smallvm

A very minimal virtual machine written in rust.

The virtual machine has:

• 8 Registers
• A stack
• A heap
• Data types include: u8, i8, u16, i16, u32, i32, u64, i64, f32, f64

Instruction Set

Root assembly instructions

Instruction	Left Input	Right Input	Operation
NOP			No Operation
MOV	Register	Variable	Move variable to register
MOVR	Register	Register	Move register contents to another register
JMP	Register		Jump to memory location
JE	Register		Jump if equal
JNE	Register		Jump not equal
JG	Register		Jump if greater
JL	Register		Jump if less
CMP	Register	Register	Compare two registers
ADD	Register	Register	Add 2 registers, push result to stack
SUB	Register	Register	Subtract 2 registers, push result to stack
MUL	Register	Register	Multiply 2 registers, push result to stack
DIV	Register	Register	Divide 2 registers, push result to stack
AND	Register	Register	Bitwise AND on 2 registers, push result to stack
OR	Register	Register	Bitwise OR on 2 registers, push result to stack
XOR	Register	Register	Bitwise Exclusive OR on 2 registers, push result to stack
SHR	Register	Variable	Shift register to the right by Variable
SHL	Register	Variable	Shift register to the left by Variable
VPUSH	Variable		Push variable contents on to stack
VPUSHR	Register		Push register contents on to stack
VPOP	Variable		Pops variable from stack to register
CALL	Register		Calls function at address in the register
RET			Return from routine
HALT			Halt CPU/Exit
VSTORE	Address	Variable	Store var into VMHeap at specific address from stack
VLOAD	Address		Load var from VMHeap and push value to stack
VSTORER	Address	Register	Store var in VMHeap from register contents
VLOADR	Register	Address	Loads a variable from VMHeap to register

Debugging assembly instructions

Instruction	Left Input	Right Input	Operation
PRINTR	Register		Print contents of register
PRINTV	Address		Print contents of variable at address

Example Program:

1 0 0 10    MOV(R0, 10)  
1 1 0 8     MOV(R1, 8)  
1 2 0 22    MOV(R2, 23) Location to jump to if R0 is greater than R1  
1 3 0 25    MOV(R3, 25) Location to jump to otherwise  
6 0 1       CMP(R0, R1)  
23 2        JG(R2) Jump if R0 is greater than R1  
3 3         JMP(R3)  
7 0         PRINTR(R0)  
22          HALT()  
7 1         PRINTR(R1)  
22          HALT()