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.
1. GCC - Any `C` compiler
2. EMACS or VIM to view the written file after execution
gcc bskit.c- An
a.outfile gets generated. Open this with Emacs to view.
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.
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
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.