diff options
Diffstat (limited to 'arch/x86/boot/bootloader/bootsect.s')
| -rw-r--r-- | arch/x86/boot/bootloader/bootsect.s | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/arch/x86/boot/bootloader/bootsect.s b/arch/x86/boot/bootloader/bootsect.s new file mode 100644 index 0000000..a6e274e --- /dev/null +++ b/arch/x86/boot/bootloader/bootsect.s @@ -0,0 +1,57 @@ +/* + bootsect.s is loaded at 0x7c00 (BIOS likes always to load the boot + sector to this address). It is first stage bootloader, it has one + task - loads setup.s (second stage) to 0x90000 and jumps there. +*/ + +.code16 # Tell GAS to generate 16 bit code + +.include "bios.inc" +.include "rm_seg.inc" + +.global _start # Make the symbol visible to ld +_start: + jmp $0x0, $_start2 # Normalize the start address + # CS = 0 and IP = _start2 +_start2: + mov $SDATASEG, %ax # We will store the boot drive at + mov %ax, %ds # $SDATASEG in the first byte + mov $SETUPSEG, %ax # Do it for disk read routine (see below) + mov %ax, %es + + cld # Set direction flag for incrementing + mov %dl, (0) # BIOS stores our boot drive in DL, + # so we remember it + mov %cs, %ax # AX = CS = 0 (see above) + mov %ax, %ds # Zero data segment register + +load_setup: + BIOS_PRINT $load_setup_msg # The routine uses only AX register + + mov $0x02, %ah # Set BIOS read sector routine + mov $0x00, %ch # Select cylinder 0 + mov $0x00, %dh # Select head 0 [has a base of 0] + mov $0x02, %cl # Select sector 2 (next after the + # boot sector) [has a base of 1] + mov $SETUPLEN, %al # Read $SETUPLEN sectors + mov $0x0, %bx # Load sectors to ES:BX ($SETUPSEG:0) + int $0x13 # Start reading from drive + jc disk_error # If carry flag set, bios failed to read + + # Make a far jump to our setup code + jmp $SETUPSEG, $0x0 + +disk_error: + BIOS_PRINT $disk_error_msg + jmp . + +load_setup_msg: + .asciz "Loading setup sectors\r\n" + +disk_error_msg: + .asciz "Disk read error!" + +# Bootsector padding +.space 512 - 2 - (. - _start), 0 +boot_flag: + .word 0xAA55 |