3 files changed, 22 insertions, 23 deletions
diff --git a/newlib/libc/stdio/fdopen.c b/newlib/libc/stdio/fdopen.c
index f4fc551c4..aa764c372 100644
--- a/newlib/libc/stdio/fdopen.c
+++ b/newlib/libc/stdio/fdopen.c
@@ -29,7 +29,7 @@ ANSI_SYNOPSIS
 	FILE *fdopen(int <[fd]>, const char *<[mode]>);
 	FILE *_fdopen_r(struct _reent *<[reent]>,
                         int <[fd]>, const char *<[mode]>);
-  
+
 TRAD_SYNOPSIS
 	#include <stdio.h>
 	FILE *fdopen(<[fd]>, <[mode]>)
@@ -96,17 +96,14 @@ _DEFUN(_fdopen_r, (ptr, fd, mode),
   _flockfile (fp);
 
   fp->_flags = flags;
-  /*
-   * If opened for appending, but underlying descriptor
-   * does not have O_APPEND bit set, assert __SAPP so that
-   * __swrite() will lseek to end before each write.
-   */
-  if ((oflags & O_APPEND)
+  /* POSIX recommends setting the O_APPEND bit on fd to match append
+     streams.  Someone may later clear O_APPEND on fileno(fp), but the
+     stream must still remain in append mode.  Rely on __sflags
+     setting __SAPP properly.  */
 #ifdef HAVE_FCNTL
-       && !(fdflags & O_APPEND)
+  if ((oflags & O_APPEND) && !(fdflags & O_APPEND))
+    _fcntl_r (ptr, fd, F_SETFL, fdflags | O_APPEND);
 #endif
-      )
-    fp->_flags |= __SAPP;
   fp->_file = fd;
   fp->_cookie = (_PTR) fp;
 
diff --git a/newlib/libc/stdio/findfp.c b/newlib/libc/stdio/findfp.c
index 43f02ba5f..4f613e537 100644
--- a/newlib/libc/stdio/findfp.c
+++ b/newlib/libc/stdio/findfp.c
@@ -204,16 +204,21 @@ _DEFUN(__sinit, (s),
 
   std (s->_stdin,  __SRD, 0, s);
 
-  /* on platforms that have true file system I/O, we can verify whether stdout
-     is an interactive terminal or not.  For all other platforms, we will
-     default to line buffered mode here.  */
+  /* On platforms that have true file system I/O, we can verify
+     whether stdout is an interactive terminal or not, as part of
+     __smakebuf on first use of the stream.  For all other platforms,
+     we will default to line buffered mode here.  Technically, POSIX
+     requires both stdin and stdout to be line-buffered, but tradition
+     leaves stdin alone on systems without fcntl.  */
 #ifdef HAVE_FCNTL
   std (s->_stdout, __SWR, 1, s);
 #else
   std (s->_stdout, __SWR | __SLBF, 1, s);
 #endif
 
-  std (s->_stderr, __SWR | __SNBF, 2, s);
+  /* POSIX requires stderr to be opened for reading and writing, even
+     when the underlying fd 2 is write-only.  */
+  std (s->_stderr, __SRW | __SNBF, 2, s);
 
   __sinit_lock_release ();
 }
diff --git a/newlib/libc/stdio64/fdopen64.c b/newlib/libc/stdio64/fdopen64.c
index 4f159e813..49d1f03aa 100644
--- a/newlib/libc/stdio64/fdopen64.c
+++ b/newlib/libc/stdio64/fdopen64.c
@@ -67,17 +67,14 @@ _DEFUN (_fdopen64_r, (ptr, fd, mode),
   _flockfile(fp);
 
   fp->_flags = flags;
-  /*
-   * If opened for appending, but underlying descriptor
-   * does not have O_APPEND bit set, assert __SAPP so that
-   * __swrite() will lseek to end before each write.
-   */
-  if ((oflags & O_APPEND)
+  /* POSIX recommends setting the O_APPEND bit on fd to match append
+     streams.  Someone may later clear O_APPEND on fileno(fp), but the
+     stream must still remain in append mode.  Rely on __sflags
+     setting __SAPP properly.  */
 #ifdef HAVE_FCNTL
-       && !(fdflags & O_APPEND)
+  if ((oflags & O_APPEND) && !(fdflags & O_APPEND))
+    _fcntl_r (ptr, fd, F_SETFL, fdflags | O_APPEND);
 #endif
-      )
-    fp->_flags |= __SAPP;
   fp->_file = fd;
   fp->_cookie = (_PTR) fp;