IJVM Emulator

01. Overview

Engineered a low-level, cycle-accurate emulator for the Integer Java Virtual Machine (IJVM). This project focused on building a robust interpreter in C that parses compiled binary files and executes them according to the stack-based microarchitecture designed by Andrew Tanenbaum.

The emulator functions as a complete virtual processor, managing its own memory, program counter, and stack frames to execute Java-like assembly code with high performance and precision.

02. Architecture & Memory

The system is designed around a strictly defined memory model that separates data and instructions into specialized regions to ensure execution stability and safety.

• Stack-Based Execution: Implemented a dynamic Operand Stack for arithmetic and logical operations, utilizing manual memory management in C to handle growth and deallocation.
• Memory Segments: Managed distinct memory areas including the Constant Pool for pre-loaded data and the Method Area for raw bytecodes.
• Frame Management: Developed a sophisticated Local Variable Frame system that tracks method parameters and local variables across nested function calls.
• Instruction Decoding: Built a Fetch-Decode-Execute loop that dispatches opcodes in real-time, supporting both standard and wide-index instructions.

03. Complex Logic & Performance

The primary technical challenge involved implementing INVOKEVIRTUAL and IRETURN. This required maintaining a secondary "Frame Stack" to save context, restore pointers, and pass return values between methods without corrupting the underlying memory.

By integrating features like the WIDE prefix for 16-bit indexing and robust error handling for stack underflows, the emulator is capable of running complex recursive programs. This project demonstrates a deep understanding of how software interacts with hardware at the most fundamental level, bridging the gap between high-level code and machine execution.