Stack Based Virtual Machine is a type of virtual machgine which uses stacks to perform operation, ex : JVM .
Its a simple implementation of VM which executes the bytecode (32bit so its a wordcode) to understand the JVM.
Stack Based virtual machine creates runtime stack. VM only performs two operations directly on Java Stacks: it pushes and pops data. While reading wordcode if the instruction is encountered it will pop 2 operand from the top of the stack and perform operation on it, push the result back to stack. If encountered word is data it will push to the stack.
VM executes postfix expression compiled into 32 bit long VM instructions.
First 2 bits distinguishes between data and instruction.
| bits | Type |
|---|---|
| 00 | Data (Positive number) |
| 01 | Operation Instruction (OI) |
| 10 | Data (negative number) |
| 11 | undefined |
0x40000001 ADD
0x40000010 SUB
0x40000011 MUL
0x40000100 DIV
0x40000000 HALT
All program must end with HALT instruction.
VM Byte code can be generated from the stack-langc compiler.
cargo run test
This repo contains file a.out with VM instruction to add two numbers, you can dump hex content to view the data.
Byteorder is in little endian, I'll explain the word stored in the file.
| Hex word | VM Value |
|---|---|
| 0x00000020 | Data (32 in decimal) |
| 0x00000016 | Data (22 in decimal) |
| 0x40000001 | OI (ADD) |
| 0x40000000 | OI (HALT) |
Run the above program.
cargo run a.out
In debug mode you can see the result 54 at the top of the stack.