CODEWITHSUNDEEP
cassemblyx86virtualization
dotslash
dotslash

Reputation:

How would I go about creating my own VM?

I'm wondering how to create a minimal virtual machine that'll be modeled after the Intel 16 bit system. This would be my first actual C project, most of my code is 100 lines or less, but I have the core fundamentals down, read K&R, and understand how things ought to work, so this pretty much is a test of wits.

Could anyone guide me in as far as documentation, tools, tutorials, or plain old tips/pointers on how to go about this, thus far I understand that I require somewhere to store data, a CPU of sorts and some sort of mechanism that functions as an interrupt controller.

I'm doing this to learn: Systems internals, ASM internals and C - three facets of computing that I want to learn in a singular project.

Please be kind enough not to tell me to do something simpler - that would only be annoying. :)

Thanks for reading, and hopefully writing!

Upvotes: 2

Views: 856

Answers (4)

E.T
E.T

Reputation: 1145

If you want to write a Virtual Machine using the x86 VMM technology you will need quite a bit of things.

There are a few instructions that are critical such as VM_ENTER/VM_EXIT (name can change depending on the chip, AMD and INTEL use different names but the functionalities are the same). Those instructions are actually privileged and therefore, you will need to write a kernel module to use them.

The first step for your VM to start is to boot it and therefore, you will need a 'BIOS' which will be loaded. Then you need to emulate devices, etc. You could even run an old version of MSDOS in such a VM if you wanted to.

All in all, it clearly isn't trivial and requires a lot of time and effort.

Now, you could do something similar to what VMWare used to do before the Virtualization ready CPUs appeared.

Upvotes: 0

Magnus Hoff
Magnus Hoff

Reputation: 22099

For a JIT, you might want to dynamically generate and execute x86 code.

Upvotes: 1

Will
Will

Reputation: 75683

Virtual machines fall into two categories: those that interpret the code instruction at a time and those that compile the code to native instructions (e.g. "JIT").

The interpretation category is usually built around an instruction execution loop, using a switch statement, computed gotos or function pointers to determine how to execute each instruction.

There is a fun platform that is worth studying for its simplicity and fun: Corewars.

Corewars is a programming challenge game where programs written in "Redcode" run on a MARS VM. There are many MARS VMs, typically written in C.

It has also inspired 8086-based versions, where programs written in 8086 assembler battle.

Upvotes: 3

Lasse V. Karlsen
Lasse V. Karlsen

Reputation: 391664

Well, for starters I would pick up a reference book for assembly language for the processor you intend to virtualize, like 80286 or similar.

Upvotes: 1

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