Introduce plugin_crt0.c that every plugin links.

It handles exit() properly, calling the handler also when the plugin returns
normally (also it makes 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 it 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@27862 a1c6a512-1295-4272-9138-f99709370657

apps/plugins/lib/pluginlib_exit.h

@@ -22,35 +22,33 @@
 #ifndef __PLUGINLIB_EXIT_H__
 #define __PLUGINLIB_EXIT_H__
 
-#include "config.h"
-#if (CONFIG_PLATFORM & PLATFORM_NATIVE)
-#include "../../codecs/lib/setjmp.h"
-#else
-#include <setjmp.h>
+/* make sure we are in sync with the real definitions, especially on
+ * hosted systems */
+#include <stdlib.h>
+#include "gcc_extensions.h"
+
+/* 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
+
+#ifndef EXIT_SUCCESS
+#define EXIT_SUCCESS 0
+#define EXIT_FAILURE 1
 #endif
 
-#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;               \
-                                     }
-
-/* 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.
+/**
+ * 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__ */