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/arch/x86/boot/header.S

https://bitbucket.org/thekraven/iscream_thunderc-2.6.35
Assembly | 320 lines | 289 code | 31 blank | 0 comment | 8 complexity | 5126365805227c5e579b94c67ea9a277 MD5 | raw file
Possible License(s): GPL-2.0, LGPL-2.0, AGPL-1.0
  1/*
  2 *	header.S
  3 *
  4 *	Copyright (C) 1991, 1992 Linus Torvalds
  5 *
  6 *	Based on bootsect.S and setup.S
  7 *	modified by more people than can be counted
  8 *
  9 *	Rewritten as a common file by H. Peter Anvin (Apr 2007)
 10 *
 11 * BIG FAT NOTE: We're in real mode using 64k segments.  Therefore segment
 12 * addresses must be multiplied by 16 to obtain their respective linear
 13 * addresses. To avoid confusion, linear addresses are written using leading
 14 * hex while segment addresses are written as segment:offset.
 15 *
 16 */
 17
 18#include <asm/segment.h>
 19#include <generated/utsrelease.h>
 20#include <asm/boot.h>
 21#include <asm/e820.h>
 22#include <asm/page_types.h>
 23#include <asm/setup.h>
 24#include "boot.h"
 25#include "voffset.h"
 26#include "zoffset.h"
 27
 28BOOTSEG		= 0x07C0		/* original address of boot-sector */
 29SYSSEG		= 0x1000		/* historical load address >> 4 */
 30
 31#ifndef SVGA_MODE
 32#define SVGA_MODE ASK_VGA
 33#endif
 34
 35#ifndef RAMDISK
 36#define RAMDISK 0
 37#endif
 38
 39#ifndef ROOT_RDONLY
 40#define ROOT_RDONLY 1
 41#endif
 42
 43	.code16
 44	.section ".bstext", "ax"
 45
 46	.global bootsect_start
 47bootsect_start:
 48
 49	# Normalize the start address
 50	ljmp	$BOOTSEG, $start2
 51
 52start2:
 53	movw	%cs, %ax
 54	movw	%ax, %ds
 55	movw	%ax, %es
 56	movw	%ax, %ss
 57	xorw	%sp, %sp
 58	sti
 59	cld
 60
 61	movw	$bugger_off_msg, %si
 62
 63msg_loop:
 64	lodsb
 65	andb	%al, %al
 66	jz	bs_die
 67	movb	$0xe, %ah
 68	movw	$7, %bx
 69	int	$0x10
 70	jmp	msg_loop
 71
 72bs_die:
 73	# Allow the user to press a key, then reboot
 74	xorw	%ax, %ax
 75	int	$0x16
 76	int	$0x19
 77
 78	# int 0x19 should never return.  In case it does anyway,
 79	# invoke the BIOS reset code...
 80	ljmp	$0xf000,$0xfff0
 81
 82	.section ".bsdata", "a"
 83bugger_off_msg:
 84	.ascii	"Direct booting from floppy is no longer supported.\r\n"
 85	.ascii	"Please use a boot loader program instead.\r\n"
 86	.ascii	"\n"
 87	.ascii	"Remove disk and press any key to reboot . . .\r\n"
 88	.byte	0
 89
 90
 91	# Kernel attributes; used by setup.  This is part 1 of the
 92	# header, from the old boot sector.
 93
 94	.section ".header", "a"
 95	.globl	hdr
 96hdr:
 97setup_sects:	.byte 0			/* Filled in by build.c */
 98root_flags:	.word ROOT_RDONLY
 99syssize:	.long 0			/* Filled in by build.c */
100ram_size:	.word 0			/* Obsolete */
101vid_mode:	.word SVGA_MODE
102root_dev:	.word 0			/* Filled in by build.c */
103boot_flag:	.word 0xAA55
104
105	# offset 512, entry point
106
107	.globl	_start
108_start:
109		# Explicitly enter this as bytes, or the assembler
110		# tries to generate a 3-byte jump here, which causes
111		# everything else to push off to the wrong offset.
112		.byte	0xeb		# short (2-byte) jump
113		.byte	start_of_setup-1f
1141:
115
116	# Part 2 of the header, from the old setup.S
117
118		.ascii	"HdrS"		# header signature
119		.word	0x020a		# header version number (>= 0x0105)
120					# or else old loadlin-1.5 will fail)
121		.globl realmode_swtch
122realmode_swtch:	.word	0, 0		# default_switch, SETUPSEG
123start_sys_seg:	.word	SYSSEG		# obsolete and meaningless, but just
124					# in case something decided to "use" it
125		.word	kernel_version-512 # pointing to kernel version string
126					# above section of header is compatible
127					# with loadlin-1.5 (header v1.5). Don't
128					# change it.
129
130type_of_loader:	.byte	0		# 0 means ancient bootloader, newer
131					# bootloaders know to change this.
132					# See Documentation/i386/boot.txt for
133					# assigned ids
134
135# flags, unused bits must be zero (RFU) bit within loadflags
136loadflags:
137LOADED_HIGH	= 1			# If set, the kernel is loaded high
138CAN_USE_HEAP	= 0x80			# If set, the loader also has set
139					# heap_end_ptr to tell how much
140					# space behind setup.S can be used for
141					# heap purposes.
142					# Only the loader knows what is free
143		.byte	LOADED_HIGH
144
145setup_move_size: .word  0x8000		# size to move, when setup is not
146					# loaded at 0x90000. We will move setup
147					# to 0x90000 then just before jumping
148					# into the kernel. However, only the
149					# loader knows how much data behind
150					# us also needs to be loaded.
151
152code32_start:				# here loaders can put a different
153					# start address for 32-bit code.
154		.long	0x100000	# 0x100000 = default for big kernel
155
156ramdisk_image:	.long	0		# address of loaded ramdisk image
157					# Here the loader puts the 32-bit
158					# address where it loaded the image.
159					# This only will be read by the kernel.
160
161ramdisk_size:	.long	0		# its size in bytes
162
163bootsect_kludge:
164		.long	0		# obsolete
165
166heap_end_ptr:	.word	_end+STACK_SIZE-512
167					# (Header version 0x0201 or later)
168					# space from here (exclusive) down to
169					# end of setup code can be used by setup
170					# for local heap purposes.
171
172ext_loader_ver:
173		.byte	0		# Extended boot loader version
174ext_loader_type:
175		.byte	0		# Extended boot loader type
176
177cmd_line_ptr:	.long	0		# (Header version 0x0202 or later)
178					# If nonzero, a 32-bit pointer
179					# to the kernel command line.
180					# The command line should be
181					# located between the start of
182					# setup and the end of low
183					# memory (0xa0000), or it may
184					# get overwritten before it
185					# gets read.  If this field is
186					# used, there is no longer
187					# anything magical about the
188					# 0x90000 segment; the setup
189					# can be located anywhere in
190					# low memory 0x10000 or higher.
191
192ramdisk_max:	.long 0x7fffffff
193					# (Header version 0x0203 or later)
194					# The highest safe address for
195					# the contents of an initrd
196					# The current kernel allows up to 4 GB,
197					# but leave it at 2 GB to avoid
198					# possible bootloader bugs.
199
200kernel_alignment:  .long CONFIG_PHYSICAL_ALIGN	#physical addr alignment
201						#required for protected mode
202						#kernel
203#ifdef CONFIG_RELOCATABLE
204relocatable_kernel:    .byte 1
205#else
206relocatable_kernel:    .byte 0
207#endif
208min_alignment:		.byte MIN_KERNEL_ALIGN_LG2	# minimum alignment
209pad3:			.word 0
210
211cmdline_size:   .long   COMMAND_LINE_SIZE-1     #length of the command line,
212                                                #added with boot protocol
213                                                #version 2.06
214
215hardware_subarch:	.long 0			# subarchitecture, added with 2.07
216						# default to 0 for normal x86 PC
217
218hardware_subarch_data:	.quad 0
219
220payload_offset:		.long ZO_input_data
221payload_length:		.long ZO_z_input_len
222
223setup_data:		.quad 0			# 64-bit physical pointer to
224						# single linked list of
225						# struct setup_data
226
227pref_address:		.quad LOAD_PHYSICAL_ADDR	# preferred load addr
228
229#define ZO_INIT_SIZE	(ZO__end - ZO_startup_32 + ZO_z_extract_offset)
230#define VO_INIT_SIZE	(VO__end - VO__text)
231#if ZO_INIT_SIZE > VO_INIT_SIZE
232#define INIT_SIZE ZO_INIT_SIZE
233#else
234#define INIT_SIZE VO_INIT_SIZE
235#endif
236init_size:		.long INIT_SIZE		# kernel initialization size
237
238# End of setup header #####################################################
239
240	.section ".entrytext", "ax"
241start_of_setup:
242#ifdef SAFE_RESET_DISK_CONTROLLER
243# Reset the disk controller.
244	movw	$0x0000, %ax		# Reset disk controller
245	movb	$0x80, %dl		# All disks
246	int	$0x13
247#endif
248
249# Force %es = %ds
250	movw	%ds, %ax
251	movw	%ax, %es
252	cld
253
254# Apparently some ancient versions of LILO invoked the kernel with %ss != %ds,
255# which happened to work by accident for the old code.  Recalculate the stack
256# pointer if %ss is invalid.  Otherwise leave it alone, LOADLIN sets up the
257# stack behind its own code, so we can't blindly put it directly past the heap.
258
259	movw	%ss, %dx
260	cmpw	%ax, %dx	# %ds == %ss?
261	movw	%sp, %dx
262	je	2f		# -> assume %sp is reasonably set
263
264	# Invalid %ss, make up a new stack
265	movw	$_end, %dx
266	testb	$CAN_USE_HEAP, loadflags
267	jz	1f
268	movw	heap_end_ptr, %dx
2691:	addw	$STACK_SIZE, %dx
270	jnc	2f
271	xorw	%dx, %dx	# Prevent wraparound
272
2732:	# Now %dx should point to the end of our stack space
274	andw	$~3, %dx	# dword align (might as well...)
275	jnz	3f
276	movw	$0xfffc, %dx	# Make sure we're not zero
2773:	movw	%ax, %ss
278	movzwl	%dx, %esp	# Clear upper half of %esp
279	sti			# Now we should have a working stack
280
281# We will have entered with %cs = %ds+0x20, normalize %cs so
282# it is on par with the other segments.
283	pushw	%ds
284	pushw	$6f
285	lretw
2866:
287
288# Check signature at end of setup
289	cmpl	$0x5a5aaa55, setup_sig
290	jne	setup_bad
291
292# Zero the bss
293	movw	$__bss_start, %di
294	movw	$_end+3, %cx
295	xorl	%eax, %eax
296	subw	%di, %cx
297	shrw	$2, %cx
298	rep; stosl
299
300# Jump to C code (should not return)
301	calll	main
302
303# Setup corrupt somehow...
304setup_bad:
305	movl	$setup_corrupt, %eax
306	calll	puts
307	# Fall through...
308
309	.globl	die
310	.type	die, @function
311die:
312	hlt
313	jmp	die
314
315	.size	die, .-die
316
317	.section ".initdata", "a"
318setup_corrupt:
319	.byte	7
320	.string	"No setup signature found...\n"