Unsafe Rust Checker
When Unsafe is Valid
| Use Case | Example |
|---|
| FFI | Calling C functions |
| Low-level abstractions | Implementing Vec, Arc |
| Performance | Measured bottleneck with safe alternative too slow |
NOT valid: Escaping borrow checker without understanding why.
Required Documentation
// SAFETY: <why this is safe>
unsafe { ... }
/// # Safety
/// <caller requirements>
pub unsafe fn dangerous() { ... }
Quick Reference
| Operation | Safety Requirements |
|---|
*ptr deref | Valid, aligned, initialized |
&*ptr | + No aliasing violations |
transmute | Same size, valid bit pattern |
extern "C" | Correct signature, ABI |
static mut | Synchronization guaranteed |
impl Send/Sync | Actually thread-safe |
Common Errors
| Error | Fix |
|---|
| Null pointer deref | Check for null before deref |
| Use after free | Ensure lifetime validity |
| Data race | Add proper synchronization |
| Alignment violation | Use #[repr(C)], check alignment |
| Invalid bit pattern | Use MaybeUninit |
| Missing SAFETY comment | Add // SAFETY: |
Deprecated → Better
| Deprecated | Use Instead |
|---|
mem::uninitialized() | MaybeUninit<T> |
mem::zeroed() for refs | MaybeUninit<T> |
| Raw pointer arithmetic | NonNull<T>, ptr::add |
CString::new().unwrap().as_ptr() | Store CString first |
static mut | AtomicT or Mutex |
| Manual extern | bindgen |
FFI Crates
| Direction | Crate |
|---|
| C → Rust | bindgen |
| Rust → C | cbindgen |
| Python | PyO3 |
| Node.js | napi-rs |
Claude knows unsafe Rust. Focus on SAFETY comments and soundness.
