/* * GRUB -- GRand Unified Bootloader * Copyright (C) 1996 Erich Boleyn * * 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. */ /* * defines for the code go here */ #define SIGNATURE 0xaa55 #define BPBEND 0x3e #define PARTSTART 0x1be /* starting address of partition table */ #define PARTEND 0x1fe /* ending addres of the partition table */ #define MINPARAMSIZ 13 /* size of extra data parameters */ #define LISTSIZ 8 /* size of sector list */ #define REALSTACK 0x2000 /* stack for this code and BIOS calls */ #define BUFFERSEG 0x7000 /* segment address of disk buffer, the disk buffer MUST be 32K long and cannot straddle a 64K boundary */ #define BIOS_HD_FLAG 0x80 /* bit set in BIOS drive number to designate a hard disk vs. a floppy */ /* 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+0x7c00) /* Print message string */ #define MSG(x) movw $x, %si; call message .file "stage1.S" .text /* Tell GAS to generate 16-bit instructions so that this code works in real mode. */ .code16 .globl _start; _start: /* * _start is loaded at 0x7c00 and is jumped to with CS:IP 0:0x7c00 */ /* * Beginning of the sector is compatible with the FAT/HPFS BIOS * parameter block. */ jmp after_BPB nop /* do I care about this ??? */ /* * This space is for the BIOS parameter block!!!! Don't change * the first jump, nor start the code anywhere but right after * this area. */ . = _start + 4 /* scratch space */ sectors: .word 0 heads: .word 0 cylinders: .word 0 /* more space... */ . = _start + BPBEND /* * End of BIOS parameter block. */ after_BPB: /* general setup */ cli /* we're not safe here! */ /* set up %ds and %ss as offset from 0 */ xorw %ax, %ax movw %ax, %ds movw %ax, %ss /* set up the REAL stack */ movw $REALSTACK, %sp sti /* we're safe again */ /* * Check if we have a forced disk reference here */ movb firstlist, %al cmpb $0xff, %al je 1f movb %al, %dl 1: /* save drive reference first thing! */ pushw %dx /* * Determine the hard disk geometry from the BIOS! * We do this first, so that LS-120 IDE floppies work correctly. */ movb $8, %ah int $0x13 jnc final_init /* * The call failed, so maybe use the floppy probe instead. */ testb $BIOS_HD_FLAG, %dl jz floppy_probe /* Nope, we definitely have a hard disk, and we're screwed. */ jmp hd_probe_error final_init: /* save number of heads */ xorb %ah, %ah movb %dh, %al incw %ax movw %ax, heads xorw %dx, %dx movb %cl, %dl shlw $2, %dx movb %ch, %al movb %dh, %ah /* save number of cylinders */ incw %ax movw %ax, cylinders xorw %ax, %ax movb %dl, %al shrb $2, %al /* save number of sectors */ movw $ABS(sectors), %si movw %ax, (%si) /* this sets up for the first run through "bootloop" */ movw $ABS(firstlist), %di /* this is the loop for reading the secondary boot-loader in */ bootloop: /* update position to load from */ subw $LISTSIZ, %di /* check the number of sectors to read */ cmpw $0, 4(%di) /* if zero, go to the start function */ je bootit /* load logical sector start (bottom half) */ movw (%di), %ax /* load logical sector start (top half) */ movw 2(%di), %dx /* divide by number of sectors */ divw (%si) /* save sector start */ movb %dl, (%di) xorw %dx, %dx /* zero %dx */ divw 2(%si) /* divide by number of heads */ /* save head start */ movb %dl, 1(%di) /* save cylinder start */ movw %ax, 2(%di) /* do we need too many cylinders? */ cmpw 4(%si), %ax jge geometry_error setup_sectors: /* determine the maximum sector length of this read */ movw (%si), %ax /* get number of sectors per track/head */ /* subtract sector start */ subb (%di), %al /* how many do we really want to read? */ cmpw %ax, 4(%di) /* compare against total number of sectors */ /* which is greater? */ jg more_sectors /* if less than, set to total */ movw 4(%di), %ax more_sectors: /* subtract from total */ subw %ax, 4(%di) /* * This is the loop for taking care of BIOS geometry translation (ugh!) */ /* get high bits of cylinder */ movb 3(%di), %dl shlb $6, %dl /* shift left by 6 bits */ movb (%di), %cl /* get sector */ incb %cl /* normalize sector (sectors go from 1-N, not 0-(N-1) ) */ orb %dl, %cl /* composite together */ movb 2(%di), %ch /* sector+hcyl in cl, cylinder in ch */ /* restore %dx */ popw %dx pushw %dx /* head number */ movb 1(%di), %dh pushw %ax /* save %ax from destruction! */ /* * BIOS call "INT 0x13 Function 0x2" to read sectors from disk into memory * Call with %ah = 0x2 * %al = number of sectors * %ch = cylinder * %cl = sector (bits 6-7 are high bits of "cylinder") * %dh = head * %dl = drive (0x80 for hard disk, 0x0 for floppy disk) * %es:%bx = segment:offset of buffer * Return: * %al = 0x0 on success; err code on failure */ movw $BUFFERSEG, %bx movw %bx, %es /* load %es segment with disk buffer */ xorw %bx, %bx /* %bx = 0, put it at 0 in the segment */ movb $0x2, %ah /* function 2 */ int $0x13 jc read_error /* save source segment */ movw %es, %dx /* load addresses for copy from disk buffer to destination */ movw 6(%di), %es /* load destination segment */ /* restore %ax */ popw %ax /* determine the next possible destination address (presuming 512 byte sectors!) */ shlw $5, %ax /* shift %ax five bits to the left */ addw %ax, 6(%di) /* add the corrected value to the destination address for next time */ /* get the copy length */ shlw $4, %ax movw %ax, %cx /* save addressing regs */ pushw %ds pushw %si pushw %di xorw %di, %di /* zero offset of destination addresses */ xorw %si, %si /* zero offset of source addresses */ movw %dx, %ds /* restore the source segment */ cld /* sets the copy direction to forward */ /* perform copy */ rep /* sets a repeat */ movsb /* this runs the actual copy */ /* restore addressing regs */ popw %di popw %si popw %ds /* check if finished with this dataset */ cmpw $0, 4(%di) je bootloop /* find out the next BIOS set to load in */ movb $0, (%di) /* set the sector start */ xorb %ah, %ah /* zero %ah */ movb 1(%di), %al /* load head number into %al */ incw %ax /* increment current head number */ cmpw 2(%si), %ax /* compare to total number of heads */ jne update_heads movw 2(%di), %ax /* load cylinder number into %ax */ incw %ax /* increment current cylinder number */ cmpw 4(%si), %ax /* compare to total number of cylinders */ je geometry_error /* display error and die if greater */ movw %ax, 2(%di) /* store new cylinder number */ movb $0, %al /* for storing new head number */ update_heads: movb %al, 1(%di) /* store new head number */ /* jump to "setup_sectors" to determine length of the new read */ jmp setup_sectors /* END OF MAIN LOOP */ /* * BIOS Geometry translation error (past the end of the disk geometry!). */ geometry_error: MSG(geometry_error_string) jmp general_error /* * Disk probe failure. */ hd_probe_error: MSG(hd_probe_error_string) jmp general_error /* * Read error on the disk. */ read_error: MSG(read_error_string) general_error: MSG(general_error_string) /* go here when you need to stop the machine hard after an error condition */ stop: jmp stop geometry_error_string: .string "Geom" hd_probe_error_string: .string "Hard Disk" read_error_string: .string "Read" general_error_string: .string " Error" /* * 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: movw $0x0001, %bx movb $0xe, %ah int $0x10 /* display a byte */ incw %si message: movb (%si), %al cmpb $0, %al jne 1b /* if not end of string, jmp to display */ ret lastlist: /* * 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. */ /* * This data area is for keeping general parameters. */ . = _start + PARTSTART - MINPARAMSIZ - LISTSIZ /* this next data area before the partition area is specifically sized, you should update "MINPARAMSIZ" to reflect any additions or deletions to this area */ .word 0 .word 0 /* fill the first data listing with the default */ #ifdef FFS_STAGE1_5 .long 2 /* this is the sector start parameter, in logical sectors from the start of the disk, sector 0 */ .word 14 /* this is the number of sectors to read */ .word 0x0200 /* this is the segment of the starting address to load the data into */ #else .long 1 /* this is the sector start parameter, in logical sectors from the start of the disk, sector 0 */ .word 90 /* this is the number of sectors to read */ .word 0x0800 /* this is the segment of the starting address to load the data into */ #endif firstlist: /* this label has to be after the list data!!! */ .byte 0xff /* the disk to load stage2 from */ /* 0xff means use the boot drive */ /* * Jump here when all data loading is done. This * goes to the second stage bootloader. */ bootit: popw %dx /* this makes sure %dl is our "boot" drive */ ljmp $0, $0x8000 /* FIXME: make 0x2000 for stage1_5 */ /* * This is the compatibility version number. * See ../stage2/shared.h for COMPAT_VERSION_* definitions used * in stage2 and stage1_5 modules. * * DO NOT MOVE THIS!!! */ .byte 2, 0 /* * This is where an MBR would go if on a hard disk. The code * here isn't even referenced unless we're on a floppy. Kinda * sneaky, huh? */ . = _start + PARTSTART probe_values: .byte 36, 18, 15, 9, 0 floppy_probe: /* * Perform floppy probe. */ movw $ABS(probe_values-1), %si probe_loop: /* reset floppy controller INT 13h AH=0 */ xorw %ax, %ax int $0x13 incw %si movb (%si), %cl /* if number of sectors is 0, display error and die */ cmpb $0, %cl jne 1f /* * Floppy disk probe failure. */ movw $fd_probe_error_string, %si call message jmp general_error fd_probe_error_string: .string "Floppy" 1: /* perform read */ movw $REALSTACK, %bx movw $0x201, %ax movb $0, %ch movb $0, %dh int $0x13 /* if error, jump to "probe_loop" */ jc probe_loop /* %cl is already the correct value! */ movb $1, %dh movb $79, %ch jmp final_init . = _start + PARTEND /* the last 2 bytes in the sector 0 contain the signature */ .word SIGNATURE