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Re: [PATCH] libio: Fix open_memstream flush (NULL)



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.
---

diff --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);
+}
-- 
2.7.4


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