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 <linux/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" 321