sandbox: Decouple program entry from sandbox init

Move the program's entry point to os.c, in preparation for a separate
fuzzing entry point to be added.

Signed-off-by: Andrew Scull <ascull@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/sandbox/cpu/os.c

@@ -27,6 +27,7 @@
 #include <linux/types.h>
 
 #include <asm/getopt.h>
+#include <asm/main.h>
 #include <asm/sections.h>
 #include <asm/state.h>
 #include <os.h>
@@ -1001,3 +1002,8 @@ void os_relaunch(char *argv[])
 	execv(argv[0], argv);
 	os_exit(1);
 }
+
+int main(int argc, char *argv[])
+{
+	return sandbox_main(argc, argv);
+}

arch/sandbox/cpu/start.c

@@ -453,7 +453,7 @@ void sandbox_reset(void)
 	os_relaunch(os_argv);
 }
 
-int main(int argc, char *argv[])
+int sandbox_main(int argc, char *argv[])
 {
 	struct sandbox_state *state;
 	void * text_base;

arch/sandbox/include/asm/main.h

@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (c) 2022 Google, Inc.
+ * Written by Andrew Scull <ascull@google.com>
+ */
+
+#ifndef __ASM_SANDBOX_MAIN_H
+#define __ASM_SANDBOX_MAIN_H
+
+/**
+ * sandbox_main() - main entrypoint for sandbox
+ *
+ * @argc:	the number of arguments passed to the program
+ * @argv:	array of argc+1 pointers, of which the last one is null
+ */
+int sandbox_main(int argc, char *argv[]);
+
+#endif /* __ASM_SANDBOX_MAIN_H */