Second try: Introduce plugin_crt0.c that every plugin links.

It handles exit() properly, calling the handler also when the plugin returns
normally (also make exit() more standard compliant while at it).
It also holds PLUGIN_HEADER, so that it doesn't need to be in each plugin anymore.

To work better together with callbacks passed to rb->default_event_handler_ex() introduce exit_on_usb() which will call the exit handler before showing the usb screen and exit() after it.
In most cases rb->default_event_handler_ex() was passed a callback which was manually called at all other return points. This can now be done via atexit().

In future plugin_crt0.c could also handle clearing bss, initializing iram and more.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@27873 a1c6a512-1295-4272-9138-f99709370657

apps/plugins/lib/pluginlib_exit.h

@@ -22,31 +22,33 @@
 #ifndef __PLUGINLIB_EXIT_H__
 #define __PLUGINLIB_EXIT_H__
 
-#include "config.h"
-#include <setjmp.h>
+/* make sure we are in sync with the real definitions, especially on
+ * hosted systems */
+#include <stdlib.h>
+#include "gcc_extensions.h"
 
-#define _PLUGINLIB_EXIT_INIT(atexit) switch(setjmp(__exit_env))   \
-                                     {                            \
-                                         case 1:                  \
-                                             atexit               \
-                                             return PLUGIN_OK;    \
-                                         case 2:                  \
-                                             atexit               \
-                                             return PLUGIN_ERROR; \
-                                         case 0:                  \
-                                         default:                 \
-                                             break;               \
-                                     }
+/* these are actually implemented in plugin_crt0.c which all plugins link */
+extern int atexit(void (*func)(void));
+extern void exit(int status) NORETURN_ATTR;
+/* these don't call the exit handlers */
+extern void _exit(int status) NORETURN_ATTR;
+/* C99 version */
+#define _Exit _exit
 
-/* Either PLUGINLIB_EXIT_INIT or PLUGINLIB_EXIT_INIT_ATEXIT needs to be placed
- * as the first line in plugin_start. The _ATEXIT version will call the named
- * no-argument function when exit() is called before exiting the plugin, to
- * allow for cleanup.
+#ifndef EXIT_SUCCESS
+#define EXIT_SUCCESS 0
+#define EXIT_FAILURE 1
+#endif
+
+/**
+ * helper function to handle USB connected events coming from
+ * button_get()
+ *
+ * it will exit the plugin if usb is detected, but it will call the atexit func
+ * before actually showing the usb screen
+ *
+ * it additionally handles power off as well, with the same behavior
  */
-#define PLUGINLIB_EXIT_INIT _PLUGINLIB_EXIT_INIT()
-#define PLUGINLIB_EXIT_INIT_ATEXIT(atexit) _PLUGINLIB_EXIT_INIT(atexit();)
-
-extern jmp_buf __exit_env;
-#define exit(status) longjmp(__exit_env, status != 0 ? 2 : 1)
+extern void exit_on_usb(int button);
 
 #endif /*  __PLUGINLIB_EXIT_H__ */