mbr.lst

Windows上的精简Linux系统

   139                                  checkpartloop:
   140 0000003C F60480                  		test byte [si],80h
   141 0000003F 7403                    		jz .notactive
   142 00000041 40                      		inc ax
   143 00000042 89F7                    		mov di,si
   144 00000044 83C610                  .notactive:	add si,byte 16
   145 00000047 E2F3                    		loop checkpartloop
   146                                  
   147 00000049 83F801                  		cmp ax,byte 1			; Better be only one
   148 0000004C 7573                    		jnz not_one_partition
   149                                  
   150                                  ;
   151                                  ; Now we have the active partition partition information in DS:DI.
   152                                  ; Check to see if we support EBIOS.
   153                                  ;
   154 0000004E 8A160008                		mov dl,[DriveNo]
   155 00000052 B80041                  		mov ax,4100h
   156 00000055 BBAA55                  		mov bx,055AAh
   157 00000058 31C9                    		xor cx,cx
   158 0000005A 30F6                    		xor dh,dh
   159 0000005C F9                      		stc
   160 0000005D CD13                    		int 13h
   161 0000005F 7223                    		jc no_ebios
   162 00000061 81FB55AA                		cmp bx,0AA55h
   163 00000065 751D                    		jne no_ebios
   164 00000067 F6C101                  		test cl,1			; LBA device access
   165 0000006A 7418                    		jz no_ebios
   166                                  ;
   167                                  ; We have EBIOS.  Load the boot sector using LBA.
   168                                  ;
   169 0000006C 57                      		push di
   170 0000006D BE[E000]                		mov si,dapa
   171 00000070 8B5D08                  		mov bx,[di+8]			; Copy the block address
   172 00000073 895C08                  		mov [si+8],bx
   173 00000076 8B5D0A                  		mov bx,[di+10]
   174 00000079 895C0A                  		mov [si+10],bx
   175 0000007C 8A160008                		mov dl,[DriveNo]
   176 00000080 B442                    		mov ah,42h			; Extended Read
   177 00000082 EB2A                    		jmp short common_tail
   178                                  ;
   179                                  ; No EBIOS.  Load the boot sector using CHS.
   180                                  ;
   181                                  no_ebios:
   182 00000084 57                      		push di
   183 00000085 8B4508                  		mov ax,[di+8]
   184 00000088 8B550A                  		mov dx,[di+10]
   185 0000008B F736[F200]              		div word [Sectors]
   186 0000008F 42                      		inc dx
   187 00000090 89D1                    		mov cx,dx			; Sector #
   188 00000092 31D2                    		xor dx,dx
   189 00000094 F736[F000]              		div word [Heads]
   190                                  		; DX = head #, AX = cylinder #
   191 00000098 88C5                    		mov ch,al
   192 0000009A D1E8                    		shr ax,1
   193 0000009C D1E8                    		shr ax,1
   194 0000009E 24C0                    		and al,0C0h
   195 000000A0 08C1                    		or cl,al
   196 000000A2 88D6                    		mov dh,dl			; Head #
   197 000000A4 8A160008                		mov dl,[DriveNo]
   198 000000A8 BB007C                  		mov bx,7C00h
   199 000000AB B80102                  		mov ax,0201h			; Read one sector
   200                                  common_tail:
   201 000000AE CD13                    		int 13h
   202 000000B0 7216                    		jc disk_error
   203 000000B2 5E                      		pop si				; DS:SI -> partition table entry
   204                                  ;
   205                                  ; Verify that we have a boot sector, jump
   206                                  ;
   207 000000B3 813EFE7D55AA            		cmp word [7C00h+510],0AA55h
   208 000000B9 7508                    		jne missing_os
   209 000000BB FA                      		cli
   210 000000BC EA007C0000              		jmp 0:7C00h			; Jump to boot sector; far
   211                                  						; jump is speculation barrier
   212                                  						; (Probably not neecessary, but
   213                                  						; there is plenty of space.)
   214                                  
   215                                  not_one_partition:
   216 000000C1 7705                    		ja too_many_os
   217                                  missing_os:
   218 000000C3 BE[F400]                		mov si,missing_os_msg
   219 000000C6 EB03                    		jmp short die
   220                                  too_many_os:
   221                                  disk_error:
   222 000000C8 BE[0F01]                		mov si,bad_disk_msg
   223                                  die:
   224                                  .msgloop:
   225 000000CB AC                      		lodsb
   226 000000CC 20C0                    		and al,al
   227 000000CE 740C                    		jz .now
   228 000000D0 B40E                    		mov ah,0Eh			; TTY output
   229 000000D2 8A3E6204                		mov bh,[BIOS_page]		; Current page
   230 000000D6 B307                    		mov bl,07h
   231 000000D8 CD10                    		int 10h
   232 000000DA EBEF                    		jmp short .msgloop
   233                                  .now:
   234 000000DC EBFE                    		jmp short .now
   235                                  
   236 000000DE 00<rept>                		align 4, db 0			; Begin data area
   237                                  
   238                                  ;
   239                                  ; EBIOS disk address packet
   240                                  ;
   241                                  dapa:
   242 000000E0 1000                    		dw 16				; Packet size
   243 000000E2 0100                    .count:		dw 1				; Block count
   244 000000E4 007C                    .off:		dw 7C00h			; Offset of buffer
   245 000000E6 0000                    .seg:		dw 0				; Segment of buffer
   246 000000E8 00000000                .lba:		dd 0				; LBA (LSW)
   247 000000EC 00000000                		dd 0				; LBA (MSW)
   248                                  
   249                                  ; CHS information
   250 000000F0 0000                    Heads:		dw 0
   251 000000F2 0000                    Sectors:	dw 0
   252                                  
   253                                  ; Error messages
   254 000000F4 4D697373696E67206F-     missing_os_msg	db 'Missing operating system', 13, 10, 0
   255 000000FD 7065726174696E6720-
   256 00000106 73797374656D0D0A00 
   257 0000010F 4F7065726174696E67-     bad_disk_msg	db 'Operating system loading error', 13, 10, 0
   258 00000118 2073797374656D206C-
   259 00000121 6F6164696E67206572-
   260 0000012A 726F720D0A00       
   261                                  
   262                                  ;
   263                                  ; Maximum MBR size: 446 bytes; end-of-boot-sector signature also needed.
   264                                  ; Note that some operating systems (NT, DR-DOS) put additional stuff at
   265                                  ; the end of the MBR, so shorter is better.  Location 440 is known to
   266                                  ; have a 4-byte attempt-at-unique-ID for some OSes.
   267                                  ;
   268                                  
   269                                  PartitionTable	equ $$+446			; Start of partition table
   270                                  
   271                                  ;
   272                                  ; BSS data; put at 800h
   273                                  ;
   274                                  DriveNo		equ 0800h