OSDev.org

.extern kernel_main

.section .multiboot2

multiboot2_header_start:
/* magic number */
.long   0xe85250d6
/* architecture */
.long   0
/* header size */
.long   multiboot2_header_end - multiboot2_header_start
/* checksum */
.long   -(0xe85250d6 + (multiboot2_header_end - multiboot2_header_start))

/* tag end */
.align 8
.short   0
.short   0
.long   8
multiboot2_header_end:

# Reserve a stack for the initial thread.
.section .bootstrap_stack, "aw", @nobits
stack_bottom:
.skip 16384 # 16 KiB
stack_top:

.section .text.init

.global _start
.type _start, @function
_start:
   movl $stack_top, %esp

   /* Reset EFLAGS. */
   pushl   $0
   popf

   pushl %ebx
   pushl %eax

   call kernel_main

   cli
   hlt
.Lhang:
   jmp .Lhang

# Set the size of the _start symbol to the current location '.' minus its start.
# This is useful when debugging or when you implement call tracing.
.size _start, . - _start   

BOOT_ADDRESS   = 0x00100000;

PAGE_SIZE      = 0x1000;

ENTRY(_start)
SECTIONS {
   . = BOOT_ADDRESS;
   .text.init : {
      . = ALIGN(8);
      *(.multiboot2)
      *(.text.init)
   } : boot

   .data.init : {
      *(.data.init)
   }

   .bss.init : {
      *(.bss.init)
   }

   .text ALIGN(PAGE_SIZE) : AT(ADDR(.text)) {
      *(.text)
   } : text

   .rodata ALIGN(PAGE_SIZE) : AT(ADDR(.rodata)) {
      *(.rodata)
   } : rodata

   .data ALIGN(PAGE_SIZE) : AT(ADDR(.data)) {
      *(.data)
   } : data

   .bss ALIGN(PAGE_SIZE) : AT(ADDR(.bss)) {
      *(.bss)
      *(.bootstrap_stack)
   }

   kernel_image_size = .;
}

PHDRS {
   headers   PT_PHDR FILEHDR PHDRS;
   boot   PT_LOAD;
   text   PT_LOAD;
   rodata   PT_LOAD;
   data   PT_LOAD;
}

#include <stddef.h>
#include <stdint.h>

void WriteCharacter(unsigned char c, unsigned char forecolour, unsigned char backcolour, int x, int y)
{
     uint16_t attrib = (backcolour << 4) | (forecolour & 0x0F);
     volatile uint16_t * where;
     where = (volatile uint16_t *)0xB8000 + (y * 80 + x) ;
     *where = c | (attrib << 8);
}

extern "C"
void kernel_main(uint32_t magic, uint32_t addr)
{
   WriteCharacter('A', 15, 0, 0, 0);
}

menuentry "myos" {
   multiboot /boot/myos.bin
}

#!/bin/bash
mkdir -p isodir/boot/grub
cp myos.bin isodir/boot/myos.bin
cp grub.cfg isodir/boot/grub/grub.cfg
grub2-mkrescue -o myos.iso isodir

i686-elf-as boot.S -o boot.o
i686-elf-g++ -std=c++14 -Wall -Wextra -pedantic -O2 -ffreestanding -fno-exceptions -fno-rtti -c main.cpp -o main.o
i686-elf-g++ -T linker.ld -o myos.bin -ffreestanding -O2 -nostdlib boot.o main.o -lgcc

grub2-mkrescue --version
grub2-mkrescue (GRUB) 2.02~beta2

menuentry "myos" {
   multiboot /boot/myos.bin
}

menuentry "myos" {
   multiboot2 /boot/myos.bin
}