Driver.cpp

//===-- Driver.cpp ----------------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "Driver.h"

#include "lldb/API/SBCommandInterpreter.h"
#include "lldb/API/SBCommandInterpreterRunOptions.h"
#include "lldb/API/SBCommandReturnObject.h"
#include "lldb/API/SBDebugger.h"
#include "lldb/API/SBFile.h"
#include "lldb/API/SBHostOS.h"
#include "lldb/API/SBLanguageRuntime.h"
#include "lldb/API/SBStream.h"
#include "lldb/API/SBStringList.h"
#include "lldb/API/SBStructuredData.h"
#include "lldb/Host/Config.h"

#include "llvm/ADT/StringRef.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/InitLLVM.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/Signals.h"
#include "llvm/Support/WithColor.h"
#include "llvm/Support/raw_ostream.h"

#include <algorithm>
#include <atomic>
#include <bitset>
#include <clocale>
#include <csignal>
#include <string>
#include <thread>
#include <utility>

#include <climits>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fcntl.h>

#if !defined(__APPLE__)
#include "llvm/Support/DataTypes.h"
#endif

using namespace lldb;
using namespace llvm;

namespace {
using namespace llvm::opt;

enum ID {
  OPT_INVALID = 0, // This is not an option ID.
#define OPTION(...) LLVM_MAKE_OPT_ID(__VA_ARGS__),
#include "Options.inc"
#undef OPTION
};

#define PREFIX(NAME, VALUE)                                                    \
  static constexpr StringLiteral NAME##_init[] = VALUE;                        \
  static constexpr ArrayRef<StringLiteral> NAME(NAME##_init,                   \
                                                std::size(NAME##_init) - 1);
#include "Options.inc"
#undef PREFIX

static constexpr opt::OptTable::Info InfoTable[] = {
#define OPTION(...) LLVM_CONSTRUCT_OPT_INFO(__VA_ARGS__),
#include "Options.inc"
#undef OPTION
};

class LLDBOptTable : public opt::GenericOptTable {
public:
  LLDBOptTable() : opt::GenericOptTable(InfoTable) {}
};
} // namespace

static void reset_stdin_termios();
static bool g_old_stdin_termios_is_valid = false;
static struct termios g_old_stdin_termios;

static bool disable_color(const raw_ostream &OS) { return false; }

static Driver *g_driver = nullptr;

// In the Driver::MainLoop, we change the terminal settings.  This function is
// added as an atexit handler to make sure we clean them up.
static void reset_stdin_termios() {
  if (g_old_stdin_termios_is_valid) {
    g_old_stdin_termios_is_valid = false;
    ::tcsetattr(STDIN_FILENO, TCSANOW, &g_old_stdin_termios);
  }
}

Driver::Driver()
    : SBBroadcaster("Driver"), m_debugger(SBDebugger::Create(false)) {
  // We want to be able to handle CTRL+D in the terminal to have it terminate
  // certain input
  m_debugger.SetCloseInputOnEOF(false);
  g_driver = this;
}

Driver::~Driver() {
  SBDebugger::Destroy(m_debugger);
  g_driver = nullptr;
}

void Driver::OptionData::AddInitialCommand(std::string command,
                                           CommandPlacement placement,
                                           bool is_file, SBError &error) {
  std::vector<InitialCmdEntry> *command_set;
  switch (placement) {
  case eCommandPlacementBeforeFile:
    command_set = &(m_initial_commands);
    break;
  case eCommandPlacementAfterFile:
    command_set = &(m_after_file_commands);
    break;
  case eCommandPlacementAfterCrash:
    command_set = &(m_after_crash_commands);
    break;
  }

  if (is_file) {
    SBFileSpec file(command.c_str());
    if (file.Exists())
      command_set->push_back(InitialCmdEntry(command, is_file));
    else if (file.ResolveExecutableLocation()) {
      char final_path[PATH_MAX];
      file.GetPath(final_path, sizeof(final_path));
      command_set->push_back(InitialCmdEntry(final_path, is_file));
    } else
      error.SetErrorStringWithFormat(
          "file specified in --source (-s) option doesn't exist: '%s'",
          command.c_str());
  } else
    command_set->push_back(InitialCmdEntry(command, is_file));
}

void Driver::WriteCommandsForSourcing(CommandPlacement placement,
                                      SBStream &strm) {
  std::vector<OptionData::InitialCmdEntry> *command_set;
  switch (placement) {
  case eCommandPlacementBeforeFile:
    command_set = &m_option_data.m_initial_commands;
    break;
  case eCommandPlacementAfterFile:
    command_set = &m_option_data.m_after_file_commands;
    break;
  case eCommandPlacementAfterCrash:
    command_set = &m_option_data.m_after_crash_commands;
    break;
  }

  for (const auto &command_entry : *command_set) {
    const char *command = command_entry.contents.c_str();
    if (command_entry.is_file) {
      bool source_quietly =
          m_option_data.m_source_quietly || command_entry.source_quietly;
      strm.Printf("command source -s %i '%s'\n",
                  static_cast<int>(source_quietly), command);
    } else
      strm.Printf("%s\n", command);
  }
}

// Check the arguments that were passed to this program to make sure they are
// valid and to get their argument values (if any).  Return a boolean value
// indicating whether or not to start up the full debugger (i.e. the Command
// Interpreter) or not.  Return FALSE if the arguments were invalid OR if the
// user only wanted help or version information.
SBError Driver::ProcessArgs(const opt::InputArgList &args, bool &exiting) {
  SBError error;

  // This is kind of a pain, but since we make the debugger in the Driver's
  // constructor, we can't know at that point whether we should read in init
  // files yet.  So we don't read them in in the Driver constructor, then set
  // the flags back to "read them in" here, and then if we see the "-n" flag,
  // we'll turn it off again.  Finally we have to read them in by hand later in
  // the main loop.
  m_debugger.SkipLLDBInitFiles(false);
  m_debugger.SkipAppInitFiles(false);

  if (args.hasArg(OPT_no_use_colors)) {
    m_debugger.SetUseColor(false);
    WithColor::setAutoDetectFunction(disable_color);
    m_option_data.m_debug_mode = true;
  }

  if (args.hasArg(OPT_version)) {
    m_option_data.m_print_version = true;
  }

  if (args.hasArg(OPT_python_path)) {
    m_option_data.m_print_python_path = true;
  }
  if (args.hasArg(OPT_print_script_interpreter_info)) {
    m_option_data.m_print_script_interpreter_info = true;
  }

  if (args.hasArg(OPT_batch)) {
    m_option_data.m_batch = true;
  }

  if (auto *arg = args.getLastArg(OPT_core)) {
    auto *arg_value = arg->getValue();
    SBFileSpec file(arg_value);
    if (!file.Exists()) {
      error.SetErrorStringWithFormat(
          "file specified in --core (-c) option doesn't exist: '%s'",
          arg_value);
      return error;
    }
    m_option_data.m_core_file = arg_value;
  }

  if (args.hasArg(OPT_editor)) {
    m_option_data.m_use_external_editor = true;
  }

  if (args.hasArg(OPT_no_lldbinit)) {
    m_debugger.SkipLLDBInitFiles(true);
    m_debugger.SkipAppInitFiles(true);
  }

  if (args.hasArg(OPT_local_lldbinit)) {
    lldb::SBDebugger::SetInternalVariable("target.load-cwd-lldbinit", "true",
                                          m_debugger.GetInstanceName());
  }

  if (auto *arg = args.getLastArg(OPT_file)) {
    auto *arg_value = arg->getValue();
    SBFileSpec file(arg_value);
    if (file.Exists()) {
      m_option_data.m_args.emplace_back(arg_value);
    } else if (file.ResolveExecutableLocation()) {
      char path[PATH_MAX];
      file.GetPath(path, sizeof(path));
      m_option_data.m_args.emplace_back(path);
    } else {
      error.SetErrorStringWithFormat(
          "file specified in --file (-f) option doesn't exist: '%s'",
          arg_value);
      return error;
    }
  }

  if (auto *arg = args.getLastArg(OPT_arch)) {
    auto *arg_value = arg->getValue();
    if (!lldb::SBDebugger::SetDefaultArchitecture(arg_value)) {
      error.SetErrorStringWithFormat(
          "invalid architecture in the -a or --arch option: '%s'", arg_value);
      return error;
    }
  }

  if (auto *arg = args.getLastArg(OPT_script_language)) {
    auto *arg_value = arg->getValue();
    m_debugger.SetScriptLanguage(m_debugger.GetScriptingLanguage(arg_value));
  }

  if (args.hasArg(OPT_source_quietly)) {
    m_option_data.m_source_quietly = true;
  }

  if (auto *arg = args.getLastArg(OPT_attach_name)) {
    auto *arg_value = arg->getValue();
    m_option_data.m_process_name = arg_value;
  }

  if (args.hasArg(OPT_wait_for)) {
    m_option_data.m_wait_for = true;
  }

  if (auto *arg = args.getLastArg(OPT_attach_pid)) {
    auto *arg_value = arg->getValue();
    char *remainder;
    m_option_data.m_process_pid = strtol(arg_value, &remainder, 0);
    if (remainder == arg_value || *remainder != '\0') {
      error.SetErrorStringWithFormat(
          "Could not convert process PID: \"%s\" into a pid.", arg_value);
      return error;
    }
  }

  if (auto *arg = args.getLastArg(OPT_repl_language)) {
    auto *arg_value = arg->getValue();
    m_option_data.m_repl_lang =
        SBLanguageRuntime::GetLanguageTypeFromString(arg_value);
    if (m_option_data.m_repl_lang == eLanguageTypeUnknown) {
      error.SetErrorStringWithFormat("Unrecognized language name: \"%s\"",
                                     arg_value);
      return error;
    }
    m_debugger.SetREPLLanguage(m_option_data.m_repl_lang);
  }

  if (args.hasArg(OPT_repl)) {
    m_option_data.m_repl = true;
  }

  if (auto *arg = args.getLastArg(OPT_repl_)) {
    m_option_data.m_repl = true;
    if (auto *arg_value = arg->getValue())
      m_option_data.m_repl_options = arg_value;
  }

  // We need to process the options below together as their relative order
  // matters.
  for (auto *arg : args.filtered(OPT_source_on_crash, OPT_one_line_on_crash,
                                 OPT_source, OPT_source_before_file,
                                 OPT_one_line, OPT_one_line_before_file)) {
    auto *arg_value = arg->getValue();
    if (arg->getOption().matches(OPT_source_on_crash)) {
      m_option_data.AddInitialCommand(arg_value, eCommandPlacementAfterCrash,
                                      true, error);
      if (error.Fail())
        return error;
    }

    if (arg->getOption().matches(OPT_one_line_on_crash)) {
      m_option_data.AddInitialCommand(arg_value, eCommandPlacementAfterCrash,
                                      false, error);
      if (error.Fail())
        return error;
    }

    if (arg->getOption().matches(OPT_source)) {
      m_option_data.AddInitialCommand(arg_value, eCommandPlacementAfterFile,
                                      true, error);
      if (error.Fail())
        return error;
    }

    if (arg->getOption().matches(OPT_source_before_file)) {
      m_option_data.AddInitialCommand(arg_value, eCommandPlacementBeforeFile,
                                      true, error);
      if (error.Fail())
        return error;
    }

    if (arg->getOption().matches(OPT_one_line)) {
      m_option_data.AddInitialCommand(arg_value, eCommandPlacementAfterFile,
                                      false, error);
      if (error.Fail())
        return error;
    }

    if (arg->getOption().matches(OPT_one_line_before_file)) {
      m_option_data.AddInitialCommand(arg_value, eCommandPlacementBeforeFile,
                                      false, error);
      if (error.Fail())
        return error;
    }
  }

  if (m_option_data.m_process_name.empty() &&
      m_option_data.m_process_pid == LLDB_INVALID_PROCESS_ID) {

    for (auto *arg : args.filtered(OPT_INPUT))
      m_option_data.m_args.push_back(arg->getAsString((args)));

    // Any argument following -- is an argument for the inferior.
    if (auto *arg = args.getLastArgNoClaim(OPT_REM)) {
      for (auto *value : arg->getValues())
        m_option_data.m_args.emplace_back(value);
    }
  } else if (args.getLastArgNoClaim() != nullptr) {
    WithColor::warning() << "program arguments are ignored when attaching.\n";
  }

  if (m_option_data.m_print_version) {
    llvm::outs() << lldb::SBDebugger::GetVersionString() << '\n';
    exiting = true;
    return error;
  }

  if (m_option_data.m_print_python_path) {
    SBFileSpec python_file_spec = SBHostOS::GetLLDBPythonPath();
    if (python_file_spec.IsValid()) {
      char python_path[PATH_MAX];
      size_t num_chars = python_file_spec.GetPath(python_path, PATH_MAX);
      if (num_chars < PATH_MAX) {
        llvm::outs() << python_path << '\n';
      } else
        llvm::outs() << "<PATH TOO LONG>\n";
    } else
      llvm::outs() << "<COULD NOT FIND PATH>\n";
    exiting = true;
    return error;
  }

  if (m_option_data.m_print_script_interpreter_info) {
    SBStructuredData info =
        m_debugger.GetScriptInterpreterInfo(m_debugger.GetScriptLanguage());
    if (!info) {
      error.SetErrorString("no script interpreter.");
    } else {
      SBStream stream;
      error = info.GetAsJSON(stream);
      if (error.Success()) {
        llvm::outs() << stream.GetData() << '\n';
      }
    }
    exiting = true;
    return error;
  }

  return error;
}

std::string EscapeString(std::string arg) {
  std::string::size_type pos = 0;
  while ((pos = arg.find_first_of("\"\\", pos)) != std::string::npos) {
    arg.insert(pos, 1, '\\');
    pos += 2;
  }
  return '"' + arg + '"';
}

int Driver::MainLoop() {
  if (::tcgetattr(STDIN_FILENO, &g_old_stdin_termios) == 0) {
    g_old_stdin_termios_is_valid = true;
    atexit(reset_stdin_termios);
  }

#ifndef _MSC_VER
  // Disabling stdin buffering with MSVC's 2015 CRT exposes a bug in fgets
  // which causes it to miss newlines depending on whether there have been an
  // odd or even number of characters.  Bug has been reported to MS via Connect.
  ::setbuf(stdin, nullptr);
#endif
  ::setbuf(stdout, nullptr);

  m_debugger.SetErrorFileHandle(stderr, false);
  m_debugger.SetOutputFileHandle(stdout, false);
  // Don't take ownership of STDIN yet...
  m_debugger.SetInputFileHandle(stdin, false);

  m_debugger.SetUseExternalEditor(m_option_data.m_use_external_editor);

  struct winsize window_size;
  if ((isatty(STDIN_FILENO) != 0) &&
      ::ioctl(STDIN_FILENO, TIOCGWINSZ, &window_size) == 0) {
    if (window_size.ws_col > 0)
      m_debugger.SetTerminalWidth(window_size.ws_col);
  }

  SBCommandInterpreter sb_interpreter = m_debugger.GetCommandInterpreter();

  // Process lldbinit files before handling any options from the command line.
  SBCommandReturnObject result;
  sb_interpreter.SourceInitFileInGlobalDirectory(result);
  if (m_option_data.m_debug_mode) {
    result.PutError(m_debugger.GetErrorFile());
    result.PutOutput(m_debugger.GetOutputFile());
  }

  sb_interpreter.SourceInitFileInHomeDirectory(result, m_option_data.m_repl);
  if (m_option_data.m_debug_mode) {
    result.PutError(m_debugger.GetErrorFile());
    result.PutOutput(m_debugger.GetOutputFile());
  }

  // Source the local .lldbinit file if it exists and we're allowed to source.
  // Here we want to always print the return object because it contains the
  // warning and instructions to load local lldbinit files.
  sb_interpreter.SourceInitFileInCurrentWorkingDirectory(result);
  result.PutError(m_debugger.GetErrorFile());
  result.PutOutput(m_debugger.GetOutputFile());

  // We allow the user to specify an exit code when calling quit which we will
  // return when exiting.
  m_debugger.GetCommandInterpreter().AllowExitCodeOnQuit(true);

  // Now we handle options we got from the command line
  SBStream commands_stream;

  // First source in the commands specified to be run before the file arguments
  // are processed.
  WriteCommandsForSourcing(eCommandPlacementBeforeFile, commands_stream);

  // If we're not in --repl mode, add the commands to process the file
  // arguments, and the commands specified to run afterwards.
  if (!m_option_data.m_repl) {
    const size_t num_args = m_option_data.m_args.size();
    if (num_args > 0) {
      char arch_name[64];
      if (lldb::SBDebugger::GetDefaultArchitecture(arch_name,
                                                   sizeof(arch_name)))
        commands_stream.Printf("target create --arch=%s %s", arch_name,
                               EscapeString(m_option_data.m_args[0]).c_str());
      else
        commands_stream.Printf("target create %s",
                               EscapeString(m_option_data.m_args[0]).c_str());

      if (!m_option_data.m_core_file.empty()) {
        commands_stream.Printf(" --core %s",
                               EscapeString(m_option_data.m_core_file).c_str());
      }
      commands_stream.Printf("\n");

      if (num_args > 1) {
        commands_stream.Printf("settings set -- target.run-args ");
        for (size_t arg_idx = 1; arg_idx < num_args; ++arg_idx)
          commands_stream.Printf(
              " %s", EscapeString(m_option_data.m_args[arg_idx]).c_str());
        commands_stream.Printf("\n");
      }
    } else if (!m_option_data.m_core_file.empty()) {
      commands_stream.Printf("target create --core %s\n",
                             EscapeString(m_option_data.m_core_file).c_str());
    } else if (!m_option_data.m_process_name.empty()) {
      commands_stream.Printf(
          "process attach --name %s",
          EscapeString(m_option_data.m_process_name).c_str());

      if (m_option_data.m_wait_for)
        commands_stream.Printf(" --waitfor");

      commands_stream.Printf("\n");

    } else if (LLDB_INVALID_PROCESS_ID != m_option_data.m_process_pid) {
      commands_stream.Printf("process attach --pid %" PRIu64 "\n",
                             m_option_data.m_process_pid);
    }

    WriteCommandsForSourcing(eCommandPlacementAfterFile, commands_stream);
  } else if (!m_option_data.m_after_file_commands.empty()) {
    // We're in repl mode and after-file-load commands were specified.
    WithColor::warning() << "commands specified to run after file load (via -o "
                            "or -s) are ignored in REPL mode.\n";
  }

  if (m_option_data.m_debug_mode) {
    result.PutError(m_debugger.GetErrorFile());
    result.PutOutput(m_debugger.GetOutputFile());
  }

  const bool handle_events = true;
  const bool spawn_thread = false;

  // Check if we have any data in the commands stream, and if so, save it to a
  // temp file
  // so we can then run the command interpreter using the file contents.
  bool go_interactive = true;
  if ((commands_stream.GetData() != nullptr) &&
      (commands_stream.GetSize() != 0u)) {
    SBError error = m_debugger.SetInputString(commands_stream.GetData());
    if (error.Fail()) {
      WithColor::error() << error.GetCString() << '\n';
      return 1;
    }

    // Set the debugger into Sync mode when running the command file. Otherwise
    // command files that run the target won't run in a sensible way.
    bool old_async = m_debugger.GetAsync();
    m_debugger.SetAsync(false);

    SBCommandInterpreterRunOptions options;
    options.SetAutoHandleEvents(true);
    options.SetSpawnThread(false);
    options.SetStopOnError(true);
    options.SetStopOnCrash(m_option_data.m_batch);
    options.SetEchoCommands(!m_option_data.m_source_quietly);

    SBCommandInterpreterRunResult results =
        m_debugger.RunCommandInterpreter(options);
    if (results.GetResult() == lldb::eCommandInterpreterResultQuitRequested)
      go_interactive = false;
    if (m_option_data.m_batch &&
        results.GetResult() != lldb::eCommandInterpreterResultInferiorCrash)
      go_interactive = false;

    // When running in batch mode and stopped because of an error, exit with a
    // non-zero exit status.
    if (m_option_data.m_batch &&
        results.GetResult() == lldb::eCommandInterpreterResultCommandError)
      return 1;

    if (m_option_data.m_batch &&
        results.GetResult() == lldb::eCommandInterpreterResultInferiorCrash &&
        !m_option_data.m_after_crash_commands.empty()) {
      SBStream crash_commands_stream;
      WriteCommandsForSourcing(eCommandPlacementAfterCrash,
                               crash_commands_stream);
      SBError error =
          m_debugger.SetInputString(crash_commands_stream.GetData());
      if (error.Success()) {
        SBCommandInterpreterRunResult local_results =
            m_debugger.RunCommandInterpreter(options);
        if (local_results.GetResult() ==
            lldb::eCommandInterpreterResultQuitRequested)
          go_interactive = false;

        // When running in batch mode and an error occurred while sourcing
        // the crash commands, exit with a non-zero exit status.
        if (m_option_data.m_batch &&
            local_results.GetResult() ==
                lldb::eCommandInterpreterResultCommandError)
          return 1;
      }
    }
    m_debugger.SetAsync(old_async);
  }

  // Now set the input file handle to STDIN and run the command interpreter
  // again in interactive mode or repl mode and let the debugger take ownership
  // of stdin.
  if (go_interactive) {
    m_debugger.SetInputFileHandle(stdin, true);

    if (m_option_data.m_repl) {
      const char *repl_options = nullptr;
      if (!m_option_data.m_repl_options.empty())
        repl_options = m_option_data.m_repl_options.c_str();
      SBError error(
          m_debugger.RunREPL(m_option_data.m_repl_lang, repl_options));
      if (error.Fail()) {
        const char *error_cstr = error.GetCString();
        if ((error_cstr != nullptr) && (error_cstr[0] != 0))
          WithColor::error() << error_cstr << '\n';
        else
          WithColor::error() << error.GetError() << '\n';
      }
    } else {
      m_debugger.RunCommandInterpreter(handle_events, spawn_thread);
    }
  }

  reset_stdin_termios();
  fclose(stdin);

  return sb_interpreter.GetQuitStatus();
}

void Driver::ResizeWindow(unsigned short col) {
  GetDebugger().SetTerminalWidth(col);
}

void sigwinch_handler(int signo) {
  struct winsize window_size;
  if ((isatty(STDIN_FILENO) != 0) &&
      ::ioctl(STDIN_FILENO, TIOCGWINSZ, &window_size) == 0) {
    if ((window_size.ws_col > 0) && g_driver != nullptr) {
      g_driver->ResizeWindow(window_size.ws_col);
    }
  }
}

void sigint_handler(int signo) {
#ifdef _WIN32 // Restore handler as it is not persistent on Windows
  signal(SIGINT, sigint_handler);
#endif
  static std::atomic_flag g_interrupt_sent = ATOMIC_FLAG_INIT;
  if (g_driver != nullptr) {
    if (!g_interrupt_sent.test_and_set()) {
      g_driver->GetDebugger().DispatchInputInterrupt();
      g_interrupt_sent.clear();
      return;
    }
  }

  _exit(signo);
}

#ifndef _WIN32
static void sigtstp_handler(int signo) {
  if (g_driver != nullptr)
    g_driver->GetDebugger().SaveInputTerminalState();

  // Unblock the signal and remove our handler.
  sigset_t set;
  sigemptyset(&set);
  sigaddset(&set, signo);
  pthread_sigmask(SIG_UNBLOCK, &set, nullptr);
  signal(signo, SIG_DFL);

  // Now re-raise the signal. We will immediately suspend...
  raise(signo);
  // ... and resume after a SIGCONT.

  // Now undo the modifications.
  pthread_sigmask(SIG_BLOCK, &set, nullptr);
  signal(signo, sigtstp_handler);

  if (g_driver != nullptr)
    g_driver->GetDebugger().RestoreInputTerminalState();
}
#endif

static void printHelp(LLDBOptTable &table, llvm::StringRef tool_name) {
  std::string usage_str = tool_name.str() + " [options]";
  table.printHelp(llvm::outs(), usage_str.c_str(), "LLDB", false);

  std::string examples = R"___(
EXAMPLES:
  The debugger can be started in several modes.

  Passing an executable as a positional argument prepares lldb to debug the
  given executable. To disambiguate between arguments passed to lldb and
  arguments passed to the debugged executable, arguments starting with a - must
  be passed after --.

    lldb --arch x86_64 /path/to/program program argument -- --arch armv7

  For convenience, passing the executable after -- is also supported.

    lldb --arch x86_64 -- /path/to/program program argument --arch armv7

  Passing one of the attach options causes lldb to immediately attach to the
  given process.

    lldb -p <pid>
    lldb -n <process-name>

  Passing --repl starts lldb in REPL mode.

    lldb -r

  Passing --core causes lldb to debug the core file.

    lldb -c /path/to/core

  Command options can be combined with these modes and cause lldb to run the
  specified commands before or after events, like loading the file or crashing,
  in the order provided on the command line.

    lldb -O 'settings set stop-disassembly-count 20' -o 'run' -o 'bt'
    lldb -S /source/before/file -s /source/after/file
    lldb -K /source/before/crash -k /source/after/crash

  Note: In REPL mode no file is loaded, so commands specified to run after
  loading the file (via -o or -s) will be ignored.)___";
  llvm::outs() << examples << '\n';
}

int main(int argc, char const *argv[]) {
  // Editline uses for example iswprint which is dependent on LC_CTYPE.
  std::setlocale(LC_ALL, "");
  std::setlocale(LC_CTYPE, "");

  // Setup LLVM signal handlers and make sure we call llvm_shutdown() on
  // destruction.
  llvm::InitLLVM IL(argc, argv, /*InstallPipeSignalExitHandler=*/false);
  llvm::setBugReportMsg("PLEASE submit a bug report to " LLDB_BUG_REPORT_URL
                        " and include the crash backtrace.\n");

  // Parse arguments.
  LLDBOptTable T;
  unsigned MissingArgIndex;
  unsigned MissingArgCount;
  ArrayRef<const char *> arg_arr = ArrayRef(argv + 1, argc - 1);
  opt::InputArgList input_args =
      T.ParseArgs(arg_arr, MissingArgIndex, MissingArgCount);
  llvm::StringRef argv0 = llvm::sys::path::filename(argv[0]);

  if (input_args.hasArg(OPT_help)) {
    printHelp(T, argv0);
    return 0;
  }

  // Check for missing argument error.
  if (MissingArgCount) {
    WithColor::error() << "argument to '"
                       << input_args.getArgString(MissingArgIndex)
                       << "' is missing\n";
  }
  // Error out on unknown options.
  if (input_args.hasArg(OPT_UNKNOWN)) {
    for (auto *arg : input_args.filtered(OPT_UNKNOWN)) {
      WithColor::error() << "unknown option: " << arg->getSpelling() << '\n';
    }
  }
  if (MissingArgCount || input_args.hasArg(OPT_UNKNOWN)) {
    llvm::errs() << "Use '" << argv0
                 << " --help' for a complete list of options.\n";
    return 1;
  }

  SBError error = SBDebugger::InitializeWithErrorHandling();
  if (error.Fail()) {
    WithColor::error() << "initialization failed: " << error.GetCString()
                       << '\n';
    return 1;
  }

  // Setup LLDB signal handlers once the debugger has been initialized.
  SBDebugger::PrintDiagnosticsOnError();

  signal(SIGINT, sigint_handler);
#if !defined(_WIN32)
  signal(SIGPIPE, SIG_IGN);
  signal(SIGWINCH, sigwinch_handler);
  signal(SIGTSTP, sigtstp_handler);
#endif

  int exit_code = 0;
  // Create a scope for driver so that the driver object will destroy itself
  // before SBDebugger::Terminate() is called.
  {
    Driver driver;

    bool exiting = false;
    SBError error(driver.ProcessArgs(input_args, exiting));
    if (error.Fail()) {
      exit_code = 1;
      if (const char *error_cstr = error.GetCString())
        WithColor::error() << error_cstr << '\n';
    } else if (!exiting) {
      exit_code = driver.MainLoop();
    }
  }

  SBDebugger::Terminate();
  return exit_code;
}