This project has been deprecated. You might be interested in its spiritual successor: rustc-builtins.

The stuff in this repository is being upstreamed (or already landed) in rust-lang/rust#35021 as part of our effort of making the std crate easily compilable with Cargo. That PR doesn't include support for Cortex-M targets though. If you need compiler-rt intrinsics for those targets, check out the rustc-builtins project where we are porting compiler-rt intrinsics to Rust. I believe that, at the time of writing this notice, rustc-builtins already supports most of the intrinsics needed by Cortex-M targets.

-- @japaric, 2016-08-23

Build compiler-rt using build.rs but without relying on its CMake build system.

WARNING Barely tested, use this at your own risk!

Rust uses LLVM for code generation and LLVM may sometimes "lower" some Rust code to "intrinsics" which are provided by the limcompiler-rt.a library. For "built-in" targets (the ones in rustc --print target-list) there are official binaries of the libcompiler-rt.a library, but for "custom" targets (the ones that need a .json specification file) one has to manually cross compile the library.

Cross compiling compiler-rt is annoying in the cases where it actually works as it requires cmake and llvm-config to be installed. But for custom targets it usually doesn't work because compiler-rt's CMake build system doesn't work with triples like thumbv7m-none-eabi even though they are valid LLVM targets.

This repository is an experiment about building compiler-rt without using the CMake build system it ships, with the goal of making it easy to cross compile compiler-rt to custom Rust targets. If this experiments succeed, I'll use this crate or the ideas developed here in my Xargo project as it's currently lacking a way to cross compile compiler-rt for custom targets.

• This crate must appear somewhere in your crate dependency graph. (*)
• You do not need to add extern crate compiler_rt anywhere.
• For custom targets, make sure that the no-compiler-rt field is set to false, which is the default. If the field is missing from your specification file, that's OK.
• The linker field must be set to $prefix-gcc or the variables CC_${TARGET//-/_} and AR_${TARGET//-/_} must be set to $prefix-gcc and $prefix-ar respectively. If both are set, the env variables take precedence.

(*) It's unclear to me what happens if two different versions of this crate appear in your dependency graph. Cargo will probably raise an error at link time.

Example for the custom target thumbv7m-none-eabi

$ tail -n2 Cargo.toml
[dependencies.compiler-rt]
git = "https://github.com/japaric/compiler-rt.rs"

# `no-compiler-rt` is not set
$ grep no-compiler-rt cortex-m3.json

$ grep linker cortex-m3.json
    "linker": "arm-none-eabi-gcc"
    
$ cargo build --target cortex-m3
(..)
   Compiling compiler-rt v0.1.0
(..)
   
$ find -name '*.a'
./target/cortex-m3/debug/build/compiler-rt-d33efb9ff92c364e/out/libcompiler-rt.a

• Doesn't work with all the built-in targets. No real blocker for this; it just has to be implemented and tested.
• Requires git to be in your $PATH. This requirement will be lifted in the future.
• Requires a nightly rustc because this crate is no_core, but it may make sense to make this crate no_std to make it usable with other channels.

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.