aboutsummaryrefslogtreecommitdiff
path: root/arch/i386/boot/compressed/head.S
blob: 3517a32aaf4152a67098f70dc43e1f43f16d5851 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
/*
 *  linux/boot/head.S
 *
 *  Copyright (C) 1991, 1992, 1993  Linus Torvalds
 */

/*
 *  head.S contains the 32-bit startup code.
 *
 * NOTE!!! Startup happens at absolute address 0x00001000, which is also where
 * the page directory will exist. The startup code will be overwritten by
 * the page directory. [According to comments etc elsewhere on a compressed
 * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC]
 *
 * Page 0 is deliberately kept safe, since System Management Mode code in 
 * laptops may need to access the BIOS data stored there.  This is also
 * useful for future device drivers that either access the BIOS via VM86 
 * mode.
 */

/*
 * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
 */
.text

#include <linux/linkage.h>
#include <asm/segment.h>
#include <asm/page.h>
#include <asm/boot.h>

.section ".text.head","ax",@progbits
	.globl startup_32

startup_32:
	cld
	cli
	movl $(__BOOT_DS),%eax
	movl %eax,%ds
	movl %eax,%es
	movl %eax,%fs
	movl %eax,%gs
	movl %eax,%ss

/* Calculate the delta between where we were compiled to run
 * at and where we were actually loaded at.  This can only be done
 * with a short local call on x86.  Nothing  else will tell us what
 * address we are running at.  The reserved chunk of the real-mode
 * data at 0x34-0x3f are used as the stack for this calculation.
 * Only 4 bytes are needed.
 */
	leal 0x40(%esi), %esp
	call 1f
1:	popl %ebp
	subl $1b, %ebp

/* %ebp contains the address we are loaded at by the boot loader and %ebx
 * contains the address where we should move the kernel image temporarily
 * for safe in-place decompression.
 */

#ifdef CONFIG_RELOCATABLE
	movl 	%ebp, %ebx
	addl    $(CONFIG_PHYSICAL_ALIGN - 1), %ebx
	andl    $(~(CONFIG_PHYSICAL_ALIGN - 1)), %ebx
#else
	movl $LOAD_PHYSICAL_ADDR, %ebx
#endif

	/* Replace the compressed data size with the uncompressed size */
	subl input_len(%ebp), %ebx
	movl output_len(%ebp), %eax
	addl %eax, %ebx
	/* Add 8 bytes for every 32K input block */
	shrl $12, %eax
	addl %eax, %ebx
	/* Add 32K + 18 bytes of extra slack */
	addl $(32768 + 18), %ebx
	/* Align on a 4K boundary */
	addl $4095, %ebx
	andl $~4095, %ebx

/* Copy the compressed kernel to the end of our buffer
 * where decompression in place becomes safe.
 */
	pushl %esi
	leal _end(%ebp), %esi
	leal _end(%ebx), %edi
	movl $(_end - startup_32), %ecx
	std
	rep
	movsb
	cld
	popl %esi

/* Compute the kernel start address.
 */
#ifdef CONFIG_RELOCATABLE
	addl    $(CONFIG_PHYSICAL_ALIGN - 1), %ebp
	andl    $(~(CONFIG_PHYSICAL_ALIGN - 1)), %ebp
#else
	movl	$LOAD_PHYSICAL_ADDR, %ebp
#endif

/*
 * Jump to the relocated address.
 */
	leal relocated(%ebx), %eax
	jmp *%eax
.section ".text"
relocated:

/*
 * Clear BSS
 */
	xorl %eax,%eax
	leal _edata(%ebx),%edi
	leal _end(%ebx), %ecx
	subl %edi,%ecx
	cld
	rep
	stosb

/*
 * Setup the stack for the decompressor
 */
	leal stack_end(%ebx), %esp

/*
 * Do the decompression, and jump to the new kernel..
 */
	movl output_len(%ebx), %eax
	pushl %eax
	pushl %ebp	# output address
	movl input_len(%ebx), %eax
	pushl %eax	# input_len
	leal input_data(%ebx), %eax
	pushl %eax	# input_data
	leal _end(%ebx), %eax
	pushl %eax	# end of the image as third argument
	pushl %esi	# real mode pointer as second arg
	call decompress_kernel
	addl $20, %esp
	popl %ecx

#if CONFIG_RELOCATABLE
/* Find the address of the relocations.
 */
	movl %ebp, %edi
	addl %ecx, %edi

/* Calculate the delta between where vmlinux was compiled to run
 * and where it was actually loaded.
 */
	movl %ebp, %ebx
	subl $LOAD_PHYSICAL_ADDR, %ebx
	jz   2f		/* Nothing to be done if loaded at compiled addr. */
/*
 * Process relocations.
 */

1:	subl $4, %edi
	movl 0(%edi), %ecx
	testl %ecx, %ecx
	jz 2f
	addl %ebx, -__PAGE_OFFSET(%ebx, %ecx)
	jmp 1b
2:
#endif

/*
 * Jump to the decompressed kernel.
 */
	xorl %ebx,%ebx
	jmp *%ebp

.bss
.balign 4
stack:
	.fill 4096, 1, 0
stack_end: