linux/arch/x86/boot/header.S
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   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"
 321
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