I tested the basic direct binary concatenation where the second file is appended to the end of the first file, preserving all bytes exactly as they are without any linking metadata or relocations with the cat command.
Let's see how can do this.
You need to create two files: kernel.fasm and kernel2.fasm.
First will like this:
org 7C00h
; First stage bootloader
start:
mov [bootdrive], dl
mov ax, 0x2000 ; Load kernel at 0x2000:0
mov es, ax
xor bx, bx ; ES:BX = buffer
mov ah, 02h ; Read sectors
mov al, 6 ; Number of sectors to read
mov ch, 0 ; Cylinder 0
mov cl, 2 ; Start from sector 2
mov dh, 0 ; Head 0
mov dl, [bootdrive]
int 13h
jmp 0x2000:0 ; Jump to second stage
bootdrive db 0
times 510-($-$$) db 0
dw 0xAA55The second one named kernel2.fasm will come with new features:
org 0
COLS equ 80
ROWS equ 25
VIDEO_MEM equ 0xB800
; Box drawing characters
BOX_DR equ 201 ; ╔
BOX_HL equ 205 ; ═
BOX_DL equ 187 ; ╗
BOX_VL equ 186 ; ║
BOX_UR equ 200 ; ╚
BOX_UL equ 188 ; ╝
BOX_BLOCK equ 219 ; █
...Use fasm and cat commands to create the bin files and the result file for qemu:
mythcat@localhost:~/fasm$ ./fasm.x64 kernel.fasm kernel.bin
flat assembler version 1.73.32 (16384 kilobytes memory, x64)
2 passes, 512 bytes.
mythcat@localhost:~/fasm$ ./fasm.x64 kernel2.fasm kernel2.bin
flat assembler version 1.73.32 (16384 kilobytes memory, x64)
2 passes, 132 bytes.
mythcat@localhost:~/fasm$ cat kernel.bin kernel2.bin > os.imgThe last step is to run qemu-system-i386 to test the result
mythcat@localhost:~/fasm$ qemu-system-i386 -fda os.imgThe result is this:
