/* * GRUB -- GRand Unified Bootloader * Copyright (C) 1994-2002 H. Peter Anvin * Copyright (C) 1999,2000,2001,2004 Free Software Foundation, Inc. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. * */ /* Most of this file was originally "isolinux.asm" from SYSLINUX package. It has been very heavily modified. */ #define ASM_FILE #include "stage1.h" #include "shared.h" #include "iso9660.h" #ifndef STAGE1_5 #include "stage2_size.h" #endif /* Absolute addresses This makes the assembler generate the address without support from the linker. (ELF can't relocate 16-bit addresses!) */ #define ABS(x) (x-_start+BOOTSEC_LOCATION) #ifdef STAGE1_5 # define STAGE_ADDR 0x2000 #else # define STAGE_ADDR 0x8000 #endif /* STAGE1_5 */ /* Print message string */ #define MSG(x) mov $ABS(x), %si; call message; .file "start_eltorito.S" .text /* Tell GAS to generate 16-bit instructions so that this code works in real mode. */ .code16 .globl start, _start /* * Primary entry point. Because BIOSes are buggy, we only load the first * CD-ROM sector (2K) of the file, so the number one priority is actually * loading the rest. */ start: _start: cli ljmp $0, $ABS(real_start) . = _start + 8 /* Pad to file offset 8 */ /* This table gets filled in by mkisofs using the -boot-info-table option */ bi_pvd: .long 0xDEADBEEF /* LBA of primary volume descript */ bi_file: .long 0xDEADBEEF /* LBA of boot file */ bi_length: .long 0xDEADBEEF /* Length of boot file */ bi_csum: .long 0xDEADBEEF /* Checksum of boot file */ bi_reserved: .space (10*4) /* Reserved */ real_start: xor %ax, %ax mov %ax, %ss mov %ax, %ds mov %ax, %es mov %ax, %fs mov %ax, %gs mov $STAGE1_STACKSEG, %sp /* set up the REAL stack */ sti cld /* save drive reference first thing! */ mov %dl, ABS(BootDrive) /* print a notification message on the screen */ MSG(notification_string) load_image: /* Set up boot file sector, size, load address */ mov ABS(bi_length), %eax add $(ISO_SECTOR_SIZE-1), %eax shr $ISO_SECTOR_BITS, %eax /* dwords->sectors */ mov %ax, %bp /* boot file sectors */ mov $(STAGE_ADDR >> 4), %bx mov %bx, %es xor %bx, %bx mov ABS(bi_file), %eax call getlinsec mov %ds, %ax mov %ax, %es MSG(notification_done) bootit: /* save the sector number of the second sector in %ebp */ mov $ABS(firstlist - BOOTSEC_LISTSIZE), %si mov (%si), %ebp mov ABS(BootDrive), %dl /* this makes sure %dl is our "boot" drive */ ljmp $0, $(STAGE_ADDR+SECTOR_SIZE) /* jump to main() in asm.S */ /* go here when you need to stop the machine hard after an error condition */ stop: jmp stop /* * Get linear sectors - EBIOS LBA addressing, 2048-byte sectors. * * Note that we can't always do this as a single request, because at least * Phoenix BIOSes has a 127-sector limit. To be on the safe side, stick * to 16 sectors (32K) per request. * * Input: * EAX - Linear sector number * ES:BX - Target buffer * BP - Sector count */ getlinsec: mov $ABS(dapa), %si /* Load up the DAPA */ mov %bx, 4(%si) mov %es, %bx mov %bx, 6(%si) mov %eax, 8(%si) 1: push %bp push %si cmp ABS(MaxTransfer), %bp jbe 2f mov ABS(MaxTransfer), %bp 2: mov %bp, 2(%si) mov ABS(BootDrive), %dl mov $0x42, %ah /* Extended Read */ call xint13 pop %si pop %bp movzwl 2(%si), %eax /* Sectors we read */ add %eax, 8(%si) /* Advance sector pointer */ sub %ax, %bp /* Sectors left */ shl $(ISO_SECTOR_BITS-4), %ax /* 2048-byte sectors -> segment */ add %ax, 6(%si) /* Advance buffer pointer */ pushal MSG(notification_step) popal cmp $0, %bp ja 1b mov 8(%si), %eax /* Return next sector */ ret /* * INT 13h with retry */ xint13: movb $6, ABS(RetryCount) .try: pushal int $0x13 jc 1f add $(8*4), %sp /* Clean up stack */ ret 1: mov %ah, %dl /* Save error code */ decb ABS(RetryCount) jz .real_error mov ABS(RetryCount), %al mov ABS(dapa+2), %ah /* Sector transfer count */ cmp $2, %al /* Only 2 attempts left */ ja 2f mov $1, %ah /* Drop transfer size to 1 */ jmp .setmaxtr 2: cmp $3, %al ja 3f /* First time, just try again */ shr $1, %ah /* Otherwise, try to reduce */ adc $0, %ah /* the max transfer size, but not */ .setmaxtr: mov %ah, ABS(MaxTransfer) mov %ah, ABS(dapa+2) 3: popal jmp .try .real_error: MSG(read_error_string) mov %dl, %al call printhex2 popal jmp stop /* * message: write the string pointed to by %si * * WARNING: trashes %si, %ax, and %bx */ /* * Use BIOS "int 10H Function 0Eh" to write character in teletype mode * %ah = 0xe %al = character * %bh = page %bl = foreground color (graphics modes) */ 1: mov $0x0001, %bx mov $0x0E, %ah int $0x10 /* display a byte */ message: lodsb or %al, %al jne 1b /* if not end of string, jmp to display */ ret /* * printhex[248]: Write a hex number in (AL, AX, EAX) to the console */ printhex2: pushal rol $24, %eax mov $2, %cx jmp 1f printhex4: pushal rol $16, %eax mov $4, %cx jmp 1f printhex8: pushal mov $8, %cx 1: rol $4, %eax push %eax and $0x0F, %al cmp $10, %al jae .high .low: add $('0'), %al jmp 2f .high: add $('A'-10), %al 2: mov $0x0001, %bx mov $0x0E, %ah int $0x10 /* display a char */ pop %eax loop 1b popal ret /**************************************************************************/ #ifdef STAGE1_5 notification_string: .string "Loading stage1.5 " #else notification_string: .string "Loading stage2 " #endif notification_step: .string "." notification_done: .string "\r\n" read_error_string: .string "Read error 0x" /* * EBIOS disk address packet */ .align 8 dapa: .byte 16 /* Packet size */ .byte 0 /* reserved */ .word 0 /* +2 Block count */ .word 0 /* +4 Offset of buffer */ .word 0 /* +6 Segment of buffer */ .long 0 /* +8 LBA (LSW) */ .long 0 /* +C LBA (MSW) */ VARIABLE(BootDrive) .byte 0xFF VARIABLE(MaxTransfer) .word 16 /* Max sectors per transfer (32Kb) */ VARIABLE(RetryCount) .byte 0 /* * This area is an empty space between the main body of code below which * grows up (fixed after compilation, but between releases it may change * in size easily), and the lists of sectors to read, which grows down * from a fixed top location. */ .word 0 .word 0 . = _start + SECTOR_SIZE - BOOTSEC_LISTSIZE /* fill the first data listing with the default */ blocklist_default_start:/* this is the sector start parameter, in logical sectors from the start of the disk, sector 0 */ .long 0 blocklist_default_len: /* this is the number of sectors to read */ #ifdef STAGE1_5 .word 0 #else .word (STAGE2_SIZE + ISO_SECTOR_SIZE - 1) >> ISO_SECTOR_BITS #endif blocklist_default_seg: /* this is the segment of the starting address to load the data into */ .word (STAGE_ADDR + SECTOR_SIZE) >> 4 firstlist: /* this label has to be after the list data!!! */
