1 ;------------------------------------------------------------------------------ 2 ;* 3 ;* Copyright (c) 2006 - 2007, Intel Corporation. All rights reserved.<BR> 4 ;* This program and the accompanying materials 5 ;* are licensed and made available under the terms and conditions of the BSD License 6 ;* which accompanies this distribution. The full text of the license may be found at 7 ;* http://opensource.org/licenses/bsd-license.php 8 ;* 9 ;* THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, 10 ;* WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED. 11 ;* 12 ;* Mbr.asm 13 ;* 14 ;* Abstract: 15 ;* 16 ;------------------------------------------------------------------------------ 17 18 .model small 19 ; .dosseg 20 .stack 21 .486p 22 .code 23 24 BLOCK_SIZE EQU 0200h 25 BLOCK_MASK EQU 01ffh 26 BLOCK_SHIFT EQU 9 27 28 ; **************************************************************************** 29 ; Code loaded by BIOS at 0x0000:0x7C00 30 ; **************************************************************************** 31 32 org 0h 33 Start: 34 35 ; **************************************************************************** 36 ; Start Print 37 ; **************************************************************************** 38 39 mov ax,0b800h 40 mov es,ax 41 mov ax, 07c0h 42 mov ds, ax 43 lea si, cs:[StartString] 44 mov cx, 10 45 mov di, 160 46 rep movsw 47 48 ; **************************************************************************** 49 ; Print over 50 ; **************************************************************************** 51 52 ; **************************************************************************** 53 ; Initialize segment registers and copy code at 0x0000:0x7c00 to 0x0000:0x0600 54 ; **************************************************************************** 55 xor ax, ax ; AX = 0x0000 56 mov bx, 07c00h ; BX = 0x7C00 57 mov bp, 0600h ; BP = 0x0600 58 mov si, OFFSET RelocatedStart ; SI = Offset(RelocatedStart) 59 mov cx, 0200h ; CX = 0x0200 60 sub cx, si ; CS = 0x0200 - Offset(RelocatedStart) 61 lea di, [bp+si] ; DI = 0x0600 + Offset(RelocatedStart) 62 lea si, [bx+si] ; BX = 0x7C00 + Offset(RelocatedStart) 63 mov ss, ax ; SS = 0x0000 64 mov sp, bx ; SP = 0x7C00 65 mov es,ax ; ES = 0x0000 66 mov ds,ax ; DS = 0x0000 67 push ax ; PUSH 0x0000 68 push di ; PUSH 0x0600 + Offset(RelocatedStart) 69 cld ; Clear the direction flag 70 rep movsb ; Copy 0x0200 bytes from 0x7C00 to 0x0600 71 retf ; JMP 0x0000:0x0600 + Offset(RelocatedStart) 72 73 ; **************************************************************************** 74 ; Code relocated to 0x0000:0x0600 75 ; **************************************************************************** 76 77 RelocatedStart: 78 ; **************************************************************************** 79 ; Get Driver Parameters to 0x0000:0x7BFC 80 ; **************************************************************************** 81 82 xor ax,ax ; AX = 0 83 mov ss,ax ; SS = 0 84 add ax,1000h 85 mov ds,ax 86 87 mov sp,07c00h ; SP = 0x7c00 88 mov bp,sp ; BP = 0x7c00 89 90 mov ah,8 ; AH = 8 - Get Drive Parameters Function 91 mov byte ptr [bp+PhysicalDrive],dl ; BBS defines that BIOS would pass the booting driver number to the loader through DL 92 int 13h ; Get Drive Parameters 93 xor ax,ax ; AX = 0 94 mov al,dh ; AL = DH 95 inc al ; MaxHead = AL + 1 96 push ax ; 0000:7bfe = MaxHead 97 mov al,cl ; AL = CL 98 and al,03fh ; MaxSector = AL & 0x3f 99 push ax ; 0000:7bfc = MaxSector 100 101 ; **************************************************************************** 102 ; Read Target DBR from hard disk to 0x0000:0x7C00 103 ; **************************************************************************** 104 105 xor ax, ax 106 mov al, byte ptr [bp+MbrPartitionIndicator] ; AX = MbrPartitionIndex 107 cmp al, 0ffh ; 0xFF means do legacy MBR boot 108 jnz EfiDbr 109 LegacyMbr: 110 mov eax, 00000600h ; Assume LegacyMBR is backuped in Sector 6 111 jmp StartReadTo7C00 ; EAX = Header/Sector/Tracker/Zero 112 113 EfiDbr: 114 cmp al, 4 ; MbrPartitionIndex should < 4 115 jae BadDbr 116 shl ax, 4 ; AX = MBREntrySize * Index 117 add ax, 1beh ; AX = MBREntryOffset 118 mov di, ax ; DI = MBREntryOffset 119 120 ; Here we don't use the C/H/S information provided by Partition table 121 ; but calculate C/H/S from LBA ourselves 122 ; Ci: Cylinder number 123 ; Hi: Header number 124 ; Si: Sector number 125 mov eax, dword ptr es:[bp + di + 8] ; Start LBA 126 mov edx, eax 127 shr edx, 16 ; DX:AX = Start LBA 128 ; = Ci * (H * S) + Hi * S + (Si - 1) 129 130 ; Calculate C/H/S according to LBA 131 mov bp, 7bfah 132 div word ptr [bp+2] ; AX = Hi + H*Ci 133 ; DX = Si - 1 134 inc dx ; DX = Si 135 push dx ; 0000:7bfa = Si <---- 136 xor dx, dx ; DX:AX = Hi + H*Ci 137 div word ptr [bp+4] ; AX = Ci <---- 138 ; DX = Hi <---- 139 140 StartReadTo7C00: 141 142 mov cl, byte ptr [bp] ; Si 143 mov ch, al ; Ci[0-7] 144 or cl, ah ; Ci[8,9] 145 mov bx, 7c00h ; ES:BX = 0000:7C00h 146 mov ah, 2h ; Function 02h 147 mov al, 1 ; 1 Sector 148 mov dh, dl ; Hi 149 mov bp, 0600h 150 mov dl, byte ptr [bp + PhysicalDrive] ; Drive number 151 int 13h 152 jc BadDbr 153 154 155 156 ; **************************************************************************** 157 ; Transfer control to BootSector - Jump to 0x0000:0x7C00 158 ; **************************************************************************** 159 xor ax, ax 160 push ax ; PUSH 0x0000 - Segment 161 mov di, 07c00h 162 push di ; PUSH 0x7C00 - Offset 163 retf ; JMP 0x0000:0x7C00 164 165 ; **************************************************************************** 166 ; ERROR Condition: 167 ; **************************************************************************** 168 169 BadDbr: 170 push ax 171 mov ax, 0b800h 172 mov es, ax 173 mov ax, 060h 174 mov ds, ax 175 lea si, cs:[ErrorString] 176 mov di, 320 177 pop ax 178 call A2C 179 mov [si+16], ah 180 mov [si+18], al 181 mov cx, 10 182 rep movsw 183 Halt: 184 jmp Halt 185 186 StartString: 187 db 'M', 0ch, 'B', 0ch, 'R', 0ch, ' ', 0ch, 'S', 0ch, 't', 0ch, 'a', 0ch, 'r', 0ch, 't', 0ch, '!', 0ch 188 ErrorString: 189 db 'M', 0ch, 'B', 0ch, 'R', 0ch, ' ', 0ch, 'E', 0ch, 'r', 0ch, 'r', 0ch, ':', 0ch, '?', 0ch, '?', 0ch 190 191 ; **************************************************************************** 192 ; A2C - convert Ascii code stored in AH to character stored in AX 193 ; **************************************************************************** 194 A2C: 195 mov al, ah 196 shr ah, 4 197 and al, 0Fh 198 add ah, '0' 199 add al, '0' 200 201 cmp ah, '9' 202 jle @f 203 add ah, 7 204 @@: 205 206 cmp al, '9' 207 jle @f 208 add al, 7 209 @@: 210 ret 211 212 213 ; **************************************************************************** 214 ; PhysicalDrive - Used to indicate which disk to be boot 215 ; Can be patched by tool 216 ; **************************************************************************** 217 org 01B6h 218 PhysicalDrive db 80h 219 220 ; **************************************************************************** 221 ; MbrPartitionIndicator - Used to indicate which MBR partition to be boot 222 ; Can be patched by tool 223 ; OxFF means boot to legacy MBR. (LBA OFFSET 6) 224 ; **************************************************************************** 225 org 01B7h 226 MbrPartitionIndicator db 0 227 228 ; **************************************************************************** 229 ; Unique MBR signature 230 ; **************************************************************************** 231 org 01B8h 232 db 'DUET' 233 234 ; **************************************************************************** 235 ; Unknown 236 ; **************************************************************************** 237 org 01BCh 238 dw 0 239 240 ; **************************************************************************** 241 ; MBR Entry - To be patched 242 ; **************************************************************************** 243 org 01BEh 244 dd 0, 0, 0, 0 245 org 01CEh 246 dd 0, 0, 0, 0 247 org 01DEh 248 dd 0, 0, 0, 0 249 org 01EEh 250 dd 0, 0, 0, 0 251 252 ; **************************************************************************** 253 ; Sector Signature 254 ; **************************************************************************** 255 256 org 01FEh 257 SectorSignature: 258 dw 0aa55h ; Boot Sector Signature 259 260 end 261 262
