Kernel Development from Scratch Part 1 – Setting up the Enviroment

Hey everyone,

We start with a Virtual Maschine.
I installed Ubuntu the LTS Version.
It has pretty much everything u need out of the box.

For easy testing I recommend u to install qemu – it is an apt package so just “sudo apt-get install qemu” – works fine.
I read tutorials and stuff on everything my own and will always refer them.
The first Site I want to refer is OS Dev Wiki.
It has insane information on our topic.
And I use the bootstrap and linker file from this tutorial.
Since this is such a basic topic a hello world kernel, pretty much everybody does it similar.

File boot.asm

# Declare constants used for creating a multiboot header.
.set ALIGN,    1<<0             # align loaded modules on page boundaries
.set MEMINFO,  1<<1             # provide memory map
.set FLAGS,    ALIGN | MEMINFO  # this is the Multiboot 'flag' field
.set MAGIC,    0x1BADB002       # 'magic number' lets bootloader find the header
.set CHECKSUM, -(MAGIC + FLAGS) # checksum of above, to prove we are multiboot

# Declare a header as in the Multiboot Standard. We put this into a special
# section so we can force the header to be in the start of the final program.
# You don't need to understand all these details as it is just magic values that
# is documented in the multiboot standard. The bootloader will search for this
# magic sequence and recognize us as a multiboot kernel.
.section .multiboot
.align 4
.long MAGIC
.long FLAGS
.long CHECKSUM

# Currently the stack pointer register (esp) points at anything and using it may
# cause massive harm. Instead, we'll provide our own stack. We will allocate
# room for a small temporary stack by creating a symbol at the bottom of it,
# then allocating 16384 bytes for it, and finally creating a symbol at the top.
.section .bootstrap_stack
stack_bottom:
.skip 16384 # 16 KiB
stack_top:

# The linker script specifies _start as the entry point to the kernel and the
# bootloader will jump to this position once the kernel has been loaded. It
# doesn't make sense to return from this function as the bootloader is gone.
.section .text
.global _start
.type _start, @function
_start:
	# Welcome to kernel mode! We now have sufficient code for the bootloader to
	# load and run our operating system. It doesn't do anything interesting yet.
	# Perhaps we would like to call printf("Hello, World\n"). You should now
	# realize one of the profound truths about kernel mode: There is nothing
	# there unless you provide it yourself. There is no printf function. There
	# is no <stdio.h> header. If you want a function, you will have to code it
	# yourself. And that is one of the best things about kernel development:
	# you get to make the entire system yourself. You have absolute and complete
	# power over the machine, there are no security restrictions, no safe
	# guards, no debugging mechanisms, there is nothing but what you build.

	# By now, you are perhaps tired of assembly language. You realize some
	# things simply cannot be done in C, such as making the multiboot header in
	# the right section and setting up the stack. However, you would like to
	# write the operating system in a higher level language, such as C or C++.
	# To that end, the next task is preparing the processor for execution of
	# such code. C doesn't expect much at this point and we only need to set up
	# a stack. Note that the processor is not fully initialized yet and stuff
	# such as floating point instructions are not available yet.

	# To set up a stack, we simply set the esp register to point to the top of
	# our stack (as it grows downwards).
	movl $stack_top, %esp

	# We are now ready to actually execute C code. We cannot embed that in an
	# assembly file, so we'll create a kernel.c file in a moment. In that file,
	# we'll create a C entry point called kernel_main and call it here.
	call kernel_main

	# In case the function returns, we'll want to put the computer into an
	# infinite loop. To do that, we use the clear interrupt ('cli') instruction
	# to disable interrupts, the halt instruction ('hlt') to stop the CPU until
	# the next interrupt arrives, and jumping to the halt instruction if it ever
	# continues execution, just to be safe. We will create a local label rather
	# than real symbol and jump to there endlessly.
	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

The bootstrap file is from the tutorial and will help us booting into C, so we can leave asm as fast as possible.

I just provide the basic Hello World Kernel by now and will go into more detail in the next part.
Most files are from the tutorial .
If u read through the tutorial. You are pretty much done with Part 2 too. After that I start brewing my own stuff. Sorry that I be a copycat for the first 2 parts.

File kernel.c

#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
 
/* Hardware text mode color constants. */
enum vga_color
{
	COLOR_BLACK = 0,
	COLOR_BLUE = 1,
	COLOR_GREEN = 2,
	COLOR_CYAN = 3,
	COLOR_RED = 4,
	COLOR_MAGENTA = 5,
	COLOR_BROWN = 6,
	COLOR_LIGHT_GREY = 7,
	COLOR_DARK_GREY = 8,
	COLOR_LIGHT_BLUE = 9,
	COLOR_LIGHT_GREEN = 10,
	COLOR_LIGHT_CYAN = 11,
	COLOR_LIGHT_RED = 12,
	COLOR_LIGHT_MAGENTA = 13,
	COLOR_LIGHT_BROWN = 14,
	COLOR_WHITE = 15,
};
 
uint8_t make_color(enum vga_color fg, enum vga_color bg)
{
	return fg | bg << 4;
}
 
uint16_t make_vgaentry(char c, uint8_t color)
{
	uint16_t c16 = c;
	uint16_t color16 = color;
	return c16 | color16 << 8;
}
 
size_t strlen(const char* str)
{
	size_t ret = 0;
	while ( str[ret] != 0 )
		ret++;
	return ret;
}
 
static const size_t VGA_WIDTH = 80;
static const size_t VGA_HEIGHT = 24;
 
size_t terminal_row;
size_t terminal_column;
uint8_t terminal_color;
uint16_t* terminal_buffer;
 
void terminal_initialize()
{
	terminal_row = 0;
	terminal_column = 0;
	terminal_color = make_color(COLOR_LIGHT_GREY, COLOR_BLACK);
	terminal_buffer = (uint16_t*) 0xB8000;
	for ( size_t y = 0; y < VGA_HEIGHT; y++ )
	{
		for ( size_t x = 0; x < VGA_WIDTH; x++ )
		{
			const size_t index = y * VGA_WIDTH + x;
			terminal_buffer[index] = make_vgaentry(' ', terminal_color);
		}
	}
}
 
void terminal_setcolor(uint8_t color)
{
	terminal_color = color;
}
 
void terminal_putentryat(char c, uint8_t color, size_t x, size_t y)
{
	const size_t index = y * VGA_WIDTH + x;
	terminal_buffer[index] = make_vgaentry(c, color);
}
 
void terminal_putchar(char c)
{
	terminal_putentryat(c, terminal_color, terminal_column, terminal_row);
	if ( ++terminal_column == VGA_WIDTH )
	{
		terminal_column = 0;
		if ( ++terminal_row == VGA_HEIGHT )
		{
			terminal_row = 0;
		}
	}
}
 
void terminal_writestring(const char* data)
{
	size_t datalen = strlen(data);
	for ( size_t i = 0; i < datalen; i++ )
		terminal_putchar(data[i]);
}
 
void kernel_main()
{
	terminal_initialize();
	/* Since there is no support for newlines in terminal_putchar yet, \n will
	   produce some VGA specific character instead. This is normal. */
	terminal_writestring("Hello, kernel World!\n");
}

File kernel.ld

/* The bootloader will look at this image and start execution at the symbol
   designated as the entry point. */
ENTRY(_start)

/* Tell where the various sections of the object files will be put in the final
   kernel image. */
SECTIONS
{
	/* Begin putting sections at 1 MiB, a conventional place for kernels to be
	   loaded at by the bootloader. */
	. = 1M;

	/* First put the multiboot header, as it is required to be put very early
	   early in the image or the bootloader won't recognize the file format.
	   Next we'll put the .text section. */
	.text BLOCK(4K) : ALIGN(4K)
	{
		*(.multiboot)
		*(.text)
	}

	/* Read-only data. */
	.rodata BLOCK(4K) : ALIGN(4K)
	{
		*(.rodata)
	}

	/* Read-write data (initialized) */
	.data BLOCK(4K) : ALIGN(4K)
	{
		*(.data)
	}

	/* Read-write data (uninitialized) and stack */
	.bss BLOCK(4K) : ALIGN(4K)
	{
		*(COMMON)
		*(.bss)
		*(.bootstrap_stack)
	}

	/* The compiler may produce other sections, by default it will put them in
	   a segment with the same name. Simply add stuff here as needed. */
}

File build.sh

#!/bin/sh
as boot.asm -o boot.o
gcc -c kernel.c -o kernel.o -std=gnu99 -ffreestanding -O2 -Wall -Wextra
ld -T kernel.ld -o kernel.bin boot.o kernel.o
rm *.o

KDSBest Kernel Source Download: Download here

Now let’s test the bare bones example.

Run this in your command line:

sh build.sh

Now there has to be a kernel.bin file.
Start QEmu with a terminal on the X-Server (Graphical User Interface):

qemu-system-i386 -kernel kernel.bin

If u get an IPX Error like me just press Enter and now you should see:
“Hello, kernel World!” with a strange character at the end because we don’t interpret “\n” by now properly.

Sorry again for mostly copying at the moment.

Stay tuned in Part 2 I explain everything in more detail,

KDSBest

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