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Diffstat (limited to 'contrib/syslinux-4.02/mbr/oldmbr.asm')
| -rw-r--r-- | contrib/syslinux-4.02/mbr/oldmbr.asm | 230 |
1 files changed, 230 insertions, 0 deletions
diff --git a/contrib/syslinux-4.02/mbr/oldmbr.asm b/contrib/syslinux-4.02/mbr/oldmbr.asm new file mode 100644 index 0000000..26fb022 --- /dev/null +++ b/contrib/syslinux-4.02/mbr/oldmbr.asm @@ -0,0 +1,230 @@ +; ----------------------------------------------------------------------- +; +; Copyright 2003-2008 H. Peter Anvin - All Rights Reserved +; +; Permission is hereby granted, free of charge, to any person +; obtaining a copy of this software and associated documentation +; files (the "Software"), to deal in the Software without +; restriction, including without limitation the rights to use, +; copy, modify, merge, publish, distribute, sublicense, and/or +; sell copies of the Software, and to permit persons to whom +; the Software is furnished to do so, subject to the following +; conditions: +; +; The above copyright notice and this permission notice shall +; be included in all copies or substantial portions of the Software. +; +; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, +; EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES +; OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND +; NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT +; HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, +; WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING +; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR +; OTHER DEALINGS IN THE SOFTWARE. +; +; ----------------------------------------------------------------------- + +; +; mbr.asm +; +; Simple Master Boot Record, including support for EBIOS extensions. +; +; The MBR lives in front of the boot sector, and is responsible for +; loading the boot sector of the active partition. The EBIOS support +; is needed if the active partition starts beyond cylinder 1024. +; +; This MBR determines all geometry info at runtime. It uses only the +; linear block field in the partition table. It does, however, pass +; the partition table information unchanged to the target OS. +; +; This MBR should be "8086-clean", i.e. not require a 386. +; + +%include "bios.inc" + +; +; Note: The MBR is actually loaded at 0:7C00h, but we quickly move it down to +; 0600h. +; + section .text + cpu 8086 + org 0600h + +_start: cli + xor ax,ax + mov ds,ax + mov es,ax + mov ss,ax + mov sp,7C00h + sti + cld + mov si,sp ; Start address + mov di,0600h ; Destination address + mov cx,512/2 + rep movsw + +; +; Now, jump to the copy at 0600h so we can load the boot sector at 7C00h. +; Since some BIOSes seem to think 0000:7C00h and 07C0:0000h are the same +; thing, use a far jump to canonicalize the address. This also makes +; sure that it is a code speculation barrier. +; + + jmp 0:next ; Jump to copy at 0600h + +next: + mov [DriveNo], dl ; Drive number stored in DL +; +; Check for CHS parameters. This doesn't work on floppy disks, +; but for an MBR we don't care. +; + mov ah,08h ; Get drive parameters + int 13h + and cx,3Fh ; Max sector number + mov [Sectors],cx + xor ax,ax + mov al,dh + inc ax ; From 0-based to count + mul cx ; Heads*Sectors + mov [SecPerCyl],ax + ; Note: we actually don't care about the number of + ; cylinders, since that's the highest-order division + +; +; Now look for one (and only one) active partition. +; + mov si,PartitionTable + xor ax,ax + mov cx,4 +checkpartloop: + test byte [si],80h + jz .notactive + inc ax + mov di,si +.notactive: add si,byte 16 + loop checkpartloop + + cmp ax,byte 1 ; Better be only one + jnz not_one_partition + +; +; Now we have the active partition partition information in DS:DI. +; Check to see if we support EBIOS. +; + mov dl,[DriveNo] + mov ax,4100h + mov bx,055AAh + xor cx,cx + xor dh,dh + stc + int 13h + jc no_ebios + cmp bx,0AA55h + jne no_ebios + test cl,1 ; LBA device access + jz no_ebios +; +; We have EBIOS. Load the boot sector using LBA. +; + push di + mov si,dapa + mov bx,[di+8] ; Copy the block address + mov [si+8],bx + mov bx,[di+10] + mov [si+10],bx + mov dl,[DriveNo] + mov ah,42h ; Extended Read + jmp short common_tail +; +; No EBIOS. Load the boot sector using CHS. +; +no_ebios: + push di + mov ax,[di+8] + mov dx,[di+10] + div word [SecPerCyl] ; AX = cylinder DX = sec in cyl + ror ah,1 + ror ah,1 + mov cl,ah + mov ch,al ; CL = cyl[9:8], CH = cyl[7:0] + + mov ax,dx + div byte [Sectors] ; AL = head AH = sector + mov dh,al + inc ah + or cl,ah ; CX = cylinder and sector + + mov dl,[DriveNo] + mov bx,7C00h + mov ax,0201h ; Read one sector +common_tail: + int 13h + jc disk_error + pop si ; DS:SI -> partition table entry +; +; Verify that we have a boot sector, jump +; + cmp word [7C00h+510],0AA55h + jne missing_os + cli + jmp 0:7C00h ; Jump to boot sector; far + ; jump is speculation barrier + ; (Probably not neecessary, but + ; there is plenty of space.) + +not_one_partition: + ja too_many_os +missing_os: + mov si,missing_os_msg + jmp short die +too_many_os: +disk_error: + mov si,bad_disk_msg +die: +.msgloop: + lodsb + and al,al + jz .now + mov ah,0Eh ; TTY output + mov bh,[BIOS_page] ; Current page + mov bl,07h + int 10h + jmp short .msgloop +.now: + jmp short .now + + align 4, db 0 ; Begin data area + +; +; EBIOS disk address packet +; +dapa: + dw 16 ; Packet size +.count: dw 1 ; Block count +.off: dw 7C00h ; Offset of buffer +.seg: dw 0 ; Segment of buffer +.lba: dd 0 ; LBA (LSW) + dd 0 ; LBA (MSW) + +; CHS information +SecPerCyl: dw 0 ; Heads*Sectors +Sectors: dw 0 + +; Error messages +missing_os_msg db 'Missing operating system', 13, 10, 0 +bad_disk_msg db 'Operating system loading error', 13, 10, 0 + +; +; Maximum MBR size: 446 bytes; end-of-boot-sector signature also needed. +; Note that some operating systems (NT, DR-DOS) put additional stuff at +; the end of the MBR, so shorter is better. Location 440 is known to +; have a 4-byte attempt-at-unique-ID for some OSes. +; + +PartitionTable equ $$+446 ; Start of partition table + +; +; BSS data; put at 800h +; +DriveNo equ 0800h |