PR libstdc++/81751 don't call fflush(NULL)

	PR libstdc++/79820
	PR libstdc++/81751
	* config/io/basic_file_stdio.cc (sys_open(FILE*, ios_base::openmode)):
	Call fflush on the stream instead of calling sync() while _M_cfile is
	null. Restore original value of errno.
	* testsuite/ext/stdio_filebuf/char/79820.cc: New.
	* testsuite/ext/stdio_filebuf/char/81751.cc: New.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@250993 138bc75d-0d04-0410-961f-82ee72b054a4

4 files changed, 106 insertions, 2 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index e36ca828e54..75a454718df 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,13 @@
+2017-08-09  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/79820
+	PR libstdc++/81751
+	* config/io/basic_file_stdio.cc (sys_open(FILE*, ios_base::openmode)):
+	Call fflush on the stream instead of calling sync() while _M_cfile is
+	null. Restore original value of errno.
+	* testsuite/ext/stdio_filebuf/char/79820.cc: New.
+	* testsuite/ext/stdio_filebuf/char/81751.cc: New.
+
 2017-07-31  Marek Polacek  <polacek@redhat.com>
 
 	PR libstdc++/81599
diff --git a/libstdc++-v3/config/io/basic_file_stdio.cc b/libstdc++-v3/config/io/basic_file_stdio.cc
index e7367016504..eeb1e5e94b6 100644
--- a/libstdc++-v3/config/io/basic_file_stdio.cc
+++ b/libstdc++-v3/config/io/basic_file_stdio.cc
@@ -195,11 +195,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     __basic_file* __ret = NULL;
     if (!this->is_open() && __file)
       {
-	int __err;
+	int __err, __save_errno = errno;
+	// POSIX guarantees that fflush sets errno on error, but C doesn't.
 	errno = 0;
 	do
-	  __err = this->sync();
+	  __err = fflush(__file);
 	while (__err && errno == EINTR);
+	errno = __save_errno;
 	if (!__err)
 	  {
 	    _M_cfile = __file;
diff --git a/libstdc++-v3/testsuite/ext/stdio_filebuf/char/79820.cc b/libstdc++-v3/testsuite/ext/stdio_filebuf/char/79820.cc
new file mode 100644
index 00000000000..ba566f869c6
--- /dev/null
+++ b/libstdc++-v3/testsuite/ext/stdio_filebuf/char/79820.cc
@@ -0,0 +1,39 @@
+// Copyright (C) 2017 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This 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 General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-require-fileio "" }
+
+#include <ext/stdio_filebuf.h>
+#include <cstdio>
+#include <cerrno>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  FILE* f = std::fopen("79820.txt", "w");
+  std::fclose(f);
+  errno = 127;
+  __gnu_cxx::stdio_filebuf<char> b(f, std::ios::out, BUFSIZ);
+  VERIFY(errno == 127); // PR libstdc++/79820
+}
+
+int
+main()
+{
+  test01();
+}
diff --git a/libstdc++-v3/testsuite/ext/stdio_filebuf/char/81751.cc b/libstdc++-v3/testsuite/ext/stdio_filebuf/char/81751.cc
new file mode 100644
index 00000000000..22191dcb6a3
--- /dev/null
+++ b/libstdc++-v3/testsuite/ext/stdio_filebuf/char/81751.cc
@@ -0,0 +1,53 @@
+// Copyright (C) 2017 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This 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 General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-require-fileio "" }
+
+#include <ext/stdio_filebuf.h>
+#include <cstdio>
+#include <cerrno>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  FILE* out = std::fopen("81751.txt", "w");
+  std::fwrite("Some words.", 1, 10, out);
+
+  FILE* in1 = std::fopen("81751.txt", "r");
+  __gnu_cxx::stdio_filebuf<char> buf1(in1, std::ios::in, BUFSIZ);
+  int c = buf1.sgetc();
+  VERIFY( c == std::char_traits<char>::eof() ); // PR libstdc++/81751
+
+  std::fflush(out);
+  FILE* in2 = std::fopen("81751.txt", "r");
+  __gnu_cxx::stdio_filebuf<char> buf2(in2, std::ios::in, BUFSIZ);
+  c = buf2.sgetc();
+  VERIFY( c == 'S' );
+
+  buf1.close();
+  buf2.close();
+  std::fclose(in1);
+  std::fclose(in2);
+  std::fclose(out);
+}
+
+int
+main()
+{
+  test01();
+}