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H. Peter Anvin62607312007-07-11 12:18:54 -07001/*
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 <linux/utsrelease.h>
20#include <asm/boot.h>
21#include <asm/e820.h>
22#include <asm/page.h>
23#include <asm/setup.h>
24#include "boot.h"
25
26SETUPSECTS = 4 /* default nr of setup-sectors */
27BOOTSEG = 0x07C0 /* original address of boot-sector */
28SYSSEG = DEF_SYSSEG /* system loaded at 0x10000 (65536) */
29SYSSIZE = DEF_SYSSIZE /* system size: # of 16-byte clicks */
30 /* to be loaded */
31ROOT_DEV = 0 /* ROOT_DEV is now written by "build" */
32SWAP_DEV = 0 /* SWAP_DEV is now written by "build" */
33
34#ifndef SVGA_MODE
35#define SVGA_MODE ASK_VGA
36#endif
37
38#ifndef RAMDISK
39#define RAMDISK 0
40#endif
41
42#ifndef ROOT_RDONLY
43#define ROOT_RDONLY 1
44#endif
45
46 .code16
47 .section ".bstext", "ax"
48
49 .global bootsect_start
50bootsect_start:
51
52 # Normalize the start address
53 ljmp $BOOTSEG, $start2
54
55start2:
56 movw %cs, %ax
57 movw %ax, %ds
58 movw %ax, %es
59 movw %ax, %ss
60 xorw %sp, %sp
61 sti
62 cld
63
64 movw $bugger_off_msg, %si
65
66msg_loop:
67 lodsb
68 andb %al, %al
69 jz bs_die
70 movb $0xe, %ah
71 movw $7, %bx
72 int $0x10
73 jmp msg_loop
74
75bs_die:
76 # Allow the user to press a key, then reboot
77 xorw %ax, %ax
78 int $0x16
79 int $0x19
80
81 # int 0x19 should never return. In case it does anyway,
82 # invoke the BIOS reset code...
83 ljmp $0xf000,$0xfff0
84
85 .section ".bsdata", "a"
86bugger_off_msg:
87 .ascii "Direct booting from floppy is no longer supported.\r\n"
88 .ascii "Please use a boot loader program instead.\r\n"
89 .ascii "\n"
90 .ascii "Remove disk and press any key to reboot . . .\r\n"
91 .byte 0
92
93
94 # Kernel attributes; used by setup. This is part 1 of the
95 # header, from the old boot sector.
96
97 .section ".header", "a"
98 .globl hdr
99hdr:
100setup_sects: .byte SETUPSECTS
101root_flags: .word ROOT_RDONLY
102syssize: .long SYSSIZE
103ram_size: .word RAMDISK
104vid_mode: .word SVGA_MODE
105root_dev: .word ROOT_DEV
106boot_flag: .word 0xAA55
107
108 # offset 512, entry point
109
110 .globl _start
111_start:
112 # Explicitly enter this as bytes, or the assembler
113 # tries to generate a 3-byte jump here, which causes
114 # everything else to push off to the wrong offset.
115 .byte 0xeb # short (2-byte) jump
116 .byte start_of_setup-1f
1171:
118
119 # Part 2 of the header, from the old setup.S
120
121 .ascii "HdrS" # header signature
Rusty Russella24e7852007-10-21 16:41:35 -0700122 .word 0x0207 # header version number (>= 0x0105)
H. Peter Anvin62607312007-07-11 12:18:54 -0700123 # or else old loadlin-1.5 will fail)
124 .globl realmode_swtch
125realmode_swtch: .word 0, 0 # default_switch, SETUPSEG
126start_sys_seg: .word SYSSEG
127 .word kernel_version-512 # pointing to kernel version string
128 # above section of header is compatible
129 # with loadlin-1.5 (header v1.5). Don't
130 # change it.
131
132type_of_loader: .byte 0 # = 0, old one (LILO, Loadlin,
133 # Bootlin, SYSLX, bootsect...)
134 # See Documentation/i386/boot.txt for
135 # assigned ids
136
137# flags, unused bits must be zero (RFU) bit within loadflags
138loadflags:
139LOADED_HIGH = 1 # If set, the kernel is loaded high
140CAN_USE_HEAP = 0x80 # If set, the loader also has set
141 # heap_end_ptr to tell how much
142 # space behind setup.S can be used for
143 # heap purposes.
144 # Only the loader knows what is free
145#ifndef __BIG_KERNEL__
146 .byte 0
147#else
148 .byte LOADED_HIGH
149#endif
150
151setup_move_size: .word 0x8000 # size to move, when setup is not
152 # loaded at 0x90000. We will move setup
153 # to 0x90000 then just before jumping
154 # into the kernel. However, only the
155 # loader knows how much data behind
156 # us also needs to be loaded.
157
158code32_start: # here loaders can put a different
159 # start address for 32-bit code.
160#ifndef __BIG_KERNEL__
161 .long 0x1000 # 0x1000 = default for zImage
162#else
163 .long 0x100000 # 0x100000 = default for big kernel
164#endif
165
166ramdisk_image: .long 0 # address of loaded ramdisk image
167 # Here the loader puts the 32-bit
168 # address where it loaded the image.
169 # This only will be read by the kernel.
170
171ramdisk_size: .long 0 # its size in bytes
172
173bootsect_kludge:
174 .long 0 # obsolete
175
H. Peter Anvin6b6815c2007-10-25 16:11:33 -0700176heap_end_ptr: .word _end+STACK_SIZE-512
177 # (Header version 0x0201 or later)
H. Peter Anvin62607312007-07-11 12:18:54 -0700178 # space from here (exclusive) down to
179 # end of setup code can be used by setup
180 # for local heap purposes.
181
182pad1: .word 0
183cmd_line_ptr: .long 0 # (Header version 0x0202 or later)
184 # If nonzero, a 32-bit pointer
185 # to the kernel command line.
186 # The command line should be
187 # located between the start of
188 # setup and the end of low
189 # memory (0xa0000), or it may
190 # get overwritten before it
191 # gets read. If this field is
192 # used, there is no longer
193 # anything magical about the
194 # 0x90000 segment; the setup
195 # can be located anywhere in
196 # low memory 0x10000 or higher.
197
H. Peter Anvincf8fa922008-01-30 13:32:51 +0100198ramdisk_max: .long 0x7fffffff
H. Peter Anvin62607312007-07-11 12:18:54 -0700199 # (Header version 0x0203 or later)
200 # The highest safe address for
201 # the contents of an initrd
H. Peter Anvincf8fa922008-01-30 13:32:51 +0100202 # The current kernel allows up to 4 GB,
203 # but leave it at 2 GB to avoid
204 # possible bootloader bugs.
H. Peter Anvin62607312007-07-11 12:18:54 -0700205
206kernel_alignment: .long CONFIG_PHYSICAL_ALIGN #physical addr alignment
207 #required for protected mode
208 #kernel
209#ifdef CONFIG_RELOCATABLE
210relocatable_kernel: .byte 1
211#else
212relocatable_kernel: .byte 0
213#endif
214pad2: .byte 0
215pad3: .word 0
216
217cmdline_size: .long COMMAND_LINE_SIZE-1 #length of the command line,
218 #added with boot protocol
219 #version 2.06
220
Rusty Russella24e7852007-10-21 16:41:35 -0700221hardware_subarch: .long 0 # subarchitecture, added with 2.07
222 # default to 0 for normal x86 PC
223
224hardware_subarch_data: .quad 0
225
H. Peter Anvin62607312007-07-11 12:18:54 -0700226# End of setup header #####################################################
227
228 .section ".inittext", "ax"
229start_of_setup:
230#ifdef SAFE_RESET_DISK_CONTROLLER
231# Reset the disk controller.
232 movw $0x0000, %ax # Reset disk controller
233 movb $0x80, %dl # All disks
234 int $0x13
235#endif
236
H. Peter Anvin62607312007-07-11 12:18:54 -0700237# Force %es = %ds
238 movw %ds, %ax
239 movw %ax, %es
240 cld
241
Jens Rottmann16252da2007-11-27 12:35:13 +0100242# Apparently some ancient versions of LILO invoked the kernel with %ss != %ds,
243# which happened to work by accident for the old code. Recalculate the stack
244# pointer if %ss is invalid. Otherwise leave it alone, LOADLIN sets up the
245# stack behind its own code, so we can't blindly put it directly past the heap.
H. Peter Anvin6b6815c2007-10-25 16:11:33 -0700246
H. Peter Anvin6b6815c2007-10-25 16:11:33 -0700247 movw %ss, %dx
248 cmpw %ax, %dx # %ds == %ss?
249 movw %sp, %dx
Jens Rottmann16252da2007-11-27 12:35:13 +0100250 je 2f # -> assume %sp is reasonably set
H. Peter Anvin6b6815c2007-10-25 16:11:33 -0700251
Jens Rottmann16252da2007-11-27 12:35:13 +0100252 # Invalid %ss, make up a new stack
253 movw $_end, %dx
254 testb $CAN_USE_HEAP, loadflags
255 jz 1f
256 movw heap_end_ptr, %dx
2571: addw $STACK_SIZE, %dx
258 jnc 2f
259 xorw %dx, %dx # Prevent wraparound
260
2612: # Now %dx should point to the end of our stack space
H. Peter Anvin6b6815c2007-10-25 16:11:33 -0700262 andw $~3, %dx # dword align (might as well...)
263 jnz 3f
264 movw $0xfffc, %dx # Make sure we're not zero
Jens Rottmann16252da2007-11-27 12:35:13 +01002653: movw %ax, %ss
H. Peter Anvin6b6815c2007-10-25 16:11:33 -0700266 movzwl %dx, %esp # Clear upper half of %esp
267 sti # Now we should have a working stack
268
269# We will have entered with %cs = %ds+0x20, normalize %cs so
270# it is on par with the other segments.
271 pushw %ds
272 pushw $6f
273 lretw
2746:
H. Peter Anvin62607312007-07-11 12:18:54 -0700275
276# Check signature at end of setup
277 cmpl $0x5a5aaa55, setup_sig
278 jne setup_bad
279
280# Zero the bss
281 movw $__bss_start, %di
282 movw $_end+3, %cx
283 xorl %eax, %eax
284 subw %di, %cx
285 shrw $2, %cx
286 rep; stosl
287
288# Jump to C code (should not return)
289 calll main
290
291# Setup corrupt somehow...
292setup_bad:
293 movl $setup_corrupt, %eax
294 calll puts
295 # Fall through...
296
297 .globl die
298 .type die, @function
299die:
300 hlt
301 jmp die
302
Paul Bollebbc15f42007-09-10 23:39:02 +0200303 .size die, .-die
H. Peter Anvin62607312007-07-11 12:18:54 -0700304
305 .section ".initdata", "a"
306setup_corrupt:
307 .byte 7
H. Peter Anvin8b608d22007-07-26 16:10:22 -0700308 .string "No setup signature found...\n"