MiniJVM

MiniJVM is a minimalistic Java Virtual Machine emulator capable of executing bytecode from a custom .mclass file format. This project demonstrates fundamental concepts of virtual machines, including a stack-based architecture and basic bytecode operations.

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Features

• Reads and executes bytecode from a .mclass file.
• Supports common bytecode instructions such as:
  • Arithmetic operations (IADD, ISUB, IMUL, IDIV, IREM)
  • Stack manipulation (PUSH, POP, DUP)
  • Variable operations (ILOAD, ISTORE, IINC)
  • Control flow (IFEQ, GOTO, RETURN)
  • Printing (PRINT)
• Implements a basic operand stack and local variable storage.

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Getting Started

Prerequisites

• A C compiler (e.g., gcc)
• make (optional, if creating a Makefile)

Compilation

Compile the program using the following command:

gcc -o minijvm main.c stack.c minijvm.c

MiniJVM Bytecode Instructions

MiniJVM supports the following bytecode instructions:

Instructions

Instruction	Description
INST_ICONST0	Pushes the integer 0 onto the stack.
INST_POP	Pops the top item off the stack.
INST_DUP	Duplicates the top item on the stack.
INST_IADD	Pops and adds the top two items on the stack.
INST_ISUB	Pops and subtracts the top two items on the stack.
INST_IMUL	Pops and multiplies the top two items on the stack.
INST_IDIV	Pops and divides the top two items on the stack.
INST_IREM	Pops and computes the remainder of the top two items.
INST_PRINT	Prints the top item on the stack.
INST_BIPUSH	Pushes a signed byte onto the stack.
INST_ILOAD	Loads a local variable onto the stack.
INST_ISTORE	Stores the top of the stack into a local variable.
INST_IINC	Increments a local variable.
INST_IFEQ	Branches if the top of the stack equals 0.
INST_GOTO	Jumps to a specified offset in the bytecode.
INST_RETURN	Ends the program.

Example .mclass File

Let's create a sample .mclass file with the following bytecode:

BIPUSH 5
BIPUSH 3
IADD
PRINT
RETURN

Bytecode Operations

This bytecode performs the following operations:

1. Pushes the value 5 onto the stack.
2. Pushes the value 3 onto the stack.
3. Adds the top two items on the stack (5 + 3).
4. Prints the top item on the stack (8).
5. Ends the program.