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 0x0209 # 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 172pad1: .word 0 173cmd_line_ptr: .long 0 # (Header version 0x0202 or later) 174 # If nonzero, a 32-bit pointer 175 # to the kernel command line. 176 # The command line should be 177 # located between the start of 178 # setup and the end of low 179 # memory (0xa0000), or it may 180 # get overwritten before it 181 # gets read. If this field is 182 # used, there is no longer 183 # anything magical about the 184 # 0x90000 segment; the setup 185 # can be located anywhere in 186 # low memory 0x10000 or higher. 187 188ramdisk_max: .long 0x7fffffff 189 # (Header version 0x0203 or later) 190 # The highest safe address for 191 # the contents of an initrd 192 # The current kernel allows up to 4 GB, 193 # but leave it at 2 GB to avoid 194 # possible bootloader bugs. 195 196kernel_alignment: .long CONFIG_PHYSICAL_ALIGN #physical addr alignment 197 #required for protected mode 198 #kernel 199#ifdef CONFIG_RELOCATABLE 200relocatable_kernel: .byte 1 201#else 202relocatable_kernel: .byte 0 203#endif 204pad2: .byte 0 205pad3: .word 0 206 207cmdline_size: .long COMMAND_LINE_SIZE-1 #length of the command line, 208 #added with boot protocol 209 #version 2.06 210 211hardware_subarch: .long 0 # subarchitecture, added with 2.07 212 # default to 0 for normal x86 PC 213 214hardware_subarch_data: .quad 0 215 216payload_offset: .long ZO_input_data 217payload_length: .long ZO_z_input_len 218 219setup_data: .quad 0 # 64-bit physical pointer to 220 # single linked list of 221 # struct setup_data 222 223# End of setup header ##################################################### 224 225 .section ".inittext", "ax" 226start_of_setup: 227#ifdef SAFE_RESET_DISK_CONTROLLER 228# Reset the disk controller. 229 movw $0x0000, %ax # Reset disk controller 230 movb $0x80, %dl # All disks 231 int $0x13 232#endif 233 234# Force %es = %ds 235 movw %ds, %ax 236 movw %ax, %es 237 cld 238 239# Apparently some ancient versions of LILO invoked the kernel with %ss != %ds, 240# which happened to work by accident for the old code. Recalculate the stack 241# pointer if %ss is invalid. Otherwise leave it alone, LOADLIN sets up the 242# stack behind its own code, so we can't blindly put it directly past the heap. 243 244 movw %ss, %dx 245 cmpw %ax, %dx # %ds == %ss? 246 movw %sp, %dx 247 je 2f # -> assume %sp is reasonably set 248 249 # Invalid %ss, make up a new stack 250 movw $_end, %dx 251 testb $CAN_USE_HEAP, loadflags 252 jz 1f 253 movw heap_end_ptr, %dx 2541: addw $STACK_SIZE, %dx 255 jnc 2f 256 xorw %dx, %dx # Prevent wraparound 257 2582: # Now %dx should point to the end of our stack space 259 andw $~3, %dx # dword align (might as well...) 260 jnz 3f 261 movw $0xfffc, %dx # Make sure we're not zero 2623: movw %ax, %ss 263 movzwl %dx, %esp # Clear upper half of %esp 264 sti # Now we should have a working stack 265 266# We will have entered with %cs = %ds+0x20, normalize %cs so 267# it is on par with the other segments. 268 pushw %ds 269 pushw $6f 270 lretw 2716: 272 273# Check signature at end of setup 274 cmpl $0x5a5aaa55, setup_sig 275 jne setup_bad 276 277# Zero the bss 278 movw $__bss_start, %di 279 movw $_end+3, %cx 280 xorl %eax, %eax 281 subw %di, %cx 282 shrw $2, %cx 283 rep; stosl 284 285# Jump to C code (should not return) 286 calll main 287 288# Setup corrupt somehow... 289setup_bad: 290 movl $setup_corrupt, %eax 291 calll puts 292 # Fall through... 293 294 .globl die 295 .type die, @function 296die: 297 hlt 298 jmp die 299 300 .size die, .-die 301 302 .section ".initdata", "a" 303setup_corrupt: 304 .byte 7 305 .string "No setup signature found...\n" 306