[PATCH v3 3/5] Introduce _REENT_GLOBAL_STDIO_STREAMS

[Sebastian Huber]

In Newlib, the stdio streams are defined to thread-specific pointers
_reent::_stdin, _reent::_stdout and _reent::_stderr.  In case
_REENT_SMALL is not defined, then these pointers are initialized via
_REENT_INIT_PTR() or _REENT_INIT_PTR_ZEROED() to thread-specific FILE
objects provided via _reent::__sf[3].  There are two problems with this
(at least in case of RTEMS).

(1) The thread-specific FILE objects are closed by _reclaim_reent().
This leads to problems with language run-time libraries that provide
wrappers to the C/POSIX stdio streams (e.g.  C++ and Ada), since they
use the thread-specific FILE objects of the initialization thread.  In
case the initialization thread is deleted, then they use freed memory.

(2) Since thread-specific FILE objects are used with a common output
device via file descriptors 0, 1 and 2, the locking at FILE object level
cannot ensure atomicity of the output, e.g. a call to printf().

Introduce a new Newlib configuration option _REENT_GLOBAL_STDIO_STREAMS
to enable the use of global stdio FILE objects.

As a side-effect this reduces the size of struct _reent by more than
50%.

The _REENT_GLOBAL_STDIO_STREAMS should not be used without
_STDIO_CLOSE_PER_REENT_STD_STREAMS.

Signed-off-by: Sebastian Huber <sebastian.huber@embedded-brains.de>
---
 newlib/libc/include/sys/reent.h | 21 +++++++++++++++------
 newlib/libc/stdio/findfp.c      | 24 ++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/newlib/libc/include/sys/reent.h b/newlib/libc/include/sys/reent.h
index 8b67889ac..c045ca549 100644
--- a/newlib/libc/include/sys/reent.h
+++ b/newlib/libc/include/sys/reent.h
@@ -644,14 +644,23 @@ struct _reent
      of the above members (on the off chance that future binary compatibility
      would be broken otherwise).  */
   struct _glue __sglue;		/* root of glue chain */
+# ifndef _REENT_GLOBAL_STDIO_STREAMS
   __FILE __sf[3];  		/* first three file descriptors */
+# endif
 };
 
+#ifdef _REENT_GLOBAL_STDIO_STREAMS
+extern __FILE __sf[3];
+#define _REENT_STDIO_STREAM(var, index) &__sf[index]
+#else
+#define _REENT_STDIO_STREAM(var, index) &(var)->__sf[index]
+#endif
+
 #define _REENT_INIT(var) \
   { 0, \
-    &(var).__sf[0], \
-    &(var).__sf[1], \
-    &(var).__sf[2], \
+    _REENT_STDIO_STREAM(&(var), 0), \
+    _REENT_STDIO_STREAM(&(var), 1), \
+    _REENT_STDIO_STREAM(&(var), 2), \
     0, \
     "", \
     0, \
@@ -696,9 +705,9 @@ struct _reent
   }
 
 #define _REENT_INIT_PTR_ZEROED(var) \
-  { (var)->_stdin = &(var)->__sf[0]; \
-    (var)->_stdout = &(var)->__sf[1]; \
-    (var)->_stderr = &(var)->__sf[2]; \
+  { (var)->_stdin = _REENT_STDIO_STREAM(var, 0); \
+    (var)->_stdout = _REENT_STDIO_STREAM(var, 1); \
+    (var)->_stderr = _REENT_STDIO_STREAM(var, 2); \
     (var)->_new._reent._rand_next = 1; \
     (var)->_new._reent._r48._seed[0] = _RAND48_SEED_0; \
     (var)->_new._reent._r48._seed[1] = _RAND48_SEED_1; \
diff --git a/newlib/libc/stdio/findfp.c b/newlib/libc/stdio/findfp.c
index b40aa9240..737bde102 100644
--- a/newlib/libc/stdio/findfp.c
+++ b/newlib/libc/stdio/findfp.c
@@ -35,6 +35,10 @@ const struct __sFILE_fake __sf_fake_stderr =
     {_NULL, 0, 0, 0, 0, {_NULL, 0}, 0, _NULL};
 #endif
 
+#ifdef _REENT_GLOBAL_STDIO_STREAMS
+__FILE __sf[3];
+#endif
+
 #if (defined (__OPTIMIZE_SIZE__) || defined (PREFER_SIZE_OVER_SPEED))
 _NOINLINE_STATIC _VOID
 #else
@@ -218,6 +222,14 @@ _DEFUN(_cleanup_r, (ptr),
   cleanup_func = _fclose_r;
 #endif
 #endif
+#ifdef _REENT_GLOBAL_STDIO_STREAMS
+  if (ptr->_stdin != &__sf[0])
+    (*cleanup_func) (ptr, ptr->_stdin);
+  if (ptr->_stdout != &__sf[1])
+    (*cleanup_func) (ptr, ptr->_stdout);
+  if (ptr->_stderr != &__sf[2])
+    (*cleanup_func) (ptr, ptr->_stderr);
+#endif
   _CAST_VOID _fwalk_reent (ptr, cleanup_func);
 }
 
@@ -250,8 +262,10 @@ _DEFUN(__sinit, (s),
 
   s->__sglue._next = NULL;
 #ifndef _REENT_SMALL
+# ifndef _REENT_GLOBAL_STDIO_STREAMS
   s->__sglue._niobs = 3;
   s->__sglue._iobs = &s->__sf[0];
+# endif
 #else
   s->__sglue._niobs = 0;
   s->__sglue._iobs = NULL;
@@ -265,9 +279,19 @@ _DEFUN(__sinit, (s),
   s->_stderr = __sfp(s);
 #endif
 
+#ifdef _REENT_GLOBAL_STDIO_STREAMS
+  if (__sf[0]._cookie == NULL) {
+    _GLOBAL_REENT->__sglue._niobs = 3;
+    _GLOBAL_REENT->__sglue._iobs = &__sf[0];
+    stdin_init (&__sf[0]);
+    stdout_init (&__sf[1]);
+    stderr_init (&__sf[2]);
+  }
+#else
   stdin_init (s->_stdin);
   stdout_init (s->_stdout);
   stderr_init (s->_stderr);
+#endif
 
   s->__sdidinit = 1;
 
-- 
2.12.3