Use global stdio streams for all configurations

The _REENT_GLOBAL_STDIO_STREAMS was introduced by commit
668a4c8722090fffd10869dbb15b879651c1370d in 2017.  Since then it was enabled by
default for RTEMS.  Recently, the option was enabled for Cygwin which
previously used an alternative implementation to use global stdio streams.

In Newlib, the stdio streams are defined to thread-specific pointers
_reent::_stdin, _reent::_stdout and _reent::_stderr.  If the option is disabled
(the default for most systems), then these pointers are initialized to
thread-specific FILE objects which use file descriptors 0, 1, and 2,
respectively.  There are at least three problems with this:

(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 (for example 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().

(3) There are resource managment issues, see:

    https://sourceware.org/pipermail/newlib/2022/019558.html

    https://bugs.linaro.org/show_bug.cgi?id=5841

This patch enables the _REENT_GLOBAL_STDIO_STREAMS behaviour for all Newlib
configurations and removes the option.  This removes a couple of #ifdef blocks.

1 files changed, 0 insertions, 6 deletions

diff --git a/newlib/README b/newlib/README
index f00e66019..dd4686eeb 100644
--- a/newlib/README
+++ b/newlib/README
@@ -294,12 +294,6 @@ One feature can be enabled by specifying `--enable-FEATURE=yes' or
      Disable dynamic allocation of atexit entries.
      Most hosts and targets have it enabled in configure.host.
 
-`--enable-newlib-global-stdio-streams'
-     Enable to move the stdio stream FILE objects out of struct _reent and make
-     them global.  The stdio stream pointers of struct _reent are initialized
-     to point to the global stdio FILE stream objects.
-     Disabled by default.
-
 `--enable-newlib-reent-small'
      Enable small reentrant struct support.
      Disabled by default.