How to compile a simple operating system and make it bootable? - gcc

Question

I'm interested in operating system concepts, so I downloaded the Hello world OS. I'd like to know how to compile and link the code and make a bootable image. I'm using an old version of Cygwin on Windows (Cygwin-b20) from 1999.
My code for main.c is:
#include "bloader.h"
int main();
unsigned int oldEBP;
struct boot_dir *viewableDirectory;
int totalMem;
char * passedParams;
void _start(int memSize, char *parms, struct boot_dir *loadedfiles)
{
asm("mov %%ebp, %0":"=m"(oldEBP));
viewableDirectory = loadedfiles; /*make file mem locations global*/
totalMem = memSize; /*make mem of system global*/
passedParams = parms; /*make paramaters passed to system global*/
main();
asm("hlt"); /* this halts the machine, solving the problem of triple-faults on
some machines, but also making it impossible to return to DOS */
}
int main()
{
char *vidmem = (char *) 0xb8000;
/* "Hello " */
vidmem[0] = 'H';
vidmem[1] = 0x7;
vidmem[2] = 'e';
vidmem[3] = 0x7;
vidmem[4] = 'l';
vidmem[5] = 0x7;
vidmem[6] = 'l';
vidmem[7] = 0x7;
vidmem[8] = 'o';
vidmem[9] = 0x7;
vidmem[10] = ' ';
vidmem[11] = 0x7;
/* "World " */
vidmem[12] = 'W';
vidmem[13] = 0x7;
vidmem[14] = 'o';
vidmem[15] = 0x7;
vidmem[16] = 'r';
vidmem[17] = 0x7;
vidmem[18] = 'l';
vidmem[19] = 0x7;
vidmem[20] = 'd';
vidmem[21] = 0x7;
vidmem[22] = ' ';
vidmem[23] = 0x7;
/* "OS" */
vidmem[24] = 'O';
vidmem[25] = 0x7;
vidmem[26] = 'S';
vidmem[27] = 0x7;
return 0;
}
I'm interested in instructions to:
Create ISO file after compile and run it with VMware (or other virtual machines)
Run this code after compiling in real machine when system boots and how to add it to bootloader (for example GRUB) entry

Answer 1

Make an empty file and give it the extension .vmdk
open it up in your favorite hex editor
and place your compiled boot loader code
its exactly the same as a hard drive
also the last 2 bytes in the sector must be 55 and AA
your bootloader code starts from 00
it will look something like this
Sector Offset Hex Values Ascii
x00000000 x000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
x010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
x020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
x030 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
x040 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
x050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
x060 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
x070 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
x080 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
x090 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
x0A0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
x0B0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
x0C0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
x0D0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
x0E0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
x0F0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
-------------
x1F0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 AA
here is a guide to make run a boot loader
http://www.codeproject.com/Articles/36907/How-to-develop-your-own-Boot-Loader#_Toc231383191