Add --enable-newlib-reent-thread-local option

By default, Newlib uses a huge object of type struct _reent to store
thread-specific data.  This object is returned by __getreent() if the
__DYNAMIC_REENT__ Newlib configuration option is defined.

The reentrancy structure contains for example errno and the standard input,
output, and error file streams.  This means that if an application only uses
errno it has a dependency on the file stream support even if it does not use
it.  This is an issue for lower end targets and applications which need to
qualify the software according to safety standards (for example ECSS-E-ST-40C,
ECSS-Q-ST-80C, IEC 61508, ISO 26262, DO-178, DO-330, DO-333).

If the new _REENT_THREAD_LOCAL configuration option is enabled, then struct
_reent is replaced by dedicated thread-local objects for each struct _reent
member.  The thread-local objects are defined in translation units which use
the corresponding object.

1 files changed, 8 insertions, 0 deletions

diff --git a/newlib/README b/newlib/README
index dd4686eeb..1b2c16cd4 100644
--- a/newlib/README
+++ b/newlib/README
@@ -304,6 +304,14 @@ One feature can be enabled by specifying `--enable-FEATURE=yes' or
      layout.
      Disabled by default.
 
+`--enable-newlib-reent-thread-local'
+     Enable thread-local storage objects as a replacement for struct _reent
+     members.  If enabled, then struct _reent is not defined and dedicated
+     thread-local storage objects are provided for each member of the default
+     struct _reent.  For statically linked executables only the objects
+     required by the application are linked in.
+     Disabled by default.
+
 `--disable-newlib-fvwrite-in-streamio'
      NEWLIB implements the vector buffer mechanism to support stream IO
      buffering required by C standard.  This feature is possibly