Squashed 'third_party/glog/' content from commit 9ef754a3023

git-subtree-dir: third_party/glog
git-subtree-split: 9ef754a3023e6fd10f20fe53dfca96dd898182e3

1 files changed, 966 insertions, 0 deletions

diff --git a/src/symbolize.cc b/src/symbolize.cc
new file mode 100644
index 000000000000..76a1b0febeec
--- /dev/null
+++ b/src/symbolize.cc
@@ -0,0 +1,966 @@
+// Copyright (c) 2006, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+// Author: Satoru Takabayashi
+// Stack-footprint reduction work done by Raksit Ashok
+//
+// Implementation note:
+//
+// We don't use heaps but only use stacks.  We want to reduce the
+// stack consumption so that the symbolizer can run on small stacks.
+//
+// Here are some numbers collected with GCC 4.1.0 on x86:
+// - sizeof(Elf32_Sym)  = 16
+// - sizeof(Elf32_Shdr) = 40
+// - sizeof(Elf64_Sym)  = 24
+// - sizeof(Elf64_Shdr) = 64
+//
+// This implementation is intended to be async-signal-safe but uses
+// some functions which are not guaranteed to be so, such as memchr()
+// and memmove().  We assume they are async-signal-safe.
+//
+// Additional header can be specified by the GLOG_BUILD_CONFIG_INCLUDE
+// macro to add platform specific defines (e.g. OS_OPENBSD).
+
+#ifdef GLOG_BUILD_CONFIG_INCLUDE
+#include GLOG_BUILD_CONFIG_INCLUDE
+#endif  // GLOG_BUILD_CONFIG_INCLUDE
+
+#include "utilities.h"
+
+#if defined(HAVE_SYMBOLIZE)
+
+#include <string.h>
+
+#include <algorithm>
+#include <limits>
+
+#include "symbolize.h"
+#include "demangle.h"
+
+_START_GOOGLE_NAMESPACE_
+
+// We don't use assert() since it's not guaranteed to be
+// async-signal-safe.  Instead we define a minimal assertion
+// macro. So far, we don't need pretty printing for __FILE__, etc.
+
+// A wrapper for abort() to make it callable in ? :.
+static int AssertFail() {
+  abort();
+  return 0;  // Should not reach.
+}
+
+#define SAFE_ASSERT(expr) ((expr) ? 0 : AssertFail())
+
+static SymbolizeCallback g_symbolize_callback = NULL;
+void InstallSymbolizeCallback(SymbolizeCallback callback) {
+  g_symbolize_callback = callback;
+}
+
+static SymbolizeOpenObjectFileCallback g_symbolize_open_object_file_callback =
+    NULL;
+void InstallSymbolizeOpenObjectFileCallback(
+    SymbolizeOpenObjectFileCallback callback) {
+  g_symbolize_open_object_file_callback = callback;
+}
+
+// This function wraps the Demangle function to provide an interface
+// where the input symbol is demangled in-place.
+// To keep stack consumption low, we would like this function to not
+// get inlined.
+static ATTRIBUTE_NOINLINE void DemangleInplace(char *out, int out_size) {
+  char demangled[256];  // Big enough for sane demangled symbols.
+  if (Demangle(out, demangled, sizeof(demangled))) {
+    // Demangling succeeded. Copy to out if the space allows.
+    size_t len = strlen(demangled);
+    if (len + 1 <= (size_t)out_size) {  // +1 for '\0'.
+      SAFE_ASSERT(len < sizeof(demangled));
+      memmove(out, demangled, len + 1);
+    }
+  }
+}
+
+_END_GOOGLE_NAMESPACE_
+
+#if defined(__ELF__)
+
+#if defined(HAVE_DLFCN_H)
+#include <dlfcn.h>
+#endif
+#if defined(OS_OPENBSD)
+#include <sys/exec_elf.h>
+#else
+#include <elf.h>
+#endif
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stddef.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "symbolize.h"
+#include "config.h"
+#include "glog/raw_logging.h"
+
+// Re-runs fn until it doesn't cause EINTR.
+#define NO_INTR(fn)   do {} while ((fn) < 0 && errno == EINTR)
+
+_START_GOOGLE_NAMESPACE_
+
+// Read up to "count" bytes from "offset" in the file pointed by file
+// descriptor "fd" into the buffer starting at "buf" while handling short reads
+// and EINTR.  On success, return the number of bytes read.  Otherwise, return
+// -1.
+static ssize_t ReadFromOffset(const int fd, void *buf, const size_t count,
+                              const off_t offset) {
+  SAFE_ASSERT(fd >= 0);
+  SAFE_ASSERT(count <= std::numeric_limits<ssize_t>::max());
+  char *buf0 = reinterpret_cast<char *>(buf);
+  ssize_t num_bytes = 0;
+  while (num_bytes < count) {
+    ssize_t len;
+    NO_INTR(len = pread(fd, buf0 + num_bytes, count - num_bytes,
+                        offset + num_bytes));
+    if (len < 0) {  // There was an error other than EINTR.
+      return -1;
+    }
+    if (len == 0) {  // Reached EOF.
+      break;
+    }
+    num_bytes += len;
+  }
+  SAFE_ASSERT(num_bytes <= count);
+  return num_bytes;
+}
+
+// Try reading exactly "count" bytes from "offset" bytes in a file
+// pointed by "fd" into the buffer starting at "buf" while handling
+// short reads and EINTR.  On success, return true. Otherwise, return
+// false.
+static bool ReadFromOffsetExact(const int fd, void *buf,
+                                const size_t count, const off_t offset) {
+  ssize_t len = ReadFromOffset(fd, buf, count, offset);
+  return len == count;
+}
+
+// Returns elf_header.e_type if the file pointed by fd is an ELF binary.
+static int FileGetElfType(const int fd) {
+  ElfW(Ehdr) elf_header;
+  if (!ReadFromOffsetExact(fd, &elf_header, sizeof(elf_header), 0)) {
+    return -1;
+  }
+  if (memcmp(elf_header.e_ident, ELFMAG, SELFMAG) != 0) {
+    return -1;
+  }
+  return elf_header.e_type;
+}
+
+// Read the section headers in the given ELF binary, and if a section
+// of the specified type is found, set the output to this section header
+// and return true.  Otherwise, return false.
+// To keep stack consumption low, we would like this function to not get
+// inlined.
+static ATTRIBUTE_NOINLINE bool
+GetSectionHeaderByType(const int fd, ElfW(Half) sh_num, const off_t sh_offset,
+                       ElfW(Word) type, ElfW(Shdr) *out) {
+  // Read at most 16 section headers at a time to save read calls.
+  ElfW(Shdr) buf[16];
+  for (int i = 0; i < sh_num;) {
+    const ssize_t num_bytes_left = (sh_num - i) * sizeof(buf[0]);
+    const ssize_t num_bytes_to_read =
+        (sizeof(buf) > num_bytes_left) ? num_bytes_left : sizeof(buf);
+    const ssize_t len = ReadFromOffset(fd, buf, num_bytes_to_read,
+                                       sh_offset + i * sizeof(buf[0]));
+    if (len == -1) {
+      return false;
+    }
+    SAFE_ASSERT(len % sizeof(buf[0]) == 0);
+    const ssize_t num_headers_in_buf = len / sizeof(buf[0]);
+    SAFE_ASSERT(num_headers_in_buf <= sizeof(buf) / sizeof(buf[0]));
+    for (int j = 0; j < num_headers_in_buf; ++j) {
+      if (buf[j].sh_type == type) {
+        *out = buf[j];
+        return true;
+      }
+    }
+    i += num_headers_in_buf;
+  }
+  return false;
+}
+
+// There is no particular reason to limit section name to 63 characters,
+// but there has (as yet) been no need for anything longer either.
+const int kMaxSectionNameLen = 64;
+
+// name_len should include terminating '\0'.
+bool GetSectionHeaderByName(int fd, const char *name, size_t name_len,
+                            ElfW(Shdr) *out) {
+  ElfW(Ehdr) elf_header;
+  if (!ReadFromOffsetExact(fd, &elf_header, sizeof(elf_header), 0)) {
+    return false;
+  }
+
+  ElfW(Shdr) shstrtab;
+  off_t shstrtab_offset = (elf_header.e_shoff +
+                           elf_header.e_shentsize * elf_header.e_shstrndx);
+  if (!ReadFromOffsetExact(fd, &shstrtab, sizeof(shstrtab), shstrtab_offset)) {
+    return false;
+  }
+
+  for (int i = 0; i < elf_header.e_shnum; ++i) {
+    off_t section_header_offset = (elf_header.e_shoff +
+                                   elf_header.e_shentsize * i);
+    if (!ReadFromOffsetExact(fd, out, sizeof(*out), section_header_offset)) {
+      return false;
+    }
+    char header_name[kMaxSectionNameLen];
+    if (sizeof(header_name) < name_len) {
+      RAW_LOG(WARNING, "Section name '%s' is too long (%" PRIuS "); "
+              "section will not be found (even if present).", name, name_len);
+      // No point in even trying.
+      return false;
+    }
+    off_t name_offset = shstrtab.sh_offset + out->sh_name;
+    ssize_t n_read = ReadFromOffset(fd, &header_name, name_len, name_offset);
+    if (n_read == -1) {
+      return false;
+    } else if (n_read != name_len) {
+      // Short read -- name could be at end of file.
+      continue;
+    }
+    if (memcmp(header_name, name, name_len) == 0) {
+      return true;
+    }
+  }
+  return false;
+}
+
+// Read a symbol table and look for the symbol containing the
+// pc. Iterate over symbols in a symbol table and look for the symbol
+// containing "pc".  On success, return true and write the symbol name
+// to out.  Otherwise, return false.
+// To keep stack consumption low, we would like this function to not get
+// inlined.
+static ATTRIBUTE_NOINLINE bool
+FindSymbol(uint64_t pc, const int fd, char *out, int out_size,
+           uint64_t symbol_offset, const ElfW(Shdr) *strtab,
+           const ElfW(Shdr) *symtab) {
+  if (symtab == NULL) {
+    return false;
+  }
+  const int num_symbols = symtab->sh_size / symtab->sh_entsize;
+  for (int i = 0; i < num_symbols;) {
+    off_t offset = symtab->sh_offset + i * symtab->sh_entsize;
+
+    // If we are reading Elf64_Sym's, we want to limit this array to
+    // 32 elements (to keep stack consumption low), otherwise we can
+    // have a 64 element Elf32_Sym array.
+#if __WORDSIZE == 64
+#define NUM_SYMBOLS 32
+#else
+#define NUM_SYMBOLS 64
+#endif
+
+    // Read at most NUM_SYMBOLS symbols at once to save read() calls.
+    ElfW(Sym) buf[NUM_SYMBOLS];
+    int num_symbols_to_read = std::min(NUM_SYMBOLS, num_symbols - i);
+    const ssize_t len =
+        ReadFromOffset(fd, &buf, sizeof(buf[0]) * num_symbols_to_read, offset);
+    SAFE_ASSERT(len % sizeof(buf[0]) == 0);
+    const ssize_t num_symbols_in_buf = len / sizeof(buf[0]);
+    SAFE_ASSERT(num_symbols_in_buf <= num_symbols_to_read);
+    for (int j = 0; j < num_symbols_in_buf; ++j) {
+      const ElfW(Sym)& symbol = buf[j];
+      uint64_t start_address = symbol.st_value;
+      start_address += symbol_offset;
+      uint64_t end_address = start_address + symbol.st_size;
+      if (symbol.st_value != 0 &&  // Skip null value symbols.
+          symbol.st_shndx != 0 &&  // Skip undefined symbols.
+          start_address <= pc && pc < end_address) {
+        ssize_t len1 = ReadFromOffset(fd, out, out_size,
+                                      strtab->sh_offset + symbol.st_name);
+        if (len1 <= 0 || memchr(out, '\0', out_size) == NULL) {
+          memset(out, 0, out_size);
+          return false;
+        }
+        return true;  // Obtained the symbol name.
+      }
+    }
+    i += num_symbols_in_buf;
+  }
+  return false;
+}
+
+// Get the symbol name of "pc" from the file pointed by "fd".  Process
+// both regular and dynamic symbol tables if necessary.  On success,
+// write the symbol name to "out" and return true.  Otherwise, return
+// false.
+static bool GetSymbolFromObjectFile(const int fd,
+                                    uint64_t pc,
+                                    char* out,
+                                    int out_size,
+                                    uint64_t base_address) {
+  // Read the ELF header.
+  ElfW(Ehdr) elf_header;
+  if (!ReadFromOffsetExact(fd, &elf_header, sizeof(elf_header), 0)) {
+    return false;
+  }
+
+  ElfW(Shdr) symtab, strtab;
+
+  // Consult a regular symbol table first.
+  if (GetSectionHeaderByType(fd, elf_header.e_shnum, elf_header.e_shoff,
+                             SHT_SYMTAB, &symtab)) {
+    if (!ReadFromOffsetExact(fd, &strtab, sizeof(strtab), elf_header.e_shoff +
+                             symtab.sh_link * sizeof(symtab))) {
+      return false;
+    }
+    if (FindSymbol(pc, fd, out, out_size, base_address, &strtab, &symtab)) {
+      return true;  // Found the symbol in a regular symbol table.
+    }
+  }
+
+  // If the symbol is not found, then consult a dynamic symbol table.
+  if (GetSectionHeaderByType(fd, elf_header.e_shnum, elf_header.e_shoff,
+                             SHT_DYNSYM, &symtab)) {
+    if (!ReadFromOffsetExact(fd, &strtab, sizeof(strtab), elf_header.e_shoff +
+                             symtab.sh_link * sizeof(symtab))) {
+      return false;
+    }
+    if (FindSymbol(pc, fd, out, out_size, base_address, &strtab, &symtab)) {
+      return true;  // Found the symbol in a dynamic symbol table.
+    }
+  }
+
+  return false;
+}
+
+namespace {
+// Thin wrapper around a file descriptor so that the file descriptor
+// gets closed for sure.
+struct FileDescriptor {
+  const int fd_;
+  explicit FileDescriptor(int fd) : fd_(fd) {}
+  ~FileDescriptor() {
+    if (fd_ >= 0) {
+      close(fd_);
+    }
+  }
+  int get() { return fd_; }
+
+ private:
+  explicit FileDescriptor(const FileDescriptor&);
+  void operator=(const FileDescriptor&);
+};
+
+// Helper class for reading lines from file.
+//
+// Note: we don't use ProcMapsIterator since the object is big (it has
+// a 5k array member) and uses async-unsafe functions such as sscanf()
+// and snprintf().
+class LineReader {
+ public:
+  explicit LineReader(int fd, char *buf, int buf_len, off_t offset)
+      : fd_(fd),
+        buf_(buf),
+        buf_len_(buf_len),
+        offset_(offset),
+        bol_(buf),
+        eol_(buf),
+        eod_(buf) {}
+
+  // Read '\n'-terminated line from file.  On success, modify "bol"
+  // and "eol", then return true.  Otherwise, return false.
+  //
+  // Note: if the last line doesn't end with '\n', the line will be
+  // dropped.  It's an intentional behavior to make the code simple.
+  bool ReadLine(const char **bol, const char **eol) {
+    if (BufferIsEmpty()) {  // First time.
+      const ssize_t num_bytes = ReadFromOffset(fd_, buf_, buf_len_, offset_);
+      if (num_bytes <= 0) {  // EOF or error.
+        return false;
+      }
+      offset_ += num_bytes;
+      eod_ = buf_ + num_bytes;
+      bol_ = buf_;
+    } else {
+      bol_ = eol_ + 1;  // Advance to the next line in the buffer.
+      SAFE_ASSERT(bol_ <= eod_);  // "bol_" can point to "eod_".
+      if (!HasCompleteLine()) {
+        const int incomplete_line_length = eod_ - bol_;
+        // Move the trailing incomplete line to the beginning.
+        memmove(buf_, bol_, incomplete_line_length);
+        // Read text from file and append it.
+        char * const append_pos = buf_ + incomplete_line_length;
+        const int capacity_left = buf_len_ - incomplete_line_length;
+        const ssize_t num_bytes =
+            ReadFromOffset(fd_, append_pos, capacity_left, offset_);
+        if (num_bytes <= 0) {  // EOF or error.
+          return false;
+        }
+        offset_ += num_bytes;
+        eod_ = append_pos + num_bytes;
+        bol_ = buf_;
+      }
+    }
+    eol_ = FindLineFeed();
+    if (eol_ == NULL) {  // '\n' not found.  Malformed line.
+      return false;
+    }
+    *eol_ = '\0';  // Replace '\n' with '\0'.
+
+    *bol = bol_;
+    *eol = eol_;
+    return true;
+  }
+
+  // Beginning of line.
+  const char *bol() {
+    return bol_;
+  }
+
+  // End of line.
+  const char *eol() {
+    return eol_;
+  }
+
+ private:
+  explicit LineReader(const LineReader&);
+  void operator=(const LineReader&);
+
+  char *FindLineFeed() {
+    return reinterpret_cast<char *>(memchr(bol_, '\n', eod_ - bol_));
+  }
+
+  bool BufferIsEmpty() {
+    return buf_ == eod_;
+  }
+
+  bool HasCompleteLine() {
+    return !BufferIsEmpty() && FindLineFeed() != NULL;
+  }
+
+  const int fd_;
+  char * const buf_;
+  const int buf_len_;
+  off_t offset_;
+  char *bol_;
+  char *eol_;
+  const char *eod_;  // End of data in "buf_".
+};
+}  // namespace
+
+// Place the hex number read from "start" into "*hex".  The pointer to
+// the first non-hex character or "end" is returned.
+static char *GetHex(const char *start, const char *end, uint64_t *hex) {
+  *hex = 0;
+  const char *p;
+  for (p = start; p < end; ++p) {
+    int ch = *p;
+    if ((ch >= '0' && ch <= '9') ||
+        (ch >= 'A' && ch <= 'F') || (ch >= 'a' && ch <= 'f')) {
+      *hex = (*hex << 4) | (ch < 'A' ? ch - '0' : (ch & 0xF) + 9);
+    } else {  // Encountered the first non-hex character.
+      break;
+    }
+  }
+  SAFE_ASSERT(p <= end);
+  return const_cast<char *>(p);
+}
+
+// Searches for the object file (from /proc/self/maps) that contains
+// the specified pc.  If found, sets |start_address| to the start address
+// of where this object file is mapped in memory, sets the module base
+// address into |base_address|, copies the object file name into
+// |out_file_name|, and attempts to open the object file.  If the object
+// file is opened successfully, returns the file descriptor.  Otherwise,
+// returns -1.  |out_file_name_size| is the size of the file name buffer
+// (including the null-terminator).
+static ATTRIBUTE_NOINLINE int
+OpenObjectFileContainingPcAndGetStartAddress(uint64_t pc,
+                                             uint64_t &start_address,
+                                             uint64_t &base_address,
+                                             char *out_file_name,
+                                             int out_file_name_size) {
+  int object_fd;
+
+  int maps_fd;
+  NO_INTR(maps_fd = open("/proc/self/maps", O_RDONLY));
+  FileDescriptor wrapped_maps_fd(maps_fd);
+  if (wrapped_maps_fd.get() < 0) {
+    return -1;
+  }
+
+  int mem_fd;
+  NO_INTR(mem_fd = open("/proc/self/mem", O_RDONLY));
+  FileDescriptor wrapped_mem_fd(mem_fd);
+  if (wrapped_mem_fd.get() < 0) {
+    return -1;
+  }
+
+  // Iterate over maps and look for the map containing the pc.  Then
+  // look into the symbol tables inside.
+  char buf[1024];  // Big enough for line of sane /proc/self/maps
+  int num_maps = 0;
+  LineReader reader(wrapped_maps_fd.get(), buf, sizeof(buf), 0);
+  while (true) {
+    num_maps++;
+    const char *cursor;
+    const char *eol;
+    if (!reader.ReadLine(&cursor, &eol)) {  // EOF or malformed line.
+      return -1;
+    }
+
+    // Start parsing line in /proc/self/maps.  Here is an example:
+    //
+    // 08048000-0804c000 r-xp 00000000 08:01 2142121    /bin/cat
+    //
+    // We want start address (08048000), end address (0804c000), flags
+    // (r-xp) and file name (/bin/cat).
+
+    // Read start address.
+    cursor = GetHex(cursor, eol, &start_address);
+    if (cursor == eol || *cursor != '-') {
+      return -1;  // Malformed line.
+    }
+    ++cursor;  // Skip '-'.
+
+    // Read end address.
+    uint64_t end_address;
+    cursor = GetHex(cursor, eol, &end_address);
+    if (cursor == eol || *cursor != ' ') {
+      return -1;  // Malformed line.
+    }
+    ++cursor;  // Skip ' '.
+
+    // Read flags.  Skip flags until we encounter a space or eol.
+    const char * const flags_start = cursor;
+    while (cursor < eol && *cursor != ' ') {
+      ++cursor;
+    }
+    // We expect at least four letters for flags (ex. "r-xp").
+    if (cursor == eol || cursor < flags_start + 4) {
+      return -1;  // Malformed line.
+    }
+
+    // Determine the base address by reading ELF headers in process memory.
+    ElfW(Ehdr) ehdr;
+    // Skip non-readable maps.
+    if (flags_start[0] == 'r' &&
+        ReadFromOffsetExact(mem_fd, &ehdr, sizeof(ElfW(Ehdr)), start_address) &&
+        memcmp(ehdr.e_ident, ELFMAG, SELFMAG) == 0) {
+      switch (ehdr.e_type) {
+        case ET_EXEC:
+          base_address = 0;
+          break;
+        case ET_DYN:
+          // Find the segment containing file offset 0. This will correspond
+          // to the ELF header that we just read. Normally this will have
+          // virtual address 0, but this is not guaranteed. We must subtract
+          // the virtual address from the address where the ELF header was
+          // mapped to get the base address.
+          //
+          // If we fail to find a segment for file offset 0, use the address
+          // of the ELF header as the base address.
+          base_address = start_address;
+          for (unsigned i = 0; i != ehdr.e_phnum; ++i) {
+            ElfW(Phdr) phdr;
+            if (ReadFromOffsetExact(
+                    mem_fd, &phdr, sizeof(phdr),
+                    start_address + ehdr.e_phoff + i * sizeof(phdr)) &&
+                phdr.p_type == PT_LOAD && phdr.p_offset == 0) {
+              base_address = start_address - phdr.p_vaddr;
+              break;
+            }
+          }
+          break;
+        default:
+          // ET_REL or ET_CORE. These aren't directly executable, so they don't
+          // affect the base address.
+          break;
+      }
+    }
+
+    // Check start and end addresses.
+    if (!(start_address <= pc && pc < end_address)) {
+      continue;  // We skip this map.  PC isn't in this map.
+    }
+
+   // Check flags.  We are only interested in "r*x" maps.
+    if (flags_start[0] != 'r' || flags_start[2] != 'x') {
+      continue;  // We skip this map.
+    }
+    ++cursor;  // Skip ' '.
+
+    // Read file offset.
+    uint64_t file_offset;
+    cursor = GetHex(cursor, eol, &file_offset);
+    if (cursor == eol || *cursor != ' ') {
+      return -1;  // Malformed line.
+    }
+    ++cursor;  // Skip ' '.
+
+    // Skip to file name.  "cursor" now points to dev.  We need to
+    // skip at least two spaces for dev and inode.
+    int num_spaces = 0;
+    while (cursor < eol) {
+      if (*cursor == ' ') {
+        ++num_spaces;
+      } else if (num_spaces >= 2) {
+        // The first non-space character after skipping two spaces
+        // is the beginning of the file name.
+        break;
+      }
+      ++cursor;
+    }
+    if (cursor == eol) {
+      return -1;  // Malformed line.
+    }
+
+    // Finally, "cursor" now points to file name of our interest.
+    NO_INTR(object_fd = open(cursor, O_RDONLY));
+    if (object_fd < 0) {
+      // Failed to open object file.  Copy the object file name to
+      // |out_file_name|.
+      strncpy(out_file_name, cursor, out_file_name_size);
+      // Making sure |out_file_name| is always null-terminated.
+      out_file_name[out_file_name_size - 1] = '\0';
+      return -1;
+    }
+    return object_fd;
+  }
+}
+
+// POSIX doesn't define any async-signal safe function for converting
+// an integer to ASCII. We'll have to define our own version.
+// itoa_r() converts a (signed) integer to ASCII. It returns "buf", if the
+// conversion was successful or NULL otherwise. It never writes more than "sz"
+// bytes. Output will be truncated as needed, and a NUL character is always
+// appended.
+// NOTE: code from sandbox/linux/seccomp-bpf/demo.cc.
+static char *itoa_r(intptr_t i, char *buf, size_t sz, int base, size_t padding) {
+  // Make sure we can write at least one NUL byte.
+  size_t n = 1;
+  if (n > sz)
+    return NULL;
+
+  if (base < 2 || base > 16) {
+    buf[0] = '\000';
+    return NULL;
+  }
+
+  char *start = buf;
+
+  uintptr_t j = i;
+
+  // Handle negative numbers (only for base 10).
+  if (i < 0 && base == 10) {
+    // This does "j = -i" while avoiding integer overflow.
+    j = static_cast<uintptr_t>(-(i + 1)) + 1;
+
+    // Make sure we can write the '-' character.
+    if (++n > sz) {
+      buf[0] = '\000';
+      return NULL;
+    }
+    *start++ = '-';
+  }
+
+  // Loop until we have converted the entire number. Output at least one
+  // character (i.e. '0').
+  char *ptr = start;
+  do {
+    // Make sure there is still enough space left in our output buffer.
+    if (++n > sz) {
+      buf[0] = '\000';
+      return NULL;
+    }
+
+    // Output the next digit.
+    *ptr++ = "0123456789abcdef"[j % base];
+    j /= base;
+
+    if (padding > 0)
+      padding--;
+  } while (j > 0 || padding > 0);
+
+  // Terminate the output with a NUL character.
+  *ptr = '\000';
+
+  // Conversion to ASCII actually resulted in the digits being in reverse
+  // order. We can't easily generate them in forward order, as we can't tell
+  // the number of characters needed until we are done converting.
+  // So, now, we reverse the string (except for the possible "-" sign).
+  while (--ptr > start) {
+    char ch = *ptr;
+    *ptr = *start;
+    *start++ = ch;
+  }
+  return buf;
+}
+
+// Safely appends string |source| to string |dest|.  Never writes past the
+// buffer size |dest_size| and guarantees that |dest| is null-terminated.
+static void SafeAppendString(const char* source, char* dest, int dest_size) {
+  int dest_string_length = strlen(dest);
+  SAFE_ASSERT(dest_string_length < dest_size);
+  dest += dest_string_length;
+  dest_size -= dest_string_length;
+  strncpy(dest, source, dest_size);
+  // Making sure |dest| is always null-terminated.
+  dest[dest_size - 1] = '\0';
+}
+
+// Converts a 64-bit value into a hex string, and safely appends it to |dest|.
+// Never writes past the buffer size |dest_size| and guarantees that |dest| is
+// null-terminated.
+static void SafeAppendHexNumber(uint64_t value, char* dest, int dest_size) {
+  // 64-bit numbers in hex can have up to 16 digits.
+  char buf[17] = {'\0'};
+  SafeAppendString(itoa_r(value, buf, sizeof(buf), 16, 0), dest, dest_size);
+}
+
+// The implementation of our symbolization routine.  If it
+// successfully finds the symbol containing "pc" and obtains the
+// symbol name, returns true and write the symbol name to "out".
+// Otherwise, returns false. If Callback function is installed via
+// InstallSymbolizeCallback(), the function is also called in this function,
+// and "out" is used as its output.
+// To keep stack consumption low, we would like this function to not
+// get inlined.
+static ATTRIBUTE_NOINLINE bool SymbolizeAndDemangle(void *pc, char *out,
+                                                    int out_size) {
+  uint64_t pc0 = reinterpret_cast<uintptr_t>(pc);
+  uint64_t start_address = 0;
+  uint64_t base_address = 0;
+  int object_fd = -1;
+
+  if (out_size < 1) {
+    return false;
+  }
+  out[0] = '\0';
+  SafeAppendString("(", out, out_size);
+
+  if (g_symbolize_open_object_file_callback) {
+    object_fd = g_symbolize_open_object_file_callback(pc0, start_address,
+                                                      base_address, out + 1,
+                                                      out_size - 1);
+  } else {
+    object_fd = OpenObjectFileContainingPcAndGetStartAddress(pc0, start_address,
+                                                             base_address,
+                                                             out + 1,
+                                                             out_size - 1);
+  }
+
+  FileDescriptor wrapped_object_fd(object_fd);
+
+#if defined(PRINT_UNSYMBOLIZED_STACK_TRACES)
+  {
+#else
+  // Check whether a file name was returned.
+  if (object_fd < 0) {
+#endif
+    if (out[1]) {
+      // The object file containing PC was determined successfully however the
+      // object file was not opened successfully.  This is still considered
+      // success because the object file name and offset are known and tools
+      // like asan_symbolize.py can be used for the symbolization.
+      out[out_size - 1] = '\0';  // Making sure |out| is always null-terminated.
+      SafeAppendString("+0x", out, out_size);
+      SafeAppendHexNumber(pc0 - base_address, out, out_size);
+      SafeAppendString(")", out, out_size);
+      return true;
+    }
+    // Failed to determine the object file containing PC.  Bail out.
+    return false;
+  }
+  int elf_type = FileGetElfType(wrapped_object_fd.get());
+  if (elf_type == -1) {
+    return false;
+  }
+  if (g_symbolize_callback) {
+    // Run the call back if it's installed.
+    // Note: relocation (and much of the rest of this code) will be
+    // wrong for prelinked shared libraries and PIE executables.
+    uint64_t relocation = (elf_type == ET_DYN) ? start_address : 0;
+    int num_bytes_written = g_symbolize_callback(wrapped_object_fd.get(),
+                                                 pc, out, out_size,
+                                                 relocation);
+    if (num_bytes_written > 0) {
+      out += num_bytes_written;
+      out_size -= num_bytes_written;
+    }
+  }
+  if (!GetSymbolFromObjectFile(wrapped_object_fd.get(), pc0,
+                               out, out_size, base_address)) {
+    if (out[1] && !g_symbolize_callback) {
+      // The object file containing PC was opened successfully however the
+      // symbol was not found. The object may have been stripped. This is still
+      // considered success because the object file name and offset are known
+      // and tools like asan_symbolize.py can be used for the symbolization.
+      out[out_size - 1] = '\0';  // Making sure |out| is always null-terminated.
+      SafeAppendString("+0x", out, out_size);
+      SafeAppendHexNumber(pc0 - base_address, out, out_size);
+      SafeAppendString(")", out, out_size);
+      return true;
+    }
+    return false;
+  }
+
+  // Symbolization succeeded.  Now we try to demangle the symbol.
+  DemangleInplace(out, out_size);
+  return true;
+}
+
+_END_GOOGLE_NAMESPACE_
+
+#elif defined(OS_MACOSX) && defined(HAVE_DLADDR)
+
+#include <dlfcn.h>
+#include <string.h>
+
+_START_GOOGLE_NAMESPACE_
+
+static ATTRIBUTE_NOINLINE bool SymbolizeAndDemangle(void *pc, char *out,
+                                                    int out_size) {
+  Dl_info info;
+  if (dladdr(pc, &info)) {
+    if ((int)strlen(info.dli_sname) < out_size) {
+      strcpy(out, info.dli_sname);
+      // Symbolization succeeded.  Now we try to demangle the symbol.
+      DemangleInplace(out, out_size);
+      return true;
+    }
+  }
+  return false;
+}
+
+_END_GOOGLE_NAMESPACE_
+
+#elif defined(OS_WINDOWS) || defined(OS_CYGWIN)
+
+#include <windows.h>
+#include <dbghelp.h>
+
+#ifdef _MSC_VER
+#pragma comment(lib, "dbghelp")
+#endif
+
+_START_GOOGLE_NAMESPACE_
+
+class SymInitializer {
+public:
+  HANDLE process;
+  bool ready;
+  SymInitializer() : process(NULL), ready(false) {
+    // Initialize the symbol handler.
+    // https://msdn.microsoft.com/en-us/library/windows/desktop/ms680344(v=vs.85).aspx
+    process = GetCurrentProcess();
+    // Defer symbol loading.
+    // We do not request undecorated symbols with SYMOPT_UNDNAME
+    // because the mangling library calls UnDecorateSymbolName.
+    SymSetOptions(SYMOPT_DEFERRED_LOADS);
+    if (SymInitialize(process, NULL, true)) {
+      ready = true;
+    }
+  }
+  ~SymInitializer() {
+    SymCleanup(process);
+    // We do not need to close `HANDLE process` because it's a "pseudo handle."
+  }
+private:
+  SymInitializer(const SymInitializer&);
+  SymInitializer& operator=(const SymInitializer&);
+};
+
+static ATTRIBUTE_NOINLINE bool SymbolizeAndDemangle(void *pc, char *out,
+                                                      int out_size) {
+  const static SymInitializer symInitializer;
+  if (!symInitializer.ready) {
+    return false;
+  }
+  // Resolve symbol information from address.
+  // https://msdn.microsoft.com/en-us/library/windows/desktop/ms680578(v=vs.85).aspx
+  char buf[sizeof(SYMBOL_INFO) + MAX_SYM_NAME];
+  SYMBOL_INFO *symbol = reinterpret_cast<SYMBOL_INFO *>(buf);
+  symbol->SizeOfStruct = sizeof(SYMBOL_INFO);
+  symbol->MaxNameLen = MAX_SYM_NAME;
+  // We use the ANSI version to ensure the string type is always `char *`.
+  // This could break if a symbol has Unicode in it.
+  BOOL ret = SymFromAddr(symInitializer.process,
+                         reinterpret_cast<DWORD64>(pc), 0, symbol);
+  if (ret == 1 && static_cast<int>(symbol->NameLen) < out_size) {
+    // `NameLen` does not include the null terminating character.
+    strncpy(out, symbol->Name, static_cast<size_t>(symbol->NameLen) + 1);
+    out[static_cast<size_t>(symbol->NameLen)] = '\0';
+    // Symbolization succeeded.  Now we try to demangle the symbol.
+    DemangleInplace(out, out_size);
+    return true;
+  }
+  return false;
+}
+
+_END_GOOGLE_NAMESPACE_
+
+#else
+# error BUG: HAVE_SYMBOLIZE was wrongly set
+#endif
+
+_START_GOOGLE_NAMESPACE_
+
+bool Symbolize(void *pc, char *out, int out_size) {
+  SAFE_ASSERT(out_size >= 0);
+  return SymbolizeAndDemangle(pc, out, out_size);
+}
+
+_END_GOOGLE_NAMESPACE_
+
+#else  /* HAVE_SYMBOLIZE */
+
+#include <assert.h>
+
+#include "config.h"
+
+_START_GOOGLE_NAMESPACE_
+
+// TODO: Support other environments.
+bool Symbolize(void *pc, char *out, int out_size) {
+  assert(0);
+  return false;
+}
+
+_END_GOOGLE_NAMESPACE_
+
+#endif