start.S revision 283505 
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: stable/10/sys/boot/arm/uboot/start.S 283505 2015-05-25 01:06:55Z ian $
27 */
28
29#include <machine/asm.h>
30#include <machine/armreg.h>
31
32	.text
33	.extern	_C_LABEL(self_reloc), _C_LABEL(main)
34	.weak	_DYNAMIC
35
36/*
37 * Entry point to the loader that U-Boot passes control to.
38 */
39	.globl	_start
40_start:
41
42#ifdef _ARM_ARCH_6
43	mrc     p15, 0, ip, c1, c0, 0
44	orr	ip, ip, #(CPU_CONTROL_UNAL_ENABLE)
45	orr	ip, ip, #(CPU_CONTROL_AFLT_ENABLE)
46	mcr     p15, 0, ip, c1, c0, 0
47#endif
48	/*
49	 * Do self-relocation when the weak external symbol _DYNAMIC is non-NULL.
50	 * When linked as a dynamic relocatable file, the linker automatically
51	 * defines _DYNAMIC with a value that is the offset of the dynamic
52	 * relocation info section.
53	 * Note that we're still on u-boot's stack here, but the self_reloc
54	 * code uses only a couple dozen bytes of stack space.
55	 */
56	adr	ip, .here_off		/* .here_off is a symbol whose value */
57	ldr	r0, [ip]		/* is its own offset in the text seg. */
58	sub	r0, ip, r0		/* Get its pc-relative address and */
59	ldr	r1, .dynamic_off	/* subtract its value and we get */
60	teq	r1, #0			/* r0 = physaddr we were loaded at. */
61	addne	r1, r1, r0		/* r1 = dynamic section physaddr. */
62	blne	_C_LABEL(self_reloc)	/* Do reloc if _DYNAMIC is non-NULL. */
63
64	/* Hint where to look for the API signature */
65	ldr	ip, =uboot_address
66	str	sp, [ip]
67
68	/* Save U-Boot's r8 and r9 */
69	ldr	ip, =saved_regs
70	str	r8, [ip, #0]
71	str	r9, [ip, #4]
72
73	/*
74	 * Start loader.  This is basically a tail-recursion call; if main()
75	 * returns, it returns to u-boot (which reports the value returned r0).
76	 */
77	b	main
78
79	/*
80	 * Data for self-relocation, in the text segment for pc-rel access.
81	 */
82.here_off:
83	.word	.
84.dynamic_off:
85	.word	_DYNAMIC
86
87/*
88 * syscall()
89 */
90ENTRY(syscall)
91	/* Save caller's lr, r8 and r9 */
92	ldr	ip, =saved_regs
93	str	r8, [ip, #8]
94	str	r9, [ip, #12]
95	str	lr, [ip, #16]
96	/* Restore U-Boot's r8 and r9 */
97	ldr	r8, [ip, #0]
98	ldr	r9, [ip, #4]
99	/* Call into U-Boot */
100	ldr	lr, =return_from_syscall
101	ldr	ip, =syscall_ptr
102	ldr	pc, [ip]
103return_from_syscall:
104	/* Restore loader's r8, r9 and lr */
105	ldr	ip, =saved_regs
106	ldr	lr, [ip, #16]
107	ldr	r9, [ip, #12]
108	ldr	r8, [ip, #8]
109	/* Return to caller */
110	mov	pc, lr
111
112/*
113 * Data section
114 */
115	.data
116	.align	4
117	.globl	syscall_ptr
118syscall_ptr:
119	.long	0
120
121	.globl	uboot_address
122uboot_address:
123	.long	0
124
125saved_regs:
126	.long	0	/* U-Boot's r8 */
127	.long	0	/* U-Boot's r9 */
128	.long	0	/* Loader's r8 */
129	.long	0	/* Loader's r9 */
130	.long	0	/* Loader's lr */
131