filename, filename_len);
filename, filename_len + 1);
main (int argc, char *argv[]){  const char *filename;  size_t filename_len;  struct exec exec;  char *buf;  FILE *fp;  /* Set locale via LC_ALL.  */  setlocale (LC_ALL, "");  /* Set the text message domain.  */  textdomain (PACKAGE);  /* We expect exactly one argument.  */  if (argc != 2)    return 1;  filename = argv[1];  /* First see whether this is really an a.out binary.  */  fp = fopen (filename, "rb");  if (fp == NULL)    error (2, errno, gettext ("cannot open `%s'"), filename);  /* Read the program header.  */  if (fread (&exec, sizeof exec, 1, fp) < 1)    error (2, errno, gettext ("cannot read header from `%s'"), filename);  /* Test for the magic numbers.  */  if (N_MAGIC (exec) != ZMAGIC && N_MAGIC (exec) != QMAGIC      && N_MAGIC (exec) != OMAGIC)    exit (3);  /* We don't need the file open anymore.  */  fclose (fp);  /* We must put `__LDD=ARGV0=<program-name>' in the environment.  */  filename_len = strlen (filename);  buf = (char *) alloca (sizeof "__LDD_ARGV0=" + filename_len);  mempcpy (mempcpy (buf, "__LDD_ARGV0=", sizeof "__LDD_ARGV0=" - 1),	   filename, filename_len);  /* ...and put the value in the environment.  */  putenv (buf);  /* Now we can execute the binary.  */  return execl (filename, NULL) ? 4 : 0;}