diff --git glibc-2.17-c758a686/libio/Makefile glibc-2.17-c758a686/libio/Makefile
index 22dbcae..488ee51 100644
--- glibc-2.17-c758a686/libio/Makefile
+++ glibc-2.17-c758a686/libio/Makefile
@@ -60,7 +60,7 @@ tests = tst_swprintf tst_wprintf tst_swscanf tst_wscanf tst_getwc tst_putwc   \
 	tst-wmemstream1 tst-wmemstream2 \
 	bug-memstream1 bug-wmemstream1 \
 	tst-setvbuf1 tst-popen1 tst-fgetwc bug-wsetpos tst-fseek \
-	tst-fwrite-error
+	tst-fwrite-error tst-ftell-active-handler
 ifeq (yes,$(build-shared))
 # Add test-fopenloc only if shared library is enabled since it depends on
 # shared localedata objects.
diff --git glibc-2.17-c758a686/libio/fileops.c glibc-2.17-c758a686/libio/fileops.c
index a3499be..2e7bc8d 100644
--- glibc-2.17-c758a686/libio/fileops.c
+++ glibc-2.17-c758a686/libio/fileops.c
@@ -929,6 +929,93 @@ _IO_file_sync_mmap (_IO_FILE *fp)
   return 0;
 }
 
+/* Get the current file offset using a system call.  This is the safest method
+   to get the current file offset, since we are sure that we get the current
+   state of the file.  Before the stream handle is activated (by using fread,
+   fwrite, etc.), an application may alter the state of the file descriptor
+   underlying it by calling read/write/lseek on it.  Using a cached offset at
+   this point will result in returning the incorrect value.  Same is the case
+   when one switches from reading in a+ mode to writing, where the buffer has
+   not been flushed - the cached offset would reflect the reading position
+   while the actual write position would be at the end of the file.
+
+   do_ftell and do_ftell_wide may resort to using the cached offset in some
+   special cases instead of calling get_file_offset, but those cases should be
+   thoroughly described.  */
+_IO_off64_t
+get_file_offset (_IO_FILE *fp)
+{
+  if ((fp->_flags & _IO_IS_APPENDING) == _IO_IS_APPENDING)
+    {
+      struct stat64 st;
+      bool ret = (_IO_SYSSTAT (fp, &st) == 0 && S_ISREG (st.st_mode));
+      if (ret)
+	return st.st_size;
+      else
+	return EOF;
+    }
+  else
+    return _IO_SYSSEEK (fp, 0, _IO_seek_cur);
+}
+
+
+/* ftell{,o} implementation.  Don't modify any state of the file pointer while
+   we try to get the current state of the stream.  */
+static _IO_off64_t
+do_ftell (_IO_FILE *fp)
+{
+  _IO_off64_t result = 0;
+  bool use_cached_offset = false;
+
+  /* No point looking at unflushed data if we haven't allocated buffers
+     yet.  */
+  if (fp->_IO_buf_base != NULL)
+    {
+      bool was_writing = (fp->_IO_write_ptr > fp->_IO_write_base
+			  || _IO_in_put_mode (fp));
+
+      /* Adjust for unflushed data.  */
+      if (!was_writing)
+	result -= fp->_IO_read_end - fp->_IO_read_ptr;
+      else
+	result += fp->_IO_write_ptr - fp->_IO_read_end;
+
+      /* It is safe to use the cached offset when available if there is
+	 unbuffered data (indicating that the file handle is active) and the
+	 handle is not for a file open in a+ mode.  The latter condition is
+	 because there could be a scenario where there is a switch from read
+	 mode to write mode using an fseek to an arbitrary position.  In this
+	 case, there would be unbuffered data due to be appended to the end of
+	 the file, but the offset may not necessarily be the end of the
+	 file.  It is fine to use the cached offset when the a+ stream is in
+	 read mode though, since the offset is maintained correctly in that
+	 case.  Note that this is not a comprehensive set of cases when the
+	 offset is reliable.  The offset may be reliable even in some cases
+	 where there is no unflushed input and the handle is active, but it's
+	 just that we don't have a way to identify that condition reliably.  */
+      use_cached_offset = (result != 0 && fp->_offset != _IO_pos_BAD
+			   && ((fp->_flags & (_IO_IS_APPENDING | _IO_NO_READS))
+			       == (_IO_IS_APPENDING | _IO_NO_READS)
+			       && was_writing));
+    }
+
+  if (use_cached_offset)
+    result += fp->_offset;
+  else
+    result += get_file_offset (fp);
+
+  if (result == EOF)
+    return result;
+
+  if (result < 0)
+    {
+      __set_errno (EINVAL);
+      return EOF;
+    }
+
+  return result;
+}
+
 
 _IO_off64_t
 _IO_new_file_seekoff (fp, offset, dir, mode)
@@ -940,6 +1027,13 @@ _IO_new_file_seekoff (fp, offset, dir, mode)
   _IO_off64_t result;
   _IO_off64_t delta, new_offset;
   long count;
+
+  /* Short-circuit into a separate function.  We don't want to mix any
+     functionality and we don't want to touch anything inside the FILE
+     object. */
+  if (mode == 0)
+    return do_ftell (fp);
+
   /* POSIX.1 8.2.3.7 says that after a call the fflush() the file
      offset of the underlying file must be exact.  */
   int must_be_exact = (fp->_IO_read_base == fp->_IO_read_end
@@ -948,9 +1042,6 @@ _IO_new_file_seekoff (fp, offset, dir, mode)
   bool was_writing = (fp->_IO_write_ptr > fp->_IO_write_base
 		      || _IO_in_put_mode (fp));
 
-  if (mode == 0)
-    dir = _IO_seek_cur, offset = 0; /* Don't move any pointers. */
-
   /* Flush unwritten characters.
      (This may do an unneeded write if we seek within the buffer.
      But to be able to switch to reading, we would need to set
@@ -958,7 +1049,7 @@ _IO_new_file_seekoff (fp, offset, dir, mode)
      which assumes file_ptr() is eGptr.  Anyway, since we probably
      end up flushing when we close(), it doesn't make much difference.)
      FIXME: simulate mem-mapped files. */
-  else if (was_writing && _IO_switch_to_get_mode (fp))
+  if (was_writing && _IO_switch_to_get_mode (fp))
     return EOF;
 
   if (fp->_IO_buf_base == NULL)
@@ -978,30 +1069,10 @@ _IO_new_file_seekoff (fp, offset, dir, mode)
     {
     case _IO_seek_cur:
       /* Adjust for read-ahead (bytes is buffer). */
-      if (mode != 0 || !was_writing)
-	offset -= fp->_IO_read_end - fp->_IO_read_ptr;
-      else
-	{
-	  /* _IO_read_end coincides with fp._offset, so the actual file position
-	     is fp._offset - (_IO_read_end - new_write_ptr).  This is fine
-	     even if fp._offset is not set, since fp->_IO_read_end is then at
-	     _IO_buf_base and this adjustment is for unbuffered output.  */
-	  offset -= fp->_IO_read_end - fp->_IO_write_ptr;
-	}
+      offset -= fp->_IO_read_end - fp->_IO_read_ptr;
 
       if (fp->_offset == _IO_pos_BAD)
-	{
-	  if (mode != 0)
-	    goto dumb;
-	  else
-	    {
-	      result = _IO_SYSSEEK (fp, 0, dir);
-	      if (result == EOF)
-		return result;
-
-	      fp->_offset = result;
-	    }
-	}
+	goto dumb;
       /* Make offset absolute, assuming current pointer is file_ptr(). */
       offset += fp->_offset;
       if (offset < 0)
@@ -1028,10 +1099,6 @@ _IO_new_file_seekoff (fp, offset, dir, mode)
     }
   /* At this point, dir==_IO_seek_set. */
 
-  /* If we are only interested in the current position we've found it now.  */
-  if (mode == 0)
-    return offset;
-
   /* If destination is within current buffer, optimize: */
   if (fp->_offset != _IO_pos_BAD && fp->_IO_read_base != NULL
       && !_IO_in_backup (fp))
diff --git glibc-2.17-c758a686/libio/iofdopen.c glibc-2.17-c758a686/libio/iofdopen.c
index 066ff19..3f266f7 100644
--- glibc-2.17-c758a686/libio/iofdopen.c
+++ glibc-2.17-c758a686/libio/iofdopen.c
@@ -141,9 +141,6 @@ _IO_new_fdopen (fd, mode)
 #ifdef _IO_MTSAFE_IO
   new_f->fp.file._lock = &new_f->lock;
 #endif
-  /* Set up initially to use the `maybe_mmap' jump tables rather than using
-     __fopen_maybe_mmap to do it, because we need them in place before we
-     call _IO_file_attach or else it will allocate a buffer immediately.  */
   _IO_no_init (&new_f->fp.file, 0, 0, &new_f->wd,
 #ifdef _G_HAVE_MMAP
 	       (use_mmap && (read_write & _IO_NO_WRITES))
@@ -159,13 +156,12 @@ _IO_new_fdopen (fd, mode)
 #if  !_IO_UNIFIED_JUMPTABLES
   new_f->fp.vtable = NULL;
 #endif
-  if (_IO_file_attach ((_IO_FILE *) &new_f->fp, fd) == NULL)
-    {
-      _IO_setb (&new_f->fp.file, NULL, NULL, 0);
-      _IO_un_link (&new_f->fp);
-      free (new_f);
-      return NULL;
-    }
+  /* We only need to record the fd because _IO_file_init will have unset the
+     offset.  It is important to unset the cached offset because the real
+     offset in the file could change between now and when the handle is
+     activated and we would then mislead ftell into believing that we have a
+     valid offset.  */
+  new_f->fp.file._fileno = fd;
   new_f->fp.file._flags &= ~_IO_DELETE_DONT_CLOSE;
 
   _IO_mask_flags (&new_f->fp.file, read_write,
diff --git glibc-2.17-c758a686/libio/iofwide.c glibc-2.17-c758a686/libio/iofwide.c
index 5cff632..64187e4 100644
--- glibc-2.17-c758a686/libio/iofwide.c
+++ glibc-2.17-c758a686/libio/iofwide.c
@@ -199,12 +199,6 @@ _IO_fwide (fp, mode)
 
       /* From now on use the wide character callback functions.  */
       ((struct _IO_FILE_plus *) fp)->vtable = fp->_wide_data->_wide_vtable;
-
-      /* One last twist: we get the current stream position.  The wide
-	 char streams have much more problems with not knowing the
-	 current position and so we should disable the optimization
-	 which allows the functions without knowing the position.  */
-      fp->_offset = _IO_SYSSEEK (fp, 0, _IO_seek_cur);
     }
 
   /* Set the mode now.  */
diff --git glibc-2.17-c758a686/libio/libioP.h glibc-2.17-c758a686/libio/libioP.h
index 4ca723c..8a7b85b 100644
--- glibc-2.17-c758a686/libio/libioP.h
+++ glibc-2.17-c758a686/libio/libioP.h
@@ -397,6 +397,7 @@ extern void _IO_wdoallocbuf (_IO_FILE *) __THROW;
 libc_hidden_proto (_IO_wdoallocbuf)
 extern void _IO_unsave_wmarkers (_IO_FILE *) __THROW;
 extern unsigned _IO_adjust_wcolumn (unsigned, const wchar_t *, int) __THROW;
+extern _IO_off64_t get_file_offset (_IO_FILE *fp);
 
 /* Marker-related function. */
 
diff --git glibc-2.17-c758a686/libio/tst-ftell-active-handler.c glibc-2.17-c758a686/libio/tst-ftell-active-handler.c
new file mode 100644
index 0000000..175e904
--- /dev/null
+++ glibc-2.17-c758a686/libio/tst-ftell-active-handler.c
@@ -0,0 +1,384 @@
+/* Verify that ftell returns the correct value at various points before and
+   after the handler on which it is called becomes active.
+   Copyright (C) 2014 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <locale.h>
+#include <wchar.h>
+
+static int do_test (void);
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
+
+#define get_handles_fdopen(filename, fd, fp, fd_mode, mode) \
+({									      \
+  int ret = 0;								      \
+  (fd) = open ((filename), (fd_mode), 0);				      \
+  if ((fd) == -1)							      \
+    {									      \
+      printf ("open failed: %m\n");					      \
+      ret = 1;								      \
+    }									      \
+  else									      \
+    {									      \
+      (fp) = fdopen ((fd), (mode));					      \
+      if ((fp) == NULL)							      \
+        {								      \
+          printf ("fdopen failed: %m\n");				      \
+          close (fd);							      \
+          ret = 1;							      \
+        }								      \
+    }									      \
+  ret;									      \
+})
+
+#define get_handles_fopen(filename, fd, fp, mode) \
+({									      \
+  int ret = 0;								      \
+  (fp) = fopen ((filename), (mode));					      \
+  if ((fp) == NULL)							      \
+    {									      \
+      printf ("fopen failed: %m\n");					      \
+      ret = 1;								      \
+    }									      \
+  else									      \
+    {									      \
+      (fd) = fileno (fp);						      \
+      if ((fd) == -1)							      \
+        {								      \
+	  printf ("fileno failed: %m\n");				      \
+	  ret = 1;							      \
+	}								      \
+    }									      \
+  ret;									      \
+})
+
+/* data points to either char_data or wide_data, depending on whether we're
+   testing regular file mode or wide mode respectively.  Similarly,
+   fputs_func points to either fputs or fputws.  data_len keeps track of the
+   length of the current data and file_len maintains the current file
+   length.  */
+static const void *data;
+static const char *char_data = "abcdef";
+static const wchar_t *wide_data = L"abcdef";
+static size_t data_len;
+static size_t file_len;
+
+typedef int (*fputs_func_t) (const void *data, FILE *fp);
+fputs_func_t fputs_func;
+
+/* Test that the value of ftell is not cached when the stream handle is not
+   active.  */
+static int
+do_ftell_test (const char *filename)
+{
+  int ret = 0;
+  struct test
+    {
+      const char *mode;
+      int fd_mode;
+      size_t old_off;
+      size_t new_off;
+    } test_modes[] = {
+	  /* In w, w+ and r+ modes, the file position should be at the
+	     beginning of the file.  After the write, the offset should be
+	     updated to data_len.  */
+	  {"w", O_WRONLY, 0, data_len},
+	  {"w+", O_RDWR, 0, data_len},
+	  {"r+", O_RDWR, 0, data_len},
+	  /* For 'a' and 'a+' modes, the initial file position should be the
+	     current end of file. After the write, the offset has data_len
+	     added to the old value.  */
+	  {"a", O_WRONLY, data_len, 2 * data_len},
+	  {"a+", O_RDWR, 2 * data_len, 3 * data_len},
+    };
+  for (int j = 0; j < 2; j++)
+    {
+      for (int i = 0; i < sizeof (test_modes) / sizeof (struct test); i++)
+	{
+	  FILE *fp;
+	  int fd;
+	  printf ("\tftell: %s (file, \"%s\"): ", j == 0 ? "fdopen" : "fopen",
+		  test_modes[i].mode);
+
+	  if (j == 0)
+	    ret = get_handles_fdopen (filename, fd, fp, test_modes[i].fd_mode,
+				      test_modes[i].mode);
+	  else
+	    ret = get_handles_fopen (filename, fd, fp, test_modes[i].mode);
+
+	  if (ret != 0)
+	    return ret;
+
+	  long off = ftell (fp);
+	  if (off != test_modes[i].old_off)
+	    {
+	      printf ("Incorrect old offset.  Expected %zu but got %ld, ",
+		      test_modes[i].old_off, off);
+	      ret |= 1;
+	    }
+	  else
+	    printf ("old offset = %ld, ", off);
+
+	  /* The effect of this write on the offset should be seen in the ftell
+	     call that follows it.  */
+	  int ret = write (fd, data, data_len);
+	  off = ftell (fp);
+
+	  if (off != test_modes[i].new_off)
+	    {
+	      printf ("Incorrect new offset.  Expected %zu but got %ld\n",
+		      test_modes[i].old_off, off);
+	      ret |= 1;
+	    }
+	  else
+	    printf ("new offset = %ld\n", off);
+
+	  fclose (fp);
+	}
+    }
+
+  return ret;
+}
+
+/* This test opens the file for writing, moves the file offset of the
+   underlying file, writes out data and then checks if ftell trips on it.  */
+static int
+do_write_test (const char *filename)
+{
+  FILE *fp = NULL;
+  int fd;
+  int ret = 0;
+  struct test
+    {
+      const char *mode;
+      int fd_mode;
+    } test_modes[] = {
+	  {"w", O_WRONLY},
+	  {"w+", O_RDWR},
+	  {"r+", O_RDWR}
+    };
+
+  for (int j = 0; j < 2; j++)
+    {
+      for (int i = 0; i < sizeof (test_modes) / sizeof (struct test); i++)
+	{
+	  printf ("\twrite: %s (file, \"%s\"): ", j == 0 ? "fopen" : "fdopen",
+		  test_modes[i].mode);
+
+	  if (j == 0)
+	    ret = get_handles_fopen (filename, fd, fp, test_modes[i].mode);
+	  else
+	    ret = get_handles_fdopen (filename, fd, fp, test_modes[i].fd_mode,
+				      test_modes[i].mode);
+
+	  if (ret != 0)
+	    return ret;
+
+	  /* Move offset to just before the end of the file.  */
+	  off_t ret = lseek (fd, file_len - 1, SEEK_SET);
+	  if (ret == -1)
+	    {
+	      printf ("lseek failed: %m\n");
+	      ret |= 1;
+	    }
+
+	  /* Write some data.  */
+	  size_t written = fputs_func (data, fp);
+
+	  if (written == EOF)
+	    {
+	      printf ("fputs[1] failed to write data\n");
+	      ret |= 1;
+	    }
+
+	  /* Verify that the offset points to the end of the file.  The length
+	     of the file would be the original length + the length of data
+	     written to it - the amount by which we moved the offset using
+	     lseek.  */
+	  long offset = ftell (fp);
+	  file_len = file_len - 1 + data_len;
+
+	  if (offset != file_len)
+	    {
+	      printf ("Incorrect offset.  Expected %zu, but got %ld\n",
+		      file_len, offset);
+
+	      ret |= 1;
+	    }
+
+	  printf ("offset = %ld\n", offset);
+	  fclose (fp);
+        }
+    }
+
+  return ret;
+}
+
+/* This test opens a file in append mode, writes some data, and then verifies
+   that ftell does not trip over it.  */
+static int
+do_append_test (const char *filename)
+{
+  FILE *fp = NULL;
+  int ret = 0;
+  int fd;
+
+  struct test
+    {
+      const char *mode;
+      int fd_mode;
+    } test_modes[] = {
+	  {"a", O_WRONLY},
+	  {"a+", O_RDWR}
+    };
+
+  for (int j = 0; j < 2; j++)
+    {
+      for (int i = 0; i < sizeof (test_modes) / sizeof (struct test); i++)
+	{
+	  printf ("\tappend: %s (file, \"%s\"): ", j == 0 ? "fopen" : "fdopen",
+		  test_modes[i].mode);
+
+	  if (j == 0)
+	    ret = get_handles_fopen (filename, fd, fp, test_modes[i].mode);
+	  else
+	    ret = get_handles_fdopen (filename, fd, fp, test_modes[i].fd_mode,
+				      test_modes[i].mode);
+
+	  if (ret != 0)
+	    return ret;
+
+	  /* Write some data.  */
+	  size_t written = fputs_func (data, fp);
+
+	  if (written == EOF)
+	    {
+	      printf ("fputs[1] failed to write all data\n");
+	      ret |= 1;
+	    }
+
+	  /* Verify that the offset points to the end of the file.  The file
+	     len is maintained by adding data_len each time to reflect the data
+	     written to it.  */
+	  long offset = ftell (fp);
+	  file_len += data_len;
+
+	  if (offset != file_len)
+	    {
+	      printf ("Incorrect offset.  Expected %zu, but got %ld\n",
+		      file_len, offset);
+
+	      ret |= 1;
+	    }
+
+	  printf ("offset = %ld\n", offset);
+	  fclose (fp);
+	}
+    }
+
+  return ret;
+}
+
+static int
+do_one_test (const char *filename)
+{
+  int ret = 0;
+
+  ret |= do_ftell_test (filename);
+  ret |= do_write_test (filename);
+  ret |= do_append_test (filename);
+
+  return ret;
+}
+
+/* Run a set of tests for ftell for regular files and wide mode files.  */
+static int
+do_test (void)
+{
+  int ret = 0;
+  FILE *fp = NULL;
+  char *filename;
+  size_t written;
+  int fd = create_temp_file ("tst-active-handler-tmp.", &filename);
+
+  if (fd == -1)
+    {
+      printf ("create_temp_file: %m\n");
+      return 1;
+    }
+
+  fp = fdopen (fd, "w");
+  if (fp == NULL)
+    {
+      printf ("fdopen[0]: %m\n");
+      close (fd);
+      return 1;
+    }
+
+  data = char_data;
+  data_len = strlen (char_data);
+  file_len = strlen (char_data);
+  written = fputs (data, fp);
+
+  if (written == EOF)
+    {
+      printf ("fputs[1] failed to write data\n");
+      ret = 1;
+    }
+
+  fclose (fp);
+  if (ret)
+    return ret;
+
+  /* Tests for regular files.  */
+  puts ("Regular mode:");
+  fputs_func = (fputs_func_t) fputs;
+  data = char_data;
+  data_len = strlen (char_data);
+  ret |= do_one_test (filename);
+
+  /* Truncate the file before repeating the tests in wide mode.  */
+  fp = fopen (filename, "w");
+  if (fp == NULL)
+    {
+      printf ("fopen failed %m\n");
+      return 1;
+    }
+  fclose (fp);
+
+  /* Tests for wide files.  */
+  puts ("Wide mode:");
+  if (setlocale (LC_ALL, "en_US.UTF-8") == NULL)
+    {
+      printf ("Cannot set en_US.UTF-8 locale.\n");
+      return 1;
+    }
+  fputs_func = (fputs_func_t) fputws;
+  data = wide_data;
+  data_len = wcslen (wide_data);
+  ret |= do_one_test (filename);
+
+  return ret;
+}
diff --git glibc-2.17-c758a686/libio/wfileops.c glibc-2.17-c758a686/libio/wfileops.c
index 9cebe77..8b2e108 100644
--- glibc-2.17-c758a686/libio/wfileops.c
+++ glibc-2.17-c758a686/libio/wfileops.c
@@ -596,29 +596,25 @@ done:
   return 0;
 }
 
-_IO_off64_t
-_IO_wfile_seekoff (fp, offset, dir, mode)
-     _IO_FILE *fp;
-     _IO_off64_t offset;
-     int dir;
-     int mode;
+/* ftell{,o} implementation for wide mode.  Don't modify any state of the file
+   pointer while we try to get the current state of the stream.  */
+static _IO_off64_t
+do_ftell_wide (_IO_FILE *fp)
 {
-  _IO_off64_t result;
-  _IO_off64_t delta, new_offset;
-  long int count;
-  /* POSIX.1 8.2.3.7 says that after a call the fflush() the file
-     offset of the underlying file must be exact.  */
-  int must_be_exact = ((fp->_wide_data->_IO_read_base
-			== fp->_wide_data->_IO_read_end)
-		       && (fp->_wide_data->_IO_write_base
-			   == fp->_wide_data->_IO_write_ptr));
+  _IO_off64_t result, offset = 0;
+  bool use_cached_offset = false;
 
-  bool was_writing = ((fp->_wide_data->_IO_write_ptr
-		       > fp->_wide_data->_IO_write_base)
-		      || _IO_in_put_mode (fp));
-
-  if (mode == 0)
+  /* No point looking for offsets in the buffer if it hasn't even been
+     allocated.  */
+  if (fp->_wide_data->_IO_buf_base != NULL)
     {
+      const wchar_t *wide_read_base;
+      const wchar_t *wide_read_ptr;
+      const wchar_t *wide_read_end;
+      bool was_writing = ((fp->_wide_data->_IO_write_ptr
+			   > fp->_wide_data->_IO_write_base)
+			  || _IO_in_put_mode (fp));
+
       /* XXX For wide stream with backup store it is not very
 	 reasonable to determine the offset.  The pushed-back
 	 character might require a state change and we need not be
@@ -633,14 +629,142 @@ _IO_wfile_seekoff (fp, offset, dir, mode)
 	      return -1;
 	    }
 
-	  /* There is no more data in the backup buffer.  We can
-	     switch back.  */
-	  _IO_switch_to_main_wget_area (fp);
+	  /* Nothing in the backup store, so note the backed up pointers
+	     without changing the state.  */
+	  wide_read_base = fp->_wide_data->_IO_save_base;
+	  wide_read_ptr = wide_read_base;
+	  wide_read_end = fp->_wide_data->_IO_save_end;
+	}
+      else
+	{
+	  wide_read_base = fp->_wide_data->_IO_read_base;
+	  wide_read_ptr = fp->_wide_data->_IO_read_ptr;
+	  wide_read_end = fp->_wide_data->_IO_read_end;
+	}
+
+      struct _IO_codecvt *cv = fp->_codecvt;
+      int clen = (*cv->__codecvt_do_encoding) (cv);
+
+      if (!was_writing)
+	{
+	  if (clen > 0)
+	    {
+	      offset -= (wide_read_end - wide_read_ptr) * clen;
+	      offset -= fp->_IO_read_end - fp->_IO_read_ptr;
+	    }
+	  else
+	    {
+	      int nread;
+
+	      size_t delta = wide_read_ptr - wide_read_base;
+	      __mbstate_t state = fp->_wide_data->_IO_last_state;
+	      nread = (*cv->__codecvt_do_length) (cv, &state,
+						  fp->_IO_read_base,
+						  fp->_IO_read_end, delta);
+	      offset -= fp->_IO_read_end - fp->_IO_read_base - nread;
+	    }
+	}
+      else
+	{
+	  if (clen > 0)
+	    offset += (fp->_wide_data->_IO_write_ptr
+		       - fp->_wide_data->_IO_write_base) * clen;
+	  else
+	    {
+	      size_t delta = (fp->_wide_data->_IO_write_ptr
+			      - fp->_wide_data->_IO_write_base);
+
+	      /* Allocate enough space for the conversion.  */
+	      size_t outsize = delta * sizeof (wchar_t);
+	      char *out = malloc (outsize);
+	      char *outstop = out;
+	      const wchar_t *in = fp->_wide_data->_IO_write_base;
+
+	      enum __codecvt_result status;
+
+	      __mbstate_t state = fp->_wide_data->_IO_last_state;
+	      status = (*cv->__codecvt_do_out) (cv, &state,
+						in, in + delta, &in,
+						out, out + outsize, &outstop);
+
+	      /* We don't check for __codecvt_partial because it can be
+		 returned on one of two conditions: either the output
+		 buffer is full or the input sequence is incomplete.  We
+		 take care to allocate enough buffer and our input
+		 sequences must be complete since they are accepted as
+		 wchar_t; if not, then that is an error.  */
+	      if (__glibc_unlikely (status != __codecvt_ok))
+		return WEOF;
+
+	      offset += outstop - out;
+	    }
+
+	  /* _IO_read_end coincides with fp._offset, so the actual file
+	     position is fp._offset - (_IO_read_end - new_write_ptr).  */
+	  offset -= fp->_IO_read_end - fp->_IO_write_ptr;
 	}
 
-      dir = _IO_seek_cur, offset = 0; /* Don't move any pointers. */
+      /* It is safe to use the cached offset when available if there is
+	 unbuffered data (indicating that the file handle is active) and
+	 the handle is not for a file open in a+ mode.  The latter
+	 condition is because there could be a scenario where there is a
+	 switch from read mode to write mode using an fseek to an arbitrary
+	 position.  In this case, there would be unbuffered data due to be
+	 appended to the end of the file, but the offset may not
+	 necessarily be the end of the file.  It is fine to use the cached
+	 offset when the a+ stream is in read mode though, since the offset
+	 is maintained correctly in that case.  Note that this is not a
+	 comprehensive set of cases when the offset is reliable.  The
+	 offset may be reliable even in some cases where there is no
+	 unflushed input and the handle is active, but it's just that we
+	 don't have a way to identify that condition reliably.  */
+      use_cached_offset = (offset != 0 && fp->_offset != _IO_pos_BAD
+			   && ((fp->_flags & (_IO_IS_APPENDING | _IO_NO_READS))
+			       == (_IO_IS_APPENDING | _IO_NO_READS)
+			       && was_writing));
     }
 
+  if (use_cached_offset)
+    result = fp->_offset;
+  else
+    result = get_file_offset (fp);
+
+  if (result == EOF)
+    return result;
+
+  result += offset;
+
+  return result;
+}
+
+_IO_off64_t
+_IO_wfile_seekoff (fp, offset, dir, mode)
+     _IO_FILE *fp;
+     _IO_off64_t offset;
+     int dir;
+     int mode;
+{
+  _IO_off64_t result;
+  _IO_off64_t delta, new_offset;
+  long int count;
+
+  /* Short-circuit into a separate function.  We don't want to mix any
+     functionality and we don't want to touch anything inside the FILE
+     object. */
+  if (mode == 0)
+    return do_ftell_wide (fp);
+
+  /* POSIX.1 8.2.3.7 says that after a call the fflush() the file
+     offset of the underlying file must be exact.  */
+  int must_be_exact = ((fp->_wide_data->_IO_read_base
+			== fp->_wide_data->_IO_read_end)
+		       && (fp->_wide_data->_IO_write_base
+			   == fp->_wide_data->_IO_write_ptr));
+
+  bool was_writing = ((fp->_wide_data->_IO_write_ptr
+		       > fp->_wide_data->_IO_write_base)
+		      || _IO_in_put_mode (fp));
+
   /* Flush unwritten characters.
      (This may do an unneeded write if we seek within the buffer.
      But to be able to switch to reading, we would need to set
@@ -648,7 +772,7 @@ _IO_wfile_seekoff (fp, offset, dir, mode)
      which assumes file_ptr() is eGptr.  Anyway, since we probably
      end up flushing when we close(), it doesn't make much difference.)
      FIXME: simulate mem-mapped files. */
-  else if (was_writing && _IO_switch_to_wget_mode (fp))
+  if (was_writing && _IO_switch_to_wget_mode (fp))
     return WEOF;
 
   if (fp->_wide_data->_IO_buf_base == NULL)
@@ -693,7 +817,6 @@ _IO_wfile_seekoff (fp, offset, dir, mode)
 	    {
 	      int nread;
 
-	    flushed:
 	      delta = (fp->_wide_data->_IO_read_ptr
 		       - fp->_wide_data->_IO_read_base);
 	      fp->_wide_data->_IO_state = fp->_wide_data->_IO_last_state;
@@ -706,80 +829,9 @@ _IO_wfile_seekoff (fp, offset, dir, mode)
 	      offset -= fp->_IO_read_end - fp->_IO_read_base - nread;
 	    }
 	}
-      else
-	{
-	  char *new_write_ptr = fp->_IO_write_ptr;
-
-	  if (clen > 0)
-	    offset += (fp->_wide_data->_IO_write_ptr
-		       - fp->_wide_data->_IO_write_base) / clen;
-	  else
-	    {
-	      enum __codecvt_result status = __codecvt_ok;
-	      delta = (fp->_wide_data->_IO_write_ptr
-		       - fp->_wide_data->_IO_write_base);
-	      const wchar_t *write_base = fp->_wide_data->_IO_write_base;
-
-	      /* FIXME: This actually ends up in two iterations of conversion,
-		 one here and the next when the buffer actually gets flushed.
-		 It may be possible to optimize this in future so that
-		 wdo_write identifies already converted content and does not
-		 redo it.  In any case, this is much better than having to
-		 flush buffers for every ftell.  */
-	      do
-		{
-		  /* There is not enough space in the buffer to do the entire
-		     conversion, so there is no point trying to avoid the
-		     buffer flush.  Just do it and go back to how it was with
-		     the read mode.  */
-		  if (status == __codecvt_partial
-		      || (delta > 0 && new_write_ptr == fp->_IO_buf_end))
-		    {
-		      if (_IO_switch_to_wget_mode (fp))
-			return WEOF;
-		      goto flushed;
-		    }
-
-		  const wchar_t *new_wbase = fp->_wide_data->_IO_write_base;
-		  fp->_wide_data->_IO_state = fp->_wide_data->_IO_last_state;
-		  status = (*cv->__codecvt_do_out) (cv,
-						    &fp->_wide_data->_IO_state,
-						    write_base,
-						    write_base + delta,
-						    &new_wbase,
-						    new_write_ptr,
-						    fp->_IO_buf_end,
-						    &new_write_ptr);
-
-		  delta -= new_wbase - write_base;
-
-		  /* If there was an error, then return WEOF.
-		     TODO: set buffer state.  */
-		  if (__builtin_expect (status == __codecvt_error, 0))
-		      return WEOF;
-		}
-	      while (delta > 0);
-	    }
-
-	  /* _IO_read_end coincides with fp._offset, so the actual file position
-	     is fp._offset - (_IO_read_end - new_write_ptr).  This is fine
-	     even if fp._offset is not set, since fp->_IO_read_end is then at
-	     _IO_buf_base and this adjustment is for unbuffered output.  */
-	  offset -= fp->_IO_read_end - new_write_ptr;
-	}
 
       if (fp->_offset == _IO_pos_BAD)
-	{
-	  if (mode != 0)
-	    goto dumb;
-	  else
-	    {
-	      result = _IO_SYSSEEK (fp, 0, dir);
-	      if (result == EOF)
-		return result;
-	      fp->_offset = result;
-	    }
-	}
+	goto dumb;
 
       /* Make offset absolute, assuming current pointer is file_ptr(). */
       offset += fp->_offset;
@@ -802,10 +854,6 @@ _IO_wfile_seekoff (fp, offset, dir, mode)
     }
   /* At this point, dir==_IO_seek_set. */
 
-  /* If we are only interested in the current position we've found it now.  */
-  if (mode == 0)
-    return offset;
-
   /* If destination is within current buffer, optimize: */
   if (fp->_offset != _IO_pos_BAD && fp->_IO_read_base != NULL
       && !_IO_in_backup (fp))