Add Miri testing for unsafe code validation

[RAprogramm]

Add Miri testing to validate all unsafe code for undefined behavior.

Objectives

• Add Miri for unsafe code validation
• Test all unsafe blocks and FFI operations
• Detect undefined behavior at compile time
• Integrate Miri into CI pipeline

What is Miri?

Miri is Rust's interpreter for detecting undefined behavior in unsafe code:

• Detects invalid memory access
• Validates pointer aliasing rules
• Checks for data races
• Verifies unsafe code soundness
• Catches UB that tests might miss

Why Critical for cstring-array?

Our library contains unsafe code in:

1. src/array.rs:84 - Pointer operations in pointer array construction
2. src/array.rs:162-163 - Raw pointer dereferencing in as_ptr
3. src/array.rs:187-189 - Mutable pointer operations
4. tests/integration.rs - Extensive unsafe FFI testing
5. Send/Sync implementations - Need validation

Unsafe Code Locations

// src/array.rs:84
pointers.extend(cstrings.iter().map(|s| s.as_ptr()));

// tests/integration.rs:31
unsafe {
    assert\!(\!(*argv).is_null());
    *argv
}

// tests/integration.rs:92
unsafe {
    let s = CStr::from_ptr(*current).to_str().unwrap();
    current = current.offset(1);
}

Implementation Plan

1. Add Miri to CI workflow

Create .github/workflows/miri.yml:

name: Miri

on:
  push:
    branches: [main]
  pull_request:
    branches: [main]
  schedule:
    - cron: '0 3 * * 1'

permissions:
  contents: read

jobs:
  miri:
    name: Miri
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      
      - name: Install Rust nightly with Miri
        uses: dtolnay/rust-toolchain@nightly
        with:
          components: miri
      
      - name: Setup Rust cache
        uses: Swatinem/rust-cache@v2
        with:
          key: miri
      
      - name: Run Miri tests
        run: |
          cargo miri setup
          cargo miri test --all-features
        env:
          MIRIFLAGS: -Zmiri-symbolic-alignment-check -Zmiri-disable-isolation

2. Add Miri-specific test configuration

Update Cargo.toml:

[target.'cfg(miri)'.dev-dependencies]
# Miri-specific test dependencies if needed

3. Fix potential Miri issues

Common issues Miri might find:

• Invalid pointer arithmetic
• Unaligned memory access
• Data races in Send/Sync
• Use-after-free
• Reading uninitialized memory

4. Add Miri documentation

Create docs section explaining:

• How to run Miri locally: cargo +nightly miri test
• What Miri validates
• How to interpret Miri errors

Expected Miri Checks

Miri will validate:

1. Pointer validity

   • All pointers are properly aligned
   • No use-after-free
   • Valid pointer arithmetic

2. Aliasing rules

   • Mutable references don't alias
   • Shared references are valid
   • Raw pointer usage is sound

3. Memory initialization

   • All memory reads are from initialized locations
   • No reading of padding bytes

4. Send/Sync safety

   • Concurrent access is safe
   • No hidden data races

Benefits

• Soundness: Prove unsafe code is correct
• UB Detection: Find undefined behavior before production
• Confidence: Mathematical proof of memory safety
• Professional: Industry-standard validation
• FFI Safety: Critical for C interop
• Documentation: Shows code is thoroughly validated

Success Criteria

• All tests pass under Miri
• CI runs Miri on every PR
• Weekly scheduled Miri runs
• Documentation includes Miri instructions
• Zero Miri warnings or errors
• REUSE 3.3 compliant

Common Miri Flags

# Standard validation
cargo +nightly miri test

# With extra checks
MIRIFLAGS="-Zmiri-symbolic-alignment-check" cargo +nightly miri test

# Disable isolation for system interactions
MIRIFLAGS="-Zmiri-disable-isolation" cargo +nightly miri test

# Track raw pointers
MIRIFLAGS="-Zmiri-track-raw-pointers" cargo +nightly miri test

References

• Miri Documentation: https://github.com/rust-lang/miri
• Rust Unsafe Code Guidelines: https://rust-lang.github.io/unsafe-code-guidelines/
• Miri in CI: https://github.com/rust-lang/miri#using-miri-on-ci