IO_vtable和IO_FILE结构

void attribute_hidden
_IO_vtable_check (void)
{
#ifdef SHARED
  /* Honor the compatibility flag.  */
  void (*flag) (void) = atomic_load_relaxed (&IO_accept_foreign_vtables);
#ifdef PTR_DEMANGLE
  PTR_DEMANGLE (flag);
#endif
  if (flag == &_IO_vtable_check)
    return;
  /* In case this libc copy is in a non-default namespace, we always
     need to accept foreign vtables because there is always a
     possibility that FILE * objects are passed across the linking
     boundary.  */
  {
    Dl_info di;
    struct link_map *l;
    if (!rtld_active ()
        || (_dl_addr (_IO_vtable_check, &di, &l, NULL) != 0
            && l->l_ns != LM_ID_BASE))
      return;
  }
#else /* !SHARED */
  /* We cannot perform vtable validation in the static dlopen case
     because FILE * handles might be passed back and forth across the
     boundary.  Therefore, we disable checking in this case.  */
  if (__dlopen != NULL)
    return;
#endif
  __libc_fatal ("Fatal error: glibc detected an invalid stdio handle\n");
}
/* Some variants of libstdc++ interpose _IO_2_1_stdin_ etc. and
   install their own vtables directly, without calling _IO_init or
   other functions.  Detect this by looking at the vtables values
   during startup, and disable vtable validation in this case.  */
#ifdef SHARED
__attribute__ ((constructor))
static void
check_stdfiles_vtables (void)
{
  if (_IO_2_1_stdin_.vtable != &_IO_file_jumps
      || _IO_2_1_stdout_.vtable != &_IO_file_jumps
      || _IO_2_1_stderr_.vtable != &_IO_file_jumps)
    IO_set_accept_foreign_vtables (&_IO_vtable_check);
}
#endif

 

struct _IO_FILE_plus
{
  FILE file;
  const struct _IO_jump_t *vtable;
};
#ifdef _IO_USE_OLD_IO_FILE
/* This structure is used by the compatibility code as if it were an
   _IO_FILE_plus, but has enough space to initialize the _mode argument
   of an _IO_FILE_complete.  */
struct _IO_FILE_complete_plus
{
  struct _IO_FILE_complete file;
  const struct _IO_jump_t *vtable;
};
#endif

struct _IO_FILE
{
  int _flags;                /* High-order word is _IO_MAGIC; rest is flags. */
  /* The following pointers correspond to the C++ streambuf protocol. */
  char *_IO_read_ptr;        /* Current read pointer */
  char *_IO_read_end;        /* End of get area. */
  char *_IO_read_base;        /* Start of putback+get area. */
  char *_IO_write_base;        /* Start of put area. */
  char *_IO_write_ptr;        /* Current put pointer. */
  char *_IO_write_end;        /* End of put area. */
  char *_IO_buf_base;        /* Start of reserve area. */
  char *_IO_buf_end;        /* End of reserve area. */
  /* The following fields are used to support backing up and undo. */
  char *_IO_save_base; /* Pointer to start of non-current get area. */
  char *_IO_backup_base;  /* Pointer to first valid character of backup area */
  char *_IO_save_end; /* Pointer to end of non-current get area. */
  struct _IO_marker *_markers;
  struct _IO_FILE *_chain;
  int _fileno;
  int _flags2;
  __off_t _old_offset; /* This used to be _offset but it's too small.  */
  /* 1+column number of pbase(); 0 is unknown. */
  unsigned short _cur_column;
  signed char _vtable_offset;
  char _shortbuf[1];
  _IO_lock_t *_lock;
#ifdef _IO_USE_OLD_IO_FILE
};
struct _IO_FILE_complete
{
  struct _IO_FILE _file;
#endif
  __off64_t _offset;
  /* Wide character stream stuff.  */
  struct _IO_codecvt *_codecvt;
  struct _IO_wide_data *_wide_data;
  struct _IO_FILE *_freeres_list;
  void *_freeres_buf;
  size_t __pad5;
  int _mode;
  /* Make sure we don't get into trouble again.  */
  char _unused2[15 * sizeof (int) - 4 * sizeof (void *) - sizeof (size_t)];
};