arch/x86/boot/header.S

   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 "offsets.h"
  26
  27 SETUPSECTS      = 4                     /* default nr of setup-sectors */
  28 BOOTSEG         = 0x07C0                /* original address of boot-sector */
  29 SYSSEG          = DEF_SYSSEG            /* system loaded at 0x10000 (65536) */
  30 SYSSIZE         = DEF_SYSSIZE           /* system size: # of 16-byte clicks */
  31                                         /* to be loaded */
  32 ROOT_DEV        = 0                     /* ROOT_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
  50 bootsect_start:
  51
  52         # Normalize the start address
  53         ljmp    $BOOTSEG, $start2
  54
  55 start2:
  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
  66 msg_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
  75 bs_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"
  86 bugger_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
  99 hdr:
 100 setup_sects:    .byte SETUPSECTS
 101 root_flags:     .word ROOT_RDONLY
 102 syssize:        .long SYSSIZE
 103 ram_size:       .word RAMDISK
 104 vid_mode:       .word SVGA_MODE
 105 root_dev:       .word ROOT_DEV
 106 boot_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
 117 1:
 118
 119         # Part 2 of the header, from the old setup.S
 120
 121                 .ascii  "HdrS"          # header signature
 122                 .word   0x0209          # header version number (>= 0x0105)
 123                                         # or else old loadlin-1.5 will fail)
 124                 .globl realmode_swtch
 125 realmode_swtch: .word   0, 0            # default_switch, SETUPSEG
 126 start_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
 132 type_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
 138 loadflags:
 139 LOADED_HIGH     = 1                     # If set, the kernel is loaded high
 140 CAN_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
 151 setup_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
 158 code32_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
 166 ramdisk_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
 171 ramdisk_size:   .long   0               # its size in bytes
 172
 173 bootsect_kludge:
 174                 .long   0               # obsolete
 175
 176 heap_end_ptr:   .word   _end+STACK_SIZE-512
 177                                         # (Header version 0x0201 or later)
 178                                         # space from here (exclusive) down to
 179                                         # end of setup code can be used by setup
 180                                         # for local heap purposes.
 181
 182 pad1:           .word   0
 183 cmd_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
 198 ramdisk_max:    .long 0x7fffffff
 199                                         # (Header version 0x0203 or later)
 200                                         # The highest safe address for
 201                                         # the contents of an initrd
 202                                         # The current kernel allows up to 4 GB,
 203                                         # but leave it at 2 GB to avoid
 204                                         # possible bootloader bugs.
 205
 206 kernel_alignment:  .long CONFIG_PHYSICAL_ALIGN  #physical addr alignment
 207                                                 #required for protected mode
 208                                                 #kernel
 209 #ifdef CONFIG_RELOCATABLE
 210 relocatable_kernel:    .byte 1
 211 #else
 212 relocatable_kernel:    .byte 0
 213 #endif
 214 pad2:                   .byte 0
 215 pad3:                   .word 0
 216
 217 cmdline_size:   .long   COMMAND_LINE_SIZE-1     #length of the command line,
 218                                                 #added with boot protocol
 219                                                 #version 2.06
 220
 221 hardware_subarch:       .long 0                 # subarchitecture, added with 2.07
 222                                                 # default to 0 for normal x86 PC
 223
 224 hardware_subarch_data:  .quad 0
 225
 226 payload_offset:         .long input_data
 227 payload_length:         .long input_data_end-input_data
 228
 229 setup_data:             .quad 0                 # 64-bit physical pointer to
 230                                                 # single linked list of
 231                                                 # struct setup_data
 232
 233 # End of setup header #####################################################
 234
 235         .section ".inittext", "ax"
 236 start_of_setup:
 237 #ifdef SAFE_RESET_DISK_CONTROLLER
 238 # Reset the disk controller.
 239         movw    $0x0000, %ax            # Reset disk controller
 240         movb    $0x80, %dl              # All disks
 241         int     $0x13
 242 #endif
 243
 244 # Force %es = %ds
 245         movw    %ds, %ax
 246         movw    %ax, %es
 247         cld
 248
 249 # Apparently some ancient versions of LILO invoked the kernel with %ss != %ds,
 250 # which happened to work by accident for the old code.  Recalculate the stack
 251 # pointer if %ss is invalid.  Otherwise leave it alone, LOADLIN sets up the
 252 # stack behind its own code, so we can't blindly put it directly past the heap.
 253
 254         movw    %ss, %dx
 255         cmpw    %ax, %dx        # %ds == %ss?
 256         movw    %sp, %dx
 257         je      2f              # -> assume %sp is reasonably set
 258
 259         # Invalid %ss, make up a new stack
 260         movw    $_end, %dx
 261         testb   $CAN_USE_HEAP, loadflags
 262         jz      1f
 263         movw    heap_end_ptr, %dx
 264 1:      addw    $STACK_SIZE, %dx
 265         jnc     2f
 266         xorw    %dx, %dx        # Prevent wraparound
 267
 268 2:      # Now %dx should point to the end of our stack space
 269         andw    $~3, %dx        # dword align (might as well...)
 270         jnz     3f
 271         movw    $0xfffc, %dx    # Make sure we're not zero
 272 3:      movw    %ax, %ss
 273         movzwl  %dx, %esp       # Clear upper half of %esp
 274         sti                     # Now we should have a working stack
 275
 276 # We will have entered with %cs = %ds+0x20, normalize %cs so
 277 # it is on par with the other segments.
 278         pushw   %ds
 279         pushw   $6f
 280         lretw
 281 6:
 282
 283 # Check signature at end of setup
 284         cmpl    $0x5a5aaa55, setup_sig
 285         jne     setup_bad
 286
 287 # Zero the bss
 288         movw    $__bss_start, %di
 289         movw    $_end+3, %cx
 290         xorl    %eax, %eax
 291         subw    %di, %cx
 292         shrw    $2, %cx
 293         rep; stosl
 294
 295 # Jump to C code (should not return)
 296         calll   main
 297
 298 # Setup corrupt somehow...
 299 setup_bad:
 300         movl    $setup_corrupt, %eax
 301         calll   puts
 302         # Fall through...
 303
 304         .globl  die
 305         .type   die, @function
 306 die:
 307         hlt
 308         jmp     die
 309
 310         .size   die, .-die
 311
 312         .section ".initdata", "a"
 313 setup_corrupt:
 314         .byte   7
 315         .string "No setup signature found...\n"