# Error code E0093

An unknown intrinsic function was declared.

Erroneous code example:

    #![feature(intrinsics)]
    #![allow(internal_features)]

    extern "rust-intrinsic" {
        fn foo(); // error: unrecognized intrinsic function: `foo`
    }

    fn main() {
        unsafe {
            foo();
        }
    }

Please check you didn't make a mistake in the function's name. All intrinsic functions are defined in `compiler/rustc_codegen_llvm/src/intrinsic.rs` and in `library/core/src/intrinsics.rs` in the Rust source code. Example:

    #![feature(intrinsics)]
    #![allow(internal_features)]

    extern "rust-intrinsic" {
        fn atomic_fence_seqcst(); // ok!
    }

    fn main() {
        unsafe {
            atomic_fence_seqcst();
        }
    }