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
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
|
/* SPDX-License-Identifier: GPL-2.0 */
/*
* 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/init.h>
#include <linux/linkage.h>
#include <asm/segment.h>
#include <asm/page_types.h>
#include <asm/boot.h>
#include <asm/asm-offsets.h>
#include <asm/bootparam.h>
/*
* The 32-bit x86 assembler in binutils 2.26 will generate R_386_GOT32X
* relocation to get the symbol address in PIC. When the compressed x86
* kernel isn't built as PIC, the linker optimizes R_386_GOT32X
* relocations to their fixed symbol addresses. However, when the
* compressed x86 kernel is loaded at a different address, it leads
* to the following load failure:
*
* Failed to allocate space for phdrs
*
* during the decompression stage.
*
* If the compressed x86 kernel is relocatable at run-time, it should be
* compiled with -fPIE, instead of -fPIC, if possible and should be built as
* Position Independent Executable (PIE) so that linker won't optimize
* R_386_GOT32X relocation to its fixed symbol address. Older
* linkers generate R_386_32 relocations against locally defined symbols,
* _bss, _ebss, _got and _egot, in PIE. It isn't wrong, just less
* optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle
* R_386_32 relocations when relocating the kernel. To generate
* R_386_RELATIVE relocations, we mark _bss, _ebss, _got and _egot as
* hidden:
*/
.hidden _bss
.hidden _ebss
.hidden _got
.hidden _egot
__HEAD
SYM_FUNC_START(startup_32)
cld
/*
* Test KEEP_SEGMENTS flag to see if the bootloader is asking
* us to not reload segments
*/
testb $KEEP_SEGMENTS, BP_loadflags(%esi)
jnz 1f
cli
movl $__BOOT_DS, %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %fs
movl %eax, %gs
movl %eax, %ss
1:
/*
* 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 0x1e4 (defined as a scratch field) are used as the stack
* for this calculation. Only 4 bytes are needed.
*/
leal (BP_scratch+4)(%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
movl BP_kernel_alignment(%esi), %eax
decl %eax
addl %eax, %ebx
notl %eax
andl %eax, %ebx
cmpl $LOAD_PHYSICAL_ADDR, %ebx
jge 1f
#endif
movl $LOAD_PHYSICAL_ADDR, %ebx
1:
/* Target address to relocate to for decompression */
movl BP_init_size(%esi), %eax
subl $_end, %eax
addl %eax, %ebx
/* Set up the stack */
leal boot_stack_end(%ebx), %esp
/* Zero EFLAGS */
pushl $0
popfl
/*
* Copy the compressed kernel to the end of our buffer
* where decompression in place becomes safe.
*/
pushl %esi
leal (_bss-4)(%ebp), %esi
leal (_bss-4)(%ebx), %edi
movl $(_bss - startup_32), %ecx
shrl $2, %ecx
std
rep movsl
cld
popl %esi
/*
* Jump to the relocated address.
*/
leal .Lrelocated(%ebx), %eax
jmp *%eax
SYM_FUNC_END(startup_32)
#ifdef CONFIG_EFI_STUB
SYM_FUNC_START(efi32_stub_entry)
SYM_FUNC_START_ALIAS(efi_stub_entry)
add $0x4, %esp
call efi_main
movl %eax, %esi
movl BP_code32_start(%esi), %eax
leal startup_32(%eax), %eax
jmp *%eax
SYM_FUNC_END(efi32_stub_entry)
SYM_FUNC_END_ALIAS(efi_stub_entry)
#endif
.text
SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
/*
* Clear BSS (stack is currently empty)
*/
xorl %eax, %eax
leal _bss(%ebx), %edi
leal _ebss(%ebx), %ecx
subl %edi, %ecx
shrl $2, %ecx
rep stosl
/*
* Adjust our own GOT
*/
leal _got(%ebx), %edx
leal _egot(%ebx), %ecx
1:
cmpl %ecx, %edx
jae 2f
addl %ebx, (%edx)
addl $4, %edx
jmp 1b
2:
/*
* Do the extraction, and jump to the new kernel..
*/
/* push arguments for extract_kernel: */
pushl $z_output_len /* decompressed length, end of relocs */
movl BP_init_size(%esi), %eax
subl $_end, %eax
movl %ebx, %ebp
subl %eax, %ebp
pushl %ebp /* output address */
pushl $z_input_len /* input_len */
leal input_data(%ebx), %eax
pushl %eax /* input_data */
leal boot_heap(%ebx), %eax
pushl %eax /* heap area */
pushl %esi /* real mode pointer */
call extract_kernel /* returns kernel location in %eax */
addl $24, %esp
/*
* Jump to the extracted kernel.
*/
xorl %ebx, %ebx
jmp *%eax
SYM_FUNC_END(.Lrelocated)
/*
* Stack and heap for uncompression
*/
.bss
.balign 4
boot_heap:
.fill BOOT_HEAP_SIZE, 1, 0
boot_stack:
.fill BOOT_STACK_SIZE, 1, 0
boot_stack_end:
|
