gecko-dev/third_party/rust/gcc/README.md

gcc-rs

A library to compile C/C++ code into a Rust library/application.

Documentation

A simple library meant to be used as a build dependency with Cargo packages in order to build a set of C/C++ files into a static archive. Note that while this crate is called "gcc", it actually calls out to the most relevant compile for a platform, for example using cl on MSVC. That is, this crate does indeed work on MSVC!

Using gcc-rs

First, you'll want to both add a build script for your crate (build.rs) and also add this crate to your Cargo.toml via:

[package]
# ...
build = "build.rs"

[build-dependencies]
gcc = "0.3"

Next up, you'll want to write a build script like so:

// build.rs

extern crate gcc;

fn main() {
    gcc::Build::new()
        .file("foo.c")
        .file("bar.c")
        .compile("foo");
}

And that's it! Running cargo build should take care of the rest and your Rust application will now have the C files foo.c and bar.c compiled into a file named libfoo.a. You can call the functions in Rust by declaring functions in your Rust code like so:

extern {
    fn foo_function();
    fn bar_function();
}

pub fn call() {
    unsafe {
        foo_function();
        bar_function();
    }
}

fn main() {
    // ...
}

External configuration via environment variables

To control the programs and flags used for building, the builder can set a number of different environment variables.

• CFLAGS - a series of space separated flags passed to "gcc". Note that individual flags cannot currently contain spaces, so doing something like: "-L=foo\ bar" is not possible.
• CC - the actual C compiler used. Note that this is used as an exact executable name, so (for example) no extra flags can be passed inside this variable, and the builder must ensure that there aren't any trailing spaces. This compiler must understand the -c flag. For certain TARGETs, it also is assumed to know about other flags (most common is -fPIC).
• AR - the ar (archiver) executable to use to build the static library.

Each of these variables can also be supplied with certain prefixes and suffixes, in the following prioritized order:

1. <var>_<target> - for example, CC_x86_64-unknown-linux-gnu
2. <var>_<target_with_underscores> - for example, CC_x86_64_unknown_linux_gnu
3. <build-kind>_<var> - for example, HOST_CC or TARGET_CFLAGS
4. <var> - a plain CC, AR as above.

If none of these variables exist, gcc-rs uses built-in defaults

In addition to the the above optional environment variables, gcc-rs has some functions with hard requirements on some variables supplied by cargo's build-script driver that it has the TARGET, OUT_DIR, OPT_LEVEL, and HOST variables.

Optional features

Currently gcc-rs supports parallel compilation (think make -jN) but this feature is turned off by default. To enable gcc-rs to compile C/C++ in parallel, you can change your dependency to:

[build-dependencies]
gcc = { version = "0.3", features = ["parallel"] }

By default gcc-rs will limit parallelism to $NUM_JOBS, or if not present it will limit it to the number of cpus on the machine. If you are using cargo, use -jN option of build, test and run commands as $NUM_JOBS is supplied by cargo.

Compile-time Requirements

To work properly this crate needs access to a C compiler when the build script is being run. This crate does not ship a C compiler with it. The compiler required varies per platform, but there are three broad categories:

• Unix platforms require cc to be the C compiler. This can be found by installing gcc/clang on Linux distributions and Xcode on OSX, for example.
• Windows platforms targeting MSVC (e.g. your target triple ends in -msvc) require cl.exe to be available and in PATH. This is typically found in standard Visual Studio installations and the PATH can be set up by running the appropriate developer tools shell.
• Windows platforms targeting MinGW (e.g. your target triple ends in -gnu) require gcc to be available in PATH. We recommend the MinGW-w64 distribution, which is using the Win-builds installation system. You may also acquire it via MSYS2, as explained here. Make sure to install the appropriate architecture corresponding to your installation of rustc. GCC from older MinGW project is compatible only with 32-bit rust compiler.

C++ support

gcc-rs supports C++ libraries compilation by using the cpp method on Build:

extern crate gcc;

fn main() {
    gcc::Build::new()
        .cpp(true) // Switch to C++ library compilation.
        .file("foo.cpp")
        .compile("libfoo.a");
}

When using C++ library compilation switch, the CXX and CXXFLAGS env variables are used instead of CC and CFLAGS and the C++ standard library is linked to the crate target.

License

gcc-rs is primarily distributed under the terms of both the MIT license and the Apache License (Version 2.0), with portions covered by various BSD-like licenses.

See LICENSE-APACHE, and LICENSE-MIT for details.