start.S revision 234908 
1/*-
2 * Copyright (c) 2008 Semihalf, Rafal Czubak
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 *
26 * $FreeBSD: head/sys/boot/arm/uboot/start.S 234908 2012-05-02 05:49:58Z kientzle $
27 */
28
29#include <machine/asm.h>
30
31/*
32 * Entry point to the loader that U-Boot passes control to.
33 */
34	.text
35	.globl	_start
36_start:
37	/* Hint where to look for the API signature */
38	ldr	ip, =uboot_address
39	str	sp, [ip]
40
41	/* Save U-Boot's r8 */
42	ldr	ip, =saved_regs
43	str	r8, [ip, #0]
44
45	/* Start loader */
46	b	main
47
48/*
49 * syscall()
50 */
51ENTRY(syscall)
52	/* Save caller's lr and r8 */
53	ldr	ip, =saved_regs
54	str	lr, [ip, #4]
55	str	r8, [ip, #8]
56	/* Restore U-Boot's r8 */
57	ldr	r8, [ip, #0]
58	/* Call into U-Boot */
59	ldr	lr, =return_from_syscall
60	ldr	ip, =syscall_ptr
61	ldr	pc, [ip]
62return_from_syscall:
63	/* Restore loader's r8 and lr */
64	ldr	ip, =saved_regs
65	ldr	r8, [ip, #8]
66	ldr	lr, [ip, #4]
67	/* Return to caller */
68	mov	pc, lr
69
70/*
71 * Data section
72 */
73	.data
74	.align	4
75	.globl	syscall_ptr
76syscall_ptr:
77	.long	0
78
79	.globl	uboot_address
80uboot_address:
81	.long	0
82
83saved_regs:
84	.long	0	/* U-Boot's r8 */
85	.long	0	/* Loader's r8 */
86	.long	0	/* Loader's lr */
87