]"
  72 void DemangleSymbols(std::string* text) {
  73   // Note: code in this function is NOT async-signal safe (std::string uses
  74   // malloc internally).
  75
  76 #if defined(__GLIBCXX__) && !defined(__UCLIBC__)
  77
  78   std::string::size_type search_from = 0;
  79   while (search_from < text->size()) {
  80     // Look for the start of a mangled symbol, from search_from.
  81     std::string::size_type mangled_start =
  82         text->find(kMangledSymbolPrefix, search_from);
  83     if (mangled_start == std::string::npos) {
  84       break;  // Mangled symbol not found.
  85     }
  86
  87     // Look for the end of the mangled symbol.
  88     std::string::size_type mangled_end =
  89         text->find_first_not_of(kSymbolCharacters, mangled_start);
  90     if (mangled_end == std::string::npos) {
  91       mangled_end = text->size();
  92     }
  93     std::string mangled_symbol =
  94         text->substr(mangled_start, mangled_end - mangled_start);
  95
  96     // Try to demangle the mangled symbol candidate.
  97     int status = 0;
  98     scoped_ptr<char, base::FreeDeleter> demangled_symbol(
  99         abi::__cxa_demangle(mangled_symbol.c_str(), NULL, 0, &status));
 100     if (status == 0) {  // Demangling is successful.
 101       // Remove the mangled symbol.
 102       text->erase(mangled_start, mangled_end - mangled_start);
 103       // Insert the demangled symbol.
 104       text->insert(mangled_start, demangled_symbol.get());
 105       // Next time, we'll start right after the demangled symbol we inserted.
 106       search_from = mangled_start + strlen(demangled_symbol.get());
 107     } else {
 108       // Failed to demangle.  Retry after the "_Z" we just found.
 109       search_from = mangled_start + 2;
 110     }
 111   }
 112
 113 #endif  // defined(__GLIBCXX__) && !defined(__UCLIBC__)
 114 }
 115 #endif  // !defined(USE_SYMBOLIZE)
 116
 117 class BacktraceOutputHandler {
 118  public:
 119   virtual void HandleOutput(const char* output) = 0;
 120
 121  protected:
 122   virtual ~BacktraceOutputHandler() {}
 123 };
 124
 125 void OutputPointer(void* pointer, BacktraceOutputHandler* handler) {
 126   // This should be more than enough to store a 64-bit number in hex:
 127   // 16 hex digits + 1 for null-terminator.
 128   char buf[17] = { '\0' };
 129   handler->HandleOutput("0x");
 130   internal::itoa_r(reinterpret_cast<intptr_t>(pointer),
 131                    buf, sizeof(buf), 16, 12);
 132   handler->HandleOutput(buf);
 133 }
 134
 135 #if defined(USE_SYMBOLIZE)
 136 void OutputFrameId(intptr_t frame_id, BacktraceOutputHandler* handler) {
 137   // Max unsigned 64-bit number in decimal has 20 digits (18446744073709551615).
 138   // Hence, 30 digits should be more than enough to represent it in decimal
 139   // (including the null-terminator).
 140   char buf[30] = { '\0' };
 141   handler->HandleOutput("#");
 142   internal::itoa_r(frame_id, buf, sizeof(buf), 10, 1);
 143   handler->HandleOutput(buf);
 144 }
 145 #endif  // defined(USE_SYMBOLIZE)
 146
 147 void ProcessBacktrace(void *const *trace,
 148                       size_t size,
 149                       BacktraceOutputHandler* handler) {
 150   // NOTE: This code MUST be async-signal safe (it's used by in-process
 151   // stack dumping signal handler). NO malloc or stdio is allowed here.
 152
 153 #if defined(USE_SYMBOLIZE)
 154   for (size_t i = 0; i < size; ++i) {
 155     OutputFrameId(i, handler);
 156     handler->HandleOutput(" ");
 157     OutputPointer(trace[i], handler);
 158     handler->HandleOutput(" ");
 159
 160     char buf[1024] = { '\0' };
 161
 162     // Subtract by one as return address of function may be in the next
 163     // function when a function is annotated as noreturn.
 164     void* address = static_cast<char*>(trace[i]) - 1;
 165     if (google::Symbolize(address, buf, sizeof(buf)))
 166       handler->HandleOutput(buf);
 167     else
 168       handler->HandleOutput("<unknown>");
 169
 170     handler->HandleOutput("\n");
 171   }
 172 #elif !defined(__UCLIBC__)
 173   bool printed = false;
 174
 175   // Below part is async-signal unsafe (uses malloc), so execute it only
 176   // when we are not executing the signal handler.
 177   if (in_signal_handler == 0) {
 178     scoped_ptr<char*, FreeDeleter>
 179         trace_symbols(backtrace_symbols(trace, size));
 180     if (trace_symbols.get()) {
 181       for (size_t i = 0; i < size; ++i) {
 182         std::string trace_symbol = trace_symbols.get()[i];
 183         DemangleSymbols(&trace_symbol);
 184         handler->HandleOutput(trace_symbol.c_str());
 185         handler->HandleOutput("\n");
 186       }
 187
 188       printed = true;
 189     }
 190   }
 191
 192   if (!printed) {
 193     for (size_t i = 0; i < size; ++i) {
 194       handler->HandleOutput(" [");
 195       OutputPointer(trace[i], handler);
 196       handler->HandleOutput("]\n");
 197     }
 198   }
 199 #endif  // defined(USE_SYMBOLIZE)
 200 }
 201
 202 void PrintToStderr(const char* output) {
 203   // NOTE: This code MUST be async-signal safe (it's used by in-process
 204   // stack dumping signal handler). NO malloc or stdio is allowed here.
 205   ignore_result(HANDLE_EINTR(write(STDERR_FILENO, output, strlen(output))));
 206 }
 207
 208 void StackDumpSignalHandler(int signal, siginfo_t* info, void* void_context) {
 209   // NOTE: This code MUST be async-signal safe.
 210   // NO malloc or stdio is allowed here.
 211
 212   // Record the fact that we are in the signal handler now, so that the rest
 213   // of StackTrace can behave in an async-signal-safe manner.
 214   in_signal_handler = 1;
 215
 216   if (BeingDebugged())
 217     BreakDebugger();
 218
 219   PrintToStderr("Received signal ");
 220   char buf[1024] = { 0 };
 221   internal::itoa_r(signal, buf, sizeof(buf), 10, 0);
 222   PrintToStderr(buf);
 223   if (signal == SIGBUS) {
 224     if (info->si_code == BUS_ADRALN)
 225       PrintToStderr(" BUS_ADRALN ");
 226     else if (info->si_code == BUS_ADRERR)
 227       PrintToStderr(" BUS_ADRERR ");
 228     else if (info->si_code == BUS_OBJERR)
 229       PrintToStderr(" BUS_OBJERR ");
 230     else
 231       PrintToStderr(" <unknown> ");
 232   } else if (signal == SIGFPE) {
 233     if (info->si_code == FPE_FLTDIV)
 234       PrintToStderr(" FPE_FLTDIV ");
 235     else if (info->si_code == FPE_FLTINV)
 236       PrintToStderr(" FPE_FLTINV ");
 237     else if (info->si_code == FPE_FLTOVF)
 238       PrintToStderr(" FPE_FLTOVF ");
 239     else if (info->si_code == FPE_FLTRES)
 240       PrintToStderr(" FPE_FLTRES ");
 241     else if (info->si_code == FPE_FLTSUB)
 242       PrintToStderr(" FPE_FLTSUB ");
 243     else if (info->si_code == FPE_FLTUND)
 244       PrintToStderr(" FPE_FLTUND ");
 245     else if (info->si_code == FPE_INTDIV)
 246       PrintToStderr(" FPE_INTDIV ");
 247     else if (info->si_code == FPE_INTOVF)
 248       PrintToStderr(" FPE_INTOVF ");
 249     else
 250       PrintToStderr(" <unknown> ");
 251   } else if (signal == SIGILL) {
 252     if (info->si_code == ILL_BADSTK)
 253       PrintToStderr(" ILL_BADSTK ");
 254     else if (info->si_code == ILL_COPROC)
 255       PrintToStderr(" ILL_COPROC ");
 256     else if (info->si_code == ILL_ILLOPN)
 257       PrintToStderr(" ILL_ILLOPN ");
 258     else if (info->si_code == ILL_ILLADR)
 259       PrintToStderr(" ILL_ILLADR ");
 260     else if (info->si_code == ILL_ILLTRP)
 261       PrintToStderr(" ILL_ILLTRP ");
 262     else if (info->si_code == ILL_PRVOPC)
 263       PrintToStderr(" ILL_PRVOPC ");
 264     else if (info->si_code == ILL_PRVREG)
 265       PrintToStderr(" ILL_PRVREG ");
 266     else
 267       PrintToStderr(" <unknown> ");
 268   } else if (signal == SIGSEGV) {
 269     if (info->si_code == SEGV_MAPERR)
 270       PrintToStderr(" SEGV_MAPERR ");
 271     else if (info->si_code == SEGV_ACCERR)
 272       PrintToStderr(" SEGV_ACCERR ");
 273     else
 274       PrintToStderr(" <unknown> ");
 275   }
 276   if (signal == SIGBUS || signal == SIGFPE ||
 277       signal == SIGILL || signal == SIGSEGV) {
 278     internal::itoa_r(reinterpret_cast<intptr_t>(info->si_addr),
 279                      buf, sizeof(buf), 16, 12);
 280     PrintToStderr(buf);
 281   }
 282   PrintToStderr("\n");
 283
 284   debug::StackTrace().Print();
 285
 286 #if defined(OS_LINUX)
 287 #if ARCH_CPU_X86_FAMILY
 288   ucontext_t* context = reinterpret_cast<ucontext_t*>(void_context);
 289   const struct {
 290     const char* label;
 291     greg_t value;
 292   } registers[] = {
 293 #if ARCH_CPU_32_BITS
 294     { "  gs: ", context->uc_mcontext.gregs[REG_GS] },
 295     { "  fs: ", context->uc_mcontext.gregs[REG_FS] },
 296     { "  es: ", context->uc_mcontext.gregs[REG_ES] },
 297     { "  ds: ", context->uc_mcontext.gregs[REG_DS] },
 298     { " edi: ", context->uc_mcontext.gregs[REG_EDI] },
 299     { " esi: ", context->uc_mcontext.gregs[REG_ESI] },
 300     { " ebp: ", context->uc_mcontext.gregs[REG_EBP] },
 301     { " esp: ", context->uc_mcontext.gregs[REG_ESP] },
 302     { " ebx: ", context->uc_mcontext.gregs[REG_EBX] },
 303     { " edx: ", context->uc_mcontext.gregs[REG_EDX] },
 304     { " ecx: ", context->uc_mcontext.gregs[REG_ECX] },
 305     { " eax: ", context->uc_mcontext.gregs[REG_EAX] },
 306     { " trp: ", context->uc_mcontext.gregs[REG_TRAPNO] },
 307     { " err: ", context->uc_mcontext.gregs[REG_ERR] },
 308     { "  ip: ", context->uc_mcontext.gregs[REG_EIP] },
 309     { "  cs: ", context->uc_mcontext.gregs[REG_CS] },
 310     { " efl: ", context->uc_mcontext.gregs[REG_EFL] },
 311     { " usp: ", context->uc_mcontext.gregs[REG_UESP] },
 312     { "  ss: ", context->uc_mcontext.gregs[REG_SS] },
 313 #elif ARCH_CPU_64_BITS
 314     { "  r8: ", context->uc_mcontext.gregs[REG_R8] },
 315     { "  r9: ", context->uc_mcontext.gregs[REG_R9] },
 316     { " r10: ", context->uc_mcontext.gregs[REG_R10] },
 317     { " r11: ", context->uc_mcontext.gregs[REG_R11] },
 318     { " r12: ", context->uc_mcontext.gregs[REG_R12] },
 319     { " r13: ", context->uc_mcontext.gregs[REG_R13] },
 320     { " r14: ", context->uc_mcontext.gregs[REG_R14] },
 321     { " r15: ", context->uc_mcontext.gregs[REG_R15] },
 322     { "  di: ", context->uc_mcontext.gregs[REG_RDI] },
 323     { "  si: ", context->uc_mcontext.gregs[REG_RSI] },
 324     { "  bp: ", context->uc_mcontext.gregs[REG_RBP] },
 325     { "  bx: ", context->uc_mcontext.gregs[REG_RBX] },
 326     { "  dx: ", context->uc_mcontext.gregs[REG_RDX] },
 327     { "  ax: ", context->uc_mcontext.gregs[REG_RAX] },
 328     { "  cx: ", context->uc_mcontext.gregs[REG_RCX] },
 329     { "  sp: ", context->uc_mcontext.gregs[REG_RSP] },
 330     { "  ip: ", context->uc_mcontext.gregs[REG_RIP] },
 331     { " efl: ", context->uc_mcontext.gregs[REG_EFL] },
 332     { " cgf: ", context->uc_mcontext.gregs[REG_CSGSFS] },
 333     { " erf: ", context->uc_mcontext.gregs[REG_ERR] },
 334     { " trp: ", context->uc_mcontext.gregs[REG_TRAPNO] },
 335     { " msk: ", context->uc_mcontext.gregs[REG_OLDMASK] },
 336     { " cr2: ", context->uc_mcontext.gregs[REG_CR2] },
 337 #endif
 338   };
 339
 340 #if ARCH_CPU_32_BITS
 341   const int kRegisterPadding = 8;
 342 #elif ARCH_CPU_64_BITS
 343   const int kRegisterPadding = 16;
 344 #endif
 345
 346   for (size_t i = 0; i < arraysize(registers); i++) {
 347     PrintToStderr(registers[i].label);
 348     internal::itoa_r(registers[i].value, buf, sizeof(buf),
 349                      16, kRegisterPadding);
 350     PrintToStderr(buf);
 351
 352     if ((i + 1) % 4 == 0)
 353       PrintToStderr("\n");
 354   }
 355   PrintToStderr("\n");
 356 #endif
 357 #elif defined(OS_MACOSX)
 358   // TODO(shess): Port to 64-bit, and ARM architecture (32 and 64-bit).
 359 #if ARCH_CPU_X86_FAMILY && ARCH_CPU_32_BITS
 360   ucontext_t* context = reinterpret_cast<ucontext_t*>(void_context);
 361   size_t len;
 362
 363   // NOTE: Even |snprintf()| is not on the approved list for signal
 364   // handlers, but buffered I/O is definitely not on the list due to
 365   // potential for |malloc()|.
 366   len = static_cast<size_t>(
 367       snprintf(buf, sizeof(buf),
 368                "ax: %x, bx: %x, cx: %x, dx: %x\n",
 369                context->uc_mcontext->__ss.__eax,
 370                context->uc_mcontext->__ss.__ebx,
 371                context->uc_mcontext->__ss.__ecx,
 372                context->uc_mcontext->__ss.__edx));
 373   write(STDERR_FILENO, buf, std::min(len, sizeof(buf) - 1));
 374
 375   len = static_cast<size_t>(
 376       snprintf(buf, sizeof(buf),
 377                "di: %x, si: %x, bp: %x, sp: %x, ss: %x, flags: %x\n",
 378                context->uc_mcontext->__ss.__edi,
 379                context->uc_mcontext->__ss.__esi,
 380                context->uc_mcontext->__ss.__ebp,
 381                context->uc_mcontext->__ss.__esp,
 382                context->uc_mcontext->__ss.__ss,
 383                context->uc_mcontext->__ss.__eflags));
 384   write(STDERR_FILENO, buf, std::min(len, sizeof(buf) - 1));
 385
 386   len = static_cast<size_t>(
 387       snprintf(buf, sizeof(buf),
 388                "ip: %x, cs: %x, ds: %x, es: %x, fs: %x, gs: %x\n",
 389                context->uc_mcontext->__ss.__eip,
 390                context->uc_mcontext->__ss.__cs,
 391                context->uc_mcontext->__ss.__ds,
 392                context->uc_mcontext->__ss.__es,
 393                context->uc_mcontext->__ss.__fs,
 394                context->uc_mcontext->__ss.__gs));
 395   write(STDERR_FILENO, buf, std::min(len, sizeof(buf) - 1));
 396 #endif  // ARCH_CPU_32_BITS
 397 #endif  // defined(OS_MACOSX)
 398   _exit(1);
 399 }
 400
 401 class PrintBacktraceOutputHandler : public BacktraceOutputHandler {
 402  public:
 403   PrintBacktraceOutputHandler() {}
 404
 405   void HandleOutput(const char* output) override {
 406     // NOTE: This code MUST be async-signal safe (it's used by in-process
 407     // stack dumping signal handler). NO malloc or stdio is allowed here.
 408     PrintToStderr(output);
 409   }
 410
 411  private:
 412   DISALLOW_COPY_AND_ASSIGN(PrintBacktraceOutputHandler);
 413 };
 414
 415 class StreamBacktraceOutputHandler : public BacktraceOutputHandler {
 416  public:
 417   explicit StreamBacktraceOutputHandler(std::ostream* os) : os_(os) {
 418   }
 419
 420   void HandleOutput(const char* output) override { (*os_) << output; }
 421
 422  private:
 423   std::ostream* os_;
 424
 425   DISALLOW_COPY_AND_ASSIGN(StreamBacktraceOutputHandler);
 426 };
 427
 428 void WarmUpBacktrace() {
 429   // Warm up stack trace infrastructure. It turns out that on the first
 430   // call glibc initializes some internal data structures using pthread_once,
 431   // and even backtrace() can call malloc(), leading to hangs.
 432   //
 433   // Example stack trace snippet (with tcmalloc):
 434   //
 435   // #8  0x0000000000a173b5 in tc_malloc
 436   //             at ./third_party/tcmalloc/chromium/src/debugallocation.cc:1161
 437   // #9  0x00007ffff7de7900 in _dl_map_object_deps at dl-deps.c:517
 438   // #10 0x00007ffff7ded8a9 in dl_open_worker at dl-open.c:262
 439   // #11 0x00007ffff7de9176 in _dl_catch_error at dl-error.c:178
 440   // #12 0x00007ffff7ded31a in _dl_open (file=0x7ffff625e298 "libgcc_s.so.1")
 441   //             at dl-open.c:639
 442   // #13 0x00007ffff6215602 in do_dlopen at dl-libc.c:89
 443   // #14 0x00007ffff7de9176 in _dl_catch_error at dl-error.c:178
 444   // #15 0x00007ffff62156c4 in dlerror_run at dl-libc.c:48
 445   // #16 __GI___libc_dlopen_mode at dl-libc.c:165
 446   // #17 0x00007ffff61ef8f5 in init
 447   //             at ../sysdeps/x86_64/../ia64/backtrace.c:53
 448   // #18 0x00007ffff6aad400 in pthread_once
 449   //             at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_once.S:104
 450   // #19 0x00007ffff61efa14 in __GI___backtrace
 451   //             at ../sysdeps/x86_64/../ia64/backtrace.c:104
 452   // #20 0x0000000000752a54 in base::debug::StackTrace::StackTrace
 453   //             at base/debug/stack_trace_posix.cc:175
 454   // #21 0x00000000007a4ae5 in
 455   //             base::(anonymous namespace)::StackDumpSignalHandler
 456   //             at base/process_util_posix.cc:172
 457   // #22 <signal handler called>
 458   StackTrace stack_trace;
 459 }
 460
 461 }  // namespace
 462
 463 #if defined(USE_SYMBOLIZE)
 464
 465 // class SandboxSymbolizeHelper.
 466 //
 467 // The purpose of this class is to prepare and install a "file open" callback
 468 // needed by the stack trace symbolization code
 469 // (base/third_party/symbolize/symbolize.h) so that it can function properly
 470 // in a sandboxed process.  The caveat is that this class must be instantiated
 471 // before the sandboxing is enabled so that it can get the chance to open all
 472 // the object files that are loaded in the virtual address space of the current
 473 // process.
 474 class SandboxSymbolizeHelper {
 475  public:
 476   // Returns the singleton instance.
 477   static SandboxSymbolizeHelper* GetInstance() {
 478     return Singleton<SandboxSymbolizeHelper>::get();
 479   }
 480
 481  private:
 482   friend struct DefaultSingletonTraits<SandboxSymbolizeHelper>;
 483
 484   SandboxSymbolizeHelper()
 485       : is_initialized_(false) {
 486     Init();
 487   }
 488
 489   ~SandboxSymbolizeHelper() {
 490     UnregisterCallback();
 491     CloseObjectFiles();
 492   }
 493
 494   // Returns a O_RDONLY file descriptor for |file_path| if it was opened
 495   // sucessfully during the initialization.  The file is repositioned at
 496   // offset 0.
 497   // IMPORTANT: This function must be async-signal-safe because it can be
 498   // called from a signal handler (symbolizing stack frames for a crash).
 499   int GetFileDescriptor(const char* file_path) {
 500     int fd = -1;
 501
 502 #if !defined(NDEBUG)
 503     if (file_path) {
 504       // The assumption here is that iterating over std::map<std::string, int>
 505       // using a const_iterator does not allocate dynamic memory, hense it is
 506       // async-signal-safe.
 507       std::map<std::string, int>::const_iterator it;
 508       for (it = modules_.begin(); it != modules_.end(); ++it) {
 509         if (strcmp((it->first).c_str(), file_path) == 0) {
 510           // POSIX.1-2004 requires an implementation to guarantee that dup()
 511           // is async-signal-safe.
 512           fd = dup(it->second);
 513           break;
 514         }
 515       }
 516       // POSIX.1-2004 requires an implementation to guarantee that lseek()
 517       // is async-signal-safe.
 518       if (fd >= 0 && lseek(fd, 0, SEEK_SET) < 0) {
 519         // Failed to seek.
 520         fd = -1;
 521       }
 522     }
 523 #endif  // !defined(NDEBUG)
 524
 525     return fd;
 526   }
 527
 528   // Searches for the object file (from /proc/self/maps) that contains
 529   // the specified pc.  If found, sets |start_address| to the start address
 530   // of where this object file is mapped in memory, sets the module base
 531   // address into |base_address|, copies the object file name into
 532   // |out_file_name|, and attempts to open the object file.  If the object
 533   // file is opened successfully, returns the file descriptor.  Otherwise,
 534   // returns -1.  |out_file_name_size| is the size of the file name buffer
 535   // (including the null terminator).
 536   // IMPORTANT: This function must be async-signal-safe because it can be
 537   // called from a signal handler (symbolizing stack frames for a crash).
 538   static int OpenObjectFileContainingPc(uint64_t pc, uint64_t& start_address,
 539                                         uint64_t& base_address, char* file_path,
 540                                         int file_path_size) {
 541     // This method can only be called after the singleton is instantiated.
 542     // This is ensured by the following facts:
 543     // * This is the only static method in this class, it is private, and
 544     //   the class has no friends (except for the DefaultSingletonTraits).
 545     //   The compiler guarantees that it can only be called after the
 546     //   singleton is instantiated.
 547     // * This method is used as a callback for the stack tracing code and
 548     //   the callback registration is done in the constructor, so logically
 549     //   it cannot be called before the singleton is created.
 550     SandboxSymbolizeHelper* instance = GetInstance();
 551
 552     // The assumption here is that iterating over
 553     // std::vector<MappedMemoryRegion> using a const_iterator does not allocate
 554     // dynamic memory, hence it is async-signal-safe.
 555     std::vector<MappedMemoryRegion>::const_iterator it;
 556     bool is_first = true;
 557     for (it = instance->regions_.begin(); it != instance->regions_.end();
 558          ++it, is_first = false) {
 559       const MappedMemoryRegion& region = *it;
 560       if (region.start <= pc && pc < region.end) {
 561         start_address = region.start;
 562         // Don't subtract 'start_address' from the first entry:
 563         // * If a binary is compiled w/o -pie, then the first entry in
 564         //   process maps is likely the binary itself (all dynamic libs
 565         //   are mapped higher in address space). For such a binary,
 566         //   instruction offset in binary coincides with the actual
 567         //   instruction address in virtual memory (as code section
 568         //   is mapped to a fixed memory range).
 569         // * If a binary is compiled with -pie, all the modules are
 570         //   mapped high at address space (in particular, higher than
 571         //   shadow memory of the tool), so the module can't be the
 572         //   first entry.
 573         base_address = (is_first ? 0U : start_address) - region.offset;
 574         if (file_path && file_path_size > 0) {
 575           strncpy(file_path, region.path.c_str(), file_path_size);
 576           // Ensure null termination.
 577           file_path[file_path_size - 1] = '\0';
 578         }
 579         return instance->GetFileDescriptor(region.path.c_str());
 580       }
 581     }
 582     return -1;
 583   }
 584
 585   // Parses /proc/self/maps in order to compile a list of all object file names
 586   // for the modules that are loaded in the current process.
 587   // Returns true on success.
 588   bool CacheMemoryRegions() {
 589     // Reads /proc/self/maps.
 590     std::string contents;
 591     if (!ReadProcMaps(&contents)) {
 592       LOG(ERROR) << "Failed to read /proc/self/maps";
 593       return false;
 594     }
 595
 596     // Parses /proc/self/maps.
 597     if (!ParseProcMaps(contents, &regions_)) {
 598       LOG(ERROR) << "Failed to parse the contents of /proc/self/maps";
 599       return false;
 600     }
 601
 602     is_initialized_ = true;
 603     return true;
 604   }
 605
 606   // Opens all object files and caches their file descriptors.
 607   void OpenSymbolFiles() {
 608     // Pre-opening and caching the file descriptors of all loaded modules is
 609     // not considered safe for retail builds.  Hence it is only done in debug
 610     // builds.  For more details, take a look at: http://crbug.com/341966
 611     // Enabling this to release mode would require approval from the security
 612     // team.
 613 #if !defined(NDEBUG)
 614     // Open the object files for all read-only executable regions and cache
 615     // their file descriptors.
 616     std::vector<MappedMemoryRegion>::const_iterator it;
 617     for (it = regions_.begin(); it != regions_.end(); ++it) {
 618       const MappedMemoryRegion& region = *it;
 619       // Only interesed in read-only executable regions.
 620       if ((region.permissions & MappedMemoryRegion::READ) ==
 621               MappedMemoryRegion::READ &&
 622           (region.permissions & MappedMemoryRegion::WRITE) == 0 &&
 623           (region.permissions & MappedMemoryRegion::EXECUTE) ==
 624               MappedMemoryRegion::EXECUTE) {
 625         if (region.path.empty()) {
 626           // Skip regions with empty file names.
 627           continue;
 628         }
 629         if (region.path[0] == '[') {
 630           // Skip pseudo-paths, like [stack], [vdso], [heap], etc ...
 631           continue;
 632         }
 633         // Avoid duplicates.
 634         if (modules_.find(region.path) == modules_.end()) {
 635           int fd = open(region.path.c_str(), O_RDONLY | O_CLOEXEC);
 636           if (fd >= 0) {
 637             modules_.insert(std::make_pair(region.path, fd));
 638           } else {
 639             LOG(WARNING) << "Failed to open file: " << region.path
 640                          << "\n  Error: " << strerror(errno);
 641           }
 642         }
 643       }
 644     }
 645 #endif  // !defined(NDEBUG)
 646   }
 647
 648   // Initializes and installs the symbolization callback.
 649   void Init() {
 650     if (CacheMemoryRegions()) {
 651       OpenSymbolFiles();
 652       google::InstallSymbolizeOpenObjectFileCallback(
 653           &OpenObjectFileContainingPc);
 654     }
 655   }
 656
 657   // Unregister symbolization callback.
 658   void UnregisterCallback() {
 659     if (is_initialized_) {
 660       google::InstallSymbolizeOpenObjectFileCallback(NULL);
 661       is_initialized_ = false;
 662     }
 663   }
 664
 665   // Closes all file descriptors owned by this instance.
 666   void CloseObjectFiles() {
 667 #if !defined(NDEBUG)
 668     std::map<std::string, int>::iterator it;
 669     for (it = modules_.begin(); it != modules_.end(); ++it) {
 670       int ret = IGNORE_EINTR(close(it->second));
 671       DCHECK(!ret);
 672       it->second = -1;
 673     }
 674     modules_.clear();
 675 #endif  // !defined(NDEBUG)
 676   }
 677
 678   // Set to true upon successful initialization.
 679   bool is_initialized_;
 680
 681 #if !defined(NDEBUG)
 682   // Mapping from file name to file descriptor.  Includes file descriptors
 683   // for all successfully opened object files and the file descriptor for
 684   // /proc/self/maps.  This code is not safe for release builds so
 685   // this is only done for DEBUG builds.
 686   std::map<std::string, int> modules_;
 687 #endif  // !defined(NDEBUG)
 688
 689   // Cache for the process memory regions.  Produced by parsing the contents
 690   // of /proc/self/maps cache.
 691   std::vector<MappedMemoryRegion> regions_;
 692
 693   DISALLOW_COPY_AND_ASSIGN(SandboxSymbolizeHelper);
 694 };
 695 #endif  // USE_SYMBOLIZE
 696
 697 bool EnableInProcessStackDumpingForSandbox() {
 698 #if defined(USE_SYMBOLIZE)
 699   SandboxSymbolizeHelper::GetInstance();
 700 #endif  // USE_SYMBOLIZE
 701
 702   return EnableInProcessStackDumping();
 703 }
 704
 705 bool EnableInProcessStackDumping() {
 706   // When running in an application, our code typically expects SIGPIPE
 707   // to be ignored.  Therefore, when testing that same code, it should run
 708   // with SIGPIPE ignored as well.
 709   struct sigaction sigpipe_action;
 710   memset(&sigpipe_action, 0, sizeof(sigpipe_action));
 711   sigpipe_action.sa_handler = SIG_IGN;
 712   sigemptyset(&sigpipe_action.sa_mask);
 713   bool success = (sigaction(SIGPIPE, &sigpipe_action, NULL) == 0);
 714
 715   // Avoid hangs during backtrace initialization, see above.
 716   WarmUpBacktrace();
 717
 718   struct sigaction action;
 719   memset(&action, 0, sizeof(action));
 720   action.sa_flags = SA_RESETHAND | SA_SIGINFO;
 721   action.sa_sigaction = &StackDumpSignalHandler;
 722   sigemptyset(&action.sa_mask);
 723
 724   success &= (sigaction(SIGILL, &action, NULL) == 0);
 725   success &= (sigaction(SIGABRT, &action, NULL) == 0);
 726   success &= (sigaction(SIGFPE, &action, NULL) == 0);
 727   success &= (sigaction(SIGBUS, &action, NULL) == 0);
 728   success &= (sigaction(SIGSEGV, &action, NULL) == 0);
 729 // On Linux, SIGSYS is reserved by the kernel for seccomp-bpf sandboxing.
 730 #if !defined(OS_LINUX)
 731   success &= (sigaction(SIGSYS, &action, NULL) == 0);
 732 #endif  // !defined(OS_LINUX)
 733
 734   return success;
 735 }
 736
 737 StackTrace::StackTrace() {
 738   // NOTE: This code MUST be async-signal safe (it's used by in-process
 739   // stack dumping signal handler). NO malloc or stdio is allowed here.
 740
 741 #if !defined(__UCLIBC__)
 742   // Though the backtrace API man page does not list any possible negative
 743   // return values, we take no chance.
 744   count_ = base::saturated_cast<size_t>(backtrace(trace_, arraysize(trace_)));
 745 #else
 746   count_ = 0;
 747 #endif
 748 }
 749
 750 void StackTrace::Print() const {
 751   // NOTE: This code MUST be async-signal safe (it's used by in-process
 752   // stack dumping signal handler). NO malloc or stdio is allowed here.
 753
 754 #if !defined(__UCLIBC__)
 755   PrintBacktraceOutputHandler handler;
 756   ProcessBacktrace(trace_, count_, &handler);
 757 #endif
 758 }
 759
 760 #if !defined(__UCLIBC__)
 761 void StackTrace::OutputToStream(std::ostream* os) const {
 762   StreamBacktraceOutputHandler handler(os);
 763   ProcessBacktrace(trace_, count_, &handler);
 764 }
 765 #endif
 766
 767 namespace internal {
 768
 769 // NOTE: code from sandbox/linux/seccomp-bpf/demo.cc.
 770 char *itoa_r(intptr_t i, char *buf, size_t sz, int base, size_t padding) {
 771   // Make sure we can write at least one NUL byte.
 772   size_t n = 1;
 773   if (n > sz)
 774     return NULL;
 775
 776   if (base < 2 || base > 16) {
 777     buf[0] = '\000';
 778     return NULL;
 779   }
 780
 781   char *start = buf;
 782
 783   uintptr_t j = i;
 784
 785   // Handle negative numbers (only for base 10).
 786   if (i < 0 && base == 10) {
 787     j = -i;
 788
 789     // Make sure we can write the '-' character.
 790     if (++n > sz) {
 791       buf[0] = '\000';
 792       return NULL;
 793     }
 794     *start++ = '-';
 795   }
 796
 797   // Loop until we have converted the entire number. Output at least one
 798   // character (i.e. '0').
 799   char *ptr = start;
 800   do {
 801     // Make sure there is still enough space left in our output buffer.
 802     if (++n > sz) {
 803       buf[0] = '\000';
 804       return NULL;
 805     }
 806
 807     // Output the next digit.
 808     *ptr++ = "0123456789abcdef"[j % base];
 809     j /= base;
 810
 811     if (padding > 0)
 812       padding--;
 813   } while (j > 0 || padding > 0);
 814
 815   // Terminate the output with a NUL character.
 816   *ptr = '\000';
 817
 818   // Conversion to ASCII actually resulted in the digits being in reverse
 819   // order. We can't easily generate them in forward order, as we can't tell
 820   // the number of characters needed until we are done converting.
 821   // So, now, we reverse the string (except for the possible "-" sign).
 822   while (--ptr > start) {
 823     char ch = *ptr;
 824     *ptr = *start;
 825     *start++ = ch;
 826   }
 827   return buf;
 828 }
 829
 830 }  // namespace internal
 831
 832 }  // namespace debug
 833 }  // namespace base