Unsafe is sometimes necessary

The Rust compiler can only enforce its rules for code that it has compiled.

fn main() {
    let pid = unsafe { libc::getpid() };
    println!("{pid}");
}

“There are some activities that require unsafe.

“The Rust compiler cannot verify that external functions comply with Rust’s memory guarantees. Therefore, invoking external functions requires an unsafe block.”

Optional:

“Working with the external environment often involves sharing memory. The interface that computers provide is a memory address (a pointer).”

“Here’s an example that asks the Linux kernel to write to memory that we control:

fn main() {
    let mut buf = [0u8; 8];
    let ptr = buf.as_mut_ptr() as *mut libc::c_void;

    let status = unsafe { libc::getrandom(ptr, buf.len(), 0) };
    if status > 0 {
        println!("{buf:?}");
    }
}

“This FFI call reaches into the operating system to fill our buffer (buf). As well as calling an external function, we must mark the boundary as unsafe because the compiler cannot verify how the OS touches that memory.”

Comprehensive Rust 🦀

Unsafe is sometimes necessary