text: /*
   * backward.hpp
   * Copyright 2013 Google Inc. All Rights Reserved.
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software and associated documentation files (the "Software"), to deal
   * in the Software without restriction, including without limitation the rights
   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
   * copies of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
   * SOFTWARE.
   */
  
  #ifndef H_6B9572DA_A64B_49E6_B234_051480991C89
  #define H_6B9572DA_A64B_49E6_B234_051480991C89
  
  #ifndef __cplusplus
  #error "It's not going to compile without a C++ compiler..."
  #endif
  
  #if defined(BACKWARD_CXX11)
  #elif defined(BACKWARD_CXX98)
  #else
  #if __cplusplus >= 201103L || (defined(_MSC_VER) && _MSC_VER >= 1800)
  #define BACKWARD_CXX11
  #define BACKWARD_ATLEAST_CXX11
  #define BACKWARD_ATLEAST_CXX98
  #if __cplusplus >= 201703L || (defined(_MSVC_LANG) && _MSVC_LANG >= 201703L)
  #define BACKWARD_ATLEAST_CXX17
  #endif
  #else
  #define BACKWARD_CXX98
  #define BACKWARD_ATLEAST_CXX98
  #endif
  #endif
  
  // You can define one of the following (or leave it to the auto-detection):
  //
  // #define BACKWARD_SYSTEM_LINUX
  //	- specialization for linux
  //
  // #define BACKWARD_SYSTEM_DARWIN
  //	- specialization for Mac OS X 10.5 and later.
  //
  // #define BACKWARD_SYSTEM_WINDOWS
  //  - specialization for Windows (Clang 9 and MSVC2017)
  //
  // #define BACKWARD_SYSTEM_UNKNOWN
  //	- placebo implementation, does nothing.
  //
  #if defined(BACKWARD_SYSTEM_LINUX)
  #elif defined(BACKWARD_SYSTEM_DARWIN)
  #elif defined(BACKWARD_SYSTEM_UNKNOWN)
  #elif defined(BACKWARD_SYSTEM_WINDOWS)
  #else
  #if defined(__linux) || defined(__linux__)
  #define BACKWARD_SYSTEM_LINUX
  #elif defined(__APPLE__)
  #define BACKWARD_SYSTEM_DARWIN
  #elif defined(_WIN32)
  #define BACKWARD_SYSTEM_WINDOWS
  #else
  #define BACKWARD_SYSTEM_UNKNOWN
  #endif
  #endif
  
  #define NOINLINE __attribute__((noinline))
  
  #include <algorithm>
  #include <cctype>
  #include <cstdio>
  #include <cstdlib>
  #include <cstring>
  #include <fstream>
  #include <iomanip>
  #include <iostream>
  #include <limits>
  #include <new>
  #include <sstream>
  #include <streambuf>
  #include <string>
  #include <vector>
  #include <exception>
  #include <iterator>
  
  #if defined(BACKWARD_SYSTEM_LINUX)
  
  // On linux, backtrace can back-trace or "walk" the stack using the following
  // libraries:
  //
  // #define BACKWARD_HAS_UNWIND 1
  //  - unwind comes from libgcc, but I saw an equivalent inside clang itself.
  //  - with unwind, the stacktrace is as accurate as it can possibly be, since
  //  this is used by the C++ runtine in gcc/clang for stack unwinding on
  //  exception.
  //  - normally libgcc is already linked to your program by default.
  //
  // #define BACKWARD_HAS_LIBUNWIND 1
  //  - libunwind provides, in some cases, a more accurate stacktrace as it knows
  //  to decode signal handler frames and lets us edit the context registers when
  //  unwinding, allowing stack traces over bad function references.
  //
  // #define BACKWARD_HAS_BACKTRACE == 1
  //  - backtrace seems to be a little bit more portable than libunwind, but on
  //  linux, it uses unwind anyway, but abstract away a tiny information that is
  //  sadly really important in order to get perfectly accurate stack traces.
  //  - backtrace is part of the (e)glib library.
  //
  // The default is:
  // #define BACKWARD_HAS_UNWIND == 1
  //
  // Note that only one of the define should be set to 1 at a time.
  //
  #if BACKWARD_HAS_UNWIND == 1
  #elif BACKWARD_HAS_LIBUNWIND == 1
  #elif BACKWARD_HAS_BACKTRACE == 1
  #else
  #undef BACKWARD_HAS_UNWIND
  #define BACKWARD_HAS_UNWIND 1
  #undef BACKWARD_HAS_LIBUNWIND
  #define BACKWARD_HAS_LIBUNWIND 0
  #undef BACKWARD_HAS_BACKTRACE
  #define BACKWARD_HAS_BACKTRACE 0
  #endif
  
  // On linux, backward can extract detailed information about a stack trace
  // using one of the following libraries:
  //
  // #define BACKWARD_HAS_DW 1
  //  - libdw gives you the most juicy details out of your stack traces:
  //    - object filename
  //    - function name
  //    - source filename
  //	  - line and column numbers
  //	  - source code snippet (assuming the file is accessible)
  //	  - variables name and values (if not optimized out)
  //  - You need to link with the lib "dw":
  //    - apt-get install libdw-dev
  //    - g++/clang++ -ldw ...
  //
  // #define BACKWARD_HAS_BFD 1
  //  - With libbfd, you get a fair amount of details:
  //    - object filename
  //    - function name
  //    - source filename
  //	  - line numbers
  //	  - source code snippet (assuming the file is accessible)
  //  - You need to link with the lib "bfd":
  //    - apt-get install binutils-dev
  //    - g++/clang++ -lbfd ...
  //
  // #define BACKWARD_HAS_DWARF 1
  //  - libdwarf gives you the most juicy details out of your stack traces:
  //    - object filename
  //    - function name
  //    - source filename
  //    - line and column numbers
  //    - source code snippet (assuming the file is accessible)
  //    - variables name and values (if not optimized out)
  //  - You need to link with the lib "dwarf":
  //    - apt-get install libdwarf-dev
  //    - g++/clang++ -ldwarf ...
  //
  // #define BACKWARD_HAS_BACKTRACE_SYMBOL 1
  //  - backtrace provides minimal details for a stack trace:
  //    - object filename
  //    - function name
  //  - backtrace is part of the (e)glib library.
  //
  // The default is:
  // #define BACKWARD_HAS_BACKTRACE_SYMBOL == 1
  //
  // Note that only one of the define should be set to 1 at a time.
  //
  #if BACKWARD_HAS_DW == 1
  #elif BACKWARD_HAS_BFD == 1
  #elif BACKWARD_HAS_DWARF == 1
  #elif BACKWARD_HAS_BACKTRACE_SYMBOL == 1
  #else
  #undef BACKWARD_HAS_DW
  #define BACKWARD_HAS_DW 0
  #undef BACKWARD_HAS_BFD
  #define BACKWARD_HAS_BFD 0
  #undef BACKWARD_HAS_DWARF
  #define BACKWARD_HAS_DWARF 0
  #undef BACKWARD_HAS_BACKTRACE_SYMBOL
  #define BACKWARD_HAS_BACKTRACE_SYMBOL 1
  #endif
  
  #include <cxxabi.h>
  #include <fcntl.h>
  #ifdef __ANDROID__
  //		Old Android API levels define _Unwind_Ptr in both link.h and
  // unwind.h 		Rename the one in link.h as we are not going to be using
  // it
  #define _Unwind_Ptr _Unwind_Ptr_Custom
  #include <link.h>
  #undef _Unwind_Ptr
  #else
  #include <link.h>
  #endif
  #include <signal.h>
  #include <sys/stat.h>
  #include <syscall.h>
  #include <unistd.h>
  
  #if BACKWARD_HAS_BFD == 1
  //              NOTE: defining PACKAGE{,_VERSION} is required before including
  //                    bfd.h on some platforms, see also:
  //                    https://sourceware.org/bugzilla/show_bug.cgi?id=14243
  #ifndef PACKAGE
  #define PACKAGE
  #endif
  #ifndef PACKAGE_VERSION
  #define PACKAGE_VERSION
  #endif
  #include <bfd.h>
  #ifndef _GNU_SOURCE
  #define _GNU_SOURCE
  #include <dlfcn.h>
  #undef _GNU_SOURCE
  #else
  #include <dlfcn.h>
  #endif
  #endif
  
  #if BACKWARD_HAS_DW == 1
  #include <dwarf.h>
  #include <elfutils/libdw.h>
  #include <elfutils/libdwfl.h>
  #endif
  
  #if BACKWARD_HAS_DWARF == 1
  #include <algorithm>
  #include <dwarf.h>
  #include <libdwarf.h>
  #include <libelf.h>
  #include <map>
  #ifndef _GNU_SOURCE
  #define _GNU_SOURCE
  #include <dlfcn.h>
  #undef _GNU_SOURCE
  #else
  #include <dlfcn.h>
  #endif
  #endif
  
  #if (BACKWARD_HAS_BACKTRACE == 1) || (BACKWARD_HAS_BACKTRACE_SYMBOL == 1)
  // then we shall rely on backtrace
  #include <execinfo.h>
  #endif
  
  #endif // defined(BACKWARD_SYSTEM_LINUX)
  
  #if defined(BACKWARD_SYSTEM_DARWIN)
  // On Darwin, backtrace can back-trace or "walk" the stack using the following
  // libraries:
  //
  // #define BACKWARD_HAS_UNWIND 1
  //  - unwind comes from libgcc, but I saw an equivalent inside clang itself.
  //  - with unwind, the stacktrace is as accurate as it can possibly be, since
  //  this is used by the C++ runtine in gcc/clang for stack unwinding on
  //  exception.
  //  - normally libgcc is already linked to your program by default.
  //
  // #define BACKWARD_HAS_LIBUNWIND 1
  //  - libunwind comes from clang, which implements an API compatible version.
  //  - libunwind provides, in some cases, a more accurate stacktrace as it knows
  //  to decode signal handler frames and lets us edit the context registers when
  //  unwinding, allowing stack traces over bad function references.
  //
  // #define BACKWARD_HAS_BACKTRACE == 1
  //  - backtrace is available by default, though it does not produce as much
  //  information as another library might.
  //
  // The default is:
  // #define BACKWARD_HAS_UNWIND == 1
  //
  // Note that only one of the define should be set to 1 at a time.
  //
  #if BACKWARD_HAS_UNWIND == 1
  #elif BACKWARD_HAS_BACKTRACE == 1
  #elif BACKWARD_HAS_LIBUNWIND == 1
  #else
  #undef BACKWARD_HAS_UNWIND
  #define BACKWARD_HAS_UNWIND 1
  #undef BACKWARD_HAS_BACKTRACE
  #define BACKWARD_HAS_BACKTRACE 0
  #undef BACKWARD_HAS_LIBUNWIND
  #define BACKWARD_HAS_LIBUNWIND 0
  #endif
  
  // On Darwin, backward can extract detailed information about a stack trace
  // using one of the following libraries:
  //
  // #define BACKWARD_HAS_BACKTRACE_SYMBOL 1
  //  - backtrace provides minimal details for a stack trace:
  //    - object filename
  //    - function name
  //
  // The default is:
  // #define BACKWARD_HAS_BACKTRACE_SYMBOL == 1
  //
  #if BACKWARD_HAS_BACKTRACE_SYMBOL == 1
  #else
  #undef BACKWARD_HAS_BACKTRACE_SYMBOL
  #define BACKWARD_HAS_BACKTRACE_SYMBOL 1
  #endif
  
  #include <cxxabi.h>
  #include <fcntl.h>
  #include <pthread.h>
  #include <signal.h>
  #include <sys/stat.h>
  #include <unistd.h>
  
  #if (BACKWARD_HAS_BACKTRACE == 1) || (BACKWARD_HAS_BACKTRACE_SYMBOL == 1)
  #include <execinfo.h>
  #endif
  #endif // defined(BACKWARD_SYSTEM_DARWIN)
  
  #if defined(BACKWARD_SYSTEM_WINDOWS)
  
  #include <condition_variable>
  #include <mutex>
  #include <thread>
  
  #include <basetsd.h>
  typedef SSIZE_T ssize_t;
  
  #define NOMINMAX
  #include <windows.h>
  #include <winnt.h>
  
  #include <psapi.h>
  #include <signal.h>
  
  #ifndef __clang__
  #undef NOINLINE
  #define NOINLINE __declspec(noinline)
  #endif
  
  #pragma comment(lib, "psapi.lib")
  #pragma comment(lib, "dbghelp.lib")
  
  // Comment / packing is from stackoverflow:
  // https://stackoverflow.com/questions/6205981/windows-c-stack-trace-from-a-running-app/28276227#28276227
  // Some versions of imagehlp.dll lack the proper packing directives themselves
  // so we need to do it.
  #pragma pack(push, before_imagehlp, 8)
  #include <imagehlp.h>
  #pragma pack(pop, before_imagehlp)
  
  // TODO maybe these should be undefined somewhere else?
  #undef BACKWARD_HAS_UNWIND
  #undef BACKWARD_HAS_BACKTRACE
  #if BACKWARD_HAS_PDB_SYMBOL == 1
  #else
  #undef BACKWARD_HAS_PDB_SYMBOL
  #define BACKWARD_HAS_PDB_SYMBOL 1
  #endif
  
  #endif
  
  #if BACKWARD_HAS_UNWIND == 1
  
  #include <unwind.h>
  // while gcc's unwind.h defines something like that:
  //  extern _Unwind_Ptr _Unwind_GetIP (struct _Unwind_Context *);
  //  extern _Unwind_Ptr _Unwind_GetIPInfo (struct _Unwind_Context *, int *);
  //
  // clang's unwind.h defines something like this:
  //  uintptr_t _Unwind_GetIP(struct _Unwind_Context* __context);
  //
  // Even if the _Unwind_GetIPInfo can be linked to, it is not declared, worse we
  // cannot just redeclare it because clang's unwind.h doesn't define _Unwind_Ptr
  // anyway.
  //
  // Luckily we can play on the fact that the guard macros have a different name:
  #ifdef __CLANG_UNWIND_H
  // In fact, this function still comes from libgcc (on my different linux boxes,
  // clang links against libgcc).
  #include <inttypes.h>
  extern "C" uintptr_t _Unwind_GetIPInfo(_Unwind_Context *, int *);
  #endif
  
  #endif // BACKWARD_HAS_UNWIND == 1
  
  #if BACKWARD_HAS_LIBUNWIND == 1
  #define UNW_LOCAL_ONLY
  #include <libunwind.h>
  #endif // BACKWARD_HAS_LIBUNWIND == 1
  
  #ifdef BACKWARD_ATLEAST_CXX11
  #include <unordered_map>
  #include <utility> // for std::swap
  namespace backward {
  namespace details {
  template <typename K, typename V> struct hashtable {
    typedef std::unordered_map<K, V> type;
  };
  using std::move;
  } // namespace details
  } // namespace backward
  #else // NOT BACKWARD_ATLEAST_CXX11
  #define nullptr NULL
  #define override
  #include <map>
  namespace backward {
  namespace details {
  template <typename K, typename V> struct hashtable {
    typedef std::map<K, V> type;
  };
  template <typename T> const T &move(const T &v) { return v; }
  template <typename T> T &move(T &v) { return v; }
  } // namespace details
  } // namespace backward
  #endif // BACKWARD_ATLEAST_CXX11
  
  namespace backward {
  namespace details {
  #if defined(BACKWARD_SYSTEM_WINDOWS)
  const char kBackwardPathDelimiter[] = ";";
  #else
  const char kBackwardPathDelimiter[] = ":";
  #endif
  } // namespace details
  } // namespace backward
  
  namespace backward {
  
  namespace system_tag {
  struct linux_tag; // seems that I cannot call that "linux" because the name
  // is already defined... so I am adding _tag everywhere.
  struct darwin_tag;
  struct windows_tag;
  struct unknown_tag;
  
  #if defined(BACKWARD_SYSTEM_LINUX)
  typedef linux_tag current_tag;
  #elif defined(BACKWARD_SYSTEM_DARWIN)
  typedef darwin_tag current_tag;
  #elif defined(BACKWARD_SYSTEM_WINDOWS)
  typedef windows_tag current_tag;
  #elif defined(BACKWARD_SYSTEM_UNKNOWN)
  typedef unknown_tag current_tag;
  #else
  #error "May I please get my system defines?"
  #endif
  } // namespace system_tag
  
  namespace trace_resolver_tag {
  #if defined(BACKWARD_SYSTEM_LINUX)
  struct libdw;
  struct libbfd;
  struct libdwarf;
  struct backtrace_symbol;
  
  #if BACKWARD_HAS_DW == 1
  typedef libdw current;
  #elif BACKWARD_HAS_BFD == 1
  typedef libbfd current;
  #elif BACKWARD_HAS_DWARF == 1
  typedef libdwarf current;
  #elif BACKWARD_HAS_BACKTRACE_SYMBOL == 1
  typedef backtrace_symbol current;
  #else
  #error "You shall not pass, until you know what you want."
  #endif
  #elif defined(BACKWARD_SYSTEM_DARWIN)
  struct backtrace_symbol;
  
  #if BACKWARD_HAS_BACKTRACE_SYMBOL == 1
  typedef backtrace_symbol current;
  #else
  #error "You shall not pass, until you know what you want."
  #endif
  #elif defined(BACKWARD_SYSTEM_WINDOWS)
  struct pdb_symbol;
  #if BACKWARD_HAS_PDB_SYMBOL == 1
  typedef pdb_symbol current;
  #else
  #error "You shall not pass, until you know what you want."
  #endif
  #endif
  } // namespace trace_resolver_tag
  
  namespace details {
  
  template <typename T> struct rm_ptr { typedef T type; };
  
  template <typename T> struct rm_ptr<T *> { typedef T type; };
  
  template <typename T> struct rm_ptr<const T *> { typedef const T type; };
  
  template <typename R, typename T, R (*F)(T)> struct deleter {
    template <typename U> void operator()(U &ptr) const { (*F)(ptr); }
  };
  
  template <typename T> struct default_delete {
    void operator()(T &ptr) const { delete ptr; }
  };
  
  template <typename T, typename Deleter = deleter<void, void *, &::free>>
  class handle {
    struct dummy;
    T _val;
    bool _empty;
  
  #ifdef BACKWARD_ATLEAST_CXX11
    handle(const handle &) = delete;
    handle &operator=(const handle &) = delete;
  #endif
  
  public:
    ~handle() {
      if (!_empty) {
        Deleter()(_val);
      }
    }
  
    explicit handle() : _val(), _empty(true) {}
    explicit handle(T val) : _val(val), _empty(false) {
      if (!_val)
        _empty = true;
    }
  
  #ifdef BACKWARD_ATLEAST_CXX11
    handle(handle &&from) : _empty(true) { swap(from); }
    handle &operator=(handle &&from) {
      swap(from);
      return *this;
    }
  #else
    explicit handle(const handle &from) : _empty(true) {
      // some sort of poor man's move semantic.
      swap(const_cast<handle &>(from));
    }
    handle &operator=(const handle &from) {
      // some sort of poor man's move semantic.
      swap(const_cast<handle &>(from));
      return *this;
    }
  #endif
  
    void reset(T new_val) {
      handle tmp(new_val);
      swap(tmp);
    }
  
    void update(T new_val) {
      _val = new_val;
      _empty = !static_cast<bool>(new_val);
    }
  
    operator const dummy *() const {
      if (_empty) {
        return nullptr;
      }
      return reinterpret_cast<const dummy *>(_val);
    }
    T get() { return _val; }
    T release() {
      _empty = true;
      return _val;
    }
    void swap(handle &b) {
      using std::swap;
      swap(b._val, _val);     // can throw, we are safe here.
      swap(b._empty, _empty); // should not throw: if you cannot swap two
      // bools without throwing... It's a lost cause anyway!
    }
  
    T &operator->() { return _val; }
    const T &operator->() const { return _val; }
  
    typedef typename rm_ptr<T>::type &ref_t;
    typedef const typename rm_ptr<T>::type &const_ref_t;
    ref_t operator*() { return *_val; }
    const_ref_t operator*() const { return *_val; }
    ref_t operator[](size_t idx) { return _val[idx]; }
  
    // Watch out, we've got a badass over here
    T *operator&() {
      _empty = false;
      return &_val;
    }
  };
  
  // Default demangler implementation (do nothing).
  template <typename TAG> struct demangler_impl {
    static std::string demangle(const char *funcname) { return funcname; }
  };
  
  #if defined(BACKWARD_SYSTEM_LINUX) || defined(BACKWARD_SYSTEM_DARWIN)
  
  template <> struct demangler_impl<system_tag::current_tag> {
    demangler_impl() : _demangle_buffer_length(0) {}
  
    std::string demangle(const char *funcname) {
      using namespace details;
      char *result = abi::__cxa_demangle(funcname, _demangle_buffer.get(),
                                         &_demangle_buffer_length, nullptr);
      if (result) {
        _demangle_buffer.update(result);
        return result;
      }
      return funcname;
    }
  
  private:
    details::handle<char *> _demangle_buffer;
    size_t _demangle_buffer_length;
  };
  
  #endif // BACKWARD_SYSTEM_LINUX || BACKWARD_SYSTEM_DARWIN
  
  struct demangler : public demangler_impl<system_tag::current_tag> {};
  
  // Split a string on the platform's PATH delimiter.  Example: if delimiter
  // is ":" then:
  //   ""              --> []
  //   ":"             --> ["",""]
  //   "::"            --> ["","",""]
  //   "/a/b/c"        --> ["/a/b/c"]
  //   "/a/b/c:/d/e/f" --> ["/a/b/c","/d/e/f"]
  //   etc.
  inline std::vector<std::string> split_source_prefixes(const std::string &s) {
    std::vector<std::string> out;
    size_t last = 0;
    size_t next = 0;
    size_t delimiter_size = sizeof(kBackwardPathDelimiter) - 1;
    while ((next = s.find(kBackwardPathDelimiter, last)) != std::string::npos) {
      out.push_back(s.substr(last, next - last));
      last = next + delimiter_size;
    }
    if (last <= s.length()) {
      out.push_back(s.substr(last));
    }
    return out;
  }
  
  } // namespace details
  
  /*************** A TRACE ***************/
  
  struct Trace {
    void *addr;
    size_t idx;
  
    Trace() : addr(nullptr), idx(0) {}
  
    explicit Trace(void *_addr, size_t _idx) : addr(_addr), idx(_idx) {}
  };
  
  struct ResolvedTrace : public Trace {
  
    struct SourceLoc {
      std::string function;
      std::string filename;
      unsigned line;
      unsigned col;
  
      SourceLoc() : line(0), col(0) {}
  
      bool operator==(const SourceLoc &b) const {
        return function == b.function && filename == b.filename &&
               line == b.line && col == b.col;
      }
  
      bool operator!=(const SourceLoc &b) const { return !(*this == b); }
    };
  
    // In which binary object this trace is located.
    std::string object_filename;
  
    // The function in the object that contain the trace. This is not the same
    // as source.function which can be an function inlined in object_function.
    std::string object_function;
  
    // The source location of this trace. It is possible for filename to be
    // empty and for line/col to be invalid (value 0) if this information
    // couldn't be deduced, for example if there is no debug information in the
    // binary object.
    SourceLoc source;
  
    // An optionals list of "inliners". All the successive sources location
    // from where the source location of the trace (the attribute right above)
    // is inlined. It is especially useful when you compiled with optimization.
    typedef std::vector<SourceLoc> source_locs_t;
    source_locs_t inliners;
  
    ResolvedTrace() : Trace() {}
    ResolvedTrace(const Trace &mini_trace) : Trace(mini_trace) {}
  };
  
  /*************** STACK TRACE ***************/
  
  // default implemention.
  template <typename TAG> class StackTraceImpl {
  public:
    size_t size() const { return 0; }
    Trace operator[](size_t) const { return Trace(); }
    size_t load_here(size_t = 0) { return 0; }
    size_t load_from(void *, size_t = 0, void * = nullptr, void * = nullptr) {
      return 0;
    }
    size_t thread_id() const { return 0; }
    void skip_n_firsts(size_t) {}
  };
  
  class StackTraceImplBase {
  public:
    StackTraceImplBase()
        : _thread_id(0), _skip(0), _context(nullptr), _error_addr(nullptr) {}
  
    size_t thread_id() const { return _thread_id; }
  
    void skip_n_firsts(size_t n) { _skip = n; }
  
  protected:
    void load_thread_info() {
  #ifdef BACKWARD_SYSTEM_LINUX
  #ifndef __ANDROID__
      _thread_id = static_cast<size_t>(syscall(SYS_gettid));
  #else
      _thread_id = static_cast<size_t>(gettid());
  #endif
      if (_thread_id == static_cast<size_t>(getpid())) {
        // If the thread is the main one, let's hide that.
        // I like to keep little secret sometimes.
        _thread_id = 0;
      }
  #elif defined(BACKWARD_SYSTEM_DARWIN)
      _thread_id = reinterpret_cast<size_t>(pthread_self());
      if (pthread_main_np() == 1) {
        // If the thread is the main one, let's hide that.
        _thread_id = 0;
      }
  #endif
    }
  
    void set_context(void *context) { _context = context; }
    void *context() const { return _context; }
  
    void set_error_addr(void *error_addr) { _error_addr = error_addr; }
    void *error_addr() const { return _error_addr; }
  
    size_t skip_n_firsts() const { return _skip; }
  
  private:
    size_t _thread_id;
    size_t _skip;
    void *_context;
    void *_error_addr;
  };
  
  class StackTraceImplHolder : public StackTraceImplBase {
  public:
    size_t size() const {
      return (_stacktrace.size() >= skip_n_firsts())
                 ? _stacktrace.size() - skip_n_firsts()
                 : 0;
    }
    Trace operator[](size_t idx) const {
      if (idx >= size()) {
        return Trace();
      }
      return Trace(_stacktrace[idx + skip_n_firsts()], idx);
    }
    void *const *begin() const {
      if (size()) {
        return &_stacktrace[skip_n_firsts()];
      }
      return nullptr;
    }
  
  protected:
    std::vector<void *> _stacktrace;
  };
  
  #if BACKWARD_HAS_UNWIND == 1
  
  namespace details {
  
  template <typename F> class Unwinder {
  public:
    size_t operator()(F &f, size_t depth) {
      _f = &f;
      _index = -1;
      _depth = depth;
      _Unwind_Backtrace(&this->backtrace_trampoline, this);
      return static_cast<size_t>(_index);
    }
  
  private:
    F *_f;
    ssize_t _index;
    size_t _depth;
  
    static _Unwind_Reason_Code backtrace_trampoline(_Unwind_Context *ctx,
                                                    void *self) {
      return (static_cast<Unwinder *>(self))->backtrace(ctx);
    }
  
    _Unwind_Reason_Code backtrace(_Unwind_Context *ctx) {
      if (_index >= 0 && static_cast<size_t>(_index) >= _depth)
        return _URC_END_OF_STACK;
  
      int ip_before_instruction = 0;
      uintptr_t ip = _Unwind_GetIPInfo(ctx, &ip_before_instruction);
  
      if (!ip_before_instruction) {
        // calculating 0-1 for unsigned, looks like a possible bug to sanitiziers,
        // so let's do it explicitly:
        if (ip == 0) {
          ip = std::numeric_limits<uintptr_t>::max(); // set it to 0xffff... (as
                                                      // from casting 0-1)
        } else {
          ip -= 1; // else just normally decrement it (no overflow/underflow will
                   // happen)
        }
      }
  
      if (_index >= 0) { // ignore first frame.
        (*_f)(static_cast<size_t>(_index), reinterpret_cast<void *>(ip));
      }
      _index += 1;
      return _URC_NO_REASON;
    }
  };
  
  template <typename F> size_t unwind(F f, size_t depth) {
    Unwinder<F> unwinder;
    return unwinder(f, depth);
  }
  
  } // namespace details
  
  template <>
  class StackTraceImpl<system_tag::current_tag> : public StackTraceImplHolder {
  public:
    NOINLINE
    size_t load_here(size_t depth = 32, void *context = nullptr,
                     void *error_addr = nullptr) {
      load_thread_info();
      set_context(context);
      set_error_addr(error_addr);
      if (depth == 0) {
        return 0;
      }
      _stacktrace.resize(depth);
      size_t trace_cnt = details::unwind(callback(*this), depth);
      _stacktrace.resize(trace_cnt);
      skip_n_firsts(0);
      return size();
    }
    size_t load_from(void *addr, size_t depth = 32, void *context = nullptr,
                     void *error_addr = nullptr) {
      load_here(depth + 8, context, error_addr);
  
      for (size_t i = 0; i < _stacktrace.size(); ++i) {
        if (_stacktrace[i] == addr) {
          skip_n_firsts(i);
          break;
        }
      }
  
      _stacktrace.resize(std::min(_stacktrace.size(), skip_n_firsts() + depth));
      return size();
    }
  
  private:
    struct callback {
      StackTraceImpl &self;
      callback(StackTraceImpl &_self) : self(_self) {}
  
      void operator()(size_t idx, void *addr) { self._stacktrace[idx] = addr; }
    };
  };
  
  #elif BACKWARD_HAS_LIBUNWIND == 1
  
  template <>
  class StackTraceImpl<system_tag::current_tag> : public StackTraceImplHolder {
  public:
    __attribute__((noinline)) size_t load_here(size_t depth = 32,
                                               void *_context = nullptr,
                                               void *_error_addr = nullptr) {
      set_context(_context);
      set_error_addr(_error_addr);
      load_thread_info();
      if (depth == 0) {
        return 0;
      }
      _stacktrace.resize(depth + 1);
  
      int result = 0;
  
      unw_context_t ctx;
      size_t index = 0;
  
      // Add the tail call. If the Instruction Pointer is the crash address it
      // means we got a bad function pointer dereference, so we "unwind" the
      // bad pointer manually by using the return address pointed to by the
      // Stack Pointer as the Instruction Pointer and letting libunwind do
      // the rest
  
      if (context()) {
        ucontext_t *uctx = reinterpret_cast<ucontext_t *>(context());
  #ifdef REG_RIP         // x86_64
        if (uctx->uc_mcontext.gregs[REG_RIP] ==
            reinterpret_cast<greg_t>(error_addr())) {
          uctx->uc_mcontext.gregs[REG_RIP] =
              *reinterpret_cast<size_t *>(uctx->uc_mcontext.gregs[REG_RSP]);
        }
        _stacktrace[index] =
            reinterpret_cast<void *>(uctx->uc_mcontext.gregs[REG_RIP]);
        ++index;
        ctx = *reinterpret_cast<unw_context_t *>(uctx);
  #elif defined(REG_EIP) // x86_32
        if (uctx->uc_mcontext.gregs[REG_EIP] ==
            reinterpret_cast<greg_t>(error_addr())) {
          uctx->uc_mcontext.gregs[REG_EIP] =
              *reinterpret_cast<size_t *>(uctx->uc_mcontext.gregs[REG_ESP]);
        }
        _stacktrace[index] =
            reinterpret_cast<void *>(uctx->uc_mcontext.gregs[REG_EIP]);
        ++index;
        ctx = *reinterpret_cast<unw_context_t *>(uctx);
  #elif defined(__arm__)
        // libunwind uses its own context type for ARM unwinding.
        // Copy the registers from the signal handler's context so we can
        // unwind
        unw_getcontext(&ctx);
        ctx.regs[UNW_ARM_R0] = uctx->uc_mcontext.arm_r0;
        ctx.regs[UNW_ARM_R1] = uctx->uc_mcontext.arm_r1;
        ctx.regs[UNW_ARM_R2] = uctx->uc_mcontext.arm_r2;
        ctx.regs[UNW_ARM_R3] = uctx->uc_mcontext.arm_r3;
        ctx.regs[UNW_ARM_R4] = uctx->uc_mcontext.arm_r4;
        ctx.regs[UNW_ARM_R5] = uctx->uc_mcontext.arm_r5;
        ctx.regs[UNW_ARM_R6] = uctx->uc_mcontext.arm_r6;
        ctx.regs[UNW_ARM_R7] = uctx->uc_mcontext.arm_r7;
        ctx.regs[UNW_ARM_R8] = uctx->uc_mcontext.arm_r8;
        ctx.regs[UNW_ARM_R9] = uctx->uc_mcontext.arm_r9;
        ctx.regs[UNW_ARM_R10] = uctx->uc_mcontext.arm_r10;
        ctx.regs[UNW_ARM_R11] = uctx->uc_mcontext.arm_fp;
        ctx.regs[UNW_ARM_R12] = uctx->uc_mcontext.arm_ip;
        ctx.regs[UNW_ARM_R13] = uctx->uc_mcontext.arm_sp;
        ctx.regs[UNW_ARM_R14] = uctx->uc_mcontext.arm_lr;
        ctx.regs[UNW_ARM_R15] = uctx->uc_mcontext.arm_pc;
  
        // If we have crashed in the PC use the LR instead, as this was
        // a bad function dereference
        if (reinterpret_cast<unsigned long>(error_addr()) ==
            uctx->uc_mcontext.arm_pc) {
          ctx.regs[UNW_ARM_R15] =
              uctx->uc_mcontext.arm_lr - sizeof(unsigned long);
        }
        _stacktrace[index] = reinterpret_cast<void *>(ctx.regs[UNW_ARM_R15]);
        ++index;
  #elif defined(__APPLE__) && defined(__x86_64__)
        unw_getcontext(&ctx);
        // OS X's implementation of libunwind uses its own context object
        // so we need to convert the passed context to libunwind's format
        // (information about the data layout taken from unw_getcontext.s
        // in Apple's libunwind source
        ctx.data[0] = uctx->uc_mcontext->__ss.__rax;
        ctx.data[1] = uctx->uc_mcontext->__ss.__rbx;
        ctx.data[2] = uctx->uc_mcontext->__ss.__rcx;
        ctx.data[3] = uctx->uc_mcontext->__ss.__rdx;
        ctx.data[4] = uctx->uc_mcontext->__ss.__rdi;
        ctx.data[5] = uctx->uc_mcontext->__ss.__rsi;
        ctx.data[6] = uctx->uc_mcontext->__ss.__rbp;
        ctx.data[7] = uctx->uc_mcontext->__ss.__rsp;
        ctx.data[8] = uctx->uc_mcontext->__ss.__r8;
        ctx.data[9] = uctx->uc_mcontext->__ss.__r9;
        ctx.data[10] = uctx->uc_mcontext->__ss.__r10;
        ctx.data[11] = uctx->uc_mcontext->__ss.__r11;
        ctx.data[12] = uctx->uc_mcontext->__ss.__r12;
        ctx.data[13] = uctx->uc_mcontext->__ss.__r13;
        ctx.data[14] = uctx->uc_mcontext->__ss.__r14;
        ctx.data[15] = uctx->uc_mcontext->__ss.__r15;
        ctx.data[16] = uctx->uc_mcontext->__ss.__rip;
  
        // If the IP is the same as the crash address we have a bad function
        // dereference The caller's address is pointed to by %rsp, so we
        // dereference that value and set it to be the next frame's IP.
        if (uctx->uc_mcontext->__ss.__rip ==
            reinterpret_cast<__uint64_t>(error_addr())) {
          ctx.data[16] =
              *reinterpret_cast<__uint64_t *>(uctx->uc_mcontext->__ss.__rsp);
        }
        _stacktrace[index] = reinterpret_cast<void *>(ctx.data[16]);
        ++index;
  #elif defined(__APPLE__)
        unw_getcontext(&ctx)
            // TODO: Convert the ucontext_t to libunwind's unw_context_t like
            // we do in 64 bits
            if (ctx.uc_mcontext->__ss.__eip ==
                reinterpret_cast<greg_t>(error_addr())) {
          ctx.uc_mcontext->__ss.__eip = ctx.uc_mcontext->__ss.__esp;
        }
        _stacktrace[index] =
            reinterpret_cast<void *>(ctx.uc_mcontext->__ss.__eip);
        ++index;
  #endif
      }
  
      unw_cursor_t cursor;
      if (context()) {
  #if defined(UNW_INIT_SIGNAL_FRAME)
        result = unw_init_local2(&cursor, &ctx, UNW_INIT_SIGNAL_FRAME);
  #else
        result = unw_init_local(&cursor, &ctx);
  #endif
      } else {
        unw_getcontext(&ctx);
        ;
        result = unw_init_local(&cursor, &ctx);
      }
  
      if (result != 0)
        return 1;
  
      unw_word_t ip = 0;
  
      while (index <= depth && unw_step(&cursor) > 0) {
        result = unw_get_reg(&cursor, UNW_REG_IP, &ip);
        if (result == 0) {
          _stacktrace[index] = reinterpret_cast<void *>(--ip);
          ++index;
        }
      }
      --index;
  
      _stacktrace.resize(index + 1);
      skip_n_firsts(0);
      return size();
    }
  
    size_t load_from(void *addr, size_t depth = 32, void *context = nullptr,
                     void *error_addr = nullptr) {
      load_here(depth + 8, context, error_addr);
  
      for (size_t i = 0; i < _stacktrace.size(); ++i) {
        if (_stacktrace[i] == addr) {
          skip_n_firsts(i);
          _stacktrace[i] = (void *)((uintptr_t)_stacktrace[i]);
          break;
        }
      }
  
      _stacktrace.resize(std::min(_stacktrace.size(), skip_n_firsts() + depth));
      return size();
    }
  };
  
  #elif defined(BACKWARD_HAS_BACKTRACE)
  
  template <>
  class StackTraceImpl<system_tag::current_tag> : public StackTraceImplHolder {
  public:
    NOINLINE
    size_t load_here(size_t depth = 32, void *context = nullptr,
                     void *error_addr = nullptr) {
      set_context(context);
      set_error_addr(error_addr);
      load_thread_info();
      if (depth == 0) {
        return 0;
      }
      _stacktrace.resize(depth + 1);
      size_t trace_cnt = backtrace(&_stacktrace[0], _stacktrace.size());
      _stacktrace.resize(trace_cnt);
      skip_n_firsts(1);
      return size();
    }
  
    size_t load_from(void *addr, size_t depth = 32, void *context = nullptr,
                     void *error_addr = nullptr) {
      load_here(depth + 8, context, error_addr);
  
      for (size_t i = 0; i < _stacktrace.size(); ++i) {
        if (_stacktrace[i] == addr) {
          skip_n_firsts(i);
          _stacktrace[i] = (void *)((uintptr_t)_stacktrace[i] + 1);
          break;
        }
      }
  
      _stacktrace.resize(std::min(_stacktrace.size(), skip_n_firsts() + depth));
      return size();
    }
  };
  
  #elif defined(BACKWARD_SYSTEM_WINDOWS)
  
  template <>
  class StackTraceImpl<system_tag::current_tag> : public StackTraceImplHolder {
  public:
    // We have to load the machine type from the image info
    // So we first initialize the resolver, and it tells us this info
    void set_machine_type(DWORD machine_type) { machine_type_ = machine_type; }
    void set_context(CONTEXT *ctx) { ctx_ = ctx; }
    void set_thread_handle(HANDLE handle) { thd_ = handle; }
  
    NOINLINE
    size_t load_here(size_t depth = 32, void *context = nullptr,
                     void *error_addr = nullptr) {
      set_context(static_cast<CONTEXT*>(context));
      set_error_addr(error_addr);
      CONTEXT localCtx; // used when no context is provided
  
      if (depth == 0) {
        return 0;
      }
  
      if (!ctx_) {
        ctx_ = &localCtx;
        RtlCaptureContext(ctx_);
      }
  
      if (!thd_) {
        thd_ = GetCurrentThread();
      }
  
      HANDLE process = GetCurrentProcess();
  
      STACKFRAME64 s;
      memset(&s, 0, sizeof(STACKFRAME64));
  
      // TODO: 32 bit context capture
      s.AddrStack.Mode = AddrModeFlat;
      s.AddrFrame.Mode = AddrModeFlat;
      s.AddrPC.Mode = AddrModeFlat;
  #ifdef _M_X64
      s.AddrPC.Offset = ctx_->Rip;
      s.AddrStack.Offset = ctx_->Rsp;
      s.AddrFrame.Offset = ctx_->Rbp;
  #else
      s.AddrPC.Offset = ctx_->Eip;
      s.AddrStack.Offset = ctx_->Esp;
      s.AddrFrame.Offset = ctx_->Ebp;
  #endif
  
      if (!machine_type_) {
  #ifdef _M_X64
        machine_type_ = IMAGE_FILE_MACHINE_AMD64;
  #else
        machine_type_ = IMAGE_FILE_MACHINE_I386;
  #endif
      }
  
      for (;;) {
        // NOTE: this only works if PDBs are already loaded!
        SetLastError(0);
        if (!StackWalk64(machine_type_, process, thd_, &s, ctx_, NULL,
                         SymFunctionTableAccess64, SymGetModuleBase64, NULL))
          break;
  
        if (s.AddrReturn.Offset == 0)
          break;
  
        _stacktrace.push_back(reinterpret_cast<void *>(s.AddrPC.Offset));
  
        if (size() >= depth)
          break;
      }
  
      return size();
    }
  
    size_t load_from(void *addr, size_t depth = 32, void *context = nullptr,
                     void *error_addr = nullptr) {
      load_here(depth + 8, context, error_addr);
  
      for (size_t i = 0; i < _stacktrace.size(); ++i) {
        if (_stacktrace[i] == addr) {
          skip_n_firsts(i);
          break;
        }
      }
  
      _stacktrace.resize(std::min(_stacktrace.size(), skip_n_firsts() + depth));
      return size();
    }
  
  private:
    DWORD machine_type_ = 0;
    HANDLE thd_ = 0;
    CONTEXT *ctx_ = nullptr;
  };
  
  #endif
  
  class StackTrace : public StackTraceImpl<system_tag::current_tag> {};
  
  /*************** TRACE RESOLVER ***************/
  
  class TraceResolverImplBase {
  public:
    virtual ~TraceResolverImplBase() {}
  
    virtual void load_addresses(void *const*addresses, int address_count) {
      (void)addresses;
      (void)address_count;
    }
  
    template <class ST> void load_stacktrace(ST &st) {
      load_addresses(st.begin(), (int)st.size());
    }
  
    virtual ResolvedTrace resolve(ResolvedTrace t) { return t; }
  
  protected:
    std::string demangle(const char *funcname) {
      return _demangler.demangle(funcname);
    }
  
  private:
    details::demangler _demangler;
  };
  
  template <typename TAG> class TraceResolverImpl;
  
  #ifdef BACKWARD_SYSTEM_UNKNOWN
  
  template <> class TraceResolverImpl<system_tag::unknown_tag>
      : public TraceResolverImplBase {};
  
  #endif
  
  #ifdef BACKWARD_SYSTEM_LINUX
  
  class TraceResolverLinuxBase : public TraceResolverImplBase {
  public:
    TraceResolverLinuxBase()
        : argv0_(get_argv0()), exec_path_(read_symlink("/proc/self/exe")) {}
    std::string resolve_exec_path(Dl_info &symbol_info) const {
      // mutates symbol_info.dli_fname to be filename to open and returns filename
      // to display
      if (symbol_info.dli_fname == argv0_) {
        // dladdr returns argv[0] in dli_fname for symbols contained in
        // the main executable, which is not a valid path if the
        // executable was found by a search of the PATH environment
        // variable; In that case, we actually open /proc/self/exe, which
        // is always the actual executable (even if it was deleted/replaced!)
        // but display the path that /proc/self/exe links to.
        // However, this right away reduces probability of successful symbol
        // resolution, because libbfd may try to find *.debug files in the
        // same dir, in case symbols are stripped. As a result, it may try
        // to find a file /proc/self/<exe_name>.debug, which obviously does
        // not exist. /proc/self/exe is a last resort. First load attempt
        // should go for the original executable file path.
        symbol_info.dli_fname = "/proc/self/exe";
        return exec_path_;
      } else {
        return symbol_info.dli_fname;
      }
    }
  
  private:
    std::string argv0_;
    std::string exec_path_;
  
    static std::string get_argv0() {
      std::string argv0;
      std::ifstream ifs("/proc/self/cmdline");
      std::getline(ifs, argv0, '\0');
      return argv0;
    }
  
    static std::string read_symlink(std::string const &symlink_path) {
      std::string path;
      path.resize(100);
  
      while (true) {
        ssize_t len =
            ::readlink(symlink_path.c_str(), &*path.begin(), path.size());
        if (len < 0) {
          return "";
        }
        if (static_cast<size_t>(len) == path.size()) {
          path.resize(path.size() * 2);
        } else {
          path.resize(static_cast<std::string::size_type>(len));
          break;
        }
      }
  
      return path;
    }
  };
  
  template <typename STACKTRACE_TAG> class TraceResolverLinuxImpl;
  
  #if BACKWARD_HAS_BACKTRACE_SYMBOL == 1
  
  template <>
  class TraceResolverLinuxImpl<trace_resolver_tag::backtrace_symbol>
      : public TraceResolverLinuxBase {
  public:
    void load_addresses(void *const*addresses, int address_count) override {
      if (address_count == 0) {
        return;
      }
      _symbols.reset(backtrace_symbols(addresses, address_count));
    }
  
    ResolvedTrace resolve(ResolvedTrace trace) override {
      char *filename = _symbols[trace.idx];
      char *funcname = filename;
      while (*funcname && *funcname != '(') {
        funcname += 1;
      }
      trace.object_filename.assign(filename,
                                   funcname); // ok even if funcname is the ending
                                              // \0 (then we assign entire string)
  
      if (*funcname) { // if it's not end of string (e.g. from last frame ip==0)
        funcname += 1;
        char *funcname_end = funcname;
        while (*funcname_end && *funcname_end != ')' && *funcname_end != '+') {
          funcname_end += 1;
        }
        *funcname_end = '\0';
        trace.object_function = this->demangle(funcname);
        trace.source.function = trace.object_function; // we cannot do better.
      }
      return trace;
    }
  
  private:
    details::handle<char **> _symbols;
  };
  
  #endif // BACKWARD_HAS_BACKTRACE_SYMBOL == 1
  
  #if BACKWARD_HAS_BFD == 1
  
  template <>
  class TraceResolverLinuxImpl<trace_resolver_tag::libbfd>
      : public TraceResolverLinuxBase {
  public:
    TraceResolverLinuxImpl() : _bfd_loaded(false) {}
  
    ResolvedTrace resolve(ResolvedTrace trace) override {
      Dl_info symbol_info;
  
      // trace.addr is a virtual address in memory pointing to some code.
      // Let's try to find from which loaded object it comes from.
      // The loaded object can be yourself btw.
      if (!dladdr(trace.addr, &symbol_info)) {
        return trace; // dat broken trace...
      }
  
      // Now we get in symbol_info:
      // .dli_fname:
      //		pathname of the shared object that contains the address.
      // .dli_fbase:
      //		where the object is loaded in memory.
      // .dli_sname:
      //		the name of the nearest symbol to trace.addr, we expect a
      //		function name.
      // .dli_saddr:
      //		the exact address corresponding to .dli_sname.
  
      if (symbol_info.dli_sname) {
        trace.object_function = demangle(symbol_info.dli_sname);
      }
  
      if (!symbol_info.dli_fname) {
        return trace;
      }
  
      trace.object_filename = resolve_exec_path(symbol_info);
      bfd_fileobject *fobj;
      // Before rushing to resolution need to ensure the executable
      // file still can be used. For that compare inode numbers of
      // what is stored by the executable's file path, and in the
      // dli_fname, which not necessarily equals to the executable.
      // It can be a shared library, or /proc/self/exe, and in the
      // latter case has drawbacks. See the exec path resolution for
      // details. In short - the dli object should be used only as
      // the last resort.
      // If inode numbers are equal, it is known dli_fname and the
      // executable file are the same. This is guaranteed by Linux,
      // because if the executable file is changed/deleted, it will
      // be done in a new inode. The old file will be preserved in
      // /proc/self/exe, and may even have inode 0. The latter can
      // happen if the inode was actually reused, and the file was
      // kept only in the main memory.
      //
      struct stat obj_stat;
      struct stat dli_stat;
      if (stat(trace.object_filename.c_str(), &obj_stat) == 0 &&
          stat(symbol_info.dli_fname, &dli_stat) == 0 &&
          obj_stat.st_ino == dli_stat.st_ino) {
        // The executable file, and the shared object containing the
        // address are the same file. Safe to use the original path.
        // this is preferable. Libbfd will search for stripped debug
        // symbols in the same directory.
        fobj = load_object_with_bfd(trace.object_filename);
      } else{
        // The original object file was *deleted*! The only hope is
        // that the debug symbols are either inside the shared
        // object file, or are in the same directory, and this is
        // not /proc/self/exe.
        fobj = nullptr;
      }
      if (fobj == nullptr || !fobj->handle) {
        fobj = load_object_with_bfd(symbol_info.dli_fname);
        if (!fobj->handle) {
          return trace;
        }
      }
  
      find_sym_result *details_selected; // to be filled.
  
      // trace.addr is the next instruction to be executed after returning
      // from the nested stack frame. In C++ this usually relate to the next
      // statement right after the function call that leaded to a new stack
      // frame. This is not usually what you want to see when printing out a
      // stacktrace...
      find_sym_result details_call_site =
          find_symbol_details(fobj, trace.addr, symbol_info.dli_fbase);
      details_selected = &details_call_site;
  
  #if BACKWARD_HAS_UNWIND == 0
      // ...this is why we also try to resolve the symbol that is right
      // before the return address. If we are lucky enough, we will get the
      // line of the function that was called. But if the code is optimized,
      // we might get something absolutely not related since the compiler
      // can reschedule the return address with inline functions and
      // tail-call optimisation (among other things that I don't even know
      // or cannot even dream about with my tiny limited brain).
      find_sym_result details_adjusted_call_site = find_symbol_details(
          fobj, (void *)(uintptr_t(trace.addr) - 1), symbol_info.dli_fbase);
  
      // In debug mode, we should always get the right thing(TM).
      if (details_call_site.found && details_adjusted_call_site.found) {
        // Ok, we assume that details_adjusted_call_site is a better estimation.
        details_selected = &details_adjusted_call_site;
        trace.addr = (void *)(uintptr_t(trace.addr) - 1);
      }
  
      if (details_selected == &details_call_site && details_call_site.found) {
        // we have to re-resolve the symbol in order to reset some
        // internal state in BFD... so we can call backtrace_inliners
        // thereafter...
        details_call_site =
            find_symbol_details(fobj, trace.addr, symbol_info.dli_fbase);
      }
  #endif // BACKWARD_HAS_UNWIND
  
      if (details_selected->found) {
        if (details_selected->filename) {
          trace.source.filename = details_selected->filename;
        }
        trace.source.line = details_selected->line;
  
        if (details_selected->funcname) {
          // this time we get the name of the function where the code is
          // located, instead of the function were the address is
          // located. In short, if the code was inlined, we get the
          // function correspoding to the code. Else we already got in
          // trace.function.
          trace.source.function = demangle(details_selected->funcname);
  
          if (!symbol_info.dli_sname) {
            // for the case dladdr failed to find the symbol name of
            // the function, we might as well try to put something
            // here.
            trace.object_function = trace.source.function;
          }
        }
  
        // Maybe the source of the trace got inlined inside the function
        // (trace.source.function). Let's see if we can get all the inlined
        // calls along the way up to the initial call site.
        trace.inliners = backtrace_inliners(fobj, *details_selected);
  
  #if 0
  			if (trace.inliners.size() == 0) {
  				// Maybe the trace was not inlined... or maybe it was and we
  				// are lacking the debug information. Let's try to make the
  				// world better and see if we can get the line number of the
  				// function (trace.source.function) now.
  				//
  				// We will get the location of where the function start (to be
  				// exact: the first instruction that really start the
  				// function), not where the name of the function is defined.
  				// This can be quite far away from the name of the function
  				// btw.
  				//
  				// If the source of the function is the same as the source of
  				// the trace, we cannot say if the trace was really inlined or
  				// not.  However, if the filename of the source is different
  				// between the function and the trace... we can declare it as
  				// an inliner.  This is not 100% accurate, but better than
  				// nothing.
  
  				if (symbol_info.dli_saddr) {
  					find_sym_result details = find_symbol_details(fobj,
  							symbol_info.dli_saddr,
  							symbol_info.dli_fbase);
  
  					if (details.found) {
  						ResolvedTrace::SourceLoc diy_inliner;
  						diy_inliner.line = details.line;
  						if (details.filename) {
  							diy_inliner.filename = details.filename;
  						}
  						if (details.funcname) {
  							diy_inliner.function = demangle(details.funcname);
  						} else {
  							diy_inliner.function = trace.source.function;
  						}
  						if (diy_inliner != trace.source) {
  							trace.inliners.push_back(diy_inliner);
  						}
  					}
  				}
  			}
  #endif
      }
  
      return trace;
    }
  
  private:
    bool _bfd_loaded;
  
    typedef details::handle<bfd *,
                            details::deleter<bfd_boolean, bfd *, &bfd_close>>
        bfd_handle_t;
  
    typedef details::handle<asymbol **> bfd_symtab_t;
  
    struct bfd_fileobject {
      bfd_handle_t handle;
      bfd_vma base_addr;
      bfd_symtab_t symtab;
      bfd_symtab_t dynamic_symtab;
    };
  
    typedef details::hashtable<std::string, bfd_fileobject>::type fobj_bfd_map_t;
    fobj_bfd_map_t _fobj_bfd_map;
  
    bfd_fileobject *load_object_with_bfd(const std::string &filename_object) {
      using namespace details;
  
      if (!_bfd_loaded) {
        using namespace details;
        bfd_init();
        _bfd_loaded = true;
      }
  
      fobj_bfd_map_t::iterator it = _fobj_bfd_map.find(filename_object);
      if (it != _fobj_bfd_map.end()) {
        return &it->second;
      }
  
      // this new object is empty for now.
      bfd_fileobject *r = &_fobj_bfd_map[filename_object];
  
      // we do the work temporary in this one;
      bfd_handle_t bfd_handle;
  
      int fd = open(filename_object.c_str(), O_RDONLY);
      bfd_handle.reset(bfd_fdopenr(filename_object.c_str(), "default", fd));
      if (!bfd_handle) {
        close(fd);
        return r;
      }
  
      if (!bfd_check_format(bfd_handle.get(), bfd_object)) {
        return r; // not an object? You lose.
      }
  
      if ((bfd_get_file_flags(bfd_handle.get()) & HAS_SYMS) == 0) {
        return r; // that's what happen when you forget to compile in debug.
      }
  
      ssize_t symtab_storage_size = bfd_get_symtab_upper_bound(bfd_handle.get());
  
      ssize_t dyn_symtab_storage_size =
          bfd_get_dynamic_symtab_upper_bound(bfd_handle.get());
  
      if (symtab_storage_size <= 0 && dyn_symtab_storage_size <= 0) {
        return r; // weird, is the file is corrupted?
      }
  
      bfd_symtab_t symtab, dynamic_symtab;
      ssize_t symcount = 0, dyn_symcount = 0;
  
      if (symtab_storage_size > 0) {
        symtab.reset(static_cast<bfd_symbol **>(
            malloc(static_cast<size_t>(symtab_storage_size))));
        symcount = bfd_canonicalize_symtab(bfd_handle.get(), symtab.get());
      }
  
      if (dyn_symtab_storage_size > 0) {
        dynamic_symtab.reset(static_cast<bfd_symbol **>(
            malloc(static_cast<size_t>(dyn_symtab_storage_size))));
        dyn_symcount = bfd_canonicalize_dynamic_symtab(bfd_handle.get(),
                                                       dynamic_symtab.get());
      }
  
      if (symcount <= 0 && dyn_symcount <= 0) {
        return r; // damned, that's a stripped file that you got there!
      }
  
      r->handle = move(bfd_handle);
      r->symtab = move(symtab);
      r->dynamic_symtab = move(dynamic_symtab);
      return r;
    }
  
    struct find_sym_result {
      bool found;
      const char *filename;
      const char *funcname;
      unsigned int line;
    };
  
    struct find_sym_context {
      TraceResolverLinuxImpl *self;
      bfd_fileobject *fobj;
      void *addr;
      void *base_addr;
      find_sym_result result;
    };
  
    find_sym_result find_symbol_details(bfd_fileobject *fobj, void *addr,
                                        void *base_addr) {
      find_sym_context context;
      context.self = this;
      context.fobj = fobj;
      context.addr = addr;
      context.base_addr = base_addr;
      context.result.found = false;
      bfd_map_over_sections(fobj->handle.get(), &find_in_section_trampoline,
                            static_cast<void *>(&context));
      return context.result;
    }
  
    static void find_in_section_trampoline(bfd *, asection *section, void *data) {
      find_sym_context *context = static_cast<find_sym_context *>(data);
      context->self->find_in_section(
          reinterpret_cast<bfd_vma>(context->addr),
          reinterpret_cast<bfd_vma>(context->base_addr), context->fobj, section,
          context->result);
    }
  
    void find_in_section(bfd_vma addr, bfd_vma base_addr, bfd_fileobject *fobj,
                         asection *section, find_sym_result &result) {
      if (result.found)
        return;
  
  #ifdef bfd_get_section_flags
      if ((bfd_get_section_flags(fobj->handle.get(), section) & SEC_ALLOC) == 0)
  #else
      if ((bfd_section_flags(section) & SEC_ALLOC) == 0)
  #endif
        return; // a debug section is never loaded automatically.
  
  #ifdef bfd_get_section_vma
      bfd_vma sec_addr = bfd_get_section_vma(fobj->handle.get(), section);
  #else
      bfd_vma sec_addr = bfd_section_vma(section);
  #endif
  #ifdef bfd_get_section_size
      bfd_size_type size = bfd_get_section_size(section);
  #else
      bfd_size_type size = bfd_section_size(section);
  #endif
  
      // are we in the boundaries of the section?
      if (addr < sec_addr || addr >= sec_addr + size) {
        addr -= base_addr; // oups, a relocated object, lets try again...
        if (addr < sec_addr || addr >= sec_addr + size) {
          return;
        }
      }
  
  #if defined(__clang__)
  #pragma clang diagnostic push
  #pragma clang diagnostic ignored "-Wzero-as-null-pointer-constant"
  #endif
      if (!result.found && fobj->symtab) {
        result.found = bfd_find_nearest_line(
            fobj->handle.get(), section, fobj->symtab.get(), addr - sec_addr,
            &result.filename, &result.funcname, &result.line);
      }
  
      if (!result.found && fobj->dynamic_symtab) {
        result.found = bfd_find_nearest_line(
            fobj->handle.get(), section, fobj->dynamic_symtab.get(),
            addr - sec_addr, &result.filename, &result.funcname, &result.line);
      }
  #if defined(__clang__)
  #pragma clang diagnostic pop
  #endif
    }
  
    ResolvedTrace::source_locs_t
    backtrace_inliners(bfd_fileobject *fobj, find_sym_result previous_result) {
      // This function can be called ONLY after a SUCCESSFUL call to
      // find_symbol_details. The state is global to the bfd_handle.
      ResolvedTrace::source_locs_t results;
      while (previous_result.found) {
        find_sym_result result;
        result.found = bfd_find_inliner_info(fobj->handle.get(), &result.filename,
                                             &result.funcname, &result.line);
  
        if (result
                .found) /* and not (
                              cstrings_eq(previous_result.filename,
                           result.filename) and
                           cstrings_eq(previous_result.funcname, result.funcname)
                              and result.line == previous_result.line
                              )) */
        {
          ResolvedTrace::SourceLoc src_loc;
          src_loc.line = result.line;
          if (result.filename) {
            src_loc.filename = result.filename;
          }
          if (result.funcname) {
            src_loc.function = demangle(result.funcname);
          }
          results.push_back(src_loc);
        }
        previous_result = result;
      }
      return results;
    }
  
    bool cstrings_eq(const char *a, const char *b) {
      if (!a || !b) {
        return false;
      }
      return strcmp(a, b) == 0;
    }
  };
  #endif // BACKWARD_HAS_BFD == 1
  
  #if BACKWARD_HAS_DW == 1
  
  template <>
  class TraceResolverLinuxImpl<trace_resolver_tag::libdw>
      : public TraceResolverLinuxBase {
  public:
    TraceResolverLinuxImpl() : _dwfl_handle_initialized(false) {}
  
    ResolvedTrace resolve(ResolvedTrace trace) override {
      using namespace details;
  
      Dwarf_Addr trace_addr = (Dwarf_Addr)trace.addr;
  
      if (!_dwfl_handle_initialized) {
        // initialize dwfl...
        _dwfl_cb.reset(new Dwfl_Callbacks);
        _dwfl_cb->find_elf = &dwfl_linux_proc_find_elf;
        _dwfl_cb->find_debuginfo = &dwfl_standard_find_debuginfo;
        _dwfl_cb->debuginfo_path = 0;
  
        _dwfl_handle.reset(dwfl_begin(_dwfl_cb.get()));
        _dwfl_handle_initialized = true;
  
        if (!_dwfl_handle) {
          return trace;
        }
  
        // ...from the current process.
        dwfl_report_begin(_dwfl_handle.get());
        int r = dwfl_linux_proc_report(_dwfl_handle.get(), getpid());
        dwfl_report_end(_dwfl_handle.get(), NULL, NULL);
        if (r < 0) {
          return trace;
        }
      }
  
      if (!_dwfl_handle) {
        return trace;
      }
  
      // find the module (binary object) that contains the trace's address.
      // This is not using any debug information, but the addresses ranges of
      // all the currently loaded binary object.
      Dwfl_Module *mod = dwfl_addrmodule(_dwfl_handle.get(), trace_addr);
      if (mod) {
        // now that we found it, lets get the name of it, this will be the
        // full path to the running binary or one of the loaded library.
        const char *module_name = dwfl_module_info(mod, 0, 0, 0, 0, 0, 0, 0);
        if (module_name) {
          trace.object_filename = module_name;
        }
        // We also look after the name of the symbol, equal or before this
        // address. This is found by walking the symtab. We should get the
        // symbol corresponding to the function (mangled) containing the
        // address. If the code corresponding to the address was inlined,
        // this is the name of the out-most inliner function.
        const char *sym_name = dwfl_module_addrname(mod, trace_addr);
        if (sym_name) {
          trace.object_function = demangle(sym_name);
        }
      }
  
      // now let's get serious, and find out the source location (file and
      // line number) of the address.
  
      // This function will look in .debug_aranges for the address and map it
      // to the location of the compilation unit DIE in .debug_info and
      // return it.
      Dwarf_Addr mod_bias = 0;
      Dwarf_Die *cudie = dwfl_module_addrdie(mod, trace_addr, &mod_bias);
  
  #if 1
      if (!cudie) {
        // Sadly clang does not generate the section .debug_aranges, thus
        // dwfl_module_addrdie will fail early. Clang doesn't either set
        // the lowpc/highpc/range info for every compilation unit.
        //
        // So in order to save the world:
        // for every compilation unit, we will iterate over every single
        // DIEs. Normally functions should have a lowpc/highpc/range, which
        // we will use to infer the compilation unit.
  
        // note that this is probably badly inefficient.
        while ((cudie = dwfl_module_nextcu(mod, cudie, &mod_bias))) {
          Dwarf_Die die_mem;
          Dwarf_Die *fundie =
              find_fundie_by_pc(cudie, trace_addr - mod_bias, &die_mem);
          if (fundie) {
            break;
          }
        }
      }
  #endif
  
  //#define BACKWARD_I_DO_NOT_RECOMMEND_TO_ENABLE_THIS_HORRIBLE_PIECE_OF_CODE
  #ifdef BACKWARD_I_DO_NOT_RECOMMEND_TO_ENABLE_THIS_HORRIBLE_PIECE_OF_CODE
      if (!cudie) {
        // If it's still not enough, lets dive deeper in the shit, and try
        // to save the world again: for every compilation unit, we will
        // load the corresponding .debug_line section, and see if we can
        // find our address in it.
  
        Dwarf_Addr cfi_bias;
        Dwarf_CFI *cfi_cache = dwfl_module_eh_cfi(mod, &cfi_bias);
  
        Dwarf_Addr bias;
        while ((cudie = dwfl_module_nextcu(mod, cudie, &bias))) {
          if (dwarf_getsrc_die(cudie, trace_addr - bias)) {
  
            // ...but if we get a match, it might be a false positive
            // because our (address - bias) might as well be valid in a
            // different compilation unit. So we throw our last card on
            // the table and lookup for the address into the .eh_frame
            // section.
  
            handle<Dwarf_Frame *> frame;
            dwarf_cfi_addrframe(cfi_cache, trace_addr - cfi_bias, &frame);
            if (frame) {
              break;
            }
          }
        }
      }
  #endif
  
      if (!cudie) {
        return trace; // this time we lost the game :/
      }
  
      // Now that we have a compilation unit DIE, this function will be able
      // to load the corresponding section in .debug_line (if not already
      // loaded) and hopefully find the source location mapped to our
      // address.
      Dwarf_Line *srcloc = dwarf_getsrc_die(cudie, trace_addr - mod_bias);
  
      if (srcloc) {
        const char *srcfile = dwarf_linesrc(srcloc, 0, 0);
        if (srcfile) {
          trace.source.filename = srcfile;
        }
        int line = 0, col = 0;
        dwarf_lineno(srcloc, &line);
        dwarf_linecol(srcloc, &col);
        trace.source.line = line;
        trace.source.col = col;
      }
  
      deep_first_search_by_pc(cudie, trace_addr - mod_bias,
                              inliners_search_cb(trace));
      if (trace.source.function.size() == 0) {
        // fallback.
        trace.source.function = trace.object_function;
      }
  
      return trace;
    }
  
  private:
    typedef details::handle<Dwfl *, details::deleter<void, Dwfl *, &dwfl_end>>
        dwfl_handle_t;
    details::handle<Dwfl_Callbacks *, details::default_delete<Dwfl_Callbacks *>>
        _dwfl_cb;
    dwfl_handle_t _dwfl_handle;
    bool _dwfl_handle_initialized;
  
    // defined here because in C++98, template function cannot take locally
    // defined types... grrr.
    struct inliners_search_cb {
      void operator()(Dwarf_Die *die) {
        switch (dwarf_tag(die)) {
          const char *name;
        case DW_TAG_subprogram:
          if ((name = dwarf_diename(die))) {
            trace.source.function = name;
          }
          break;
  
        case DW_TAG_inlined_subroutine:
          ResolvedTrace::SourceLoc sloc;
          Dwarf_Attribute attr_mem;
  
          if ((name = dwarf_diename(die))) {
            sloc.function = name;
          }
          if ((name = die_call_file(die))) {
            sloc.filename = name;
          }
  
          Dwarf_Word line = 0, col = 0;
          dwarf_formudata(dwarf_attr(die, DW_AT_call_line, &attr_mem), &line);
          dwarf_formudata(dwarf_attr(die, DW_AT_call_column, &attr_mem), &col);
          sloc.line = (unsigned)line;
          sloc.col = (unsigned)col;
  
          trace.inliners.push_back(sloc);
          break;
        };
      }
      ResolvedTrace &trace;
      inliners_search_cb(ResolvedTrace &t) : trace(t) {}
    };
  
    static bool die_has_pc(Dwarf_Die *die, Dwarf_Addr pc) {
      Dwarf_Addr low, high;
  
      // continuous range
      if (dwarf_hasattr(die, DW_AT_low_pc) && dwarf_hasattr(die, DW_AT_high_pc)) {
        if (dwarf_lowpc(die, &low) != 0) {
          return false;
        }
        if (dwarf_highpc(die, &high) != 0) {
          Dwarf_Attribute attr_mem;
          Dwarf_Attribute *attr = dwarf_attr(die, DW_AT_high_pc, &attr_mem);
          Dwarf_Word value;
          if (dwarf_formudata(attr, &value) != 0) {
            return false;
          }
          high = low + value;
        }
        return pc >= low && pc < high;
      }
  
      // non-continuous range.
      Dwarf_Addr base;
      ptrdiff_t offset = 0;
      while ((offset = dwarf_ranges(die, offset, &base, &low, &high)) > 0) {
        if (pc >= low && pc < high) {
          return true;
        }
      }
      return false;
    }
  
    static Dwarf_Die *find_fundie_by_pc(Dwarf_Die *parent_die, Dwarf_Addr pc,
                                        Dwarf_Die *result) {
      if (dwarf_child(parent_die, result) != 0) {
        return 0;
      }
  
      Dwarf_Die *die = result;
      do {
        switch (dwarf_tag(die)) {
        case DW_TAG_subprogram:
        case DW_TAG_inlined_subroutine:
          if (die_has_pc(die, pc)) {
            return result;
          }
        };
        bool declaration = false;
        Dwarf_Attribute attr_mem;
        dwarf_formflag(dwarf_attr(die, DW_AT_declaration, &attr_mem),
                       &declaration);
        if (!declaration) {
          // let's be curious and look deeper in the tree,
          // function are not necessarily at the first level, but
          // might be nested inside a namespace, structure etc.
          Dwarf_Die die_mem;
          Dwarf_Die *indie = find_fundie_by_pc(die, pc, &die_mem);
          if (indie) {
            *result = die_mem;
            return result;
          }
        }
      } while (dwarf_siblingof(die, result) == 0);
      return 0;
    }
  
    template <typename CB>
    static bool deep_first_search_by_pc(Dwarf_Die *parent_die, Dwarf_Addr pc,
                                        CB cb) {
      Dwarf_Die die_mem;
      if (dwarf_child(parent_die, &die_mem) != 0) {
        return false;
      }
  
      bool branch_has_pc = false;
      Dwarf_Die *die = &die_mem;
      do {
        bool declaration = false;
        Dwarf_Attribute attr_mem;
        dwarf_formflag(dwarf_attr(die, DW_AT_declaration, &attr_mem),
                       &declaration);
        if (!declaration) {
          // let's be curious and look deeper in the tree, function are
          // not necessarily at the first level, but might be nested
          // inside a namespace, structure, a function, an inlined
          // function etc.
          branch_has_pc = deep_first_search_by_pc(die, pc, cb);
        }
        if (!branch_has_pc) {
          branch_has_pc = die_has_pc(die, pc);
        }
        if (branch_has_pc) {
          cb(die);
        }
      } while (dwarf_siblingof(die, &die_mem) == 0);
      return branch_has_pc;
    }
  
    static const char *die_call_file(Dwarf_Die *die) {
      Dwarf_Attribute attr_mem;
      Dwarf_Word file_idx = 0;
  
      dwarf_formudata(dwarf_attr(die, DW_AT_call_file, &attr_mem), &file_idx);
  
      if (file_idx == 0) {
        return 0;
      }
  
      Dwarf_Die die_mem;
      Dwarf_Die *cudie = dwarf_diecu(die, &die_mem, 0, 0);
      if (!cudie) {
        return 0;
      }
  
      Dwarf_Files *files = 0;
      size_t nfiles;
      dwarf_getsrcfiles(cudie, &files, &nfiles);
      if (!files) {
        return 0;
      }
  
      return dwarf_filesrc(files, file_idx, 0, 0);
    }
  };
  #endif // BACKWARD_HAS_DW == 1
  
  #if BACKWARD_HAS_DWARF == 1
  
  template <>
  class TraceResolverLinuxImpl<trace_resolver_tag::libdwarf>
      : public TraceResolverLinuxBase {
  public:
    TraceResolverLinuxImpl() : _dwarf_loaded(false) {}
  
    ResolvedTrace resolve(ResolvedTrace trace) override {
      // trace.addr is a virtual address in memory pointing to some code.
      // Let's try to find from which loaded object it comes from.
      // The loaded object can be yourself btw.
  
      Dl_info symbol_info;
      int dladdr_result = 0;
  #if defined(__GLIBC__)
      link_map *link_map;
      // We request the link map so we can get information about offsets
      dladdr_result =
          dladdr1(trace.addr, &symbol_info, reinterpret_cast<void **>(&link_map),
                  RTLD_DL_LINKMAP);
  #else
      // Android doesn't have dladdr1. Don't use the linker map.
      dladdr_result = dladdr(trace.addr, &symbol_info);
  #endif
      if (!dladdr_result) {
        return trace; // dat broken trace...
      }
  
      // Now we get in symbol_info:
      // .dli_fname:
      //      pathname of the shared object that contains the address.
      // .dli_fbase:
      //      where the object is loaded in memory.
      // .dli_sname:
      //      the name of the nearest symbol to trace.addr, we expect a
      //      function name.
      // .dli_saddr:
      //      the exact address corresponding to .dli_sname.
      //
      // And in link_map:
      // .l_addr:
      //      difference between the address in the ELF file and the address
      //      in memory
      // l_name:
      //      absolute pathname where the object was found
  
      if (symbol_info.dli_sname) {
        trace.object_function = demangle(symbol_info.dli_sname);
      }
  
      if (!symbol_info.dli_fname) {
        return trace;
      }
  
      trace.object_filename = resolve_exec_path(symbol_info);
      dwarf_fileobject &fobj = load_object_with_dwarf(symbol_info.dli_fname);
      if (!fobj.dwarf_handle) {
        return trace; // sad, we couldn't load the object :(
      }
  
  #if defined(__GLIBC__)
      // Convert the address to a module relative one by looking at
      // the module's loading address in the link map
      Dwarf_Addr address = reinterpret_cast<uintptr_t>(trace.addr) -
                           reinterpret_cast<uintptr_t>(link_map->l_addr);
  #else
      Dwarf_Addr address = reinterpret_cast<uintptr_t>(trace.addr);
  #endif
  
      if (trace.object_function.empty()) {
        symbol_cache_t::iterator it = fobj.symbol_cache.lower_bound(address);
  
        if (it != fobj.symbol_cache.end()) {
          if (it->first != address) {
            if (it != fobj.symbol_cache.begin()) {
              --it;
            }
          }
          trace.object_function = demangle(it->second.c_str());
        }
      }
  
      // Get the Compilation Unit DIE for the address
      Dwarf_Die die = find_die(fobj, address);
  
      if (!die) {
        return trace; // this time we lost the game :/
      }
  
      // libdwarf doesn't give us direct access to its objects, it always
      // allocates a copy for the caller. We keep that copy alive in a cache
      // and we deallocate it later when it's no longer required.
      die_cache_entry &die_object = get_die_cache(fobj, die);
      if (die_object.isEmpty())
        return trace; // We have no line section for this DIE
  
      die_linemap_t::iterator it = die_object.line_section.lower_bound(address);
  
      if (it != die_object.line_section.end()) {
        if (it->first != address) {
          if (it == die_object.line_section.begin()) {
            // If we are on the first item of the line section
            // but the address does not match it means that
            // the address is below the range of the DIE. Give up.
            return trace;
          } else {
            --it;
          }
        }
      } else {
        return trace; // We didn't find the address.
      }
  
      // Get the Dwarf_Line that the address points to and call libdwarf
      // to get source file, line and column info.
      Dwarf_Line line = die_object.line_buffer[it->second];
      Dwarf_Error error = DW_DLE_NE;
  
      char *filename;
      if (dwarf_linesrc(line, &filename, &error) == DW_DLV_OK) {
        trace.source.filename = std::string(filename);
        dwarf_dealloc(fobj.dwarf_handle.get(), filename, DW_DLA_STRING);
      }
  
      Dwarf_Unsigned number = 0;
      if (dwarf_lineno(line, &number, &error) == DW_DLV_OK) {
        trace.source.line = number;
      } else {
        trace.source.line = 0;
      }
  
      if (dwarf_lineoff_b(line, &number, &error) == DW_DLV_OK) {
        trace.source.col = number;
      } else {
        trace.source.col = 0;
      }
  
      std::vector<std::string> namespace_stack;
      deep_first_search_by_pc(fobj, die, address, namespace_stack,
                              inliners_search_cb(trace, fobj, die));
  
      dwarf_dealloc(fobj.dwarf_handle.get(), die, DW_DLA_DIE);
  
      return trace;
    }
  
  public:
    static int close_dwarf(Dwarf_Debug dwarf) {
      return dwarf_finish(dwarf, NULL);
    }
  
  private:
    bool _dwarf_loaded;
  
    typedef details::handle<int, details::deleter<int, int, &::close>>
        dwarf_file_t;
  
    typedef details::handle<Elf *, details::deleter<int, Elf *, &elf_end>>
        dwarf_elf_t;
  
    typedef details::handle<Dwarf_Debug,
                            details::deleter<int, Dwarf_Debug, &close_dwarf>>
        dwarf_handle_t;
  
    typedef std::map<Dwarf_Addr, int> die_linemap_t;
  
    typedef std::map<Dwarf_Off, Dwarf_Off> die_specmap_t;
  
    struct die_cache_entry {
      die_specmap_t spec_section;
      die_linemap_t line_section;
      Dwarf_Line *line_buffer;
      Dwarf_Signed line_count;
      Dwarf_Line_Context line_context;
  
      inline bool isEmpty() {
        return line_buffer == NULL || line_count == 0 || line_context == NULL ||
               line_section.empty();
      }
  
      die_cache_entry() : line_buffer(0), line_count(0), line_context(0) {}
  
      ~die_cache_entry() {
        if (line_context) {
          dwarf_srclines_dealloc_b(line_context);
        }
      }
    };
  
    typedef std::map<Dwarf_Off, die_cache_entry> die_cache_t;
  
    typedef std::map<uintptr_t, std::string> symbol_cache_t;
  
    struct dwarf_fileobject {
      dwarf_file_t file_handle;
      dwarf_elf_t elf_handle;
      dwarf_handle_t dwarf_handle;
      symbol_cache_t symbol_cache;
  
      // Die cache
      die_cache_t die_cache;
      die_cache_entry *current_cu;
    };
  
    typedef details::hashtable<std::string, dwarf_fileobject>::type
        fobj_dwarf_map_t;
    fobj_dwarf_map_t _fobj_dwarf_map;
  
    static bool cstrings_eq(const char *a, const char *b) {
      if (!a || !b) {
        return false;
      }
      return strcmp(a, b) == 0;
    }
  
    dwarf_fileobject &load_object_with_dwarf(const std::string &filename_object) {
  
      if (!_dwarf_loaded) {
        // Set the ELF library operating version
        // If that fails there's nothing we can do
        _dwarf_loaded = elf_version(EV_CURRENT) != EV_NONE;
      }
  
      fobj_dwarf_map_t::iterator it = _fobj_dwarf_map.find(filename_object);
      if (it != _fobj_dwarf_map.end()) {
        return it->second;
      }
  
      // this new object is empty for now
      dwarf_fileobject &r = _fobj_dwarf_map[filename_object];
  
      dwarf_file_t file_handle;
      file_handle.reset(open(filename_object.c_str(), O_RDONLY));
      if (file_handle.get() < 0) {
        return r;
      }
  
      // Try to get an ELF handle. We need to read the ELF sections
      // because we want to see if there is a .gnu_debuglink section
      // that points to a split debug file
      dwarf_elf_t elf_handle;
      elf_handle.reset(elf_begin(file_handle.get(), ELF_C_READ, NULL));
      if (!elf_handle) {
        return r;
      }
  
      const char *e_ident = elf_getident(elf_handle.get(), 0);
      if (!e_ident) {
        return r;
      }
  
      // Get the number of sections
      // We use the new APIs as elf_getshnum is deprecated
      size_t shdrnum = 0;
      if (elf_getshdrnum(elf_handle.get(), &shdrnum) == -1) {
        return r;
      }
  
      // Get the index to the string section
      size_t shdrstrndx = 0;
      if (elf_getshdrstrndx(elf_handle.get(), &shdrstrndx) == -1) {
        return r;
      }
  
      std::string debuglink;
      // Iterate through the ELF sections to try to get a gnu_debuglink
      // note and also to cache the symbol table.
      // We go the preprocessor way to avoid having to create templated
      // classes or using gelf (which might throw a compiler error if 64 bit
      // is not supported
  #define ELF_GET_DATA(ARCH)                                                     \
    Elf_Scn *elf_section = 0;                                                    \
    Elf_Data *elf_data = 0;                                                      \
    Elf##ARCH##_Shdr *section_header = 0;                                        \
    Elf_Scn *symbol_section = 0;                                                 \
    size_t symbol_count = 0;                                                     \
    size_t symbol_strings = 0;                                                   \
    Elf##ARCH##_Sym *symbol = 0;                                                 \
    const char *section_name = 0;                                                \
                                                                                 \
    while ((elf_section = elf_nextscn(elf_handle.get(), elf_section)) != NULL) { \
      section_header = elf##ARCH##_getshdr(elf_section);                         \
      if (section_header == NULL) {                                              \
        return r;                                                                \
      }                                                                          \
                                                                                 \
      if ((section_name = elf_strptr(elf_handle.get(), shdrstrndx,               \
                                     section_header->sh_name)) == NULL) {        \
        return r;                                                                \
      }                                                                          \
                                                                                 \
      if (cstrings_eq(section_name, ".gnu_debuglink")) {                         \
        elf_data = elf_getdata(elf_section, NULL);                               \
        if (elf_data && elf_data->d_size > 0) {                                  \
          debuglink =                                                            \
              std::string(reinterpret_cast<const char *>(elf_data->d_buf));      \
        }                                                                        \
      }                                                                          \
                                                                                 \
      switch (section_header->sh_type) {                                         \
      case SHT_SYMTAB:                                                           \
        symbol_section = elf_section;                                            \
        symbol_count = section_header->sh_size / section_header->sh_entsize;     \
        symbol_strings = section_header->sh_link;                                \
        break;                                                                   \
                                                                                 \
      /* We use .dynsyms as a last resort, we prefer .symtab */                  \
      case SHT_DYNSYM:                                                           \
        if (!symbol_section) {                                                   \
          symbol_section = elf_section;                                          \
          symbol_count = section_header->sh_size / section_header->sh_entsize;   \
          symbol_strings = section_header->sh_link;                              \
        }                                                                        \
        break;                                                                   \
      }                                                                          \
    }                                                                            \
                                                                                 \
    if (symbol_section && symbol_count && symbol_strings) {                      \
      elf_data = elf_getdata(symbol_section, NULL);                              \
      symbol = reinterpret_cast<Elf##ARCH##_Sym *>(elf_data->d_buf);             \
      for (size_t i = 0; i < symbol_count; ++i) {                                \
        int type = ELF##ARCH##_ST_TYPE(symbol->st_info);                         \
        if (type == STT_FUNC && symbol->st_value > 0) {                          \
          r.symbol_cache[symbol->st_value] = std::string(                        \
              elf_strptr(elf_handle.get(), symbol_strings, symbol->st_name));    \
        }                                                                        \
        ++symbol;                                                                \
      }                                                                          \
    }
  
      if (e_ident[EI_CLASS] == ELFCLASS32) {
        ELF_GET_DATA(32)
      } else if (e_ident[EI_CLASS] == ELFCLASS64) {
        // libelf might have been built without 64 bit support
  #if __LIBELF64
        ELF_GET_DATA(64)
  #endif
      }
  
      if (!debuglink.empty()) {
        // We have a debuglink section! Open an elf instance on that
        // file instead. If we can't open the file, then return
        // the elf handle we had already opened.
        dwarf_file_t debuglink_file;
        debuglink_file.reset(open(debuglink.c_str(), O_RDONLY));
        if (debuglink_file.get() > 0) {
          dwarf_elf_t debuglink_elf;
          debuglink_elf.reset(elf_begin(debuglink_file.get(), ELF_C_READ, NULL));
  
          // If we have a valid elf handle, return the new elf handle
          // and file handle and discard the original ones
          if (debuglink_elf) {
            elf_handle = move(debuglink_elf);
            file_handle = move(debuglink_file);
          }
        }
      }
  
      // Ok, we have a valid ELF handle, let's try to get debug symbols
      Dwarf_Debug dwarf_debug;
      Dwarf_Error error = DW_DLE_NE;
      dwarf_handle_t dwarf_handle;
  
      int dwarf_result = dwarf_elf_init(elf_handle.get(), DW_DLC_READ, NULL, NULL,
                                        &dwarf_debug, &error);
  
      // We don't do any special handling for DW_DLV_NO_ENTRY specially.
      // If we get an error, or the file doesn't have debug information
      // we just return.
      if (dwarf_result != DW_DLV_OK) {
        return r;
      }
  
      dwarf_handle.reset(dwarf_debug);
  
      r.file_handle = move(file_handle);
      r.elf_handle = move(elf_handle);
      r.dwarf_handle = move(dwarf_handle);
  
      return r;
    }
  
    die_cache_entry &get_die_cache(dwarf_fileobject &fobj, Dwarf_Die die) {
      Dwarf_Error error = DW_DLE_NE;
  
      // Get the die offset, we use it as the cache key
      Dwarf_Off die_offset;
      if (dwarf_dieoffset(die, &die_offset, &error) != DW_DLV_OK) {
        die_offset = 0;
      }
  
      die_cache_t::iterator it = fobj.die_cache.find(die_offset);
  
      if (it != fobj.die_cache.end()) {
        fobj.current_cu = &it->second;
        return it->second;
      }
  
      die_cache_entry &de = fobj.die_cache[die_offset];
      fobj.current_cu = &de;
  
      Dwarf_Addr line_addr;
      Dwarf_Small table_count;
  
      // The addresses in the line section are not fully sorted (they might
      // be sorted by block of code belonging to the same file), which makes
      // it necessary to do so before searching is possible.
      //
      // As libdwarf allocates a copy of everything, let's get the contents
      // of the line section and keep it around. We also create a map of
      // program counter to line table indices so we can search by address
      // and get the line buffer index.
      //
      // To make things more difficult, the same address can span more than
      // one line, so we need to keep the index pointing to the first line
      // by using insert instead of the map's [ operator.
  
      // Get the line context for the DIE
      if (dwarf_srclines_b(die, 0, &table_count, &de.line_context, &error) ==
          DW_DLV_OK) {
        // Get the source lines for this line context, to be deallocated
        // later
        if (dwarf_srclines_from_linecontext(de.line_context, &de.line_buffer,
                                            &de.line_count,
                                            &error) == DW_DLV_OK) {
  
          // Add all the addresses to our map
          for (int i = 0; i < de.line_count; i++) {
            if (dwarf_lineaddr(de.line_buffer[i], &line_addr, &error) !=
                DW_DLV_OK) {
              line_addr = 0;
            }
            de.line_section.insert(std::pair<Dwarf_Addr, int>(line_addr, i));
          }
        }
      }
  
      // For each CU, cache the function DIEs that contain the
      // DW_AT_specification attribute. When building with -g3 the function
      // DIEs are separated in declaration and specification, with the
      // declaration containing only the name and parameters and the
      // specification the low/high pc and other compiler attributes.
      //
      // We cache those specifications so we don't skip over the declarations,
      // because they have no pc, and we can do namespace resolution for
      // DWARF function names.
      Dwarf_Debug dwarf = fobj.dwarf_handle.get();
      Dwarf_Die current_die = 0;
      if (dwarf_child(die, &current_die, &error) == DW_DLV_OK) {
        for (;;) {
          Dwarf_Die sibling_die = 0;
  
          Dwarf_Half tag_value;
          dwarf_tag(current_die, &tag_value, &error);
  
          if (tag_value == DW_TAG_subprogram ||
              tag_value == DW_TAG_inlined_subroutine) {
  
            Dwarf_Bool has_attr = 0;
            if (dwarf_hasattr(current_die, DW_AT_specification, &has_attr,
                              &error) == DW_DLV_OK) {
              if (has_attr) {
                Dwarf_Attribute attr_mem;
                if (dwarf_attr(current_die, DW_AT_specification, &attr_mem,
                               &error) == DW_DLV_OK) {
                  Dwarf_Off spec_offset = 0;
                  if (dwarf_formref(attr_mem, &spec_offset, &error) ==
                      DW_DLV_OK) {
                    Dwarf_Off spec_die_offset;
                    if (dwarf_dieoffset(current_die, &spec_die_offset, &error) ==
                        DW_DLV_OK) {
                      de.spec_section[spec_offset] = spec_die_offset;
                    }
                  }
                }
                dwarf_dealloc(dwarf, attr_mem, DW_DLA_ATTR);
              }
            }
          }
  
          int result = dwarf_siblingof(dwarf, current_die, &sibling_die, &error);
          if (result == DW_DLV_ERROR) {
            break;
          } else if (result == DW_DLV_NO_ENTRY) {
            break;
          }
  
          if (current_die != die) {
            dwarf_dealloc(dwarf, current_die, DW_DLA_DIE);
            current_die = 0;
          }
  
          current_die = sibling_die;
        }
      }
      return de;
    }
  
    static Dwarf_Die get_referenced_die(Dwarf_Debug dwarf, Dwarf_Die die,
                                        Dwarf_Half attr, bool global) {
      Dwarf_Error error = DW_DLE_NE;
      Dwarf_Attribute attr_mem;
  
      Dwarf_Die found_die = NULL;
      if (dwarf_attr(die, attr, &attr_mem, &error) == DW_DLV_OK) {
        Dwarf_Off offset;
        int result = 0;
        if (global) {
          result = dwarf_global_formref(attr_mem, &offset, &error);
        } else {
          result = dwarf_formref(attr_mem, &offset, &error);
        }
  
        if (result == DW_DLV_OK) {
          if (dwarf_offdie(dwarf, offset, &found_die, &error) != DW_DLV_OK) {
            found_die = NULL;
          }
        }
        dwarf_dealloc(dwarf, attr_mem, DW_DLA_ATTR);
      }
      return found_die;
    }
  
    static std::string get_referenced_die_name(Dwarf_Debug dwarf, Dwarf_Die die,
                                               Dwarf_Half attr, bool global) {
      Dwarf_Error error = DW_DLE_NE;
      std::string value;
  
      Dwarf_Die found_die = get_referenced_die(dwarf, die, attr, global);
  
      if (found_die) {
        char *name;
        if (dwarf_diename(found_die, &name, &error) == DW_DLV_OK) {
          if (name) {
            value = std::string(name);
          }
          dwarf_dealloc(dwarf, name, DW_DLA_STRING);
        }
        dwarf_dealloc(dwarf, found_die, DW_DLA_DIE);
      }
  
      return value;
    }
  
    // Returns a spec DIE linked to the passed one. The caller should
    // deallocate the DIE
    static Dwarf_Die get_spec_die(dwarf_fileobject &fobj, Dwarf_Die die) {
      Dwarf_Debug dwarf = fobj.dwarf_handle.get();
      Dwarf_Error error = DW_DLE_NE;
      Dwarf_Off die_offset;
      if (fobj.current_cu &&
          dwarf_die_CU_offset(die, &die_offset, &error) == DW_DLV_OK) {
        die_specmap_t::iterator it =
            fobj.current_cu->spec_section.find(die_offset);
  
        // If we have a DIE that completes the current one, check if
        // that one has the pc we are looking for
        if (it != fobj.current_cu->spec_section.end()) {
          Dwarf_Die spec_die = 0;
          if (dwarf_offdie(dwarf, it->second, &spec_die, &error) == DW_DLV_OK) {
            return spec_die;
          }
        }
      }
  
      // Maybe we have an abstract origin DIE with the function information?
      return get_referenced_die(fobj.dwarf_handle.get(), die,
                                DW_AT_abstract_origin, true);
    }
  
    static bool die_has_pc(dwarf_fileobject &fobj, Dwarf_Die die, Dwarf_Addr pc) {
      Dwarf_Addr low_pc = 0, high_pc = 0;
      Dwarf_Half high_pc_form = 0;
      Dwarf_Form_Class return_class;
      Dwarf_Error error = DW_DLE_NE;
      Dwarf_Debug dwarf = fobj.dwarf_handle.get();
      bool has_lowpc = false;
      bool has_highpc = false;
      bool has_ranges = false;
  
      if (dwarf_lowpc(die, &low_pc, &error) == DW_DLV_OK) {
        // If we have a low_pc check if there is a high pc.
        // If we don't have a high pc this might mean we have a base
        // address for the ranges list or just an address.
        has_lowpc = true;
  
        if (dwarf_highpc_b(die, &high_pc, &high_pc_form, &return_class, &error) ==
            DW_DLV_OK) {
          // We do have a high pc. In DWARF 4+ this is an offset from the
          // low pc, but in earlier versions it's an absolute address.
  
          has_highpc = true;
          // In DWARF 2/3 this would be a DW_FORM_CLASS_ADDRESS
          if (return_class == DW_FORM_CLASS_CONSTANT) {
            high_pc = low_pc + high_pc;
          }
  
          // We have low and high pc, check if our address
          // is in that range
          return pc >= low_pc && pc < high_pc;
        }
      } else {
        // Reset the low_pc, in case dwarf_lowpc failing set it to some
        // undefined value.
        low_pc = 0;
      }
  
      // Check if DW_AT_ranges is present and search for the PC in the
      // returned ranges list. We always add the low_pc, as it not set it will
      // be 0, in case we had a DW_AT_low_pc and DW_AT_ranges pair
      bool result = false;
  
      Dwarf_Attribute attr;
      if (dwarf_attr(die, DW_AT_ranges, &attr, &error) == DW_DLV_OK) {
  
        Dwarf_Off offset;
        if (dwarf_global_formref(attr, &offset, &error) == DW_DLV_OK) {
          Dwarf_Ranges *ranges;
          Dwarf_Signed ranges_count = 0;
          Dwarf_Unsigned byte_count = 0;
  
          if (dwarf_get_ranges_a(dwarf, offset, die, &ranges, &ranges_count,
                                 &byte_count, &error) == DW_DLV_OK) {
            has_ranges = ranges_count != 0;
            for (int i = 0; i < ranges_count; i++) {
              if (ranges[i].dwr_addr1 != 0 &&
                  pc >= ranges[i].dwr_addr1 + low_pc &&
                  pc < ranges[i].dwr_addr2 + low_pc) {
                result = true;
                break;
              }
            }
            dwarf_ranges_dealloc(dwarf, ranges, ranges_count);
          }
        }
      }
  
      // Last attempt. We might have a single address set as low_pc.
      if (!result && low_pc != 0 && pc == low_pc) {
        result = true;
      }
  
      // If we don't have lowpc, highpc and ranges maybe this DIE is a
      // declaration that relies on a DW_AT_specification DIE that happens
      // later. Use the specification cache we filled when we loaded this CU.
      if (!result && (!has_lowpc && !has_highpc && !has_ranges)) {
        Dwarf_Die spec_die = get_spec_die(fobj, die);
        if (spec_die) {
          result = die_has_pc(fobj, spec_die, pc);
          dwarf_dealloc(dwarf, spec_die, DW_DLA_DIE);
        }
      }
  
      return result;
    }
  
    static void get_type(Dwarf_Debug dwarf, Dwarf_Die die, std::string &type) {
      Dwarf_Error error = DW_DLE_NE;
  
      Dwarf_Die child = 0;
      if (dwarf_child(die, &child, &error) == DW_DLV_OK) {
        get_type(dwarf, child, type);
      }
  
      if (child) {
        type.insert(0, "::");
        dwarf_dealloc(dwarf, child, DW_DLA_DIE);
      }
  
      char *name;
      if (dwarf_diename(die, &name, &error) == DW_DLV_OK) {
        type.insert(0, std::string(name));
        dwarf_dealloc(dwarf, name, DW_DLA_STRING);
      } else {
        type.insert(0, "<unknown>");
      }
    }
  
    static std::string get_type_by_signature(Dwarf_Debug dwarf, Dwarf_Die die) {
      Dwarf_Error error = DW_DLE_NE;
  
      Dwarf_Sig8 signature;
      Dwarf_Bool has_attr = 0;
      if (dwarf_hasattr(die, DW_AT_signature, &has_attr, &error) == DW_DLV_OK) {
        if (has_attr) {
          Dwarf_Attribute attr_mem;
          if (dwarf_attr(die, DW_AT_signature, &attr_mem, &error) == DW_DLV_OK) {
            if (dwarf_formsig8(attr_mem, &signature, &error) != DW_DLV_OK) {
              return std::string("<no type signature>");
            }
          }
          dwarf_dealloc(dwarf, attr_mem, DW_DLA_ATTR);
        }
      }
  
      Dwarf_Unsigned next_cu_header;
      Dwarf_Sig8 tu_signature;
      std::string result;
      bool found = false;
  
      while (dwarf_next_cu_header_d(dwarf, 0, 0, 0, 0, 0, 0, 0, &tu_signature, 0,
                                    &next_cu_header, 0, &error) == DW_DLV_OK) {
  
        if (strncmp(signature.signature, tu_signature.signature, 8) == 0) {
          Dwarf_Die type_cu_die = 0;
          if (dwarf_siblingof_b(dwarf, 0, 0, &type_cu_die, &error) == DW_DLV_OK) {
            Dwarf_Die child_die = 0;
            if (dwarf_child(type_cu_die, &child_die, &error) == DW_DLV_OK) {
              get_type(dwarf, child_die, result);
              found = !result.empty();
              dwarf_dealloc(dwarf, child_die, DW_DLA_DIE);
            }
            dwarf_dealloc(dwarf, type_cu_die, DW_DLA_DIE);
          }
        }
      }
  
      if (found) {
        while (dwarf_next_cu_header_d(dwarf, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                                      &next_cu_header, 0, &error) == DW_DLV_OK) {
          // Reset the cu header state. Unfortunately, libdwarf's
          // next_cu_header API keeps its own iterator per Dwarf_Debug
          // that can't be reset. We need to keep fetching elements until
          // the end.
        }
      } else {
        // If we couldn't resolve the type just print out the signature
        std::ostringstream string_stream;
        string_stream << "<0x" << std::hex << std::setfill('0');
        for (int i = 0; i < 8; ++i) {
          string_stream << std::setw(2) << std::hex
                        << (int)(unsigned char)(signature.signature[i]);
        }
        string_stream << ">";
        result = string_stream.str();
      }
      return result;
    }
  
    struct type_context_t {
      bool is_const;
      bool is_typedef;
      bool has_type;
      bool has_name;
      std::string text;
  
      type_context_t()
          : is_const(false), is_typedef(false), has_type(false), has_name(false) {
      }
    };
  
    // Types are resolved from right to left: we get the variable name first
    // and then all specifiers (like const or pointer) in a chain of DW_AT_type
    // DIEs. Call this function recursively until we get a complete type
    // string.
    static void set_parameter_string(dwarf_fileobject &fobj, Dwarf_Die die,
                                     type_context_t &context) {
      char *name;
      Dwarf_Error error = DW_DLE_NE;
  
      // typedefs contain also the base type, so we skip it and only
      // print the typedef name
      if (!context.is_typedef) {
        if (dwarf_diename(die, &name, &error) == DW_DLV_OK) {
          if (!context.text.empty()) {
            context.text.insert(0, " ");
          }
          context.text.insert(0, std::string(name));
          dwarf_dealloc(fobj.dwarf_handle.get(), name, DW_DLA_STRING);
        }
      } else {
        context.is_typedef = false;
        context.has_type = true;
        if (context.is_const) {
          context.text.insert(0, "const ");
          context.is_const = false;
        }
      }
  
      bool next_type_is_const = false;
      bool is_keyword = true;
  
      Dwarf_Half tag = 0;
      Dwarf_Bool has_attr = 0;
      if (dwarf_tag(die, &tag, &error) == DW_DLV_OK) {
        switch (tag) {
        case DW_TAG_structure_type:
        case DW_TAG_union_type:
        case DW_TAG_class_type:
        case DW_TAG_enumeration_type:
          context.has_type = true;
          if (dwarf_hasattr(die, DW_AT_signature, &has_attr, &error) ==
              DW_DLV_OK) {
            // If we have a signature it means the type is defined
            // in .debug_types, so we need to load the DIE pointed
            // at by the signature and resolve it
            if (has_attr) {
              std::string type =
                  get_type_by_signature(fobj.dwarf_handle.get(), die);
              if (context.is_const)
                type.insert(0, "const ");
  
              if (!context.text.empty())
                context.text.insert(0, " ");
              context.text.insert(0, type);
            }
  
            // Treat enums like typedefs, and skip printing its
            // base type
            context.is_typedef = (tag == DW_TAG_enumeration_type);
          }
          break;
        case DW_TAG_const_type:
          next_type_is_const = true;
          break;
        case DW_TAG_pointer_type:
          context.text.insert(0, "*");
          break;
        case DW_TAG_reference_type:
          context.text.insert(0, "&");
          break;
        case DW_TAG_restrict_type:
          context.text.insert(0, "restrict ");
          break;
        case DW_TAG_rvalue_reference_type:
          context.text.insert(0, "&&");
          break;
        case DW_TAG_volatile_type:
          context.text.insert(0, "volatile ");
          break;
        case DW_TAG_typedef:
          // Propagate the const-ness to the next type
          // as typedefs are linked to its base type
          next_type_is_const = context.is_const;
          context.is_typedef = true;
          context.has_type = true;
          break;
        case DW_TAG_base_type:
          context.has_type = true;
          break;
        case DW_TAG_formal_parameter:
          context.has_name = true;
          break;
        default:
          is_keyword = false;
          break;
        }
      }
  
      if (!is_keyword && context.is_const) {
        context.text.insert(0, "const ");
      }
  
      context.is_const = next_type_is_const;
  
      Dwarf_Die ref =
          get_referenced_die(fobj.dwarf_handle.get(), die, DW_AT_type, true);
      if (ref) {
        set_parameter_string(fobj, ref, context);
        dwarf_dealloc(fobj.dwarf_handle.get(), ref, DW_DLA_DIE);
      }
  
      if (!context.has_type && context.has_name) {
        context.text.insert(0, "void ");
        context.has_type = true;
      }
    }
  
    // Resolve the function return type and parameters
    static void set_function_parameters(std::string &function_name,
                                        std::vector<std::string> &ns,
                                        dwarf_fileobject &fobj, Dwarf_Die die) {
      Dwarf_Debug dwarf = fobj.dwarf_handle.get();
      Dwarf_Error error = DW_DLE_NE;
      Dwarf_Die current_die = 0;
      std::string parameters;
      bool has_spec = true;
      // Check if we have a spec DIE. If we do we use it as it contains
      // more information, like parameter names.
      Dwarf_Die spec_die = get_spec_die(fobj, die);
      if (!spec_die) {
        has_spec = false;
        spec_die = die;
      }
  
      std::vector<std::string>::const_iterator it = ns.begin();
      std::string ns_name;
      for (it = ns.begin(); it < ns.end(); ++it) {
        ns_name.append(*it).append("::");
      }
  
      if (!ns_name.empty()) {
        function_name.insert(0, ns_name);
      }
  
      // See if we have a function return type. It can be either on the
      // current die or in its spec one (usually true for inlined functions)
      std::string return_type =
          get_referenced_die_name(dwarf, die, DW_AT_type, true);
      if (return_type.empty()) {
        return_type = get_referenced_die_name(dwarf, spec_die, DW_AT_type, true);
      }
      if (!return_type.empty()) {
        return_type.append(" ");
        function_name.insert(0, return_type);
      }
  
      if (dwarf_child(spec_die, &current_die, &error) == DW_DLV_OK) {
        for (;;) {
          Dwarf_Die sibling_die = 0;
  
          Dwarf_Half tag_value;
          dwarf_tag(current_die, &tag_value, &error);
  
          if (tag_value == DW_TAG_formal_parameter) {
            // Ignore artificial (ie, compiler generated) parameters
            bool is_artificial = false;
            Dwarf_Attribute attr_mem;
            if (dwarf_attr(current_die, DW_AT_artificial, &attr_mem, &error) ==
                DW_DLV_OK) {
              Dwarf_Bool flag = 0;
              if (dwarf_formflag(attr_mem, &flag, &error) == DW_DLV_OK) {
                is_artificial = flag != 0;
              }
              dwarf_dealloc(dwarf, attr_mem, DW_DLA_ATTR);
            }
  
            if (!is_artificial) {
              type_context_t context;
              set_parameter_string(fobj, current_die, context);
  
              if (parameters.empty()) {
                parameters.append("(");
              } else {
                parameters.append(", ");
              }
              parameters.append(context.text);
            }
          }
  
          int result = dwarf_siblingof(dwarf, current_die, &sibling_die, &error);
          if (result == DW_DLV_ERROR) {
            break;
          } else if (result == DW_DLV_NO_ENTRY) {
            break;
          }
  
          if (current_die != die) {
            dwarf_dealloc(dwarf, current_die, DW_DLA_DIE);
            current_die = 0;
          }
  
          current_die = sibling_die;
        }
      }
      if (parameters.empty())
        parameters = "(";
      parameters.append(")");
  
      // If we got a spec DIE we need to deallocate it
      if (has_spec)
        dwarf_dealloc(dwarf, spec_die, DW_DLA_DIE);
  
      function_name.append(parameters);
    }
  
    // defined here because in C++98, template function cannot take locally
    // defined types... grrr.
    struct inliners_search_cb {
      void operator()(Dwarf_Die die, std::vector<std::string> &ns) {
        Dwarf_Error error = DW_DLE_NE;
        Dwarf_Half tag_value;
        Dwarf_Attribute attr_mem;
        Dwarf_Debug dwarf = fobj.dwarf_handle.get();
  
        dwarf_tag(die, &tag_value, &error);
  
        switch (tag_value) {
          char *name;
        case DW_TAG_subprogram:
          if (!trace.source.function.empty())
            break;
          if (dwarf_diename(die, &name, &error) == DW_DLV_OK) {
            trace.source.function = std::string(name);
            dwarf_dealloc(dwarf, name, DW_DLA_STRING);
          } else {
            // We don't have a function name in this DIE.
            // Check if there is a referenced non-defining
            // declaration.
            trace.source.function =
                get_referenced_die_name(dwarf, die, DW_AT_abstract_origin, true);
            if (trace.source.function.empty()) {
              trace.source.function =
                  get_referenced_die_name(dwarf, die, DW_AT_specification, true);
            }
          }
  
          // Append the function parameters, if available
          set_function_parameters(trace.source.function, ns, fobj, die);
  
          // If the object function name is empty, it's possible that
          // there is no dynamic symbol table (maybe the executable
          // was stripped or not built with -rdynamic). See if we have
          // a DWARF linkage name to use instead. We try both
          // linkage_name and MIPS_linkage_name because the MIPS tag
          // was the unofficial one until it was adopted in DWARF4.
          // Old gcc versions generate MIPS_linkage_name
          if (trace.object_function.empty()) {
            details::demangler demangler;
  
            if (dwarf_attr(die, DW_AT_linkage_name, &attr_mem, &error) !=
                DW_DLV_OK) {
              if (dwarf_attr(die, DW_AT_MIPS_linkage_name, &attr_mem, &error) !=
                  DW_DLV_OK) {
                break;
              }
            }
  
            char *linkage;
            if (dwarf_formstring(attr_mem, &linkage, &error) == DW_DLV_OK) {
              trace.object_function = demangler.demangle(linkage);
              dwarf_dealloc(dwarf, linkage, DW_DLA_STRING);
            }
            dwarf_dealloc(dwarf, attr_mem, DW_DLA_ATTR);
          }
          break;
  
        case DW_TAG_inlined_subroutine:
          ResolvedTrace::SourceLoc sloc;
  
          if (dwarf_diename(die, &name, &error) == DW_DLV_OK) {
            sloc.function = std::string(name);
            dwarf_dealloc(dwarf, name, DW_DLA_STRING);
          } else {
            // We don't have a name for this inlined DIE, it could
            // be that there is an abstract origin instead.
            // Get the DW_AT_abstract_origin value, which is a
            // reference to the source DIE and try to get its name
            sloc.function =
                get_referenced_die_name(dwarf, die, DW_AT_abstract_origin, true);
          }
  
          set_function_parameters(sloc.function, ns, fobj, die);
  
          std::string file = die_call_file(dwarf, die, cu_die);
          if (!file.empty())
            sloc.filename = file;
  
          Dwarf_Unsigned number = 0;
          if (dwarf_attr(die, DW_AT_call_line, &attr_mem, &error) == DW_DLV_OK) {
            if (dwarf_formudata(attr_mem, &number, &error) == DW_DLV_OK) {
              sloc.line = number;
            }
            dwarf_dealloc(dwarf, attr_mem, DW_DLA_ATTR);
          }
  
          if (dwarf_attr(die, DW_AT_call_column, &attr_mem, &error) ==
              DW_DLV_OK) {
            if (dwarf_formudata(attr_mem, &number, &error) == DW_DLV_OK) {
              sloc.col = number;
            }
            dwarf_dealloc(dwarf, attr_mem, DW_DLA_ATTR);
          }
  
          trace.inliners.push_back(sloc);
          break;
        };
      }
      ResolvedTrace &trace;
      dwarf_fileobject &fobj;
      Dwarf_Die cu_die;
      inliners_search_cb(ResolvedTrace &t, dwarf_fileobject &f, Dwarf_Die c)
          : trace(t), fobj(f), cu_die(c) {}
    };
  
    static Dwarf_Die find_fundie_by_pc(dwarf_fileobject &fobj,
                                       Dwarf_Die parent_die, Dwarf_Addr pc,
                                       Dwarf_Die result) {
      Dwarf_Die current_die = 0;
      Dwarf_Error error = DW_DLE_NE;
      Dwarf_Debug dwarf = fobj.dwarf_handle.get();
  
      if (dwarf_child(parent_die, &current_die, &error) != DW_DLV_OK) {
        return NULL;
      }
  
      for (;;) {
        Dwarf_Die sibling_die = 0;
        Dwarf_Half tag_value;
        dwarf_tag(current_die, &tag_value, &error);
  
        switch (tag_value) {
        case DW_TAG_subprogram:
        case DW_TAG_inlined_subroutine:
          if (die_has_pc(fobj, current_die, pc)) {
            return current_die;
          }
        };
        bool declaration = false;
        Dwarf_Attribute attr_mem;
        if (dwarf_attr(current_die, DW_AT_declaration, &attr_mem, &error) ==
            DW_DLV_OK) {
          Dwarf_Bool flag = 0;
          if (dwarf_formflag(attr_mem, &flag, &error) == DW_DLV_OK) {
            declaration = flag != 0;
          }
          dwarf_dealloc(dwarf, attr_mem, DW_DLA_ATTR);
        }
  
        if (!declaration) {
          // let's be curious and look deeper in the tree, functions are
          // not necessarily at the first level, but might be nested
          // inside a namespace, structure, a function, an inlined
          // function etc.
          Dwarf_Die die_mem = 0;
          Dwarf_Die indie = find_fundie_by_pc(fobj, current_die, pc, die_mem);
          if (indie) {
            result = die_mem;
            return result;
          }
        }
  
        int res = dwarf_siblingof(dwarf, current_die, &sibling_die, &error);
        if (res == DW_DLV_ERROR) {
          return NULL;
        } else if (res == DW_DLV_NO_ENTRY) {
          break;
        }
  
        if (current_die != parent_die) {
          dwarf_dealloc(dwarf, current_die, DW_DLA_DIE);
          current_die = 0;
        }
  
        current_die = sibling_die;
      }
      return NULL;
    }
  
    template <typename CB>
    static bool deep_first_search_by_pc(dwarf_fileobject &fobj,
                                        Dwarf_Die parent_die, Dwarf_Addr pc,
                                        std::vector<std::string> &ns, CB cb) {
      Dwarf_Die current_die = 0;
      Dwarf_Debug dwarf = fobj.dwarf_handle.get();
      Dwarf_Error error = DW_DLE_NE;
  
      if (dwarf_child(parent_die, &current_die, &error) != DW_DLV_OK) {
        return false;
      }
  
      bool branch_has_pc = false;
      bool has_namespace = false;
      for (;;) {
        Dwarf_Die sibling_die = 0;
  
        Dwarf_Half tag;
        if (dwarf_tag(current_die, &tag, &error) == DW_DLV_OK) {
          if (tag == DW_TAG_namespace || tag == DW_TAG_class_type) {
            char *ns_name = NULL;
            if (dwarf_diename(current_die, &ns_name, &error) == DW_DLV_OK) {
              if (ns_name) {
                ns.push_back(std::string(ns_name));
              } else {
                ns.push_back("<unknown>");
              }
              dwarf_dealloc(dwarf, ns_name, DW_DLA_STRING);
            } else {
              ns.push_back("<unknown>");
            }
            has_namespace = true;
          }
        }
  
        bool declaration = false;
        Dwarf_Attribute attr_mem;
        if (tag != DW_TAG_class_type &&
            dwarf_attr(current_die, DW_AT_declaration, &attr_mem, &error) ==
                DW_DLV_OK) {
          Dwarf_Bool flag = 0;
          if (dwarf_formflag(attr_mem, &flag, &error) == DW_DLV_OK) {
            declaration = flag != 0;
          }
          dwarf_dealloc(dwarf, attr_mem, DW_DLA_ATTR);
        }
  
        if (!declaration) {
          // let's be curious and look deeper in the tree, function are
          // not necessarily at the first level, but might be nested
          // inside a namespace, structure, a function, an inlined
          // function etc.
          branch_has_pc = deep_first_search_by_pc(fobj, current_die, pc, ns, cb);
        }
  
        if (!branch_has_pc) {
          branch_has_pc = die_has_pc(fobj, current_die, pc);
        }
  
        if (branch_has_pc) {
          cb(current_die, ns);
        }
  
        int result = dwarf_siblingof(dwarf, current_die, &sibling_die, &error);
        if (result == DW_DLV_ERROR) {
          return false;
        } else if (result == DW_DLV_NO_ENTRY) {
          break;
        }
  
        if (current_die != parent_die) {
          dwarf_dealloc(dwarf, current_die, DW_DLA_DIE);
          current_die = 0;
        }
  
        if (has_namespace) {
          has_namespace = false;
          ns.pop_back();
        }
        current_die = sibling_die;
      }
  
      if (has_namespace) {
        ns.pop_back();
      }
      return branch_has_pc;
    }
  
    static std::string die_call_file(Dwarf_Debug dwarf, Dwarf_Die die,
                                     Dwarf_Die cu_die) {
      Dwarf_Attribute attr_mem;
      Dwarf_Error error = DW_DLE_NE;
      Dwarf_Unsigned file_index;
  
      std::string file;
  
      if (dwarf_attr(die, DW_AT_call_file, &attr_mem, &error) == DW_DLV_OK) {
        if (dwarf_formudata(attr_mem, &file_index, &error) != DW_DLV_OK) {
          file_index = 0;
        }
        dwarf_dealloc(dwarf, attr_mem, DW_DLA_ATTR);
  
        if (file_index == 0) {
          return file;
        }
  
        char **srcfiles = 0;
        Dwarf_Signed file_count = 0;
        if (dwarf_srcfiles(cu_die, &srcfiles, &file_count, &error) == DW_DLV_OK) {
          if (file_count > 0 && file_index <= static_cast<Dwarf_Unsigned>(file_count)) {
            file = std::string(srcfiles[file_index - 1]);
  	}
  
          // Deallocate all strings!
          for (int i = 0; i < file_count; ++i) {
            dwarf_dealloc(dwarf, srcfiles[i], DW_DLA_STRING);
          }
          dwarf_dealloc(dwarf, srcfiles, DW_DLA_LIST);
        }
      }
      return file;
    }
  
    Dwarf_Die find_die(dwarf_fileobject &fobj, Dwarf_Addr addr) {
      // Let's get to work! First see if we have a debug_aranges section so
      // we can speed up the search
  
      Dwarf_Debug dwarf = fobj.dwarf_handle.get();
      Dwarf_Error error = DW_DLE_NE;
      Dwarf_Arange *aranges;
      Dwarf_Signed arange_count;
  
      Dwarf_Die returnDie;
      bool found = false;
      if (dwarf_get_aranges(dwarf, &aranges, &arange_count, &error) !=
          DW_DLV_OK) {
        aranges = NULL;
      }
  
      if (aranges) {
        // We have aranges. Get the one where our address is.
        Dwarf_Arange arange;
        if (dwarf_get_arange(aranges, arange_count, addr, &arange, &error) ==
            DW_DLV_OK) {
  
          // We found our address. Get the compilation-unit DIE offset
          // represented by the given address range.
          Dwarf_Off cu_die_offset;
          if (dwarf_get_cu_die_offset(arange, &cu_die_offset, &error) ==
              DW_DLV_OK) {
            // Get the DIE at the offset returned by the aranges search.
            // We set is_info to 1 to specify that the offset is from
            // the .debug_info section (and not .debug_types)
            int dwarf_result =
                dwarf_offdie_b(dwarf, cu_die_offset, 1, &returnDie, &error);
  
            found = dwarf_result == DW_DLV_OK;
          }
          dwarf_dealloc(dwarf, arange, DW_DLA_ARANGE);
        }
      }
  
      if (found)
        return returnDie; // The caller is responsible for freeing the die
  
      // The search for aranges failed. Try to find our address by scanning
      // all compilation units.
      Dwarf_Unsigned next_cu_header;
      Dwarf_Half tag = 0;
      returnDie = 0;
  
      while (!found &&
             dwarf_next_cu_header_d(dwarf, 1, 0, 0, 0, 0, 0, 0, 0, 0,
                                    &next_cu_header, 0, &error) == DW_DLV_OK) {
  
        if (returnDie)
          dwarf_dealloc(dwarf, returnDie, DW_DLA_DIE);
  
        if (dwarf_siblingof(dwarf, 0, &returnDie, &error) == DW_DLV_OK) {
          if ((dwarf_tag(returnDie, &tag, &error) == DW_DLV_OK) &&
              tag == DW_TAG_compile_unit) {
            if (die_has_pc(fobj, returnDie, addr)) {
              found = true;
            }
          }
        }
      }
  
      if (found) {
        while (dwarf_next_cu_header_d(dwarf, 1, 0, 0, 0, 0, 0, 0, 0, 0,
                                      &next_cu_header, 0, &error) == DW_DLV_OK) {
          // Reset the cu header state. Libdwarf's next_cu_header API
          // keeps its own iterator per Dwarf_Debug that can't be reset.
          // We need to keep fetching elements until the end.
        }
      }
  
      if (found)
        return returnDie;
  
      // We couldn't find any compilation units with ranges or a high/low pc.
      // Try again by looking at all DIEs in all compilation units.
      Dwarf_Die cudie;
      while (dwarf_next_cu_header_d(dwarf, 1, 0, 0, 0, 0, 0, 0, 0, 0,
                                    &next_cu_header, 0, &error) == DW_DLV_OK) {
        if (dwarf_siblingof(dwarf, 0, &cudie, &error) == DW_DLV_OK) {
          Dwarf_Die die_mem = 0;
          Dwarf_Die resultDie = find_fundie_by_pc(fobj, cudie, addr, die_mem);
  
          if (resultDie) {
            found = true;
            break;
          }
        }
      }
  
      if (found) {
        while (dwarf_next_cu_header_d(dwarf, 1, 0, 0, 0, 0, 0, 0, 0, 0,
                                      &next_cu_header, 0, &error) == DW_DLV_OK) {
          // Reset the cu header state. Libdwarf's next_cu_header API
          // keeps its own iterator per Dwarf_Debug that can't be reset.
          // We need to keep fetching elements until the end.
        }
      }
  
      if (found)
        return cudie;
  
      // We failed.
      return NULL;
    }
  };
  #endif // BACKWARD_HAS_DWARF == 1
  
  template <>
  class TraceResolverImpl<system_tag::linux_tag>
      : public TraceResolverLinuxImpl<trace_resolver_tag::current> {};
  
  #endif // BACKWARD_SYSTEM_LINUX
  
  #ifdef BACKWARD_SYSTEM_DARWIN
  
  template <typename STACKTRACE_TAG> class TraceResolverDarwinImpl;
  
  template <>
  class TraceResolverDarwinImpl<trace_resolver_tag::backtrace_symbol>
      : public TraceResolverImplBase {
  public:
    void load_addresses(void *const*addresses, int address_count) override {
      if (address_count == 0) {
        return;
      }
      _symbols.reset(backtrace_symbols(addresses, address_count));
    }
  
    ResolvedTrace resolve(ResolvedTrace trace) override {
      // parse:
      // <n>  <file>  <addr>  <mangled-name> + <offset>
      char *filename = _symbols[trace.idx];
  
      // skip "<n>  "
      while (*filename && *filename != ' ')
        filename++;
      while (*filename == ' ')
        filename++;
  
      // find start of <mangled-name> from end (<file> may contain a space)
      char *p = filename + strlen(filename) - 1;
      // skip to start of " + <offset>"
      while (p > filename && *p != ' ')
        p--;
      while (p > filename && *p == ' ')
        p--;
      while (p > filename && *p != ' ')
        p--;
      while (p > filename && *p == ' ')
        p--;
      char *funcname_end = p + 1;
  
      // skip to start of "<manged-name>"
      while (p > filename && *p != ' ')
        p--;
      char *funcname = p + 1;
  
      // skip to start of "  <addr>  "
      while (p > filename && *p == ' ')
        p--;
      while (p > filename && *p != ' ')
        p--;
      while (p > filename && *p == ' ')
        p--;
  
      // skip "<file>", handling the case where it contains a
      char *filename_end = p + 1;
      if (p == filename) {
        // something went wrong, give up
        filename_end = filename + strlen(filename);
        funcname = filename_end;
      }
      trace.object_filename.assign(
          filename, filename_end); // ok even if filename_end is the ending \0
                                   // (then we assign entire string)
  
      if (*funcname) { // if it's not end of string
        *funcname_end = '\0';
  
        trace.object_function = this->demangle(funcname);
        trace.object_function += " ";
        trace.object_function += (funcname_end + 1);
        trace.source.function = trace.object_function; // we cannot do better.
      }
      return trace;
    }
  
  private:
    details::handle<char **> _symbols;
  };
  
  template <>
  class TraceResolverImpl<system_tag::darwin_tag>
      : public TraceResolverDarwinImpl<trace_resolver_tag::current> {};
  
  #endif // BACKWARD_SYSTEM_DARWIN
  
  #ifdef BACKWARD_SYSTEM_WINDOWS
  
  // Load all symbol info
  // Based on:
  // https://stackoverflow.com/questions/6205981/windows-c-stack-trace-from-a-running-app/28276227#28276227
  
  struct module_data {
    std::string image_name;
    std::string module_name;
    void *base_address;
    DWORD load_size;
  };
  
  class get_mod_info {
    HANDLE process;
    static const int buffer_length = 4096;
  
  public:
    get_mod_info(HANDLE h) : process(h) {}
  
    module_data operator()(HMODULE module) {
      module_data ret;
      char temp[buffer_length];
      MODULEINFO mi;
  
      GetModuleInformation(process, module, &mi, sizeof(mi));
      ret.base_address = mi.lpBaseOfDll;
      ret.load_size = mi.SizeOfImage;
  
      GetModuleFileNameExA(process, module, temp, sizeof(temp));
      ret.image_name = temp;
      GetModuleBaseNameA(process, module, temp, sizeof(temp));
      ret.module_name = temp;
      std::vector<char> img(ret.image_name.begin(), ret.image_name.end());
      std::vector<char> mod(ret.module_name.begin(), ret.module_name.end());
      SymLoadModule64(process, 0, &img[0], &mod[0], (DWORD64)ret.base_address,
                      ret.load_size);
      return ret;
    }
  };
  
  template <> class TraceResolverImpl<system_tag::windows_tag>
      : public TraceResolverImplBase {
  public:
    TraceResolverImpl() {
  
      HANDLE process = GetCurrentProcess();
  
      std::vector<module_data> modules;
      DWORD cbNeeded;
      std::vector<HMODULE> module_handles(1);
      SymInitialize(process, NULL, false);
      DWORD symOptions = SymGetOptions();
      symOptions |= SYMOPT_LOAD_LINES | SYMOPT_UNDNAME;
      SymSetOptions(symOptions);
      EnumProcessModules(process, &module_handles[0],
                         module_handles.size() * sizeof(HMODULE), &cbNeeded);
      module_handles.resize(cbNeeded / sizeof(HMODULE));
      EnumProcessModules(process, &module_handles[0],
                         module_handles.size() * sizeof(HMODULE), &cbNeeded);
      std::transform(module_handles.begin(), module_handles.end(),
                     std::back_inserter(modules), get_mod_info(process));
      void *base = modules[0].base_address;
      IMAGE_NT_HEADERS *h = ImageNtHeader(base);
      image_type = h->FileHeader.Machine;
    }
  
    static const int max_sym_len = 255;
    struct symbol_t {
      SYMBOL_INFO sym;
      char buffer[max_sym_len];
    } sym;
  
    DWORD64 displacement;
  
    ResolvedTrace resolve(ResolvedTrace t) override {
      HANDLE process = GetCurrentProcess();
  
      char name[256];
  
      memset(&sym, 0, sizeof(sym));
      sym.sym.SizeOfStruct = sizeof(SYMBOL_INFO);
      sym.sym.MaxNameLen = max_sym_len;
  
      if (!SymFromAddr(process, (ULONG64)t.addr, &displacement, &sym.sym)) {
        // TODO:  error handling everywhere
        char* lpMsgBuf;
        DWORD dw = GetLastError();
  
        FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER |
                          FORMAT_MESSAGE_FROM_SYSTEM |
                          FORMAT_MESSAGE_IGNORE_INSERTS,
                      NULL, dw, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
                      (char*)&lpMsgBuf, 0, NULL);
  
        printf(lpMsgBuf);
  
        // abort();
      }
      UnDecorateSymbolName(sym.sym.Name, (PSTR)name, 256, UNDNAME_COMPLETE);
  
      DWORD offset = 0;
      IMAGEHLP_LINE line;
      if (SymGetLineFromAddr(process, (ULONG64)t.addr, &offset, &line)) {
        t.object_filename = line.FileName;
        t.source.filename = line.FileName;
        t.source.line = line.LineNumber;
        t.source.col = offset;
      }
  
      t.source.function = name;
      t.object_filename = "";
      t.object_function = name;
  
      return t;
    }
  
    DWORD machine_type() const { return image_type; }
  
  private:
    DWORD image_type;
  };
  
  #endif
  
  class TraceResolver : public TraceResolverImpl<system_tag::current_tag> {};
  
  /*************** CODE SNIPPET ***************/
  
  class SourceFile {
  public:
    typedef std::vector<std::pair<unsigned, std::string>> lines_t;
  
    SourceFile() {}
    SourceFile(const std::string &path) {
      // 1. If BACKWARD_CXX_SOURCE_PREFIXES is set then assume it contains
      //    a colon-separated list of path prefixes.  Try prepending each
      //    to the given path until a valid file is found.
      const std::vector<std::string> &prefixes = get_paths_from_env_variable();
      for (size_t i = 0; i < prefixes.size(); ++i) {
        // Double slashes (//) should not be a problem.
        std::string new_path = prefixes[i] + '/' + path;
        _file.reset(new std::ifstream(new_path.c_str()));
        if (is_open())
          break;
      }
      // 2. If no valid file found then fallback to opening the path as-is.
      if (!_file || !is_open()) {
        _file.reset(new std::ifstream(path.c_str()));
      }
    }
    bool is_open() const { return _file->is_open(); }
  
    lines_t &get_lines(unsigned line_start, unsigned line_count, lines_t &lines) {
      using namespace std;
      // This function make uses of the dumbest algo ever:
      //	1) seek(0)
      //	2) read lines one by one and discard until line_start
      //	3) read line one by one until line_start + line_count
      //
      // If you are getting snippets many time from the same file, it is
      // somewhat a waste of CPU, feel free to benchmark and propose a
      // better solution ;)
  
      _file->clear();
      _file->seekg(0);
      string line;
      unsigned line_idx;
  
      for (line_idx = 1; line_idx < line_start; ++line_idx) {
        std::getline(*_file, line);
        if (!*_file) {
          return lines;
        }
      }
  
      // think of it like a lambda in C++98 ;)
      // but look, I will reuse it two times!
      // What a good boy am I.
      struct isspace {
        bool operator()(char c) { return std::isspace(c); }
      };
  
      bool started = false;
      for (; line_idx < line_start + line_count; ++line_idx) {
        getline(*_file, line);
        if (!*_file) {
          return lines;
        }
        if (!started) {
          if (std::find_if(line.begin(), line.end(), not_isspace()) == line.end())
            continue;
          started = true;
        }
        lines.push_back(make_pair(line_idx, line));
      }
  
      lines.erase(
          std::find_if(lines.rbegin(), lines.rend(), not_isempty()).base(),
          lines.end());
      return lines;
    }
  
    lines_t get_lines(unsigned line_start, unsigned line_count) {
      lines_t lines;
      return get_lines(line_start, line_count, lines);
    }
  
    // there is no find_if_not in C++98, lets do something crappy to
    // workaround.
    struct not_isspace {
      bool operator()(char c) { return !std::isspace(c); }
    };
    // and define this one here because C++98 is not happy with local defined
    // struct passed to template functions, fuuuu.
    struct not_isempty {
      bool operator()(const lines_t::value_type &p) {
        return !(std::find_if(p.second.begin(), p.second.end(), not_isspace()) ==
                 p.second.end());
      }
    };
  
    void swap(SourceFile &b) { _file.swap(b._file); }
  
  #ifdef BACKWARD_ATLEAST_CXX11
    SourceFile(SourceFile &&from) : _file(nullptr) { swap(from); }
    SourceFile &operator=(SourceFile &&from) {
      swap(from);
      return *this;
    }
  #else
    explicit SourceFile(const SourceFile &from) {
      // some sort of poor man's move semantic.
      swap(const_cast<SourceFile &>(from));
    }
    SourceFile &operator=(const SourceFile &from) {
      // some sort of poor man's move semantic.
      swap(const_cast<SourceFile &>(from));
      return *this;
    }
  #endif
  
  private:
    details::handle<std::ifstream *, details::default_delete<std::ifstream *>>
        _file;
  
    std::vector<std::string> get_paths_from_env_variable_impl() {
      std::vector<std::string> paths;
      const char *prefixes_str = std::getenv("BACKWARD_CXX_SOURCE_PREFIXES");
      if (prefixes_str && prefixes_str[0]) {
        paths = details::split_source_prefixes(prefixes_str);
      }
      return paths;
    }
  
    const std::vector<std::string> &get_paths_from_env_variable() {
      static std::vector<std::string> paths = get_paths_from_env_variable_impl();
      return paths;
    }
  
  #ifdef BACKWARD_ATLEAST_CXX11
    SourceFile(const SourceFile &) = delete;
    SourceFile &operator=(const SourceFile &) = delete;
  #endif
  };
  
  class SnippetFactory {
  public:
    typedef SourceFile::lines_t lines_t;
  
    lines_t get_snippet(const std::string &filename, unsigned line_start,
                        unsigned context_size) {
  
      SourceFile &src_file = get_src_file(filename);
      unsigned start = line_start - context_size / 2;
      return src_file.get_lines(start, context_size);
    }
  
    lines_t get_combined_snippet(const std::string &filename_a, unsigned line_a,
                                 const std::string &filename_b, unsigned line_b,
                                 unsigned context_size) {
      SourceFile &src_file_a = get_src_file(filename_a);
      SourceFile &src_file_b = get_src_file(filename_b);
  
      lines_t lines =
          src_file_a.get_lines(line_a - context_size / 4, context_size / 2);
      src_file_b.get_lines(line_b - context_size / 4, context_size / 2, lines);
      return lines;
    }
  
    lines_t get_coalesced_snippet(const std::string &filename, unsigned line_a,
                                  unsigned line_b, unsigned context_size) {
      SourceFile &src_file = get_src_file(filename);
  
      using std::max;
      using std::min;
      unsigned a = min(line_a, line_b);
      unsigned b = max(line_a, line_b);
  
      if ((b - a) < (context_size / 3)) {
        return src_file.get_lines((a + b - context_size + 1) / 2, context_size);
      }
  
      lines_t lines = src_file.get_lines(a - context_size / 4, context_size / 2);
      src_file.get_lines(b - context_size / 4, context_size / 2, lines);
      return lines;
    }
  
  private:
    typedef details::hashtable<std::string, SourceFile>::type src_files_t;
    src_files_t _src_files;
  
    SourceFile &get_src_file(const std::string &filename) {
      src_files_t::iterator it = _src_files.find(filename);
      if (it != _src_files.end()) {
        return it->second;
      }
      SourceFile &new_src_file = _src_files[filename];
      new_src_file = SourceFile(filename);
      return new_src_file;
    }
  };
  
  /*************** PRINTER ***************/
  
  namespace ColorMode {
  enum type { automatic, never, always };
  }
  
  class cfile_streambuf : public std::streambuf {
  public:
    cfile_streambuf(FILE *_sink) : sink(_sink) {}
    int_type underflow() override { return traits_type::eof(); }
    int_type overflow(int_type ch) override {
      if (traits_type::not_eof(ch) && fputc(ch, sink) != EOF) {
        return ch;
      }
      return traits_type::eof();
    }
  
    std::streamsize xsputn(const char_type *s, std::streamsize count) override {
      return static_cast<std::streamsize>(
          fwrite(s, sizeof *s, static_cast<size_t>(count), sink));
    }
  
  #ifdef BACKWARD_ATLEAST_CXX11
  public:
    cfile_streambuf(const cfile_streambuf &) = delete;
    cfile_streambuf &operator=(const cfile_streambuf &) = delete;
  #else
  private:
    cfile_streambuf(const cfile_streambuf &);
    cfile_streambuf &operator=(const cfile_streambuf &);
  #endif
  
  private:
    FILE *sink;
    std::vector<char> buffer;
  };
  
  #ifdef BACKWARD_SYSTEM_LINUX
  
  namespace Color {
  enum type { yellow = 33, purple = 35, reset = 39 };
  } // namespace Color
  
  class Colorize {
  public:
    Colorize(std::ostream &os) : _os(os), _reset(false), _enabled(false) {}
  
    void activate(ColorMode::type mode) { _enabled = mode == ColorMode::always; }
  
    void activate(ColorMode::type mode, FILE *fp) { activate(mode, fileno(fp)); }
  
    void set_color(Color::type ccode) {
      if (!_enabled)
        return;
  
      // I assume that the terminal can handle basic colors. Seriously I
      // don't want to deal with all the termcap shit.
      _os << "\033[" << static_cast<int>(ccode) << "m";
      _reset = (ccode != Color::reset);
    }
  
    ~Colorize() {
      if (_reset) {
        set_color(Color::reset);
      }
    }
  
  private:
    void activate(ColorMode::type mode, int fd) {
      activate(mode == ColorMode::automatic && isatty(fd) ? ColorMode::always
                                                          : mode);
    }
  
    std::ostream &_os;
    bool _reset;
    bool _enabled;
  };
  
  #else // ndef BACKWARD_SYSTEM_LINUX
  
  namespace Color {
  enum type { yellow = 0, purple = 0, reset = 0 };
  } // namespace Color
  
  class Colorize {
  public:
    Colorize(std::ostream &) {}
    void activate(ColorMode::type) {}
    void activate(ColorMode::type, FILE *) {}
    void set_color(Color::type) {}
  };
  
  #endif // BACKWARD_SYSTEM_LINUX
  
  class Printer {
  public:
    bool snippet;
    ColorMode::type color_mode;
    bool address;
    bool object;
    int inliner_context_size;
    int trace_context_size;
  
    Printer()
        : snippet(true), color_mode(ColorMode::automatic), address(false),
          object(false), inliner_context_size(5), trace_context_size(7) {}
  
    template <typename ST> FILE *print(ST &st, FILE *fp = stderr) {
      cfile_streambuf obuf(fp);
      std::ostream os(&obuf);
      Colorize colorize(os);
      colorize.activate(color_mode, fp);
      print_stacktrace(st, os, colorize);
      return fp;
    }
  
    template <typename ST> std::ostream &print(ST &st, std::ostream &os) {
      Colorize colorize(os);
      colorize.activate(color_mode);
      print_stacktrace(st, os, colorize);
      return os;
    }
  
    template <typename IT>
    FILE *print(IT begin, IT end, FILE *fp = stderr, size_t thread_id = 0) {
      cfile_streambuf obuf(fp);
      std::ostream os(&obuf);
      Colorize colorize(os);
      colorize.activate(color_mode, fp);
      print_stacktrace(begin, end, os, thread_id, colorize);
      return fp;
    }
  
    template <typename IT>
    std::ostream &print(IT begin, IT end, std::ostream &os,
                        size_t thread_id = 0) {
      Colorize colorize(os);
      colorize.activate(color_mode);
      print_stacktrace(begin, end, os, thread_id, colorize);
      return os;
    }
  
    TraceResolver const &resolver() const { return _resolver; }
  
  private:
    TraceResolver _resolver;
    SnippetFactory _snippets;
  
    template <typename ST>
    void print_stacktrace(ST &st, std::ostream &os, Colorize &colorize) {
      print_header(os, st.thread_id());
      _resolver.load_stacktrace(st);
      for (size_t trace_idx = st.size(); trace_idx > 0; --trace_idx) {
        print_trace(os, _resolver.resolve(st[trace_idx - 1]), colorize);
      }
    }
  
    template <typename IT>
    void print_stacktrace(IT begin, IT end, std::ostream &os, size_t thread_id,
                          Colorize &colorize) {
      print_header(os, thread_id);
      for (; begin != end; ++begin) {
        print_trace(os, *begin, colorize);
      }
    }
  
    void print_header(std::ostream &os, size_t thread_id) {
      os << "Stack trace (most recent call last)";
      if (thread_id) {
        os << " in thread " << thread_id;
      }
      os << ":\n";
    }
  
    void print_trace(std::ostream &os, const ResolvedTrace &trace,
                     Colorize &colorize) {
      os << "#" << std::left << std::setw(2) << trace.idx << std::right;
      bool already_indented = true;
  
      if (!trace.source.filename.size() || object) {
        os << "   Object \"" << trace.object_filename << "\", at " << trace.addr
           << ", in " << trace.object_function << "\n";
        already_indented = false;
      }
  
      for (size_t inliner_idx = trace.inliners.size(); inliner_idx > 0;
           --inliner_idx) {
        if (!already_indented) {
          os << "   ";
        }
        const ResolvedTrace::SourceLoc &inliner_loc =
            trace.inliners[inliner_idx - 1];
        print_source_loc(os, " | ", inliner_loc);
        if (snippet) {
          print_snippet(os, "    | ", inliner_loc, colorize, Color::purple,
                        inliner_context_size);
        }
        already_indented = false;
      }
  
      if (trace.source.filename.size()) {
        if (!already_indented) {
          os << "   ";
        }
        print_source_loc(os, "   ", trace.source, trace.addr);
        if (snippet) {
          print_snippet(os, "      ", trace.source, colorize, Color::yellow,
                        trace_context_size);
        }
      }
    }
  
    void print_snippet(std::ostream &os, const char *indent,
                       const ResolvedTrace::SourceLoc &source_loc,
                       Colorize &colorize, Color::type color_code,
                       int context_size) {
      using namespace std;
      typedef SnippetFactory::lines_t lines_t;
  
      lines_t lines = _snippets.get_snippet(source_loc.filename, source_loc.line,
                                            static_cast<unsigned>(context_size));
  
      for (lines_t::const_iterator it = lines.begin(); it != lines.end(); ++it) {
        if (it->first == source_loc.line) {
          colorize.set_color(color_code);
          os << indent << ">";
        } else {
          os << indent << " ";
        }
        os << std::setw(4) << it->first << ": " << it->second << "\n";
        if (it->first == source_loc.line) {
          colorize.set_color(Color::reset);
        }
      }
    }
  
    void print_source_loc(std::ostream &os, const char *indent,
                          const ResolvedTrace::SourceLoc &source_loc,
                          void *addr = nullptr) {
      os << indent << "Source \"" << source_loc.filename << "\", line "
         << source_loc.line << ", in " << source_loc.function;
  
      if (address && addr != nullptr) {
        os << " [" << addr << "]";
      }
      os << "\n";
    }
  };
  
  /*************** SIGNALS HANDLING ***************/
  
  #if defined(BACKWARD_SYSTEM_LINUX) || defined(BACKWARD_SYSTEM_DARWIN)
  
  class SignalHandling {
  public:
    static std::vector<int> make_default_signals() {
      const int posix_signals[] = {
        // Signals for which the default action is "Core".
        SIGABRT, // Abort signal from abort(3)
        SIGBUS,  // Bus error (bad memory access)
        SIGFPE,  // Floating point exception
        SIGILL,  // Illegal Instruction
        SIGIOT,  // IOT trap. A synonym for SIGABRT
        SIGQUIT, // Quit from keyboard
        SIGSEGV, // Invalid memory reference
        SIGSYS,  // Bad argument to routine (SVr4)
        SIGTRAP, // Trace/breakpoint trap
        SIGXCPU, // CPU time limit exceeded (4.2BSD)
        SIGXFSZ, // File size limit exceeded (4.2BSD)
  #if defined(BACKWARD_SYSTEM_DARWIN)
        SIGEMT, // emulation instruction executed
  #endif
      };
      return std::vector<int>(posix_signals,
                              posix_signals +
                                  sizeof posix_signals / sizeof posix_signals[0]);
    }
  
    SignalHandling(const std::vector<int> &posix_signals = make_default_signals())
        : _loaded(false) {
      bool success = true;
  
      const size_t stack_size = 1024 * 1024 * 8;
      _stack_content.reset(static_cast<char *>(malloc(stack_size)));
      if (_stack_content) {
        stack_t ss;
        ss.ss_sp = _stack_content.get();
        ss.ss_size = stack_size;
        ss.ss_flags = 0;
        if (sigaltstack(&ss, nullptr) < 0) {
          success = false;
        }
      } else {
        success = false;
      }
  
      for (size_t i = 0; i < posix_signals.size(); ++i) {
        struct sigaction action;
        memset(&action, 0, sizeof action);
        action.sa_flags =
            static_cast<int>(SA_SIGINFO | SA_ONSTACK | SA_NODEFER | SA_RESETHAND);
        sigfillset(&action.sa_mask);
        sigdelset(&action.sa_mask, posix_signals[i]);
  #if defined(__clang__)
  #pragma clang diagnostic push
  #pragma clang diagnostic ignored "-Wdisabled-macro-expansion"
  #endif
        action.sa_sigaction = &sig_handler;
  #if defined(__clang__)
  #pragma clang diagnostic pop
  #endif
  
        int r = sigaction(posix_signals[i], &action, nullptr);
        if (r < 0)
          success = false;
      }
  
      _loaded = success;
    }
  
    bool loaded() const { return _loaded; }
  
    static void handleSignal(int, siginfo_t *info, void *_ctx) {
      ucontext_t *uctx = static_cast<ucontext_t *>(_ctx);
  
      StackTrace st;
      void *error_addr = nullptr;
  #ifdef REG_RIP // x86_64
      error_addr = reinterpret_cast<void *>(uctx->uc_mcontext.gregs[REG_RIP]);
  #elif defined(REG_EIP) // x86_32
      error_addr = reinterpret_cast<void *>(uctx->uc_mcontext.gregs[REG_EIP]);
  #elif defined(__arm__)
      error_addr = reinterpret_cast<void *>(uctx->uc_mcontext.arm_pc);
  #elif defined(__aarch64__)
      #if defined(__APPLE__)
        error_addr = reinterpret_cast<void *>(uctx->uc_mcontext->__ss.__pc);
      #else
        error_addr = reinterpret_cast<void *>(uctx->uc_mcontext.pc);
      #endif
  #elif defined(__mips__)
      error_addr = reinterpret_cast<void *>(
          reinterpret_cast<struct sigcontext *>(&uctx->uc_mcontext)->sc_pc);
  #elif defined(__ppc__) || defined(__powerpc) || defined(__powerpc__) ||        \
      defined(__POWERPC__)
      error_addr = reinterpret_cast<void *>(uctx->uc_mcontext.regs->nip);
  #elif defined(__riscv)
      error_addr = reinterpret_cast<void *>(uctx->uc_mcontext.__gregs[REG_PC]);
  #elif defined(__s390x__)
      error_addr = reinterpret_cast<void *>(uctx->uc_mcontext.psw.addr);
  #elif defined(__APPLE__) && defined(__x86_64__)
      error_addr = reinterpret_cast<void *>(uctx->uc_mcontext->__ss.__rip);
  #elif defined(__APPLE__)
      error_addr = reinterpret_cast<void *>(uctx->uc_mcontext->__ss.__eip);
  #else
  #warning ":/ sorry, ain't know no nothing none not of your architecture!"
  #endif
      if (error_addr) {
        st.load_from(error_addr, 32, reinterpret_cast<void *>(uctx),
                     info->si_addr);
      } else {
        st.load_here(32, reinterpret_cast<void *>(uctx), info->si_addr);
      }
  
      Printer printer;
      printer.address = true;
      printer.print(st, stderr);
  
  #if _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
      psiginfo(info, nullptr);
  #else
      (void)info;
  #endif
    }
  
  private:
    details::handle<char *> _stack_content;
    bool _loaded;
  
  #ifdef __GNUC__
    __attribute__((noreturn))
  #endif
    static void
    sig_handler(int signo, siginfo_t *info, void *_ctx) {
      handleSignal(signo, info, _ctx);
  
      // try to forward the signal.
      raise(info->si_signo);
  
      // terminate the process immediately.
      puts("watf? exit");
      _exit(EXIT_FAILURE);
    }
  };
  
  #endif // BACKWARD_SYSTEM_LINUX || BACKWARD_SYSTEM_DARWIN
  
  #ifdef BACKWARD_SYSTEM_WINDOWS
  
  class SignalHandling {
  public:
    SignalHandling(const std::vector<int> & = std::vector<int>())
        : reporter_thread_([]() {
            /* We handle crashes in a utility thread:
              backward structures and some Windows functions called here
              need stack space, which we do not have when we encounter a
              stack overflow.
              To support reporting stack traces during a stack overflow,
              we create a utility thread at startup, which waits until a
              crash happens or the program exits normally. */
  
            {
              std::unique_lock<std::mutex> lk(mtx());
              cv().wait(lk, [] { return crashed() != crash_status::running; });
            }
            if (crashed() == crash_status::crashed) {
              handle_stacktrace(skip_recs());
            }
            {
              std::unique_lock<std::mutex> lk(mtx());
              crashed() = crash_status::ending;
            }
            cv().notify_one();
          }) {
      SetUnhandledExceptionFilter(crash_handler);
  
      signal(SIGABRT, signal_handler);
      _set_abort_behavior(0, _WRITE_ABORT_MSG | _CALL_REPORTFAULT);
  
      std::set_terminate(&terminator);
  #ifndef BACKWARD_ATLEAST_CXX17
      std::set_unexpected(&terminator);
  #endif
      _set_purecall_handler(&terminator);
      _set_invalid_parameter_handler(&invalid_parameter_handler);
    }
    bool loaded() const { return true; }
  
    ~SignalHandling() {
      {
        std::unique_lock<std::mutex> lk(mtx());
        crashed() = crash_status::normal_exit;
      }
  
      cv().notify_one();
  
      reporter_thread_.join();
    }
  
  private:
    static CONTEXT *ctx() {
      static CONTEXT data;
      return &data;
    }
  
    enum class crash_status { running, crashed, normal_exit, ending };
  
    static crash_status &crashed() {
      static crash_status data;
      return data;
    }
  
    static std::mutex &mtx() {
      static std::mutex data;
      return data;
    }
  
    static std::condition_variable &cv() {
      static std::condition_variable data;
      return data;
    }
  
    static HANDLE &thread_handle() {
      static HANDLE handle;
      return handle;
    }
  
    std::thread reporter_thread_;
  
    // TODO: how not to hardcode these?
    static const constexpr int signal_skip_recs =
  #ifdef __clang__
        // With clang, RtlCaptureContext also captures the stack frame of the
        // current function Below that, there ar 3 internal Windows functions
        4
  #else
        // With MSVC cl, RtlCaptureContext misses the stack frame of the current
        // function The first entries during StackWalk are the 3 internal Windows
        // functions
        3
  #endif
        ;
  
    static int &skip_recs() {
      static int data;
      return data;
    }
  
    static inline void terminator() {
      crash_handler(signal_skip_recs);
      abort();
    }
  
    static inline void signal_handler(int) {
      crash_handler(signal_skip_recs);
      abort();
    }
  
    static inline void __cdecl invalid_parameter_handler(const wchar_t *,
                                                         const wchar_t *,
                                                         const wchar_t *,
                                                         unsigned int,
                                                         uintptr_t) {
      crash_handler(signal_skip_recs);
      abort();
    }
  
    NOINLINE static LONG WINAPI crash_handler(EXCEPTION_POINTERS *info) {
      // The exception info supplies a trace from exactly where the issue was,
      // no need to skip records
      crash_handler(0, info->ContextRecord);
      return EXCEPTION_CONTINUE_SEARCH;
    }
  
    NOINLINE static void crash_handler(int skip, CONTEXT *ct = nullptr) {
  
      if (ct == nullptr) {
        RtlCaptureContext(ctx());
      } else {
        memcpy(ctx(), ct, sizeof(CONTEXT));
      }
      DuplicateHandle(GetCurrentProcess(), GetCurrentThread(),
                      GetCurrentProcess(), &thread_handle(), 0, FALSE,
                      DUPLICATE_SAME_ACCESS);
  
      skip_recs() = skip;
  
      {
        std::unique_lock<std::mutex> lk(mtx());
        crashed() = crash_status::crashed;
      }
  
      cv().notify_one();
  
      {
        std::unique_lock<std::mutex> lk(mtx());
        cv().wait(lk, [] { return crashed() != crash_status::crashed; });
      }
    }
  
    static void handle_stacktrace(int skip_frames = 0) {
      // printer creates the TraceResolver, which can supply us a machine type
      // for stack walking. Without this, StackTrace can only guess using some
      // macros.
      // StackTrace also requires that the PDBs are already loaded, which is done
      // in the constructor of TraceResolver
      Printer printer;
  
      StackTrace st;
      st.set_machine_type(printer.resolver().machine_type());
      st.set_thread_handle(thread_handle());
      st.load_here(32 + skip_frames, ctx());
      st.skip_n_firsts(skip_frames);
  
      printer.address = true;
      printer.print(st, std::cerr);
    }
  };
  
  #endif // BACKWARD_SYSTEM_WINDOWS
  
  #ifdef BACKWARD_SYSTEM_UNKNOWN
  
  class SignalHandling {
  public:
    SignalHandling(const std::vector<int> & = std::vector<int>()) {}
    bool init() { return false; }
    bool loaded() { return false; }
  };
  
  #endif // BACKWARD_SYSTEM_UNKNOWN
  
  } // namespace backward
  
  #endif /* H_GUARD */
  