D Bare Bones
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Difficulty level |
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![]() Beginner |
Kernel Designs |
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Models |
Other Concepts |
In this Tutorial we will write a kernel in the D language and boot it.
Preface
The following tutorial assumes basic knowledge of a compiler, linker and assembler toolchain. It also of course assumes prior knowledge of the D programming language.
Overview
In this tutorial we will create a simple D kernel that prints 'D' on to the screen. The basic setup will consist of three files:
- start.asm
- kernel.main.d
- linker.ld
start.asm
global start
extern main ; Allow main() to be called from the assembly code
extern start_ctors, end_ctors, start_dtors, end_dtors
MODULEALIGN equ 1<<0
MEMINFO equ 1<<1
FLAGS equ MODULEALIGN | MEMINFO
MAGIC equ 0x1BADB002
CHECKSUM equ -(MAGIC + FLAGS)
section .text ; Next is the Grub Multiboot Header
align 4
MultiBootHeader:
dd MAGIC
dd FLAGS
dd CHECKSUM
STACKSIZE equ 0x4000 ; 16 KiB if you're wondering
static_ctors_loop:
mov ebx, start_ctors
jmp .test
.body:
call [ebx]
add ebx,4
.test:
cmp ebx, end_ctors
jb .body
start:
mov esp, STACKSIZE+stack
push eax
push ebx
call main
static_dtors_loop:
mov ebx, start_dtors
jmp .test
.body:
call [ebx]
add ebx,4
.test:
cmp ebx, end_dtors
jb .body
cpuhalt:
hlt
jmp cpuhalt
section .bss
align 32
stack:
resb STACKSIZE
Assemble that with:
nasm -f elf -o start.o start.asm
kernel.main.d
module kernel.main;
extern(C) void main(uint magic, uint addr) {
int ypos = 0; //Starting points of the cursor
int xpos = 0;
const uint COLUMNS = 80; //Screensize
const uint LINES = 25;
ubyte* vidmem = cast(ubyte*)0xFFFF_8000_000B_8000; //Video memory address
for (int i = 0; i < COLUMNS * LINES * 2; i++) { //Loops through the screen and clears it
volatile *(vidmem + i) = 0;
}
volatile *(vidmem + (xpos + ypos * COLUMNS) * 2) = 'D' & 0xFF; //Prints the letter D
volatile *(vidmem + (xpos + ypos * COLUMNS) * 2 + 1) = 0x07; //Sets the colour for D to be light grey (0x07)
for (;;) { //Loop forever. You can add your kernel logic here
}
}
You then compile that with:
gdc -c kernel.main.d -o kernel.main.o -g
linker.ld
OUTPUT_FORMAT(elf32-i386)
ENTRY (start)
SECTIONS{
. = 0x00100000;
.text :{
code = .; _code = .; __code = .;
*(.text)
*(.rodata)
}
.rodata ALIGN (0x1000) : {
*(.rodata)
}
.data ALIGN (0x1000) : {
data = .; _data = .; __data = .;
*(.data)
start_ctors = .; *(.ctors) end_ctors = .;
start_dtors = .; *(.dtors) end_dtors = .;
}
.bss : {
sbss = .;
bss = .; _bss = .; __bss = .;
*(COMMON)
*(.bss)
ebss = .;
}
end = .; _end = .; __end = .;
}
Now finally you can link all of that with:
ld -T linker.ld -o kernel.bin start.o kernel.main.o
Your kernel is now kernel.bin, and can now be booted by grub.
Keep in mind that to add other classes, functions, enums, etc. You must add the D runtime.
Hopefully this has gotten you started on writing your operating system in the D programming language.