compiler_builtins_lib - The Rust Unstable Book

# `compiler_builtins_lib`

The tracking issue for this feature is: None.

This feature is required to link to the `compiler_builtins` crate which contains "compiler intrinsics". Compiler intrinsics are software implementations of basic operations like multiplication of `u64`s. These intrinsics are only required on platforms where these operations don't directly map to a hardware instruction.

You should never need to explicitly link to the `compiler_builtins` crate when building "std" programs as `compiler_builtins` is already in the dependency graph of `std`. But you may need it when building `no_std` binary crates. If you get a linker error like:

    $PWD/src/main.rs:11: undefined reference to `__aeabi_lmul'
    $PWD/src/main.rs:11: undefined reference to `__aeabi_uldivmod'

That means that you need to link to this crate.

When you link to this crate, make sure it only appears once in your crate dependency graph. Also, it doesn't matter where in the dependency graph you place the `compiler_builtins` crate.

    #![feature(compiler_builtins_lib)]
    #![no_std]

    extern crate compiler_builtins;