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/plugin_crt0.c

@@ -0,0 +1,112 @@
+/***************************************************************************
+*             __________               __   ___.
+*   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+*   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+*   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+*   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+*                     \/            \/     \/    \/            \/
+* $Id$
+*
+* Copyright (C) 2010 by Thomas Martitz
+*
+* This program is free software; you can redistribute it and/or
+* modify it under the terms of the GNU General Public License
+* as published by the Free Software Foundation; either version 2
+* of the License, or (at your option) any later version.
+*
+* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+* KIND, either express or implied.
+*
+****************************************************************************/
+
+
+#include "plugin.h"
+#include <setjmp.h>
+
+PLUGIN_HEADER
+
+/*
+ * EXIT_MAGIC magic, because 0 cannot be used due to setjmp()
+ * must be > 0
+ */                      
+#define EXIT_MAGIC 0x0CDEBABE
+
+extern enum plugin_status plugin_start(const void*);
+
+static jmp_buf __exit_env;
+/* only 1 atexit handler for now, chain in the exit handler if you need more */
+static void (*atexit_handler)(void);
+
+int atexit(void (*fn)(void))
+{
+    if (atexit_handler)
+        return -1;
+    atexit_handler = fn;
+    return 0;
+}
+
+void exit(int status)
+{   /* jump back in time to before starting the plugin */
+    longjmp(__exit_env, status != 0 ? status : EXIT_MAGIC);
+}
+
+void _exit(int status)
+{   /* don't call exit handler */
+    atexit_handler = NULL;
+    exit(status);
+}
+
+enum plugin_status plugin__start(const void *param)
+{
+    int exit_ret;
+    enum plugin_status ret;
+
+    /* we come back here if exit() was called or the plugin returned normally */
+    exit_ret = setjmp(__exit_env);
+    if (exit_ret == 0)
+    {   /* start the plugin */
+        ret = plugin_start(param);
+    }
+    else
+    {   /* plugin exit via exit() */
+        if (exit_ret == EXIT_MAGIC)
+        {   /* exit(EXIT_SUCCESS) */
+            ret = PLUGIN_OK;
+        }
+        else if (exit_ret < INTERNAL_PLUGIN_RETVAL_START)
+        {   /* exit(EXIT_FAILURE) */
+            ret = PLUGIN_ERROR;
+        }
+        else
+        {   /* exit(PLUGIN_XXX) */
+            ret = (enum plugin_status)exit_ret;
+        }
+    }
+
+    /* before finishing, call the exit handler if there was one */
+    if (atexit_handler != NULL)
+        atexit_handler();
+
+    return ret;
+}
+
+static void cleanup_wrapper(void *param)
+{
+    (void)param;
+    if (atexit_handler)
+        atexit_handler();
+}
+
+void exit_on_usb(int button)
+{   /* the default handler will call the exit handler before
+     * showing the usb screen; after that we don't want the exit handler
+     * to be called a second time, hence _exit()
+     *
+     * if not usb, then the handler will only be called if powering off
+     * if poweroff, the plugin doesn't want to run any further so exit as well*/
+    long result = rb->default_event_handler_ex(button, cleanup_wrapper, NULL);
+    if (result == SYS_USB_CONNECTED)
+        _exit(PLUGIN_USB_CONNECTED);
+    else if (result == SYS_POWEROFF)
+        _exit(PLUGIN_POWEROFF);
+}