*p-- = '\0';
*--p = '\0';
_strerror_internal (int errnum, char *buf, size_t buflen){  int system;   int sub;  int code;  const struct error_system *es;  extern void __mach_error_map_compat (int *);  __mach_error_map_compat (&errnum);  system = err_get_system (errnum);  sub = err_get_sub (errnum);  code = err_get_code (errnum);  if (system > err_max_system || ! __mach_error_systems[system].bad_sub)    {      const char *unk = _("Error in unknown error system: ");      const size_t unklen = strlen (unk);      char *p = buf + buflen;      *p-- = '\0';      p = _itoa (errnum, p, 16, 1);      return memcpy (p - unklen, unk, unklen);    }  es = &__mach_error_systems[system];  if (sub >= es->max_sub)    return (char *) es->bad_sub;  if (code >= es->subsystem[sub].max_code)    {      const char *unk = _("Unknown error ");      const size_t unklen = strlen (unk);      char *p = buf + buflen;      size_t len = strlen (es->subsystem[sub].subsys_name);      *p-- = '\0';      p = _itoa (errnum, p, 16, 1);      *p-- = ' ';      p = memcpy (p - len, es->subsystem[sub].subsys_name, len);      return memcpy (p - unklen, unk, unklen);    }  return (char *) _(es->subsystem[sub].codes[code]);}