| /* |
| * GRUB -- GRand Unified Bootloader |
| * Copyright (C) 1996 Erich Boleyn <erich@uruk.org> |
| * Copyright (C) 1999 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. |
| */ |
| |
| #include <stage1.h> |
| |
| /* |
| * defines for the code go here |
| */ |
| |
| /* 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: |
| .long 0 |
| heads: |
| .long 0 |
| cylinders: |
| .word 0 |
| sector_start: |
| .byte 0 |
| head_start: |
| .byte 0 |
| cylinder_start: |
| .word 0 |
| /* more space... */ |
| |
| . = _start + STAGE1_BPBEND |
| |
| /* |
| * End of BIOS parameter block. |
| */ |
| |
| stage1_id: |
| .byte STAGE1_ID_CHS |
| |
| 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 $STAGE1_STACKSEG, %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 $STAGE1_BIOS_HD_FLAG, %dl |
| jz floppy_probe |
| |
| /* Nope, we definitely have a hard disk, and we're screwed. */ |
| jmp hd_probe_error |
| |
| final_init: |
| /* set %si to sectors */ |
| movw $ABS(sectors), %si |
| |
| /* save number of heads */ |
| xorl %eax, %eax |
| movb %dh, %al |
| incw %ax |
| movl %eax, 4(%si) |
| |
| xorw %dx, %dx |
| movb %cl, %dl |
| shlw $2, %dx |
| movb %ch, %al |
| movb %dh, %ah |
| |
| /* save number of cylinders */ |
| incw %ax |
| movw %ax, 8(%si) |
| |
| xorw %ax, %ax |
| movb %dl, %al |
| shrb $2, %al |
| |
| /* save number of sectors */ |
| movl %eax, (%si) |
| |
| /* this sets up for the first run through "bootloop" */ |
| movw $ABS(firstlist - STAGE1_LISTSIZE), %di |
| |
| |
| /* this is the loop for reading the secondary boot-loader in */ |
| bootloop: |
| |
| /* check the number of sectors to read */ |
| cmpw $0, 4(%di) |
| |
| /* if zero, go to the start function */ |
| je bootit |
| |
| setup_sectors: |
| /* load logical sector start (bottom half) */ |
| movl (%di), %eax |
| |
| /* zero %edx */ |
| xorl %edx, %edx |
| |
| /* divide by number of sectors */ |
| divl (%si) |
| |
| /* save sector start */ |
| movb %dl, 10(%si) |
| |
| xorl %edx, %edx /* zero %edx */ |
| divl 4(%si) /* divide by number of heads */ |
| |
| /* save head start */ |
| movb %dl, 11(%si) |
| |
| /* save cylinder start */ |
| movw %ax, 12(%si) |
| |
| /* do we need too many cylinders? */ |
| cmpw 8(%si), %ax |
| jge geometry_error |
| |
| /* determine the maximum sector length of this read */ |
| movw (%si), %ax /* get number of sectors per track/head */ |
| |
| /* subtract sector start */ |
| subb 10(%si), %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) |
| |
| /* add into logical sector start */ |
| addl %eax, (%di) |
| |
| /* |
| * This is the loop for taking care of BIOS geometry translation (ugh!) |
| */ |
| |
| /* get high bits of cylinder */ |
| movb 13(%si), %dl |
| |
| shlb $6, %dl /* shift left by 6 bits */ |
| movb 10(%si), %cl /* get sector */ |
| |
| incb %cl /* normalize sector (sectors go |
| from 1-N, not 0-(N-1) ) */ |
| orb %dl, %cl /* composite together */ |
| movb 12(%si), %ch /* sector+hcyl in cl, cylinder in ch */ |
| |
| /* restore %dx */ |
| popw %dx |
| pushw %dx |
| |
| /* head number */ |
| movb 11(%si), %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 $STAGE1_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) |
| jne setup_sectors |
| |
| /* update position to load from */ |
| subw $STAGE1_LISTSIZE, %di |
| |
| /* jump to bootloop */ |
| jmp bootloop |
| |
| /* 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 + STAGE1_PARTSTART - STAGE1_MINPARAMSIZE - STAGE1_LISTSIZE |
| |
| /* this next data area before the partition area is specifically |
| sized, you should update "STAGE1_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 130 /* 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 stage1.h for COMPAT_VERSION_* definitions used |
| * in stage2 and stage1_5 modules. |
| * |
| * DO NOT MOVE THIS!!! |
| */ |
| .byte COMPAT_VERSION_MAJOR, COMPAT_VERSION_MINOR |
| |
| /* |
| * 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 + STAGE1_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 $STAGE1_BUFFERSEG, %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 + STAGE1_PARTEND |
| |
| /* the last 2 bytes in the sector 0 contain the signature */ |
| .word STAGE1_SIGNATURE |