CODEWITHSUNDEEP
operating-system
Mr X
Mr X

Reputation: 354

OS development tools: advice needed

So I got a new computer for Christmas and it came with Windows 8 pre-installed. Now I've had MORE than enough trouble getting it to run both Linux Ubuntu and W8 on the same drive. Having 2 operating systems of a single hard drive requires that the drive be partitioned so that 2 OS's do not conflict with each other. Now there is a program called Mini Partition Tool Wizard which runs inside Windows 8(and there is a similar program for Linux called gparted) which allows you to created and resize hard disk partitions so long as you don't overwrite the operating system that you're currently using.

To make a long story short: I am wanting to write my very own mini operating system that is to be used exclusively for boot control and hard disk management. That is, once I get it written, debugged, and compiled into executable code I will put it on a USB memory stick that I can boot from in the BIOS menu and then directly set up hard drive partitions and even format my hard drive if necessary. I'm quite astonished that BIOS doesn't have the user options of doing it yourself.

So my question is: Can I do this exclusively using the tools of C/C++? Or do I need to have inline assembly code? Or perhaps write an assembly code module that is used in a C++ program. Pretty sure that Mini Partition Tool Wizard is not open source(neither is Windows). Never written and OS before so I'm a n00b to this but willing and able to take the time to learn how it's done.

Upvotes: 2

Views: 1352

Answers (1)

Alexey Frunze
Alexey Frunze

Reputation: 62096

Can I do this exclusively using the tools of C/C++? Or do I need to have inline assembly code?

You will need some assembly and not the inline kind. Your compiled C/C++ code expects a number things to be set up and configured already (e.g. the 32-bit protected mode of the CPU, the stack, values of the various CPU registers, device drivers, interrupts, the C/C++ memory manager, etc), while the BIOS simply loads one 512-byte-long sector from a disk and transfers control to it, without setting up anything, with the CPU still being in the 16-bit mode.

So, you'd need to write some assembly code to:

  • load more stuff from the disk, you don't suppose everything will fit into 512 bytes, do you?
  • switch the CPU into the 32-bit protected mode
  • reconfigure the interrupt controller so the interrupts do not map onto the same interrupt vectors as protected mode exceptions (well, this tiny part can be done in C)
  • write exception handlers
  • write interrupt handlers for the basic stuff like the timer and the keyboard (if designed carefully, you may only need to do a small part of this in assembly and the rest can be done in C)

And then you'll need to write 32-bit I/O device drivers for everything else since after the switch you can't use the BIOS's. Alternatively, you could implement a virtual 8086 machine (using the virtual 8086 mode) in order to delegate this stuff back to the BIOS and that's not a trivial thing either. Most of this can be done in C, but some knowledge or use of assembly code will still be necessary.

You'll also need to reimplement some parts of the standard library of C (C++), so malloc()/new, putch(), getchar(), fopen(), time() and so on use your low-level APIs instead of Windows' or Linux'.

Prepare to burn a couple of years to get from nothing and lack of knowledge and experience to something working.

And yeah, you can indeed start learning stuff at osdev.org. There are some useful newsgroups as well: comp.lang.asm.x86 and alt.os.development.

Upvotes: 1

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