BSKIT -- Virtual-machine

To gain a deeper understanding of how computers work at a low level I built out a simple implementation of a virtual machine written in C.

Prerequisites to run bskit:

1. GCC - Any `C` compiler
2. EMACS or VIM to view the written file after execution

Running bskit:

1. gcc bskit.c
2. An a.out file gets generated. Open this with Emacs to view.

BSKIT

bskit is a really simple virtual machine. It's written in C and is only one small C file.

The virtual machine is a set of registers: A, B, C, D, E, and F. These are general purpose registers, which means that they can be used for storing anything.

Registers

register	purpose
-------------------------------
A			general purpose
B			general purpose
C			general purpose
D			general purpose
E			general purpose
F			general purpose
EX 			extra
EXA 		extra
IP			instruction pointer
SP			stack pointer

Instructions

The program will be a read-only sequence of instructions. The virtual machine is a stack-based virtual machine, which means that it has a stack we can push and pop values to, and a few registers we can use too. These are also a lot more simpler to implement than a register-based virtual machine.

These are some of the sets of instructions I have implemented:

operation   value & usage    	function
---------------------------------------------------------------------
HLT  0      hlt 	 			         halts program
PSH  1      psh val  			      pushes <val> to stack
POP  2      pop 	 			         pops value from stack
ADD  3      add 	 			         adds top two vals on stack
MUL  4      mul 	 			         multiplies top two vals on stack
DIV  5      div 	 			         divides top two vals on stack
SUB  6      sub 	 			         subtracts top two vals on stack
MOV  7      mov reg_a, reg_b 	movs the value in reg_a to reg_b 
SET  8      set reg, val 		   sets the reg to value
LOG  9      log a 				        prints out a
IF   10     if reg val ip 		  if the register == val branch to the ip
IFN  11     ifn reg val ip 		 if the register != val branch to the ip
GLD  10     gld reg 			       loads a register to the stack
GPT  11     gpt reg 			       pushes top of stack to the given register
NOP  12     nop 				          nothing

In addition to the program itself you can pass in files to the program and run command executions on it with the format ~/.bskit extension. Here I have used the ~/.test.bskit which is passed as an argument to the program ./bskit test.bskit and it will execute the program.