arch/x86_64/boot/bootsect.S

   1 /*
   2  *      bootsect.S              Copyright (C) 1991, 1992 Linus Torvalds
   3  *
   4  *      modified by Drew Eckhardt
   5  *      modified by Bruce Evans (bde)
   6  *      modified by Chris Noe (May 1999) (as86 -> gas)
   7  *      gutted by H. Peter Anvin (Jan 2003)
   8  *
   9  * BIG FAT NOTE: We're in real mode using 64k segments.  Therefore segment
  10  * addresses must be multiplied by 16 to obtain their respective linear
  11  * addresses. To avoid confusion, linear addresses are written using leading
  12  * hex while segment addresses are written as segment:offset.
  13  *
  14  */
  15
  16 #include <asm/boot.h>
  17
  18 SETUPSECTS      = 4                     /* default nr of setup-sectors */
  19 BOOTSEG         = 0x07C0                /* original address of boot-sector */
  20 INITSEG         = DEF_INITSEG           /* we move boot here - out of the way */
  21 SETUPSEG        = DEF_SETUPSEG          /* setup starts here */
  22 SYSSEG          = DEF_SYSSEG            /* system loaded at 0x10000 (65536) */
  23 SYSSIZE         = DEF_SYSSIZE           /* system size: # of 16-byte clicks */
  24                                         /* to be loaded */
  25 ROOT_DEV        = 0                     /* ROOT_DEV is now written by "build" */
  26 SWAP_DEV        = 0                     /* SWAP_DEV is now written by "build" */
  27
  28 #ifndef SVGA_MODE
  29 #define SVGA_MODE ASK_VGA
  30 #endif
  31
  32 #ifndef RAMDISK
  33 #define RAMDISK 0
  34 #endif
  35
  36 #ifndef ROOT_RDONLY
  37 #define ROOT_RDONLY 1
  38 #endif
  39
  40 .code16
  41 .text
  42
  43 .global _start
  44 _start:
  45
  46         # Normalize the start address
  47         jmpl    $BOOTSEG, $start2
  48
  49 start2:
  50         movw    %cs, %ax
  51         movw    %ax, %ds
  52         movw    %ax, %es
  53         movw    %ax, %ss
  54         movw    $0x7c00, %sp
  55         sti
  56         cld
  57
  58         movw    $bugger_off_msg, %si
  59
  60 msg_loop:
  61         lodsb
  62         andb    %al, %al
  63         jz      die
  64         movb    $0xe, %ah
  65         movw    $7, %bx
  66         int     $0x10
  67         jmp     msg_loop
  68
  69 die:
  70         # Allow the user to press a key, then reboot
  71         xorw    %ax, %ax
  72         int     $0x16
  73         int     $0x19
  74
  75         # int 0x19 should never return.  In case it does anyway,
  76         # invoke the BIOS reset code...
  77         ljmp    $0xf000,$0xfff0
  78
  79
  80 bugger_off_msg:
  81         .ascii  "Direct booting from floppy is no longer supported.\r\n"
  82         .ascii  "Please use a boot loader program instead.\r\n"
  83         .ascii  "\n"
  84         .ascii  "Remove disk and press any key to reboot . . .\r\n"
  85         .byte   0
  86
  87
  88         # Kernel attributes; used by setup
  89
  90         .org 497
  91 setup_sects:    .byte SETUPSECTS
  92 root_flags:     .word ROOT_RDONLY
  93 syssize:        .word SYSSIZE
  94 swap_dev:       .word SWAP_DEV
  95 ram_size:       .word RAMDISK
  96 vid_mode:       .word SVGA_MODE
  97 root_dev:       .word ROOT_DEV
  98 boot_flag:      .word 0xAA55