diff options
Diffstat (limited to 'grub-core/boot/i386/pc/boot.S')
| -rw-r--r-- | grub-core/boot/i386/pc/boot.S | 542 |
1 files changed, 542 insertions, 0 deletions
diff --git a/grub-core/boot/i386/pc/boot.S b/grub-core/boot/i386/pc/boot.S new file mode 100644 index 0000000..2bd0b2d --- /dev/null +++ b/grub-core/boot/i386/pc/boot.S @@ -0,0 +1,542 @@ +/* -*-Asm-*- */ +/* + * GRUB -- GRand Unified Bootloader + * Copyright (C) 1999,2000,2001,2002,2005,2006,2007,2008,2009 Free Software Foundation, Inc. + * + * GRUB 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 3 of the License, or + * (at your option) any later version. + * + * GRUB 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 GRUB. If not, see <http://www.gnu.org/licenses/>. + */ + +#include <grub/symbol.h> +#include <grub/machine/boot.h> + +/* + * defines for the code go here + */ + + /* Print message string */ +#define MSG(x) movw $x, %si; call LOCAL(message) +#define ERR(x) movw $x, %si; jmp LOCAL(error_message) + + .macro floppy +part_start: + +LOCAL(probe_values): + .byte 36, 18, 15, 9, 0 + +LOCAL(floppy_probe): + pushw %dx +/* + * Perform floppy probe. + */ +#ifdef __APPLE__ + LOCAL(probe_values_minus_one) = LOCAL(probe_values) - 1 + movw MACRO_DOLLAR(LOCAL(probe_values_minus_one)), %si +#else + movw MACRO_DOLLAR(LOCAL(probe_values)) - 1, %si +#endif + +LOCAL(probe_loop): + /* reset floppy controller INT 13h AH=0 */ + xorw %ax, %ax + int MACRO_DOLLAR(0x13) + + incw %si + movb (%si), %cl + + /* if number of sectors is 0, display error and die */ + testb %cl, %cl + jnz 1f + +/* + * Floppy disk probe failure. + */ + MSG(fd_probe_error_string) + jmp LOCAL(general_error) + +/* "Floppy" */ +fd_probe_error_string: .asciz "Floppy" + +1: + /* perform read */ + movw MACRO_DOLLAR(GRUB_BOOT_MACHINE_BUFFER_SEG), %bx + movw %bx, %es + xorw %bx, %bx + movw MACRO_DOLLAR(0x201), %ax + movb MACRO_DOLLAR(0), %ch + movb MACRO_DOLLAR(0), %dh + int MACRO_DOLLAR(0x13) + + /* if error, jump to "LOCAL(probe_loop)" */ + jc LOCAL(probe_loop) + + /* %cl is already the correct value! */ + movb MACRO_DOLLAR(1), %dh + movb MACRO_DOLLAR(79), %ch + + jmp LOCAL(final_init) + .endm + + .macro scratch + + /* scratch space */ +mode: + .byte 0 +disk_address_packet: +sectors: + .long 0 +heads: + .long 0 +cylinders: + .word 0 +sector_start: + .byte 0 +head_start: + .byte 0 +cylinder_start: + .word 0 + /* more space... */ + .endm + + .file "boot.S" + + .text + + /* Tell GAS to generate 16-bit instructions so that this code works + in real mode. */ + .code16 + +.globl _start, start; +_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 LOCAL(after_BPB) + nop /* do I care about this ??? */ + +#ifdef HYBRID_BOOT + nop + nop + nop + nop + nop + nop + nop + nop + nop + nop + nop + nop + nop + + nop + nop + nop + nop + nop + nop + nop + nop + + nop + nop + jmp LOCAL(after_BPB) +#else + /* + * This space is for the BIOS parameter block!!!! Don't change + * the first jump, nor start the code anywhere but right after + * this area. + */ + + .org GRUB_BOOT_MACHINE_BPB_START + .org 4 +#endif +#ifdef HYBRID_BOOT + floppy +#else + scratch +#endif + + .org GRUB_BOOT_MACHINE_BPB_END + /* + * End of BIOS parameter block. + */ + +LOCAL(kernel_address): + .word GRUB_BOOT_MACHINE_KERNEL_ADDR + +#ifndef HYBRID_BOOT + .org GRUB_BOOT_MACHINE_KERNEL_SECTOR +LOCAL(kernel_sector): + .long 1 +LOCAL(kernel_sector_high): + .long 0 +#endif + + .org GRUB_BOOT_MACHINE_BOOT_DRIVE +boot_drive: + .byte 0xff /* the disk to load kernel from */ + /* 0xff means use the boot drive */ + +LOCAL(after_BPB): + +/* general setup */ + cli /* we're not safe here! */ + + /* + * This is a workaround for buggy BIOSes which don't pass boot + * drive correctly. If GRUB is installed into a HDD, check if + * DL is masked correctly. If not, assume that the BIOS passed + * a bogus value and set DL to 0x80, since this is the only + * possible boot drive. If GRUB is installed into a floppy, + * this does nothing (only jump). + */ + .org GRUB_BOOT_MACHINE_DRIVE_CHECK +boot_drive_check: + jmp 3f /* grub-setup may overwrite this jump */ + testb $0x80, %dl + jz 2f +3: + /* Ignore %dl different from 0-0x0f and 0x80-0x8f. */ + testb $0x70, %dl + jz 1f +2: + movb $0x80, %dl +1: + /* + * ljmp to the next instruction because some bogus BIOSes + * jump to 07C0:0000 instead of 0000:7C00. + */ + ljmp $0, $real_start + +real_start: + + /* set up %ds and %ss as offset from 0 */ + xorw %ax, %ax + movw %ax, %ds + movw %ax, %ss + + /* set up the REAL stack */ + movw $GRUB_BOOT_MACHINE_STACK_SEG, %sp + + sti /* we're safe again */ + + /* + * Check if we have a forced disk reference here + */ + movb boot_drive, %al + cmpb $0xff, %al + je 1f + movb %al, %dl +1: + /* save drive reference first thing! */ + pushw %dx + + /* print a notification message on the screen */ + MSG(notification_string) + + /* set %si to the disk address packet */ + movw $disk_address_packet, %si + + /* check if LBA is supported */ + movb $0x41, %ah + movw $0x55aa, %bx + int $0x13 + + /* + * %dl may have been clobbered by INT 13, AH=41H. + * This happens, for example, with AST BIOS 1.04. + */ + popw %dx + pushw %dx + + /* use CHS if fails */ + jc LOCAL(chs_mode) + cmpw $0xaa55, %bx + jne LOCAL(chs_mode) + + andw $1, %cx + jz LOCAL(chs_mode) + +LOCAL(lba_mode): + xorw %ax, %ax + movw %ax, 4(%si) + + incw %ax + /* set the mode to non-zero */ + movb %al, -1(%si) + + /* the blocks */ + movw %ax, 2(%si) + + /* the size and the reserved byte */ + movw $0x0010, (%si) + + /* the absolute address */ + movl LOCAL(kernel_sector), %ebx + movl %ebx, 8(%si) + movl LOCAL(kernel_sector_high), %ebx + movl %ebx, 12(%si) + + /* the segment of buffer address */ + movw $GRUB_BOOT_MACHINE_BUFFER_SEG, 6(%si) + +/* + * BIOS call "INT 0x13 Function 0x42" to read sectors from disk into memory + * Call with %ah = 0x42 + * %dl = drive number + * %ds:%si = segment:offset of disk address packet + * Return: + * %al = 0x0 on success; err code on failure + */ + + movb $0x42, %ah + int $0x13 + + /* LBA read is not supported, so fallback to CHS. */ + jc LOCAL(chs_mode) + + movw $GRUB_BOOT_MACHINE_BUFFER_SEG, %bx + jmp LOCAL(copy_buffer) + +LOCAL(chs_mode): + /* + * 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 LOCAL(final_init) + + popw %dx + /* + * The call failed, so maybe use the floppy probe instead. + */ + testb %dl, %dl + jnb LOCAL(floppy_probe) + + /* Nope, we definitely have a hard disk, and we're screwed. */ + ERR(hd_probe_error_string) + +LOCAL(final_init): + /* set the mode to zero */ + movzbl %dh, %eax + movb %ah, -1(%si) + + /* save number of heads */ + incw %ax + movl %eax, 4(%si) + + movzbw %cl, %dx + shlw $2, %dx + movb %ch, %al + movb %dh, %ah + + /* save number of cylinders */ + incw %ax + movw %ax, 8(%si) + + movzbw %dl, %ax + shrb $2, %al + + /* save number of sectors */ + movl %eax, (%si) + +setup_sectors: + /* load logical sector start (top half) */ + movl LOCAL(kernel_sector_high), %eax + + orl %eax, %eax + jnz LOCAL(geometry_error) + + /* load logical sector start (bottom half) */ + movl LOCAL(kernel_sector), %eax + + /* zero %edx */ + xorl %edx, %edx + + /* divide by number of sectors */ + divl (%si) + + /* save sector start */ + movb %dl, %cl + + xorw %dx, %dx /* zero %edx */ + divl 4(%si) /* divide by number of heads */ + + /* do we need too many cylinders? */ + cmpw 8(%si), %ax + jge LOCAL(geometry_error) + + /* normalize sector start (1-based) */ + incb %cl + + /* low bits of cylinder start */ + movb %al, %ch + + /* high bits of cylinder start */ + xorb %al, %al + shrw $2, %ax + orb %al, %cl + + /* save head start */ + movb %dl, %al + + /* restore %dl */ + popw %dx + + /* head start */ + movb %al, %dh + +/* + * 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 $GRUB_BOOT_MACHINE_BUFFER_SEG, %bx + movw %bx, %es /* load %es segment with disk buffer */ + + xorw %bx, %bx /* %bx = 0, put it at 0 in the segment */ + movw $0x0201, %ax /* function 2 */ + int $0x13 + + jc LOCAL(read_error) + + movw %es, %bx + +LOCAL(copy_buffer): + /* + * We need to save %cx and %si because the startup code in + * kernel uses them without initializing them. + */ + pusha + pushw %ds + + movw $0x100, %cx + movw %bx, %ds + xorw %si, %si + movw $GRUB_BOOT_MACHINE_KERNEL_ADDR, %di + movw %si, %es + + cld + + rep + movsw + + popw %ds + popa + + /* boot kernel */ + jmp *(LOCAL(kernel_address)) + +/* END OF MAIN LOOP */ + +/* + * BIOS Geometry translation error (past the end of the disk geometry!). + */ +LOCAL(geometry_error): + ERR(geometry_error_string) + +/* + * Read error on the disk. + */ +LOCAL(read_error): + movw $read_error_string, %si +LOCAL(error_message): + call LOCAL(message) +LOCAL(general_error): + MSG(general_error_string) + +/* go here when you need to stop the machine hard after an error condition */ + /* tell the BIOS a boot failure, which may result in no effect */ + int $0x18 +LOCAL(stop): + jmp LOCAL(stop) + +notification_string: .asciz "GRUB " +geometry_error_string: .asciz "Geom" +hd_probe_error_string: .asciz "Hard Disk" +read_error_string: .asciz "Read" +general_error_string: .asciz " Error\r\n" + +/* + * 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 */ +LOCAL(message): + lodsb + cmpb $0, %al + jne 1b /* if not end of string, jmp to display */ + ret + + /* + * Windows NT breaks compatibility by embedding a magic + * number here. + */ + +#ifdef HYBRID_BOOT + .org 0x1b0 +LOCAL(kernel_sector): + .long 1 +LOCAL(kernel_sector_high): + .long 0 +#endif + .org GRUB_BOOT_MACHINE_WINDOWS_NT_MAGIC +nt_magic: + .long 0 + .word 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? + */ + + .org GRUB_BOOT_MACHINE_PART_START + +#ifndef HYBRID_BOOT + floppy +#else + scratch +#endif + + .org GRUB_BOOT_MACHINE_PART_END + +/* the last 2 bytes in the sector 0 contain the signature */ + .word GRUB_BOOT_MACHINE_SIGNATURE |