D Bare Bones
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.
WAIT! Have you read Getting Started, Beginner Mistakes, and some of the related OS theory?
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 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 ; 16k 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) { byte *videoram = cast( byte * ) 0xb8000; // Set up video memory videoram[0] = 'D'; videoram[1] = 0x07; }
You then compile that with:
gdc -nostdlib -nodefaultlibs -g -c -o kernel.main.o kernel.main.d
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) __CTOR_LIST__ = .; LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2) *(.ctors) LONG(0) __CTOR_END__ = .; __DTOR_LIST__ = .; LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2) *(.dtors) LONG(0) __DTOR_END__ = .; } } .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.
Hopefully this has gotten you started on writing your operating system in the D programming language.