gcc 源码阅读---程序入口

在gcc 默认编译中，会编译出gcc/g++,cc1这几个程序，

gcc 是个驱动型程序，完成c/c++转为汇编程，调用汇编程序转为.o文件，再调用link程序生成elf执行程序

cc1程序是真正的将c编译为汇篇程序，这是整个编译的核 心

gcc 入口:

gcc_main.c 

                

int
main (int argc, char **argv)
{
  driver d (false, /* can_finalize */
        false); /* debug */

  return d.main (argc, argv);
}
最后调用gcc.c

driver::main (int argc, char **argv)

cc1 入口

main.cc

int
main (int argc, char **argv)
{
  toplev toplev (NULL, /* external_timer */
         true /* init_signals */);

  int r = toplev.main (argc, argv);

  if (flag_checking && !seen_error ())
    toplev.finalize ();

  return r;
}
最后调用 toplev.cc

int
toplev::main (int argc, char **argv)
{
  /* Parsing and gimplification sometimes need quite large stack.
     Increase stack size limits if possible.  */
  stack_limit_increase (64 * 1024 * 1024);

  /* Stash a copy of the original argv before expansion
     for use by SARIF output.  */
  unique_argv original_argv (dupargv (argv));

  expandargv (&argc, &argv);

  /* Initialization of GCC's environment, and diagnostics.  */
  general_init (argv[0], m_init_signals, std::move (original_argv));

  /* One-off initialization of options that does not need to be
     repeated when options are added for particular functions.  */
  init_options_once ();
  init_opts_obstack ();

  /* Initialize global options structures; this must be repeated for
     each structure used for parsing options.  */
  init_options_struct (&global_options, &global_options_set);
  lang_hooks.init_options_struct (&global_options);

  /* Init GGC heuristics must be caller after we initialize
     options.  */
  init_ggc_heuristics ();

  /* Convert the options to an array.  */
  decode_cmdline_options_to_array_default_mask (argc,
                        CONST_CAST2 (const char **,
                                 char **, argv),
                        &save_decoded_options,
                        &save_decoded_options_count);

  /* Save Optimization decoded options.  */
  save_opt_decoded_options = new vec<cl_decoded_option> ();
  for (unsigned i = 1; i < save_decoded_options_count; ++i)
    if (save_decoded_options[i].opt_index < cl_options_count
    && cl_options[save_decoded_options[i].opt_index].flags & CL_OPTIMIZATION)
      save_opt_decoded_options->safe_push (save_decoded_options[i]);

  /* Perform language-specific options initialization.  */
  lang_hooks.init_options (save_decoded_options_count, save_decoded_options);

  /* Parse the options and do minimal processing; basically just
     enough to default flags appropriately.  */
  decode_options (&global_options, &global_options_set,
          save_decoded_options, save_decoded_options_count,
          UNKNOWN_LOCATION, global_dc,
          targetm.target_option.override);

  global_dc->get_file_cache ().tune (param_file_cache_files,
                     param_file_cache_lines);

  handle_common_deferred_options ();

  init_local_tick ();

  initialize_plugins ();

  /* Handle the dump options now that plugins have had a chance to install new
     passes.  */
  handle_deferred_dump_options ();

  if (version_flag)
    print_version (stderr, "", true);

  if (help_flag)
    print_plugins_help (stderr, "");

  /* Exit early if we can (e.g. -help).  */
  if (!exit_after_options)
    {
      /* Just in case lang_hooks.post_options ends up calling a debug_hook.
     This can happen with incorrect pre-processed input. */
      debug_hooks = &do_nothing_debug_hooks;
      /* Allow the front end to perform consistency checks and do further
     initialization based on the command line options.  This hook also
     sets the original filename if appropriate (e.g. foo.i -> foo.c)
     so we can correctly initialize debug output.  */
      no_backend = lang_hooks.post_options (&main_input_filename);

      process_options ();

      if (m_use_TV_TOTAL)
    start_timevars ();
      do_compile ();

      if (flag_self_test && !seen_error ())
    {
      if (no_backend)
        error_at (UNKNOWN_LOCATION, "self-tests incompatible with %<-E%>");
      else
        run_self_tests ();
    }
    }

  if (warningcount || errorcount || werrorcount)
    print_ignored_options ();

  /* Invoke registered plugin callbacks if any.  Some plugins could
     emit some diagnostics here.  */
  invoke_plugin_callbacks (PLUGIN_FINISH, NULL);

  if (auto edit_context_ptr = global_dc->get_edit_context ())
    {
      pretty_printer pp;
      pp_show_color (&pp) = pp_show_color (global_dc->get_reference_printer ());
      edit_context_ptr->print_diff (&pp, true);
      pp_flush (&pp);
    }

  diagnostic_finish (global_dc);

  finalize_plugins ();

  after_memory_report = true;

  if (global_dc->execution_failed_p ())
    return (FATAL_EXIT_CODE);

  return (SUCCESS_EXIT_CODE);
}