How to build a Rust app free of shared libraries?

Question

How does one compile a Rust application without having to load shared libraries at all?

What have I tried:

ex.rs

fn main() {
  println!("Try to compile me statically!");
}

According to https://rust-lang.github.io/rfcs/1721-crt-static.html I performed the following:

$ rustc -C target-feature=+crt-static ./ex.rs
$ ldd ./ex
    linux-vdso.so.1 (0x00007ffc4e3ef000)
    libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fc30b8c4000)
    librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007fc30b6bc000)
    libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fc30b49d000)
    libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007fc30b285000)
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fc30ae94000)
    /lib64/ld-linux-x86-64.so.2 (0x00007fc30bcfb000)

Why isn't libc compiled statically? And how to get rid of linking all other shared libraries?

Answer 1

MUSL support for fully static binaries:
By default, Rust will statically link all Rust code. However, if you use the standard library, it will dynamically link to the system's libc implementation.

If you'd like a 100% static binary, the MUSL libc can be used on Linux:

rustup target add x86_64-unknown-linux-musl 

RUSTFLAGS='-C link-arg=-s' cargo build --release --target x86_64-unknown-linux-musl

main.rs file:

use actix_web::{web, App, HttpServer, Responder};

async fn index(info: web::Path<(String, u32)>) -> impl Responder {
    format!("Hello {}! id:{}", info.0, info.1)
}

#[actix_rt::main]
async fn main() -> std::io::Result<()> {
    HttpServer::new(|| App::new().service(web::resource("/{name}/{id}/index.html").to(index)))
        .bind("127.0.0.1:8080")?
        .run()
        .await
}

Cargo.toml file:

[profile.release]
opt-level = 's'  # Optimize for size.
lto = true # Link Time Optimization (LTO)
# codegen-units = 1 # Set this to 1 to allow for maximum size reduction optimizations:
# panic = 'abort' # removes the need for this extra unwinding code.

[dependencies]
actix-web = "2.0.0" # Actix web is a simple, pragmatic and extremely fast web framework for Rust.
actix-rt = "1.0.0"  # Actix runtime

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