Formally Verified Compiler Pipeline: ZLang → APPC_ISA

This project implements a complete formally verified compiler pipeline demonstrating three key verification techniques:

Languages

ZLang (Source Language)

• Minimal imperative language
• Features: arithmetic expressions, variable assignments, statement sequencing
• No loops or functions (for simplicity)
• Example: x = 2 + 3; y = x * 4

APPC_ISA (Target Language)

• PowerPC-like assembly language
• Instructions: LOAD, LOADVAR, STORE, ADD, SUB, MUL, NOP
• Register-based architecture with 8 registers (R0-R7)

Verification Techniques

Technique 1: Verified Compiler (Coq)

• Location: coq/ directory
• Purpose: Trusted reference compiler with formal correctness proof
• Key Files:
  • ZLang.v: ZLang syntax and operational semantics
  • APPC_ISA.v: Assembly language definition and execution semantics
  • Compiler.v: Compilation algorithm with correctness theorem
• Theorem: ∀ S, s, s'. eval_zlang(S, s, s') → exec_appc(compile(S), s) = s'

Technique 2: Verified Validator (Coq + Rust)

• Location: coq/Validator.v + rust/ directory
• Purpose: Validate untrusted compiler output against trusted specification
• Process:
  1. Untrusted Rust compiler produces assembly code
  2. Coq validator performs symbolic execution comparison
  3. Validation ensures semantic equivalence
• Theorem: Validate(S, C) = true → S ≡ C

Technique 3: Certificate Checker (Python)

• Location: python/certificate_checker.py
• Purpose: Verify compiler optimizations using certificates
• Features:
  • Constant folding verification
  • Dead code elimination checking
  • Semantic preservation validation
• Certificate: Compiler emits optimization log for independent verification

Usage

Quick Start

./verified_compiler_pipeline.sh
cd verified_compiler/examples
./run_all_techniques.sh

Individual Components

1. Coq Verified Compiler

cd coq/
coq_makefile -f _CoqProject *.v -o Makefile
make

2. Rust Untrusted Compiler

cd rust/
cargo run

3. Python Certificate Checker

python3 python/certificate_checker.py examples/certificate.json

Project Structure

verified_compiler/
├── coq/                    # Technique 1: Verified Compiler
│   ├── ZLang.v            # Source language definition
│   ├── APPC_ISA.v         # Target language definition
│   ├── Compiler.v         # Compilation + correctness proof
│   └── Validator.v        # Technique 2: Validation logic
├── rust/                   # Technique 2: Untrusted Compiler
│   ├── Cargo.toml
│   └── src/main.rs        # Optimizing compiler + certificates
├── python/                 # Technique 3: Certificate Checker
│   └── certificate_checker.py
├── examples/              # Test programs and integration
│   ├── test_program.zlang
│   ├── run_all_techniques.sh
│   ├── compiled.json      # Generated assembly
│   └── certificate.json   # Generated certificates
└── README.md

Verification Guarantees

1. Soundness: Verified compiler preserves program semantics
2. Completeness: Validator catches incorrect transformations
3. Transparency: Certificates enable independent verification
4. Composability: All three techniques work together

Example Verification Flow

1. Input: x = 2 + 3; y = x * 0 + 5
2. Technique 1: Coq proves compilation correctness
3. Technique 2: Rust compiles with optimizations, Coq validates
4. Technique 3: Python verifies optimization certificates
5. Output: Provably correct assembly code

Dependencies

• Coq (8.13+): For formal verification
• Rust (1.60+): For untrusted compiler
• Python (3.8+): For certificate checking
• Standard build tools (make, cargo, etc.)

Academic Context

This implementation demonstrates formal methods in compiler verification:

• Translation Validation: Technique 2 approach
• Proof-Carrying Code: Similar to Technique 3 certificates
• Verified Compilation: Technique 1 foundational approach

The combination provides multiple layers of assurance for compiler correctness.

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Technique from Prof	Key File(s) in the Project	How it Happens in the Pipeline
(a) Compiler Verification	coq/Compiler.v	A trusted ZLang->APPC_ISA compiler is defined and its correctness theorem is stated in Coq. This framework is type-checked when you run make in the coq directory.
(b) Validator Verification	coq/Validator.v & python/certificate_checker.py	Formal: The goal of proving APPC_from_Rust ≡ APPC_from_Coq is stated as a theorem in Validator.v (checked by make). Heuristic/Practical: The Python script executes this comparison by simulating ZLang (A''s semantics) and compiled.json (A) and checking if final states match. This is where your bug was caught.
(c) Certificate-Checker Verification	rust/src/main.rs & python/certificate_checker.py	Rust compiler generates a real certificate (certificate.json). Python script loads and checks the claims within this certificate. This is a complete, dynamic workflow demonstration.

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Check how this is different from my previous approach