; Copyright (c) 1999-2003 Apple Computer, Inc. All rights reserved. ; ; @APPLE_LICENSE_HEADER_START@ ; ; Portions Copyright (c) 1999-2003 Apple Computer, Inc. All Rights ; Reserved. This file contains Original Code and/or Modifications of ; Original Code as defined in and that are subject to the Apple Public ; Source License Version 2.0 (the "License"). You may not use this file ; except in compliance with the License. Please obtain a copy of the ; License at http://www.apple.com/publicsource and read it before using ; this file. ; ; The Original Code and all software distributed under the License are ; distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER ; EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, ; INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, ; FITNESS FOR A PARTICULAR PURPOSE OR NON- INFRINGEMENT. Please see the ; License for the specific language governing rights and limitations ; under the License. ; ; @APPLE_LICENSE_HEADER_END@ ; ; Boot Loader: boot0 ; ; A small boot sector program written in x86 assembly whose only ; responsibility is to locate the active partition, load the ; partition booter into memory, and jump to the booter's entry point. ; It leaves the boot drive in DL and a pointer to the partition entry in SI. ; ; This boot loader must be placed in the Master Boot Record. ; ; In order to coexist with a fdisk partition table (64 bytes), and ; leave room for a two byte signature (0xAA55) in the end, boot0 is ; restricted to 446 bytes (512 - 64 - 2). If boot0 did not have to ; live in the MBR, then we would have 510 bytes to work with. ; ; boot0 is always loaded by the BIOS or another booter to 0:7C00h. ; ; This code is written for the NASM assembler. ; nasm boot0.s -o boot0 ; ; Set to 1 to enable obscure debug messages. ; DEBUG EQU 0 ; ; Set to 1 to support loading the partition booter (boot1) from a ; logical partition. ; EXT_PART_SUPPORT EQU 1 CHS_SUPPORT EQU 1 ; ; Various constants. ; kBoot0Segment EQU 0x0000 kBoot0Stack EQU 0xFFF0 ; boot0 stack pointer kBoot0LoadAddr EQU 0x7C00 ; boot0 load address kBoot0RelocAddr EQU 0xE000 ; boot0 relocated address kMBRBuffer EQU 0x1000 ; MBR buffer address kExtBuffer EQU 0x1200 ; EXT boot block buffer address kPartTableOffset EQU 0x1be kMBRPartTable EQU kMBRBuffer + kPartTableOffset kExtPartTable EQU kExtBuffer + kPartTableOffset kSectorBytes EQU 512 ; sector size in bytes kBootSignature EQU 0xAA55 ; boot sector signature kPartCount EQU 4 ; number of paritions per table kPartTypeBoot EQU 0xab ; boot2 partition type kPartTypeExtDOS EQU 0x05 ; DOS extended partition type kPartTypeExtWin EQU 0x0f ; Windows extended partition type kPartTypeExtLinux EQU 0x85 ; Linux extended partition type kPartActive EQU 0x80 %ifdef FLOPPY kDriveNumber EQU 0x00 %else kDriveNumber EQU 0x80 %endif ; ; Format of fdisk partition entry. ; ; The symbol 'part_size' is automatically defined as an `EQU' ; giving the size of the structure. ; struc part .bootid: resb 1 ; bootable or not .head: resb 1 ; starting head, sector, cylinder .sect: resb 1 ; .cyl: resb 1 ; .type: resb 1 ; partition type .endhead resb 1 ; ending head, sector, cylinder .endsect: resb 1 ; .endcyl: resb 1 ; .lba: resd 1 ; starting lba .sectors resd 1 ; size in sectors endstruc ; ; Macros. ; %macro DebugCharMacro 1 mov al, %1 call print_char %endmacro %if DEBUG %define DebugChar(x) DebugCharMacro x %else %define DebugChar(x) %endif ;-------------------------------------------------------------------------- ; Start of text segment. SEGMENT .text ORG 0xE000 ; must match kBoot0RelocAddr ;-------------------------------------------------------------------------- ; Boot code is loaded at 0:7C00h. ; start ; ; Set up the stack to grow down from kBoot0Segment:kBoot0Stack. ; Interrupts should be off while the stack is being manipulated. ; cli ; interrupts off xor ax, ax ; zero ax mov ss, ax ; ss <- 0 mov sp, kBoot0Stack ; sp <- top of stack sti ; reenable interrupts mov es, ax ; es <- 0 mov ds, ax ; ds <- 0 ; ; Relocate boot0 code. ; mov si, kBoot0LoadAddr ; si <- source mov di, kBoot0RelocAddr ; di <- destination ; cld ; auto-increment SI and/or DI registers mov cx, kSectorBytes/2 ; copy 256 words repnz movsw ; repeat string move (word) operation ; Code relocated, jump to start_reloc in relocated location. ; jmp 0:start_reloc ;-------------------------------------------------------------------------- ; Start execution from the relocated location. ; start_reloc: DebugChar('>') .loop: %if DEBUG mov al, dl call print_hex %endif ; ; Clear various flags in memory. ; xor eax, eax mov [first_part], eax ; clear EBIOS LBA offset mov [this_part], eax %if CHS_SUPPORT mov [ebios_present], al ; clear EBIOS support flag ; ; Check if EBIOS is supported for this hard drive. ; mov ah, 0x41 ; Function 0x41 mov bx, 0x55AA ; check signature int 0x13 ; ; If successful, the return values are as follows: ; ; carry = 0 ; ah = major version of EBIOS extensions (0x21 = version 1.1) ; al = altered ; bx = 0xAA55 ; cx = support bits. bit 0 must be set for function 0x42. ; jc .ebios_check_done cmp bx, 0xAA55 ; check BX = 0xAA55 jnz .ebios_check_done test cl, 0x01 ; check enhanced drive read support setnz [ebios_present] ; EBIOS supported, set flag DebugChar('E') ; EBIOS supported .ebios_check_done: %else inc al mov [ebios_present], al %endif ; ; Since this code may not always reside in the MBR, always start by ; loading the MBR to kMBRBuffer. ; mov al, 1 ; load one sector xor bx, bx mov es, bx ; MBR load segment = 0 mov bx, kMBRBuffer ; MBR load address mov si, bx ; pointer to fake partition entry %if CHS_SUPPORT mov WORD [si], 0x0000 ; CHS DX: head = 0 mov WORD [si + 2], 0x0001 ; CHS CX: cylinder = 0, sector = 1 %endif mov DWORD [si + part.lba], 0x00000000 ; LBA sector 0 call load jc .next_drive ; MBR load error ; ; Look for the booter partition in the MBR partition table, ; which is at offset kMBRPartTable. ; mov di, kMBRPartTable ; pointer to partition table call find_boot ; will not return on success .next_drive: inc dl ; next drive number test dl, 0x4 ; went through all 4 drives? jz .loop ; not yet, loop again error: mov si, boot_error_str call print_string hang: hlt jmp SHORT hang ;-------------------------------------------------------------------------- ; Find the active (boot) partition and load the booter from the partition. ; ; Arguments: ; DL = drive number (0x80 + unit number) ; DI = pointer to fdisk partition table. ; ; Clobber list: ; EAX, BX, EBP ; find_boot: push cx ; preserve CX and SI push si ; ; Check for boot block signature 0xAA55 following the 4 partition ; entries. ; cmp WORD [di + part_size * kPartCount], kBootSignature jne NEAR .exit ; boot signature not found mov si, di ; make SI a pointer to partition table mov cx, kPartCount ; number of partition entries per table .loop: ; ; First scan through the partition table looking for the active ; partition. Postpone walking the extended partition chain for ; the second pass. Do not merge the two without changing the ; buffering scheme used to store extended partition tables. ; %if DEBUG mov al, [si + part.type] ; print partition type call print_hex %endif cmp BYTE [si + part.type], 0 je .continue cmp BYTE [si + part.bootid], kPartActive jne .continue DebugChar('*') ; fix offset for load mov eax, [this_part] mov [first_part], eax ; ; Found boot partition, read boot sector to memory. ; mov al, 1 mov bx, kBoot0Segment mov es, bx mov bx, kBoot0LoadAddr call load ; will not return on success jc error ; load error, keep looking? ; ; Fix up absolute block location in partition record. ; mov eax, [si + part.lba] add eax, [this_part] mov [si + part.lba], eax DebugChar('J') ; ; Jump to partition booter. The drive number is already in register DL. ; SI is pointing to the modified partition entry. ; jmp kBoot0Segment:kBoot0LoadAddr .continue: add si, part_size ; advance SI to next partition entry loop .loop ; loop through all partition entries %if EXT_PART_SUPPORT ; ; No primary (or logical) boot partition found in the current ; partition table. Restart and look for extended partitions. ; mov si, di ; make SI a pointer to partition table mov cx, kPartCount ; number of partition entries per table .ext_loop: mov al, [si + part.type] ; AL <- partition type cmp al, kPartTypeExtDOS ; Extended DOS je .ext_load cmp al, kPartTypeExtWin ; Extended Windows(95) je .ext_load cmp al, kPartTypeExtLinux ; Extended Linux je .ext_load .ext_continue: ; ; Advance si to the next partition entry in the extended ; partition table. ; add si, part_size ; advance SI to next partition entry loop .ext_loop ; loop through all partition entries jmp .exit ; boot partition not found .ext_load: DebugChar('L') ; Save current partition offset, since for extended ; partitions we will overwrite it when loading the new ; table. ; mov ebp, [si + part.lba] ; ; Setup the arguments for the load function call to bring the ; extended partition table into memory. ; Remember that SI points to the extended partition entry. ; mov al, 1 ; read 1 sector xor bx, bx mov es, bx ; es = 0 mov bx, kExtBuffer ; load extended boot sector call load jc .ext_continue ; load error ; ; The LBA address of all extended partitions is relative based ; on the LBA address of the extended partition in the MBR, or ; the extended partition at the head of the chain. Thus it is ; necessary to save the LBA address of the first extended partition. ; DebugChar('+') add ebp, [first_part] mov [this_part], ebp mov eax,[first_part] or eax, eax jnz .ext_find_boot mov [first_part], ebp %if DEBUG DebugChar('=') mov eax, ebp call print_hex %endif .ext_find_boot: ; ; Call find_boot recursively to scan through the extended partition ; table. Load DI with a pointer to the extended table in memory. ; mov di, kExtPartTable ; partition table pointer call find_boot ; recursion... ; ; Since there is an "unwritten" rule that limits each partition table ; to have 0 or 1 extended partitions, there is no point in looking for ; any additional extended partition entries at this point. There is no ; boot partition linked beyond the extended partition that was loaded ; above. ; %endif ; EXT_PART_SUPPORT .exit: ; ; Boot partition not found. Giving up. ; pop si pop cx ret ;-------------------------------------------------------------------------- ; load - Load one or more sectors from a partition. ; ; Arguments: ; AL = number of 512-byte sectors to read. ; ES:BX = pointer to where the sectors should be stored. ; DL = drive number (0x80 + unit number) ; SI = pointer to the partition entry. ; ; Returns: ; CF = 0 success ; 1 error ; load: push cx %if CHS_SUPPORT test BYTE [ebios_present], 1 jz .chs %endif .ebios: mov cx, 5 ; load retry count .ebios_loop: call read_lba ; use INT13/F42 jnc .exit loop .ebios_loop %if CHS_SUPPORT .chs: mov cx, 5 ; load retry count .chs_loop: call read_chs ; use INT13/F2 jnc .exit loop .chs_loop %endif .exit pop cx ret %if CHS_SUPPORT ;-------------------------------------------------------------------------- ; read_chs - Read sectors from a partition using CHS addressing. ; ; Arguments: ; AL = number of 512-byte sectors to read. ; ES:BX = pointer to where the sectors should be stored. ; DL = drive number (0x80 + unit number) ; SI = pointer to the partition entry. ; ; Returns: ; CF = 0 success ; 1 error ; read_chs: pusha ; save all registers ; ; Read the CHS start values from the partition entry. ; mov dh, [ si + part.head ] ; drive head mov cx, [ si + part.sect ] ; drive sector + cylinder ; ; INT13 Func 2 - Read Disk Sectors ; ; Arguments: ; AH = 2 ; AL = number of sectors to read ; CH = lowest 8 bits of the 10-bit cylinder number ; CL = bits 6 & 7: cylinder number bits 8 and 9 ; bits 0 - 5: starting sector number (1-63) ; DH = starting head number (0 to 255) ; DL = drive number (80h + drive unit) ; es:bx = pointer where to place sectors read from disk ; ; Returns: ; AH = return status (sucess is 0) ; AL = burst error length if ah=0x11 (ECC corrected) ; carry = 0 success ; 1 error ; mov ah, 0x02 ; Func 2 int 0x13 ; INT 13 jnc .exit DebugChar('r') ; indicate INT13/F2 error ; ; Issue a disk reset on error. ; Should this be changed to Func 0xD to skip the diskette controller ; reset? ; xor ax, ax ; Func 0 int 0x13 ; INT 13 stc ; set carry to indicate error .exit: popa ret %endif ;-------------------------------------------------------------------------- ; read_lba - Read sectors from a partition using LBA addressing. ; ; Arguments: ; AL = number of 512-byte sectors to read (valid from 1-127). ; ES:BX = pointer to where the sectors should be stored. ; DL = drive number (0x80 + unit number) ; SI = pointer to the partition entry. ; ; Returns: ; CF = 0 success ; 1 error ; read_lba: pusha ; save all registers mov bp, sp ; save current SP ; ; Create the Disk Address Packet structure for the ; INT13/F42 (Extended Read Sectors) on the stack. ; ; push DWORD 0 ; offset 12, upper 32-bit LBA push ds ; For sake of saving memory, push ds ; push DS register, which is 0. mov ecx, [first_part] ; offset 8, lower 32-bit LBA add ecx, [si + part.lba] push ecx push es ; offset 6, memory segment push bx ; offset 4, memory offset xor ah, ah ; offset 3, must be 0 push ax ; offset 2, number of sectors push WORD 16 ; offset 0-1, packet size DebugChar('<') %if DEBUG mov eax, ecx call print_hex %endif ; ; INT13 Func 42 - Extended Read Sectors ; ; Arguments: ; AH = 0x42 ; DL = drive number (80h + drive unit) ; DS:SI = pointer to Disk Address Packet ; ; Returns: ; AH = return status (sucess is 0) ; carry = 0 success ; 1 error ; ; Packet offset 2 indicates the number of sectors read ; successfully. ; mov si, sp mov ah, 0x42 int 0x13 jnc .exit DebugChar('R') ; indicate INT13/F42 error ; ; Issue a disk reset on error. ; Should this be changed to Func 0xD to skip the diskette controller ; reset? ; xor ax, ax ; Func 0 int 0x13 ; INT 13 stc ; set carry to indicate error .exit: mov sp, bp ; restore SP popa ret ;-------------------------------------------------------------------------- ; Write a string to the console. ; ; Arguments: ; DS:SI pointer to a NULL terminated string. ; ; Clobber list: ; AX, BX, SI ; print_string mov bx, 1 ; BH=0, BL=1 (blue) cld ; increment SI after each lodsb call .loop lodsb ; load a byte from DS:SI into AL cmp al, 0 ; Is it a NULL? je .exit ; yes, all done mov ah, 0xE ; INT10 Func 0xE int 0x10 ; display byte in tty mode jmp short .loop .exit ret ;-------------------------------------------------------------------------- ; Write a ASCII character to the console. ; ; Arguments: ; AL = ASCII character. ; print_char pusha mov bx, 1 ; BH=0, BL=1 (blue) mov ah, 0x0e ; bios INT 10, Function 0xE int 0x10 ; display byte in tty mode popa ret %if DEBUG ;-------------------------------------------------------------------------- ; Write the 4-byte value to the console in hex. ; ; Arguments: ; EAX = Value to be displayed in hex. ; print_hex: pushad mov cx, WORD 4 bswap eax .loop push ax ror al, 4 call print_nibble ; display upper nibble pop ax call print_nibble ; display lower nibble ror eax, 8 loop .loop mov al, 10 ; carriage return call print_char mov al, 13 call print_char popad ret print_nibble: and al, 0x0f add al, '0' cmp al, '9' jna .print_ascii add al, 'A' - '9' - 1 .print_ascii: call print_char ret getc: pusha mov ah, 0 int 0x16 popa ret %endif ;DEBUG ;-------------------------------------------------------------------------- ; NULL terminated strings. ; boot_error_str db 10, 13, 'b0 error', 0 ;-------------------------------------------------------------------------- ; Pad the rest of the 512 byte sized booter with zeroes. The last ; two bytes is the mandatory boot sector signature. ; ; If the booter code becomes too large, then nasm will complain ; that the 'times' argument is negative. pad_boot times 446-($-$$) db 0 %ifdef FLOPPY ;-------------------------------------------------------------------------- ; Put fake partition entries for the bootable floppy image ; part1bootid db 0x80 ; first partition active part1head db 0x00 ; head # part1sect db 0x02 ; sector # (low 6 bits) part1cyl db 0x00 ; cylinder # (+ high 2 bits of above) part1systid db 0xab ; Apple boot partition times 3 db 0x00 ; ignore head/cyl/sect #'s part1relsect dd 0x00000001 ; start at sector 1 part1numsect dd 0x00000080 ; 64K for booter part2bootid db 0x00 ; not active times 3 db 0x00 ; ignore head/cyl/sect #'s part2systid db 0xa8 ; Apple UFS partition times 3 db 0x00 ; ignore head/cyl/sect #'s part2relsect dd 0x00000082 ; start after booter ; part2numsect dd 0x00000abe ; 1.44MB - 65K part2numsect dd 0x000015fe ; 2.88MB - 65K %endif pad_table_and_sig times 510-($-$$) db 0 dw kBootSignature ABSOLUTE 0xE400 ; ; In memory variables. ; first_part resd 1 ; starting LBA of the intial extended partition. this_part resd 1 ; starting LBA of the current extended partition. ebios_present resb 1 ; 1 if EBIOS is supported, 0 otherwise. END