libio: Fix open_memstream flush (NULL)

Message ID 1499703585-17933-1-git-send-email-adhemerval.zanella@linaro.org
State New
Headers show

Commit Message

Adhemerval Zanella July 10, 2017, 4:19 p.m.
POSIX specifies that the state and size after a fflush on a stream
opened by open_memstream should be updated and current implementation
does not act accordingly on a fflush (NULL) (meant to act on all opened
streams).

This patch fixes it for open_{w}memstream and also adjust the
tst-memstream3 to use libsupport.

Checked on x86_64-linux-gnu.

	[BZ #21735]
	* libio/memstream.c (_IO_mem_overflow): New function.
	(_IO_mem_jumps): User _IO_mem_overflow instead of _IO_str_overflow.
	(__open_memstream): Call _IO_link_in on the internal FILE object.
	* libio/wmemstream.c (_IO_wmem_overflow): New function.
	(_IO_wmem_jumps): User _IO_wmem_overflow instead of _IO_wstr_overflow.
	(__open_wmemstream): Call _IO_link_in on the internal FILE object.
	* libio/tst-memstream3.c (mcheck_abort): Use libsupport.
	(do_test_bz18241): Likewise.
	(do_test_bz20181): Likewise.
	(do_test_bz21735): New function.
---
 ChangeLog              | 14 +++++++
 libio/memstream.c      | 15 +++++++-
 libio/tst-memstream3.c | 99 +++++++++++++++++++++++++++++---------------------
 libio/wmemstream.c     | 16 +++++++-
 4 files changed, 100 insertions(+), 44 deletions(-)

-- 
2.7.4

Comments

Florian Weimer July 11, 2017, 11:40 p.m. | #1
* Adhemerval Zanella:

> POSIX specifies that the state and size after a fflush on a stream

> opened by open_memstream should be updated and current implementation

> does not act accordingly on a fflush (NULL) (meant to act on all opened

> streams).

>

> This patch fixes it for open_{w}memstream and also adjust the

> tst-memstream3 to use libsupport.


Subject is wrong, it should be fflush.

Please put the test case into a new file, and change it to call fflush
(NULL); it currently calls fflush (fp).  As a result, it does not
actually test the change.

You also need to verify that this does not call malloc:

#include <stdio.h>
#include <stdlib.h>
#include <err.h>

int
main (void)
{
  char * buffer = NULL;
  size_t length = 0;
  FILE *fp = open_memstream (&buffer, &length);
  if (fp == NULL)
    err (1, "open_memstream");
  abort ();
}

I think we don't want the malloc call for a call to exit, either.
Similarly for __stack_chk_fail, but that's something we need to fix
there.

> +static int

> +_IO_mem_overflow (_IO_FILE *fp, int c)

> +{

> +  int ret = _IO_str_overflow (fp, c);

> +

> +  struct _IO_FILE_memstream *mp = (struct _IO_FILE_memstream *) fp;

> +  *mp->sizeloc = fp->_IO_write_ptr - fp->_IO_write_base;

> +

> +  return ret;

> +}


_IO_str_overflow does not correctly process an EOF argument, but
_IO_flush_all_lockp calls the overflow function with EOF.  This is the
reason why the test with fflush (NULL) fails.

The most direct fix appears to be to call _IO_mem_sync for c == EOF.

Let me suggest again that libio changes are not appropriate during the
freeze.
Adhemerval Zanella July 12, 2017, 2:52 p.m. | #2
On 11/07/2017 20:40, Florian Weimer wrote:
> * Adhemerval Zanella:

> 

>> POSIX specifies that the state and size after a fflush on a stream

>> opened by open_memstream should be updated and current implementation

>> does not act accordingly on a fflush (NULL) (meant to act on all opened

>> streams).

>>

>> This patch fixes it for open_{w}memstream and also adjust the

>> tst-memstream3 to use libsupport.

> 

> Subject is wrong, it should be fflush.


Ack, fixed locally.

> 

> Please put the test case into a new file, and change it to call fflush

> (NULL); it currently calls fflush (fp).  As a result, it does not

> actually test the change.


Indeed, I used you suggestion to call _IO_mem_sync for EOF. For tests,
used the previous tst-{w}memstream3.c one to avoid all the boilerplate
required to add a new tests, but I think adding a new one should be
better to reference the bug and backport.

> 

> You also need to verify that this does not call malloc:

> 

> #include <stdio.h>

> #include <stdlib.h>

> #include <err.h>

> 

> int

> main (void)

> {

>   char * buffer = NULL;

>   size_t length = 0;

>   FILE *fp = open_memstream (&buffer, &length);

>   if (fp == NULL)

>     err (1, "open_memstream");

>   abort ();

> }

> 

> I think we don't want the malloc call for a call to exit, either.

> Similarly for __stack_chk_fail, but that's something we need to fix

> there.


I am not following, what exactly should not call malloc here? Since
the open_memstream is a valid call, it will allocate both the initial
internal FILE object (libio/memstream.c:77) and initial buffer 
(libio/memstream.c:84). Are you saying that we should start with an
empty buffer instead? If it is the for I think we can do it, but it
would require more intrusive changes I think.

> 

>> +static int

>> +_IO_mem_overflow (_IO_FILE *fp, int c)

>> +{

>> +  int ret = _IO_str_overflow (fp, c);

>> +

>> +  struct _IO_FILE_memstream *mp = (struct _IO_FILE_memstream *) fp;

>> +  *mp->sizeloc = fp->_IO_write_ptr - fp->_IO_write_base;

>> +

>> +  return ret;

>> +}

> 

> _IO_str_overflow does not correctly process an EOF argument, but

> _IO_flush_all_lockp calls the overflow function with EOF.  This is the

> reason why the test with fflush (NULL) fails.

> 

> The most direct fix appears to be to call _IO_mem_sync for c == EOF.

> 

> Let me suggest again that libio changes are not appropriate during the

> freeze.

> 


So do you prefer to just add a workaround to disable the single-thread
optimization for open_memstream and fix it on 2.27?  IMHO this fix touches
only the open_memstream itself, so it should not regress any other libio
code so I would prefer than carry a workaround for 2.26.

In any case, I updated the patch based on your review below.  It passed
both your threaded case for open_memstream that is failing on master the
testcase for BZ#21735.

---
	[BZ #21735]
	* libio/memstream.c (_IO_mem_overflow): New function.
	(_IO_mem_jumps): User _IO_mem_overflow instead of _IO_str_overflow.
	(__open_memstream): Call _IO_link_in on the internal FILE object.
	* libio/wmemstream.c (_IO_wmem_overflow): New function.
	(_IO_wmem_jumps): User _IO_wmem_overflow instead of _IO_wstr_overflow.
	(__open_wmemstream): Call _IO_link_in on the internal FILE object.
	* libio/Makefile (test): Add tst-memstream4 and tst-wmemstream4.
	* libio/tst-memstream4.c: New file.
	* libio/tst-wmemstream4.c: Likewise.
	* libio/tst-memstream.h: Likewise.
---

-- 
2.7.4diff --git a/libio/Makefile b/libio/Makefile
index a002a33..6ee809a 100644
--- a/libio/Makefile
+++ b/libio/Makefile
@@ -57,8 +57,8 @@ tests = tst_swprintf tst_wprintf tst_swscanf tst_wscanf tst_getwc tst_putwc   \
 	tst-mmap-eofsync tst-mmap-fflushsync bug-mmap-fflush \
 	tst-mmap2-eofsync tst-mmap-offend bug-fopena+ bug-wfflush \
 	bug-ungetc2 bug-ftell bug-ungetc3 bug-ungetc4 tst-fopenloc2 \
-	tst-memstream1 tst-memstream2 tst-memstream3 \
-	tst-wmemstream1 tst-wmemstream2 tst-wmemstream3 \
+	tst-memstream1 tst-memstream2 tst-memstream3 tst-memstream4 \
+	tst-wmemstream1 tst-wmemstream2 tst-wmemstream3 tst-wmemstream4 \
 	bug-memstream1 bug-wmemstream1 \
 	tst-setvbuf1 tst-popen1 tst-fgetwc bug-wsetpos tst-fseek \
 	tst-fwrite-error tst-ftell-partial-wide tst-ftell-active-handler \
diff --git a/libio/memstream.c b/libio/memstream.c
index f83d4a5..5fdd071 100644
--- a/libio/memstream.c
+++ b/libio/memstream.c
@@ -31,13 +31,14 @@ struct _IO_FILE_memstream
 
 static int _IO_mem_sync (_IO_FILE* fp) __THROW;
 static void _IO_mem_finish (_IO_FILE* fp, int) __THROW;
+static int _IO_mem_overflow (_IO_FILE *fp, int c) __THROW;
 
 
 static const struct _IO_jump_t _IO_mem_jumps libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT (finish, _IO_mem_finish),
-  JUMP_INIT (overflow, _IO_str_overflow),
+  JUMP_INIT (overflow, _IO_mem_overflow),
   JUMP_INIT (underflow, _IO_str_underflow),
   JUMP_INIT (uflow, _IO_default_uflow),
   JUMP_INIT (pbackfail, _IO_str_pbackfail),
@@ -87,6 +88,7 @@ __open_memstream (char **bufloc, _IO_size_t *sizeloc)
       return NULL;
     }
   _IO_init_internal (&new_f->fp._sf._sbf._f, 0);
+  _IO_link_in ((struct _IO_FILE_plus *) &new_f->fp._sf._sbf);
   _IO_JUMPS_FILE_plus (&new_f->fp._sf._sbf) = &_IO_mem_jumps;
   _IO_str_init_static_internal (&new_f->fp._sf, buf, _IO_BUFSIZ, buf);
   new_f->fp._sf._sbf._f._flags &= ~_IO_USER_BUF;
@@ -137,3 +139,12 @@ _IO_mem_finish (_IO_FILE *fp, int dummy)
 
   _IO_str_finish (fp, 0);
 }
+
+static int
+_IO_mem_overflow (_IO_FILE *fp, int c)
+{
+  /* Updates the returned size location on stream flush.  */
+  if (c == EOF)
+    return _IO_mem_sync (fp);
+  return _IO_str_overflow (fp, c);
+}
diff --git a/libio/tst-memstream.h b/libio/tst-memstream.h
new file mode 100644
index 0000000..249a588
--- /dev/null
+++ b/libio/tst-memstream.h
@@ -0,0 +1,64 @@
+/* Common definitions for open_memstream tests.
+   Copyright (C) 2017 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 <mcheck.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdarg.h>
+#include <errno.h>
+
+#include <support/check.h>
+
+#ifdef TEST_WCHAR
+# include <wchar.h>
+
+/* Straighforward implementation so tst-memstream3 could use check
+   fwrite on open_memstream.  */
+static size_t __attribute__ ((used))
+fwwrite (const void *ptr, size_t size, size_t nmemb, FILE *arq)
+{
+  const wchar_t *wcs = (const wchar_t*) (ptr);
+  for (size_t s = 0; s < size; s++)
+    {
+      for (size_t n = 0; n < nmemb; n++)
+        if (fputwc (wcs[n], arq) == WEOF)
+          return n;
+    }
+  return size * nmemb;
+}
+
+# define CHAR_T wchar_t
+# define W(o) L##o
+# define OPEN_MEMSTREAM open_wmemstream
+# define PRINTF wprintf
+# define FWRITE fwwrite
+# define FPUTC  fputwc
+# define STRCMP wcscmp
+#else
+# define CHAR_T char
+# define W(o) o
+# define OPEN_MEMSTREAM open_memstream
+# define PRINTF printf
+# define FWRITE fwrite
+# define FPUTC fputc
+# define STRCMP strcmp
+#endif
+
+#define S(s) S1 (s)
+#define S1(s) #s
diff --git a/libio/tst-memstream4.c b/libio/tst-memstream4.c
new file mode 100644
index 0000000..d810063
--- /dev/null
+++ b/libio/tst-memstream4.c
@@ -0,0 +1,58 @@
+/* Test for open_memstream BZ #21735.
+   Copyright (C) 2017 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 "tst-memstream.h"
+
+static void
+mcheck_abort (enum mcheck_status ev)
+{
+  printf ("mecheck failed with status %d\n", (int) ev);
+  exit (1);
+}
+
+static int
+do_test (void)
+{
+  mcheck_pedantic (mcheck_abort);
+
+  CHAR_T *buf;
+  size_t size;
+
+  FILE *fp = OPEN_MEMSTREAM (&buf, &size);
+  if (fp == NULL)
+    FAIL_RET ("%s failed", S(OPEN_MEMSTREAM));
+
+  if (FPUTC (W('a'), fp) != W('a'))
+    FAIL_RET ("%s failed: %m", S(FPUTC));
+
+  if (fflush (NULL) != 0)
+    FAIL_RET ("fflush failed: %m");
+
+  if (size != 1)
+    FAIL_RET ("size != 1");
+
+  if (fileno (fp) != -1)
+    FAIL_RET ("fileno returned a valid integer descriptor");
+
+  if (fclose (fp) != 0)
+    FAIL_RET ("fclose: %m");
+
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/libio/tst-wmemstream4.c b/libio/tst-wmemstream4.c
new file mode 100644
index 0000000..9dbf615
--- /dev/null
+++ b/libio/tst-wmemstream4.c
@@ -0,0 +1,20 @@
+/* Test for open_wmemstream BZ #21735.
+   Copyright (C) 2017 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/>.  */
+
+#define TEST_WCHAR
+#include <libio/tst-memstream4.c>
diff --git a/libio/wmemstream.c b/libio/wmemstream.c
index 5bc77f5..3aa5f8a 100644
--- a/libio/wmemstream.c
+++ b/libio/wmemstream.c
@@ -32,13 +32,14 @@ struct _IO_FILE_wmemstream
 
 static int _IO_wmem_sync (_IO_FILE* fp) __THROW;
 static void _IO_wmem_finish (_IO_FILE* fp, int) __THROW;
+static int _IO_wmem_overflow (_IO_FILE *fp, int c) __THROW;
 
 
 static const struct _IO_jump_t _IO_wmem_jumps libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT (finish, _IO_wmem_finish),
-  JUMP_INIT (overflow, (_IO_overflow_t) _IO_wstr_overflow),
+  JUMP_INIT (overflow, (_IO_overflow_t) _IO_wmem_overflow),
   JUMP_INIT (underflow, (_IO_underflow_t) _IO_wstr_underflow),
   JUMP_INIT (uflow, (_IO_underflow_t) _IO_wdefault_uflow),
   JUMP_INIT (pbackfail, (_IO_pbackfail_t) _IO_wstr_pbackfail),
@@ -89,6 +90,7 @@ open_wmemstream (wchar_t **bufloc, _IO_size_t *sizeloc)
     }
   _IO_no_init (&new_f->fp._sf._sbf._f, 0, 0, &new_f->wd, &_IO_wmem_jumps);
   _IO_fwide (&new_f->fp._sf._sbf._f, 1);
+  _IO_link_in ((struct _IO_FILE_plus *) &new_f->fp._sf._sbf);
   _IO_wstr_init_static (&new_f->fp._sf._sbf._f, buf,
 			_IO_BUFSIZ / sizeof (wchar_t), buf);
   new_f->fp._sf._sbf._f._flags2 &= ~_IO_FLAGS2_USER_WBUF;
@@ -142,3 +144,12 @@ _IO_wmem_finish (_IO_FILE *fp, int dummy)
 
   _IO_wstr_finish (fp, 0);
 }
+
+static int
+_IO_wmem_overflow (_IO_FILE *fp, int c)
+{
+  /* Updates the returned size location on stream flush.  */
+  if (c == EOF)
+    return _IO_wmem_sync (fp);
+  return _IO_wstr_overflow (fp, c);
+}

Florian Weimer July 12, 2017, 3:01 p.m. | #3
* Adhemerval Zanella:

>> I think we don't want the malloc call for a call to exit, either.

>> Similarly for __stack_chk_fail, but that's something we need to fix

>> there.

>

> I am not following, what exactly should not call malloc here? Since

> the open_memstream is a valid call, it will allocate both the initial

> internal FILE object (libio/memstream.c:77) and initial buffer 

> (libio/memstream.c:84). Are you saying that we should start with an

> empty buffer instead? If it is the for I think we can do it, but it

> would require more intrusive changes I think.


I think we should make sure that writing the null terminator does not
trigger malloc during abort (or __stack_chk_fail).  That would be
quite wrong IMHO.

I wasn't aware that the buffer is pre-allocated.  Then we probably
need a test which is aware of the size of the preallocated buffer.

> So do you prefer to just add a workaround to disable the single-thread

> optimization for open_memstream and fix it on 2.27?  IMHO this fix touches

> only the open_memstream itself, so it should not regress any other libio

> code so I would prefer than carry a workaround for 2.26.


Which fix?  Linking open_memstream into the global list has quite
far-reaching consequences.  Conservatively setting the flag instead
should be fine.

I'm also not sure that the intent of POSIX is that open_memstream
streams should be affected by fflush (NULL).  I expect that
open_memstream was added without considering the interaction with
fflush (NULL).
Adhemerval Zanella July 13, 2017, 2:06 p.m. | #4
On 12/07/2017 12:01, Florian Weimer wrote:
> * Adhemerval Zanella:

> 

>>> I think we don't want the malloc call for a call to exit, either.

>>> Similarly for __stack_chk_fail, but that's something we need to fix

>>> there.

>>

>> I am not following, what exactly should not call malloc here? Since

>> the open_memstream is a valid call, it will allocate both the initial

>> internal FILE object (libio/memstream.c:77) and initial buffer 

>> (libio/memstream.c:84). Are you saying that we should start with an

>> empty buffer instead? If it is the for I think we can do it, but it

>> would require more intrusive changes I think.

> 

> I think we should make sure that writing the null terminator does not

> trigger malloc during abort (or __stack_chk_fail).  That would be

> quite wrong IMHO.

> 

> I wasn't aware that the buffer is pre-allocated.  Then we probably

> need a test which is aware of the size of the preallocated buffer.


Right, so in this case we can't call _IO_mem_sync for _IO_mem_overflow
with EOF to avoid the possible malloc during abort.  I updated the patch
to check for correct buffer output in such case.

> 

>> So do you prefer to just add a workaround to disable the single-thread

>> optimization for open_memstream and fix it on 2.27?  IMHO this fix touches

>> only the open_memstream itself, so it should not regress any other libio

>> code so I would prefer than carry a workaround for 2.26.

> 

> Which fix?  Linking open_memstream into the global list has quite

> far-reaching consequences.  Conservatively setting the flag instead

> should be fine.


I agree, but I also though adding the single-thread optimization close to
freeze was also not the safe move.  I do not have a strong preference here
and I think we can delay this fix to 2.27. 

> 

> I'm also not sure that the intent of POSIX is that open_memstream

> streams should be affected by fflush (NULL).  I expect that

> open_memstream was added without considering the interaction with

> fflush (NULL).

> 


I would say to not make the open_memstream stream an exception and
have different semantics than other streams.


---

-- 
2.7.4diff --git a/libio/Makefile b/libio/Makefile
index a002a33..6ee809a 100644
--- a/libio/Makefile
+++ b/libio/Makefile
@@ -57,8 +57,8 @@ tests = tst_swprintf tst_wprintf tst_swscanf tst_wscanf tst_getwc tst_putwc   \
 	tst-mmap-eofsync tst-mmap-fflushsync bug-mmap-fflush \
 	tst-mmap2-eofsync tst-mmap-offend bug-fopena+ bug-wfflush \
 	bug-ungetc2 bug-ftell bug-ungetc3 bug-ungetc4 tst-fopenloc2 \
-	tst-memstream1 tst-memstream2 tst-memstream3 \
-	tst-wmemstream1 tst-wmemstream2 tst-wmemstream3 \
+	tst-memstream1 tst-memstream2 tst-memstream3 tst-memstream4 \
+	tst-wmemstream1 tst-wmemstream2 tst-wmemstream3 tst-wmemstream4 \
 	bug-memstream1 bug-wmemstream1 \
 	tst-setvbuf1 tst-popen1 tst-fgetwc bug-wsetpos tst-fseek \
 	tst-fwrite-error tst-ftell-partial-wide tst-ftell-active-handler \
diff --git a/libio/memstream.c b/libio/memstream.c
index f83d4a5..67ecc09 100644
--- a/libio/memstream.c
+++ b/libio/memstream.c
@@ -31,13 +31,14 @@ struct _IO_FILE_memstream
 
 static int _IO_mem_sync (_IO_FILE* fp) __THROW;
 static void _IO_mem_finish (_IO_FILE* fp, int) __THROW;
+static int _IO_mem_overflow (_IO_FILE *fp, int c) __THROW;
 
 
 static const struct _IO_jump_t _IO_mem_jumps libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT (finish, _IO_mem_finish),
-  JUMP_INIT (overflow, _IO_str_overflow),
+  JUMP_INIT (overflow, _IO_mem_overflow),
   JUMP_INIT (underflow, _IO_str_underflow),
   JUMP_INIT (uflow, _IO_default_uflow),
   JUMP_INIT (pbackfail, _IO_str_pbackfail),
@@ -87,6 +88,7 @@ __open_memstream (char **bufloc, _IO_size_t *sizeloc)
       return NULL;
     }
   _IO_init_internal (&new_f->fp._sf._sbf._f, 0);
+  _IO_link_in ((struct _IO_FILE_plus *) &new_f->fp._sf._sbf);
   _IO_JUMPS_FILE_plus (&new_f->fp._sf._sbf) = &_IO_mem_jumps;
   _IO_str_init_static_internal (&new_f->fp._sf, buf, _IO_BUFSIZ, buf);
   new_f->fp._sf._sbf._f._flags &= ~_IO_USER_BUF;
@@ -137,3 +139,17 @@ _IO_mem_finish (_IO_FILE *fp, int dummy)
 
   _IO_str_finish (fp, 0);
 }
+
+static int
+_IO_mem_overflow (_IO_FILE *fp, int c)
+{
+  if (c == EOF)
+    {
+      /* Updates the returned size location on stream flush.  */
+      struct _IO_FILE_memstream *mp = (struct _IO_FILE_memstream *) fp;
+      *mp->bufloc = fp->_IO_write_base;
+      *mp->sizeloc = fp->_IO_write_ptr - fp->_IO_write_base;
+      return 0;
+    }
+  return _IO_str_overflow (fp, c);
+}
diff --git a/libio/tst-memstream.h b/libio/tst-memstream.h
new file mode 100644
index 0000000..ffc2a65
--- /dev/null
+++ b/libio/tst-memstream.h
@@ -0,0 +1,66 @@
+/* Common definitions for open_memstream tests.
+   Copyright (C) 2017 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 <mcheck.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdarg.h>
+#include <errno.h>
+
+#include <support/check.h>
+
+#ifdef TEST_WCHAR
+# include <wchar.h>
+
+/* Straighforward implementation so tst-memstream3 could use check
+   fwrite on open_memstream.  */
+static size_t __attribute__ ((used))
+fwwrite (const void *ptr, size_t size, size_t nmemb, FILE *arq)
+{
+  const wchar_t *wcs = (const wchar_t*) (ptr);
+  for (size_t s = 0; s < size; s++)
+    {
+      for (size_t n = 0; n < nmemb; n++)
+        if (fputwc (wcs[n], arq) == WEOF)
+          return n;
+    }
+  return size * nmemb;
+}
+
+# define CHAR_T wchar_t
+# define W(o) L##o
+# define OPEN_MEMSTREAM open_wmemstream
+# define PRINTF wprintf
+# define FWRITE fwwrite
+# define FPUTC  fputwc
+# define STRCMP wcscmp
+# define STRLEN wcslen
+#else
+# define CHAR_T char
+# define W(o) o
+# define OPEN_MEMSTREAM open_memstream
+# define PRINTF printf
+# define FWRITE fwrite
+# define FPUTC fputc
+# define STRCMP strcmp
+# define STRLEN strlen
+#endif
+
+#define S(s) S1 (s)
+#define S1(s) #s
diff --git a/libio/tst-memstream4.c b/libio/tst-memstream4.c
new file mode 100644
index 0000000..e98ca51
--- /dev/null
+++ b/libio/tst-memstream4.c
@@ -0,0 +1,99 @@
+/* Test for open_memstream BZ #21735.
+   Copyright (C) 2017 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 "tst-memstream.h"
+
+static void
+mcheck_abort (enum mcheck_status ev)
+{
+  printf ("mecheck failed with status %d\n", (int) ev);
+  exit (1);
+}
+
+static int
+do_test (void)
+{
+  mcheck_pedantic (mcheck_abort);
+
+  CHAR_T *buf;
+  size_t size;
+
+  FILE *fp = OPEN_MEMSTREAM (&buf, &size);
+  if (fp == NULL)
+    FAIL_RET ("%s failed", S(OPEN_MEMSTREAM));
+
+  /* Basic test to check if 'fflush (NULL)' flushed all stream including
+     open_memstream ones.  */
+  {
+    if (FPUTC (W('a'), fp) != W('a'))
+      FAIL_RET ("%s failed: %m", S(FPUTC));
+
+    if (fflush (NULL) != 0)
+      FAIL_RET ("fflush failed: %m");
+
+    if (size != 1)
+      FAIL_RET ("size != 1");
+
+    TEST_VERIFY (STRCMP (buf, W("a")) == 0);
+  }
+
+  /* Same as before now with a buf close and equal to BUFSIZ.  */
+  {
+    const size_t bufsize = BUFSIZ - 1;
+    CHAR_T bufcmp[bufsize + 2];
+    size_t i;
+
+    bufcmp[0] = W('a');
+    for (i=1; i<bufsize; i++)
+      {
+	bufcmp[i] = W('a');
+	FPUTC (W('a'), fp);
+      }
+    bufcmp[i] = W('\0');
+
+    if (fflush (NULL) != 0)
+      FAIL_RET ("fflush failed: %m");
+
+    if (size != bufsize)
+      FAIL_RET ("size != %zu", bufsize);
+
+    TEST_VERIFY (STRCMP (buf, bufcmp) == 0);
+
+    bufcmp[i] = W('a');
+    bufcmp[i + 1] = W('\0');
+    FPUTC (W('a'), fp);
+
+    if (fflush (NULL) != 0)
+      FAIL_RET ("fflush failed: %m");
+
+    if (size != (bufsize + 1))
+      FAIL_RET ("size != %zu", bufsize);
+
+    TEST_VERIFY (STRCMP (buf, bufcmp) == 0);
+  }
+
+  if (fileno (fp) != -1)
+    FAIL_RET ("fileno returned a valid integer descriptor");
+
+  if (fclose (fp) != 0)
+    FAIL_RET ("fclose: %m");
+
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/libio/tst-wmemstream4.c b/libio/tst-wmemstream4.c
new file mode 100644
index 0000000..9dbf615
--- /dev/null
+++ b/libio/tst-wmemstream4.c
@@ -0,0 +1,20 @@
+/* Test for open_wmemstream BZ #21735.
+   Copyright (C) 2017 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/>.  */
+
+#define TEST_WCHAR
+#include <libio/tst-memstream4.c>
diff --git a/libio/wmemstream.c b/libio/wmemstream.c
index 5bc77f5..d68334b 100644
--- a/libio/wmemstream.c
+++ b/libio/wmemstream.c
@@ -32,13 +32,14 @@ struct _IO_FILE_wmemstream
 
 static int _IO_wmem_sync (_IO_FILE* fp) __THROW;
 static void _IO_wmem_finish (_IO_FILE* fp, int) __THROW;
+static int _IO_wmem_overflow (_IO_FILE *fp, int c) __THROW;
 
 
 static const struct _IO_jump_t _IO_wmem_jumps libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT (finish, _IO_wmem_finish),
-  JUMP_INIT (overflow, (_IO_overflow_t) _IO_wstr_overflow),
+  JUMP_INIT (overflow, (_IO_overflow_t) _IO_wmem_overflow),
   JUMP_INIT (underflow, (_IO_underflow_t) _IO_wstr_underflow),
   JUMP_INIT (uflow, (_IO_underflow_t) _IO_wdefault_uflow),
   JUMP_INIT (pbackfail, (_IO_pbackfail_t) _IO_wstr_pbackfail),
@@ -89,6 +90,7 @@ open_wmemstream (wchar_t **bufloc, _IO_size_t *sizeloc)
     }
   _IO_no_init (&new_f->fp._sf._sbf._f, 0, 0, &new_f->wd, &_IO_wmem_jumps);
   _IO_fwide (&new_f->fp._sf._sbf._f, 1);
+  _IO_link_in ((struct _IO_FILE_plus *) &new_f->fp._sf._sbf);
   _IO_wstr_init_static (&new_f->fp._sf._sbf._f, buf,
 			_IO_BUFSIZ / sizeof (wchar_t), buf);
   new_f->fp._sf._sbf._f._flags2 &= ~_IO_FLAGS2_USER_WBUF;
@@ -142,3 +144,18 @@ _IO_wmem_finish (_IO_FILE *fp, int dummy)
 
   _IO_wstr_finish (fp, 0);
 }
+
+static int
+_IO_wmem_overflow (_IO_FILE *fp, int c)
+{
+  if (c == EOF)
+    {
+      /* Updates the returned size location on stream flush.  */
+      struct _IO_FILE_wmemstream *mp = (struct _IO_FILE_wmemstream *) fp;
+      *mp->bufloc = fp->_wide_data->_IO_write_base;
+      *mp->sizeloc = (fp->_wide_data->_IO_write_ptr
+		     - fp->_wide_data->_IO_write_base);
+      return 0;
+    }
+  return _IO_wstr_overflow (fp, c);
+}

Szabolcs Nagy July 13, 2017, 5:05 p.m. | #5
On 13/07/17 15:06, Adhemerval Zanella wrote:
> On 12/07/2017 12:01, Florian Weimer wrote:

>> * Adhemerval Zanella:

>>> So do you prefer to just add a workaround to disable the single-thread

>>> optimization for open_memstream and fix it on 2.27?  IMHO this fix touches

>>> only the open_memstream itself, so it should not regress any other libio

>>> code so I would prefer than carry a workaround for 2.26.

>>

>> Which fix?  Linking open_memstream into the global list has quite

>> far-reaching consequences.  Conservatively setting the flag instead

>> should be fine.

> 

> I agree, but I also though adding the single-thread optimization close to

> freeze was also not the safe move.  I do not have a strong preference here

> and I think we can delay this fix to 2.27. 

> 


i think the single thread optimization is fine, but
it's better to just disable it for cases that are
problematic.

if there is no other complaints then i will commit
my patch tomorrow that disables the optimization
for open_memstream instead of reverting the entire
thing.
Carlos O'Donell July 13, 2017, 5:23 p.m. | #6
On 07/13/2017 01:05 PM, Szabolcs Nagy wrote:
> On 13/07/17 15:06, Adhemerval Zanella wrote:

>> On 12/07/2017 12:01, Florian Weimer wrote:

>>> * Adhemerval Zanella:

>>>> So do you prefer to just add a workaround to disable the single-thread

>>>> optimization for open_memstream and fix it on 2.27?  IMHO this fix touches

>>>> only the open_memstream itself, so it should not regress any other libio

>>>> code so I would prefer than carry a workaround for 2.26.

>>>

>>> Which fix?  Linking open_memstream into the global list has quite

>>> far-reaching consequences.  Conservatively setting the flag instead

>>> should be fine.

>>

>> I agree, but I also though adding the single-thread optimization close to

>> freeze was also not the safe move.  I do not have a strong preference here

>> and I think we can delay this fix to 2.27. 

>>

> 

> i think the single thread optimization is fine, but

> it's better to just disable it for cases that are

> problematic.

> 

> if there is no other complaints then i will commit

> my patch tomorrow that disables the optimization

> for open_memstream instead of reverting the entire

> thing.

 
This sounds good to me.

-- 
Cheers,
Carlos.
Adhemerval Zanella July 13, 2017, 6:38 p.m. | #7
On 13/07/2017 14:05, Szabolcs Nagy wrote:
> On 13/07/17 15:06, Adhemerval Zanella wrote:

>> On 12/07/2017 12:01, Florian Weimer wrote:

>>> * Adhemerval Zanella:

>>>> So do you prefer to just add a workaround to disable the single-thread

>>>> optimization for open_memstream and fix it on 2.27?  IMHO this fix touches

>>>> only the open_memstream itself, so it should not regress any other libio

>>>> code so I would prefer than carry a workaround for 2.26.

>>>

>>> Which fix?  Linking open_memstream into the global list has quite

>>> far-reaching consequences.  Conservatively setting the flag instead

>>> should be fine.

>>

>> I agree, but I also though adding the single-thread optimization close to

>> freeze was also not the safe move.  I do not have a strong preference here

>> and I think we can delay this fix to 2.27. 

>>

> 

> i think the single thread optimization is fine, but

> it's better to just disable it for cases that are

> problematic.

> 

> if there is no other complaints then i will commit

> my patch tomorrow that disables the optimization

> for open_memstream instead of reverting the entire

> thing.


LGTM too and I also do not think reverting the single-thread
is the best course of action.  What I would like we focus on
next releases is to try push such patches earlier in release
so we have more time to catch such issues.

Patch

diff --git a/libio/memstream.c b/libio/memstream.c
index f83d4a5..3be5b58 100644
--- a/libio/memstream.c
+++ b/libio/memstream.c
@@ -31,13 +31,14 @@  struct _IO_FILE_memstream
 
 static int _IO_mem_sync (_IO_FILE* fp) __THROW;
 static void _IO_mem_finish (_IO_FILE* fp, int) __THROW;
+static int _IO_mem_overflow (_IO_FILE *fp, int c) __THROW;
 
 
 static const struct _IO_jump_t _IO_mem_jumps libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT (finish, _IO_mem_finish),
-  JUMP_INIT (overflow, _IO_str_overflow),
+  JUMP_INIT (overflow, _IO_mem_overflow),
   JUMP_INIT (underflow, _IO_str_underflow),
   JUMP_INIT (uflow, _IO_default_uflow),
   JUMP_INIT (pbackfail, _IO_str_pbackfail),
@@ -87,6 +88,7 @@  __open_memstream (char **bufloc, _IO_size_t *sizeloc)
       return NULL;
     }
   _IO_init_internal (&new_f->fp._sf._sbf._f, 0);
+  _IO_link_in ((struct _IO_FILE_plus *) &new_f->fp._sf._sbf);
   _IO_JUMPS_FILE_plus (&new_f->fp._sf._sbf) = &_IO_mem_jumps;
   _IO_str_init_static_internal (&new_f->fp._sf, buf, _IO_BUFSIZ, buf);
   new_f->fp._sf._sbf._f._flags &= ~_IO_USER_BUF;
@@ -137,3 +139,14 @@  _IO_mem_finish (_IO_FILE *fp, int dummy)
 
   _IO_str_finish (fp, 0);
 }
+
+static int
+_IO_mem_overflow (_IO_FILE *fp, int c)
+{
+  int ret = _IO_str_overflow (fp, c);
+
+  struct _IO_FILE_memstream *mp = (struct _IO_FILE_memstream *) fp;
+  *mp->sizeloc = fp->_IO_write_ptr - fp->_IO_write_base;
+
+  return ret;
+}
diff --git a/libio/tst-memstream3.c b/libio/tst-memstream3.c
index ce201d1..395e5c2 100644
--- a/libio/tst-memstream3.c
+++ b/libio/tst-memstream3.c
@@ -23,6 +23,7 @@ 
 #include <stdarg.h>
 #include <errno.h>
 
+#include <support/check.h>
 
 #ifndef CHAR_T
 # define CHAR_T char
@@ -40,24 +41,9 @@ 
 static void
 mcheck_abort (enum mcheck_status ev)
 {
-  printf ("mecheck failed with status %d\n", (int) ev);
-  exit (1);
+  FAIL_EXIT1 ("mecheck failed with status %d", (int) ev);
 }
 
-static void
-error_printf (int line, const char *fmt, ...)
-{
-  va_list ap;
-
-  printf ("error: %s:%i: ", __FILE__, line);
-  va_start (ap, fmt);
-  vprintf (fmt, ap);
-  va_end (ap);
-}
-
-#define ERROR_RET1(...) \
-  { error_printf(__LINE__, __VA_ARGS__); return 1; }
-
 static int
 do_test_bz18241 (void)
 {
@@ -66,37 +52,37 @@  do_test_bz18241 (void)
 
   FILE *fp = OPEN_MEMSTREAM (&buf, &size);
   if (fp == NULL)
-    ERROR_RET1 ("%s failed\n", S(OPEN_MEMSTREAM));
+    FAIL_RET ("%s failed", S(OPEN_MEMSTREAM));
 
   if (FPUTC (W('a'), fp) != W('a'))
-    ERROR_RET1 ("%s failed (errno = %d)\n", S(FPUTC), errno);
+    FAIL_RET ("%s failed: %m", S(FPUTC));
   if (fflush (fp) != 0)
-    ERROR_RET1 ("fflush failed (errno = %d)\n", errno);
+    FAIL_RET ("fflush failed: %m");
   if (fseek (fp, -2, SEEK_SET) != -1)
-    ERROR_RET1 ("fseek failed (errno = %d)\n", errno);
+    FAIL_RET ("fseek failed: %m");
   if (errno != EINVAL)
-    ERROR_RET1 ("errno != EINVAL\n");
+    FAIL_RET ("errno != EINVAL");
   if (ftell (fp) != 1)
-    ERROR_RET1 ("ftell failed (errno = %d)\n", errno);
+    FAIL_RET ("ftell failed: %m");
   if (ferror (fp) != 0)
-    ERROR_RET1 ("ferror != 0\n");
+    FAIL_RET ("ferror != 0");
 
   if (fseek (fp, -1, SEEK_CUR) == -1)
-    ERROR_RET1 ("fseek failed (errno = %d)\n", errno);
+    FAIL_RET ("fseek failed: %m");
   if (ftell (fp) != 0)
-    ERROR_RET1 ("ftell failed (errno = %d)\n", errno);
+    FAIL_RET ("ftell failed: %m");
   if (ferror (fp) != 0)
-    ERROR_RET1 ("ferror != 0\n");
+    FAIL_RET ("ferror != 0");
   if (FPUTC (W('b'), fp) != W('b'))
-    ERROR_RET1 ("%s failed (errno = %d)\n", S(FPUTC), errno);
+    FAIL_RET ("%s failed: %m", S(FPUTC));
   if (fflush (fp) != 0)
-    ERROR_RET1 ("fflush failed (errno = %d)\n", errno);
+    FAIL_RET ("fflush failed: %m");
 
   if (fclose (fp) != 0)
-    ERROR_RET1 ("fclose failed (errno = %d\n", errno);
+    FAIL_RET ("fclose failed: %m");
 
   if (STRCMP (buf, W("b")) != 0)
-    ERROR_RET1 ("%s failed\n", S(STRCMP));
+    FAIL_RET ("%s failed", S(STRCMP));
 
   free (buf);
 
@@ -112,45 +98,74 @@  do_test_bz20181 (void)
 
   FILE *fp = OPEN_MEMSTREAM (&buf, &size);
   if (fp == NULL)
-    ERROR_RET1 ("%s failed\n", S(OPEN_MEMSTREAM));
+    FAIL_RET ("%s failed\n", S(OPEN_MEMSTREAM));
 
   if ((ret = FWRITE (W("abc"), 1, 3, fp)) != 3)
-    ERROR_RET1 ("%s failed (errno = %d)\n", S(FWRITE), errno);
+    FAIL_RET ("%s failed (errno = %d)\n", S(FWRITE), errno);
 
   if (fseek (fp, 0, SEEK_SET) != 0)
-    ERROR_RET1 ("fseek failed (errno = %d)\n", errno);
+    FAIL_RET ("fseek failed (errno = %d)\n", errno);
 
   if (FWRITE (W("z"), 1, 1, fp) != 1)
-    ERROR_RET1 ("%s failed (errno = %d)\n", S(FWRITE), errno);
+    FAIL_RET ("%s failed (errno = %d)\n", S(FWRITE), errno);
 
   if (fflush (fp) != 0)
-    ERROR_RET1 ("fflush failed (errno = %d)\n", errno);
+    FAIL_RET ("fflush failed (errno = %d)\n", errno);
 
   /* Avoid truncating the buffer on close.  */
   if (fseek (fp, 3, SEEK_SET) != 0)
-    ERROR_RET1 ("fseek failed (errno = %d)\n", errno);
+    FAIL_RET ("fseek failed (errno = %d)\n", errno);
 
   if (fclose (fp) != 0)
-    ERROR_RET1 ("fclose failed (errno = %d\n", errno);
+    FAIL_RET ("fclose failed (errno = %d\n", errno);
 
   if (size != 3)
-    ERROR_RET1 ("size != 3\n");
+    FAIL_RET ("size != 3\n");
 
   if (buf[0] != W('z')
       || buf[1] != W('b')
       || buf[2] != W('c'))
     {
       PRINTF (W("error: buf {%c,%c,%c} != {z,b,c}\n"),
-	      buf[0], buf[1], buf[2]);
-      return 1;
+             buf[0], buf[1], buf[2]);
+      FAIL_RET (NULL);
     }
 
+
   free (buf);
 
   return 0;
 }
 
 static int
+do_test_bz21735 (void)
+{
+  CHAR_T *buf;
+  size_t size;
+
+  FILE *fp = OPEN_MEMSTREAM (&buf, &size);
+  if (fp == NULL)
+    FAIL_RET ("%s failed", S(OPEN_MEMSTREAM));
+
+  if (FPUTC (W('a'), fp) != W('a'))
+    FAIL_RET ("%s failed: %m", S(FPUTC));
+
+  if (fflush (fp) != 0)
+    FAIL_RET ("fflush failed: %m");
+
+  if (size != 1)
+    FAIL_RET ("size != 1");
+
+  if (fileno (fp) != -1)
+    FAIL_RET ("fileno returned a valid integer descriptor");
+
+  if (fclose (fp) != 0)
+    FAIL_RET ("fclose: %m");
+
+  return 0;
+}
+
+static int
 do_test (void)
 {
   int ret = 0;
@@ -159,9 +174,9 @@  do_test (void)
 
   ret += do_test_bz18241 ();
   ret += do_test_bz20181 ();
+  ret += do_test_bz21735 ();
 
   return ret;
 }
 
-#define TEST_FUNCTION do_test ()
-#include "../test-skeleton.c"
+#include <support/test-driver.c>
diff --git a/libio/wmemstream.c b/libio/wmemstream.c
index 5bc77f5..f6d9f14 100644
--- a/libio/wmemstream.c
+++ b/libio/wmemstream.c
@@ -32,13 +32,14 @@  struct _IO_FILE_wmemstream
 
 static int _IO_wmem_sync (_IO_FILE* fp) __THROW;
 static void _IO_wmem_finish (_IO_FILE* fp, int) __THROW;
+static int _IO_wmem_overflow (_IO_FILE *fp, int c) __THROW;
 
 
 static const struct _IO_jump_t _IO_wmem_jumps libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT (finish, _IO_wmem_finish),
-  JUMP_INIT (overflow, (_IO_overflow_t) _IO_wstr_overflow),
+  JUMP_INIT (overflow, (_IO_overflow_t) _IO_wmem_overflow),
   JUMP_INIT (underflow, (_IO_underflow_t) _IO_wstr_underflow),
   JUMP_INIT (uflow, (_IO_underflow_t) _IO_wdefault_uflow),
   JUMP_INIT (pbackfail, (_IO_pbackfail_t) _IO_wstr_pbackfail),
@@ -89,6 +90,7 @@  open_wmemstream (wchar_t **bufloc, _IO_size_t *sizeloc)
     }
   _IO_no_init (&new_f->fp._sf._sbf._f, 0, 0, &new_f->wd, &_IO_wmem_jumps);
   _IO_fwide (&new_f->fp._sf._sbf._f, 1);
+  _IO_link_in ((struct _IO_FILE_plus *) &new_f->fp._sf._sbf);
   _IO_wstr_init_static (&new_f->fp._sf._sbf._f, buf,
 			_IO_BUFSIZ / sizeof (wchar_t), buf);
   new_f->fp._sf._sbf._f._flags2 &= ~_IO_FLAGS2_USER_WBUF;
@@ -142,3 +144,15 @@  _IO_wmem_finish (_IO_FILE *fp, int dummy)
 
   _IO_wstr_finish (fp, 0);
 }
+
+static int
+_IO_wmem_overflow (_IO_FILE *fp, int c)
+{
+  int ret = _IO_wstr_overflow (fp, c);
+
+  struct _IO_FILE_wmemstream *mp = (struct _IO_FILE_wmemstream *) fp;
+  *mp->sizeloc = (fp->_wide_data->_IO_write_ptr
+		  - fp->_wide_data->_IO_write_base);
+
+  return ret;
+}