DataFlow for `va_start`

LLVM Project
1

Hi, How can I taint the Variable parameter using dfsan ?

like this function:

TIFFSetField(tif, dp->tdir_tag, data);
int TIFFSetField(TIFF *tif, uint32_t tag, ...)
{
    va_list ap;
    int status;

    va_start(ap, tag);
    status = TIFFVSetField(tif, tag, ap);
    va_end(ap);
    return (status);
}

I found I miss the data taint info after va_start .