UbixOS  2.0
start.S
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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: releng/10.2/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  */
90 ENTRY(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]
103 return_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
118 syscall_ptr:
119  .long 0
120 
121  .globl uboot_address
122 uboot_address:
123  .long 0
124 
125 saved_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 */