summaryrefslogtreecommitdiffstats
path: root/arch/x86/boot/header.S
blob: f3140e596d407d892eb75aa0c486bd7411e1dcb2 (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
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
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
/*
 *	header.S
 *
 *	Copyright (C) 1991, 1992 Linus Torvalds
 *
 *	Based on bootsect.S and setup.S
 *	modified by more people than can be counted
 *
 *	Rewritten as a common file by H. Peter Anvin (Apr 2007)
 *
 * BIG FAT NOTE: We're in real mode using 64k segments.  Therefore segment
 * addresses must be multiplied by 16 to obtain their respective linear
 * addresses. To avoid confusion, linear addresses are written using leading
 * hex while segment addresses are written as segment:offset.
 *
 */

#include <asm/segment.h>
#include <linux/utsrelease.h>
#include <asm/boot.h>
#include <asm/e820.h>
#include <asm/page.h>
#include <asm/setup.h>
#include "boot.h"

SETUPSECTS	= 4			/* default nr of setup-sectors */
BOOTSEG		= 0x07C0		/* original address of boot-sector */
SYSSEG		= DEF_SYSSEG		/* system loaded at 0x10000 (65536) */
SYSSIZE		= DEF_SYSSIZE		/* system size: # of 16-byte clicks */
					/* to be loaded */
ROOT_DEV	= 0			/* ROOT_DEV is now written by "build" */
SWAP_DEV	= 0			/* SWAP_DEV is now written by "build" */

#ifndef SVGA_MODE
#define SVGA_MODE ASK_VGA
#endif

#ifndef RAMDISK
#define RAMDISK 0
#endif

#ifndef ROOT_RDONLY
#define ROOT_RDONLY 1
#endif

	.code16
	.section ".bstext", "ax"

	.global bootsect_start
bootsect_start:

	# Normalize the start address
	ljmp	$BOOTSEG, $start2

start2:
	movw	%cs, %ax
	movw	%ax, %ds
	movw	%ax, %es
	movw	%ax, %ss
	xorw	%sp, %sp
	sti
	cld

	movw	$bugger_off_msg, %si

msg_loop:
	lodsb
	andb	%al, %al
	jz	bs_die
	movb	$0xe, %ah
	movw	$7, %bx
	int	$0x10
	jmp	msg_loop

bs_die:
	# Allow the user to press a key, then reboot
	xorw	%ax, %ax
	int	$0x16
	int	$0x19

	# int 0x19 should never return.  In case it does anyway,
	# invoke the BIOS reset code...
	ljmp	$0xf000,$0xfff0

	.section ".bsdata", "a"
bugger_off_msg:
	.ascii	"Direct booting from floppy is no longer supported.\r\n"
	.ascii	"Please use a boot loader program instead.\r\n"
	.ascii	"\n"
	.ascii	"Remove disk and press any key to reboot . . .\r\n"
	.byte	0


	# Kernel attributes; used by setup.  This is part 1 of the
	# header, from the old boot sector.

	.section ".header", "a"
	.globl	hdr
hdr:
setup_sects:	.byte SETUPSECTS
root_flags:	.word ROOT_RDONLY
syssize:	.long SYSSIZE
ram_size:	.word RAMDISK
vid_mode:	.word SVGA_MODE
root_dev:	.word ROOT_DEV
boot_flag:	.word 0xAA55

	# offset 512, entry point

	.globl	_start
_start:
		# Explicitly enter this as bytes, or the assembler
		# tries to generate a 3-byte jump here, which causes
		# everything else to push off to the wrong offset.
		.byte	0xeb		# short (2-byte) jump
		.byte	start_of_setup-1f
1:

	# Part 2 of the header, from the old setup.S

		.ascii	"HdrS"		# header signature
		.word	0x0206		# header version number (>= 0x0105)
					# or else old loadlin-1.5 will fail)
		.globl realmode_swtch
realmode_swtch:	.word	0, 0		# default_switch, SETUPSEG
start_sys_seg:	.word	SYSSEG
		.word	kernel_version-512 # pointing to kernel version string
					# above section of header is compatible
					# with loadlin-1.5 (header v1.5). Don't
					# change it.

type_of_loader:	.byte	0		# = 0, old one (LILO, Loadlin,
					#      Bootlin, SYSLX, bootsect...)
					# See Documentation/i386/boot.txt for
					# assigned ids

# flags, unused bits must be zero (RFU) bit within loadflags
loadflags:
LOADED_HIGH	= 1			# If set, the kernel is loaded high
CAN_USE_HEAP	= 0x80			# If set, the loader also has set
					# heap_end_ptr to tell how much
					# space behind setup.S can be used for
					# heap purposes.
					# Only the loader knows what is free
#ifndef __BIG_KERNEL__
		.byte	0
#else
		.byte	LOADED_HIGH
#endif

setup_move_size: .word  0x8000		# size to move, when setup is not
					# loaded at 0x90000. We will move setup
					# to 0x90000 then just before jumping
					# into the kernel. However, only the
					# loader knows how much data behind
					# us also needs to be loaded.

code32_start:				# here loaders can put a different
					# start address for 32-bit code.
#ifndef __BIG_KERNEL__
		.long	0x1000		#   0x1000 = default for zImage
#else
		.long	0x100000	# 0x100000 = default for big kernel
#endif

ramdisk_image:	.long	0		# address of loaded ramdisk image
					# Here the loader puts the 32-bit
					# address where it loaded the image.
					# This only will be read by the kernel.

ramdisk_size:	.long	0		# its size in bytes

bootsect_kludge:
		.long	0		# obsolete

heap_end_ptr:	.word	_end+1024	# (Header version 0x0201 or later)
					# space from here (exclusive) down to
					# end of setup code can be used by setup
					# for local heap purposes.

pad1:		.word	0
cmd_line_ptr:	.long	0		# (Header version 0x0202 or later)
					# If nonzero, a 32-bit pointer
					# to the kernel command line.
					# The command line should be
					# located between the start of
					# setup and the end of low
					# memory (0xa0000), or it may
					# get overwritten before it
					# gets read.  If this field is
					# used, there is no longer
					# anything magical about the
					# 0x90000 segment; the setup
					# can be located anywhere in
					# low memory 0x10000 or higher.

ramdisk_max:	.long (-__PAGE_OFFSET-(512 << 20)-1) & 0x7fffffff
					# (Header version 0x0203 or later)
					# The highest safe address for
					# the contents of an initrd

kernel_alignment:  .long CONFIG_PHYSICAL_ALIGN	#physical addr alignment
						#required for protected mode
						#kernel
#ifdef CONFIG_RELOCATABLE
relocatable_kernel:    .byte 1
#else
relocatable_kernel:    .byte 0
#endif
pad2:			.byte 0
pad3:			.word 0

cmdline_size:   .long   COMMAND_LINE_SIZE-1     #length of the command line,
                                                #added with boot protocol
                                                #version 2.06

# End of setup header #####################################################

	.section ".inittext", "ax"
start_of_setup:
#ifdef SAFE_RESET_DISK_CONTROLLER
# Reset the disk controller.
	movw	$0x0000, %ax		# Reset disk controller
	movb	$0x80, %dl		# All disks
	int	$0x13
#endif

# We will have entered with %cs = %ds+0x20, normalize %cs so
# it is on par with the other segments.
	pushw	%ds
	pushw	$setup2
	lretw

setup2:
# Force %es = %ds
	movw	%ds, %ax
	movw	%ax, %es
	cld

# Stack paranoia: align the stack and make sure it is good
# for both 16- and 32-bit references.  In particular, if we
# were meant to have been using the full 16-bit segment, the
# caller might have set %sp to zero, which breaks %esp-based
# references.
	andw	$~3, %sp	# dword align (might as well...)
	jnz	1f
	movw	$0xfffc, %sp	# Make sure we're not zero
1:	movzwl	%sp, %esp	# Clear upper half of %esp
	sti

# Check signature at end of setup
	cmpl	$0x5a5aaa55, setup_sig
	jne	setup_bad

# Zero the bss
	movw	$__bss_start, %di
	movw	$_end+3, %cx
	xorl	%eax, %eax
	subw	%di, %cx
	shrw	$2, %cx
	rep; stosl

# Jump to C code (should not return)
	calll	main

# Setup corrupt somehow...
setup_bad:
	movl	$setup_corrupt, %eax
	calll	puts
	# Fall through...

	.globl	die
	.type	die, @function
die:
	hlt
	jmp	die

	.size	die, .-die

	.section ".initdata", "a"
setup_corrupt:
	.byte	7
	.string	"No setup signature found...\n"
OpenPOWER on IntegriCloud