ltdl misuse? (Gary... :-)

[akim]

Hi!

I believe -M is dead broken.  I don't know ltdl too well (i.e., not at
all), but according to the weird behavior of multi -M, and according
to fprintf, I think this code is broken:

      case 'M':
        {
          const char *search_path = lt_dlgetsearchpath ();
          if (lt_dlsetsearchpath (optarg) != 0)
          {
            const char *dlerr = lt_dlerror();
            if (dlerr == NULL)
              M4ERROR ((EXIT_FAILURE, 0,
                        _("ERROR: failed to add search directory `%s'"),
                        optarg));
            else
              M4ERROR ((EXIT_FAILURE, 0,
                        _("ERROR: failed to add search directory `%s': %s"),
                        optarg, dlerr));
          }
          if (search_path)
            lt_dladdsearchdir (search_path);
        }
        break;

My guess is that lt_dlgetsearchpath returns a privately allocated
string which has no reason to be kept alive accross lt_dlsetsearchpath
calls.  Therefore, the last lt_dladdsearchdir part has no reason to
do what was expected.  In particular, unless there is reallocation,
in most cases it just means setting the path to twice optarg.

I suppose the goal is to preprend optarg instead of appending it.  But
then, either we need to strdup somewhere, or ltdl should provide means
to do that cleanly.