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MyOS(二)：用Java和汇编开发一个helloworld操作系统内核

news 来源：原创 2024/4/27 3:42:52

我们开发程序的时候，操作系统给我们提供API
我们开发操作系统的时候，BIOS给我们提供API

只有汇编支持我们直接操作计算机的硬件(寄存器)，C语言也不行
只有汇编语言和C语言，能够通过指针访问内存

函数调用时需要传递参数，那么调用bios提供的函数时，怎么传递参数呢，做法是，把需要传递的参数放入到指定的寄存器中，例如想要在屏幕上输出字符，那么bios提供的编号为0x10的库函数可以实现这个功能，同时按规定，要把寄存器ah设置为0x0e, 把要输出的字符的ascii值放入到寄存器al, 同时要把寄存器设bh的值设置成0，字符的颜色可以通过寄存器bl的值来设定

其实这里和上一篇用Java做一个最小的操作系统内核是一样的，上次是直接把二进制代码写出来了，这次是先自己写汇编，然后用nasm将汇编程序编译成.bin文件，再在java中打开bin文件，将里面的内容写入到生成的img文件中，不够的补0，再添加55aa

org是指示BIOS在将我们这段代码加载进内存的时候，写入到内存0x7c00的位置

entry将寄存器初始化

boot.asm

org  0x7c00


entry:
    mov  ax, 0
    mov  ss, ax
    mov  ds, ax
    mov  es, ax
    mov  si, msg

putloop:
    mov  al, [si]
    add  si, 1
    cmp  al, 0
    je   fin
    mov  ah, 0x0e
    mov  bx, 15
    int  0x10 ;调用BIOS
    jmp  putloop

fin:
    HLT
    jmp  fin

msg:
    DB    0x0a,  0x0a
    db    "hello, world"
    db    0x0a
    db    0

这是nasm编译后的boot.bin

将boot.bin复制到java工作目录下

用java将boot.bin读入，然后写入到system.img

import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;


public class OperatingSystem {
    // private int[] imgContent = new int[]{
    //     0xeb,0x4e,0x90,0x48,0x45,0x4c,0x4c,0x4f,0x49,0x50,0x4c,0x00,0x02,0x01,0x01,0x00,0x02,0xe0,
    //     0x00,0x40,0x0b,0xf0,0x09,0x00,0x12,0x00,0x02,0x00,0x00,0x00,0x00,0x00,0x40,0x0b,0x00,0x00,0x00,0x00,0x29,
    //     0xff,0xff,0xff,0xff,0x48,0x45,0x4c,0x4c,0x4f,0x2d,0x4f,0x53,0x20,0x20,0x20,0x46,0x41,0x54,0x31,0x32,
    //     0x20,0x20,0x20,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0xb8,0x00,0x00,0x8e,
    //     0xd0,0xbc,0x00,0x7c,0x8e,0xd8,0x8e,0xc0,0xbe,0x74,0x7c,0x8a,
    //     0x04,0x83,0xc6,0x01,0x3c,0x00,0x74,0x09,0xb4,0x0e,0xbb,0x0f,0x00,0xcd,0x10,0xeb,0xee,0xf4,0xeb,0xfd
    // };

    private ArrayList<Integer> imgByteToWrite = new ArrayList<Integer>();

    private void readKernelFromFile(String fileName) {
        File file = new File(fileName);
        InputStream in = null;

        try {
            in = new FileInputStream(file);
            int tempbyte;
            while ((tempbyte = in.read()) != -1) {
                imgByteToWrite.add(tempbyte);
            }
        } catch(IOException e) {
            e.printStackTrace();
            return;
        }

        imgByteToWrite.add(0x55);
        imgByteToWrite.add(0xaa);
        imgByteToWrite.add(0xf0);
        imgByteToWrite.add(0xff);
        imgByteToWrite.add(0xff);

    }

    public OperatingSystem(String s) {
    /*  for (int i = 0; i < imgContent.length; i++) {
            imgByteToWrite.add(imgContent[i]);
        }

        imgByteToWrite.add(0x0a);
        imgByteToWrite.add(0x0a);
        for (int j = 0; j < s.length(); j++) {
            imgByteToWrite.add((int)s.charAt(j));
        }
        imgByteToWrite.add(0x0a);

        int len = 0x1fe;
        int curSize = imgByteToWrite.size();
        for (int k = 0; k < len - curSize; k++) {
            imgByteToWrite.add(0);
        }

        //0x1fe-0x1f: 0x55, 0xaa
        //0x200-0x203: f0 ff  ff
        imgByteToWrite.add(0x55);
        imgByteToWrite.add(0xaa);
        imgByteToWrite.add(0xf0);
        imgByteToWrite.add(0xff);
        imgByteToWrite.add(0xff);
      */

        readKernelFromFile("boot.bin");

        int len = 0x168000;
        int curSize = imgByteToWrite.size();
        for (int l = 0; l < len - curSize; l++) {
            imgByteToWrite.add(0);
        }

    }

    public void makeFllopy()   {
        try {
            DataOutputStream out = new DataOutputStream(new FileOutputStream("system.img"));
            for (int i = 0; i < imgByteToWrite.size(); i++) {
                out.writeByte(imgByteToWrite.get(i).byteValue());
            }
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    public static void main(String[] args) {
        OperatingSystem op = new OperatingSystem("hello, this is my first line of my operating system code");
        op.makeFllopy();
    }
}