🐍 Solid Snake VM

A low-level bytecode virtual machine with strong abstraction, designed to support future development of a Python-like language with Rust-inspired guarantees.

Trademarked by Konami? Perhaps. But we’re not building a stealth action game — just a hardened VM that doesn’t mess around.

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📌 Project Goals

• ✅ Current Phase:
  Building a clean, extensible low-level bytecode VM, with support for:

  • Basic arithmetic
  • Memory and register manipulation
  • Function calls and a sliding stack
  • Heap allocation and memory access

• 🔭 Longer-Term Vision:
  A high-level, Python-like language that:

  • Compiles to this VM's bytecode
  • Supports strong typing and safety constraints
  • Embraces Python-style ergonomics with Rust-like semantics
  • Can serve as a robust scripting language or backend DSL

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🧱 Design Philosophy

• Low-level but ergonomic:
  Bytecode is explicit, but the VM is built with Rust macros and abstractions to reduce boilerplate and increase clarity.

• Macro-driven instruction system:
  Instructions are defined via declarative Rust macros that auto-generate:

  • Opcode bindings
  • Argument parsing
  • Byte encoding/decoding
  • Execution dispatch

• Register Semantics:
  All values are stored as raw u64, interpreted per instruction. No global typing—each opcode defines how to decode inputs.

• Sliding Stack Model:

  • On CallFunction, the stack pointer is incremented
  • Arguments in R1–R2 are copied to the new frame
  • Return value is placed in R0
  • R3 is reserved for future or scratch use, not preserved between calls

• Memory Model:

  • Heap memory uses segment-indexed allocations
  • All accesses are bounds-checked
  • Instructions support:
    • Direct and indirect load/store
    • Memory section creation/destruction
    • Block operations (Memcpy, MemSet)
  • Memory is untyped at runtime; type interpretation is deferred to compilers and high-level tools

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✨ Highlights

• ✅ Modular instruction definition with low boilerplate
• ✅ Fully dynamic instruction encoding/decoding
• ✅ Strong separation between definition, binary format, and execution
• ✅ Log-driven bytecode debugging (via log crate)
• ✅ Memory-safe execution model
• ✅ Safe Rust, with deliberate unsafe boundaries only where necessary (FFI)

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🧪 Development Status

• Arithmetic (int + float)
• Memory alloc/store/load/copy
• Function call and return
• Branching and loops
• Error handling (overflow, invalid op, etc.)
• Documentation per instruction, flags (HeapAccess, Pure, Commutative, etc.), shorter notation support, generate InstructionDoc per instruction, write generator for .md, .json, or both cargo doc maybe
• Ability to fork, join threads
• Shared memory pool and related instructions for syncronization and data passing
• Builtin functions
• File format (header, data, etc)
• Fused instructions
• Importing code files
• Importing bytecode (or do we even?)
• Native extensions
• Symbolic assembler with label resolution

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🔌 Language-Agnostic Compilation Target

While originally designed for a custom language, Solid Snake VM is language-agnostic and structured to support external compilers.

Any language that:

• Supports static typing
• Has analyzable control flow
• Manages memory through segment-based allocation

...can target this VM directly, including potential Rust backend support or embedded DSLs.

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🔐 Safety Considerations (Planned)

• ✅ All memory is bounds-checked
• 🧪 Optional segment isolation for threads (in progress)
• 🧠 Atomics-only shared memory segment for message passing
• 🧪 ARC-style handle system for controlled shared memory access
• ⚙️ Future borrow-checker-inspired ownership hints
• 💡 Optional read-only memory views for safe sharing

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🧠 Future Considerations

• SSA-style register tracking
• Debug-friendly symbolic stack traces
• Memory aliasing support
• Formal calling convention (R0 = return, R1–Rn = args, reserved scratch registers)
• Declarative FFI system with auto-generated bindings
• Extension-safe APIs with type registries

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🧪 Example Bytecode Execution (TBD)

Sample test cases and full bytecode listings to come.
For now, expect something like:

let bytecode = vec![
    Instruction::LoadImmediateI64((RegisterType(1), -123)),
    Instruction::LoadImmediateI64((RegisterType(2), 456)),
    Instruction::AddI64((RegisterType(3), RegisterType(1), RegisterType(2))),
    Instruction::DebugPrintI64((RegisterType(3))),
    Instruction::Halt,
];

execute_bytecode(&bytecode).unwrap();

Expected output:

Load: R1 <= -123
Load: R2 <= 456
Add: R3 = R1 + R2 => 333
Debug: R3 = 333

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🤝 Contributing

Currently in early development. Core structure and instruction system stable. Contributors welcome, especially around:

• Instruction set design
• Testing macros and debug tooling
• Language frontend and parser
• Extensions or FFI ideas

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🏁 Final Thoughts

Solid Snake VM is a platform for experimentation with strong guarantees, minimalist design, and future-facing features. It's an evolving foundation for a new kind of scripting runtime—Python-flavored, but battle-hardened.

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🔧 “A VM should be small, sharp, and clear—like a knife. Not a suitcase full of opinions.”