2013-07-02 Joey Ye <joey.ye@arm.com>

        Lite exit support.
        * README: Add information about lite-exit.
        * acconfig.h (_LITE_EXIT): New macro.
        * configure.in (enable-lite-exit): New option.
        (_LITE_EXIT): Define new macro.
        * configure: Regenerated.
        * newlib.hin (_LITE_EXIT): New macro.
        * libc/stdlib/__atexit.c [_LITE_EXIT]: Add dummy explicit
        reference to __call_exitprocs.
        * libc/stdlib/cxa_atexit.c [_LITE_EXIT]: Make __register_exitproc a
        weak reference.
        * libc/stdlib/exit.c (exit)[_LITE_EXIT]: Remove TWS and weakly reference
        __call_exitprocs.

3 files changed, 53 insertions, 3 deletions

diff --git a/newlib/libc/stdlib/__atexit.c b/newlib/libc/stdlib/__atexit.c
index f04f00d8e..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>
@@ -11,6 +41,12 @@
 /* Make this a weak reference to avoid pulling in malloc.  */
 void * malloc(size_t) _ATTRIBUTE((__weak__));
 
+#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
diff --git a/newlib/libc/stdlib/cxa_atexit.c b/newlib/libc/stdlib/cxa_atexit.c
index 8c39236de..c3c0d2a17 100644
--- a/newlib/libc/stdlib/cxa_atexit.c
+++ b/newlib/libc/stdlib/cxa_atexit.c
@@ -19,5 +19,14 @@ _DEFUN (__cxa_atexit,
 	void *arg _AND
 	void *d)
 {
-  return __register_exitproc (__et_cxa, (void (*)(void)) fn, arg, d);
+#ifdef _LITE_EXIT
+  /* Refer to comments in __atexit.c for more details of lite exit.  */
+  int __register_exitproc _PARAMS ((int, void (*fn) (void), _PTR, _PTR))
+    __attribute__ ((weak));
+
+  if (!__register_exitproc)
+    return 0;
+  else
+#endif
+    return __register_exitproc (__et_cxa, (void (*)(void)) fn, arg, d);
 }
diff --git a/newlib/libc/stdlib/exit.c b/newlib/libc/stdlib/exit.c
index 195b72454..1dc56944a 100644
--- a/newlib/libc/stdlib/exit.c
+++ b/newlib/libc/stdlib/exit.c
@@ -54,11 +54,16 @@ Supporting OS subroutines required: <<_exit>>.
  * Exit, flushing stdio buffers if necessary.
  */
 
-void 
+void
 _DEFUN (exit, (code),
 	int code)
 {
-  __call_exitprocs (code, NULL);
+#ifdef _LITE_EXIT
+  /* Refer to comments in __atexit.c for more details of lite exit.  */
+  void __call_exitprocs _PARAMS ((int, _PTR)) __attribute__((weak));
+  if (__call_exitprocs)
+#endif
+    __call_exitprocs (code, NULL);
 
   if (_GLOBAL_REENT->__cleanup)
     (*_GLOBAL_REENT->__cleanup) (_GLOBAL_REENT);