Re: [PATCH 2/2] libio: Fix seek-past-end returned size for open_{w}memstream (BZ#15298)

[Florian Weimer <fweimer at redhat dot com>]

On 08/05/2016 07:40 PM, Adhemerval Zanella wrote:
> +static _IO_off64_t
> +_IO_wmem_seekoff (_IO_FILE *fp, _IO_off64_t offset, int dir, int mode)
> +{
> +  struct _IO_FILE_wmemstream *mp = (struct _IO_FILE_wmemstream *) fp;
> +  if (fp->_wide_data->_IO_write_ptr != mp->seekwriteptr)
> +    mp->prevwriteptr = fp->_wide_data->_IO_write_ptr;
> +  _IO_off64_t ret = _IO_wstr_seekoff (fp, offset, dir, mode);
> +  mp->seekwriteptr = fp->_wide_data->_IO_write_ptr;
> +  return ret;
> +}

As far as I can see, glibc will not call seekoff from the vfprintf code, 
ever, and _IO_wstr_jumps is only used for that.  This means the only 
actual use of _IO_wstr_seekoff is in the wmemstream code.  So you could 
rename/move _IO_wstr_seekoff and change it directly.  It should be fine 
to use a NULL pointer in _IO_wstr_jumops, just like _IO_obstack_jumps does.

In contrast, _IO_str_seekoff is used from libstdc++ in GCC 2.95, so we 
cannot change it.

Florian