Hello!
Some time ago, when i was sitting on 32Bit machine,
i created a Win32 Bootloader that is emulated using Bochs Emulator.
; *************************************************
; *************************************************
;
This is: NASM x86 Win32 Bootloader
; Author: J.K. Encryptor256
; Date: Tuesday, October 1, 2013
; *************************************************
;
Using: Netwide assembler and Bochs emulator
; Nasm: Generates .obj file
; Bochs: Emulates generated file as a hard disk
; *************************************************
;
Bochs emulator:
; In order to emulate bootloader as a hard disk, we have to make
; this NASM .obj result file a bit larger, so, bochs could read it,
; ... more info a the end of file.
; *************************************************
;
Compile:
; Nasm: "nasm -fbin bootloader.asm"
; *************************************************
;
TASK:
; 1. Create bootloader
; 2. Compile with NASM
; 3. Configure Bochs (visual demo, find on youtube, link below)
; 4. Emulate with Bochs (visual demo, find on youtube, link below)
; *************************************************
; *************************************************
Source code:
; START:
; Tell compiler to generate 16 bit code
bits 16
; Bootloader specification states, that Bootloader program will be loaded
; at segment 0x0000 and address 0x07C0.
; We can use "org" directive to set program origin.
; Fixed address is of 0x0000 and 0x07C0 is 0x7C00.
;org 0x7c00 ; But i don't like it, so i will setup segments manually.
; A. Jump to the code --------------------------------------
jmp bootloader
; B.Define data, procedures here ---------------------------
message db 13,10," * [ !!! NASM: Hello World :NASM !!! ] *",13,10,0
printMessage:
; -----------------
push ax
; -----------------
.loop:
; -----------
lodsb
or al,al
jz .quitLoop
mov ah,0x0e
int 0x10
jmp .loop
; -----------------
.quitLoop:
; -----------------
pop ax
; -----------------
ret
; Here, with label "bootloader" starts our code: --------------
bootloader:
; CLI - Interrupts:
; disable interrupts when setting up segments,
; because, changes in segment registers,
; could fire some interrut and ruin something for us.
cli
; Setup segments, just here where we are loaded at.
mov ax,0x07c0
mov ds,ax
mov gs,ax
mov fs,ax
mov es,ax
; Setup stack segment.
; Bios memory map description on the internet states, that:
; Address:
; from: 0x00007E00,
; to: 0x0007FFFF
; is (480.5 KiB, RAM (guaranteed free for use), Conventional memory)
; So let's setup our stack segment there.
; Setup stack segment address
mov ax,0x07e0
mov ss,ax
mov bp,ax
; Setup stack segment pointer (roof) of 256 bytes
mov sp,0xff
; STI - Interrupts:
; enable interrupts, so, software and hardware can call them.
sti
; Display message on the screen
mov si,message
call printMessage
; Display message on the screen
mov si,message
call printMessage
; Display message on the screen
mov si,message
call printMessage
; Now stop cpu, so we could see the result
; Clear interrupts and halt cpu
cli
hlt
; Finish Bootloader: -------------------------------------------------------------
; Bootloader, must be, total in sizeof 512 bytes.
; The last two bytes are constant numbers.
; Fill rest of file with zeroes, how many zeroes needed?
; 510 - (Current location) - (Start of file) define bytes with value of zero
times 510 - ($-$$) db 0
; Here comes last two signature bytes,
; so, cpu can recoginze, that this is a valid bootloader
DB 0x55
DB 0xAA
; END, but for Bochs emulator, this file will be recognized as a hard disk,
; so, let's make it a bit bigger, just to fool Bochs
times 1024*1024 db 0
Attachment:
Attachment includes source code file, plus Bochs config file.
Config file might be required to be reconfigured again.
Video:
Watch full source code and runtime demo on youtube:
NASM Bootloader x86 The Netwide Assembler Bochs Emulator I think that's it, that i wanted to share,
bye,
Encryptor256!!!
