1 files changed, 51 insertions, 5 deletions

diff --git a/newlib/libc/stdlib/__atexit.c b/newlib/libc/stdlib/__atexit.c
index 4687d0023..d36a1a4e5 100644
--- a/newlib/libc/stdlib/__atexit.c
+++ b/newlib/libc/stdlib/__atexit.c
@@ -1,5 +1,35 @@
 /*
  *  Common routine to implement atexit-like functionality.
+ *
+ *  This is also the key function to be configured as lite exit, a size-reduced
+ *  implementation of exit that doesn't invoke clean-up functions such as _fini
+ *  or global destructors.
+ *
+ *  Default (without lite exit) call graph is like:
+ *  _start -> atexit -> __register_exitproc
+ *  _start -> __libc_init_array -> __cxa_atexit -> __register_exitproc
+ *  on_exit -> __register_exitproc
+ *  _start -> exit -> __call_exitprocs
+ *
+ *  Here an -> means arrow tail invokes arrow head. All invocations here
+ *  are non-weak reference in current newlib/libgloss.
+ *
+ *  Lite exit makes some of above calls as weak reference, so that size expansive
+ *  functions __register_exitproc and __call_exitprocs may not be linked. These
+ *  calls are:
+ *    _start w-> atexit
+ *    __cxa_atexit w-> __register_exitproc
+ *    exit w-> __call_exitprocs
+ *
+ *  Lite exit also makes sure that __call_exitprocs will be referenced as non-weak
+ *  whenever __register_exitproc is referenced as non-weak.
+ *
+ *  Thus with lite exit libs, a program not explicitly calling atexit or on_exit
+ *  will escape from the burden of cleaning up code. A program with atexit or on_exit
+ *  will work consistently to normal libs.
+ *
+ *  Lite exit is enabled with --enable-lite-exit, and is controlled with macro
+ *  _LITE_EXIT.
  */
 
 #include <stddef.h>
@@ -10,7 +40,23 @@
 
 /* Make this a weak reference to avoid pulling in malloc.  */
 void * malloc(size_t) _ATTRIBUTE((__weak__));
-__LOCK_INIT_RECURSIVE(, __atexit_lock);
+
+#ifdef _LITE_EXIT
+/* As __call_exitprocs is weak reference in lite exit, make a
+   non-weak reference to it here.  */
+const void * __atexit_dummy = &__call_exitprocs;
+#endif
+
+#ifndef __SINGLE_THREAD__
+extern _LOCK_RECURSIVE_T __atexit_lock;
+#endif
+
+#ifdef _REENT_GLOBAL_ATEXIT
+static struct _atexit _global_atexit0 = _ATEXIT_INIT;
+# define _GLOBAL_ATEXIT0 (&_global_atexit0)
+#else
+# define _GLOBAL_ATEXIT0 (&_GLOBAL_REENT->_atexit0)
+#endif
 
 /*
  * Register a function to be performed at exit or on shared library unload.
@@ -31,9 +77,9 @@ _DEFUN (__register_exitproc,
   __lock_acquire_recursive(__atexit_lock);
 #endif
 
-  p = _GLOBAL_REENT->_atexit;
+  p = _GLOBAL_ATEXIT;
   if (p == NULL)
-    _GLOBAL_REENT->_atexit = p = &_GLOBAL_REENT->_atexit0;
+    _GLOBAL_ATEXIT = p = _GLOBAL_ATEXIT0;
   if (p->_ind >= _ATEXIT_SIZE)
     {
 #ifndef _ATEXIT_DYNAMIC_ALLOC
@@ -53,8 +99,8 @@ _DEFUN (__register_exitproc,
 	  return -1;
 	}
       p->_ind = 0;
-      p->_next = _GLOBAL_REENT->_atexit;
-      _GLOBAL_REENT->_atexit = p;
+      p->_next = _GLOBAL_ATEXIT;
+      _GLOBAL_ATEXIT = p;
 #ifndef _REENT_SMALL
       p->_on_exit_args._fntypes = 0;
       p->_on_exit_args._is_cxa = 0;