Compiler Repository Toolkit

The Compiler Repository Toolkit is a set of bazel rules meant to make building a C/C++ toolchain easier.

This was inspired by bazel-embedded; I hope I've managed to improve things.

Features

• Simplified toolchain setup.
• A bazel-ish approach to compiler features and flags.
• More concise target device configuration.
• Emulator configuration for executing target code

Simplified toolchain setup

Each of the toolchains is configured in //toolchains/... by two files.

• repository.bzl describes the path or URL to the compiler archive.
• BUILD.bzl initializes the toolchains for each target device. Most of the configuration comes from the individual device configurations (more on that later). The other elemets of the BUILD.bazel file describe the files which make up the compiler and the various include paths needed by the compiler.

A bazel-ish approach to compiler features and flags

Compiler featurs and flags are defined by a feature_set which aggregates compiler flags for activating different features, such as optimization modes or warning levels. The feature_set aggregates a collection of feature rules together and provides a facility for supplying substitutions to those flags so that minor variations in configuration don't require an entire new configuration. Feature sets may be chained together; features supplied later in the chain override features earlier in the chain. Substitutions may be supplied at any point in the feature_set chain or by the device configuration.

More concise target device configuration

Target devices are defined in //platforms/<arch>/devices.bzl. Each device configuration creates a device struct containing the architecture, constraints, feature set and substitutions to supply to the feature set.

Each target device should correspond to a bazel platform definition. Bazel will use the platform constraints to select the toolchain for the device with the same constraints.

Emulator configuration for target code

In addition to defining the toolchains, crt also defines an exec_config that can be used to execute target code under a system emulator. Sample configurtions using qemu are supplied.

How to use

In your WORKSPACE file, add:

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
http_archive(
    name = "crt",
    url = "https://github.com/cfrantz/crt/archive/refs/tags/v0.3.0.tar.gz",
    sha256 = "...",
    strip_prefix = "crt-0.3.0",
)

load("@crt//:repos.bzl", "crt_repos")
crt_repos()
load("@crt//:deps.bzl", "crt_deps")
crt_deps()

load("@crt//config:registration.bzl", "crt_register_toolchains")
crt_register_toolchains(
    arm = True,     # Pick the toolchains you want.
    m6502 = True,
    riscv32 = True,
    win64 = True,
)

Releasing CRT

To perform a release of CRT:

The release process assumes you have your git and GitHub CLI credentials in $HOME/.git and $HOME/.config/gh repsectively.

1. Commit your changes.
2. Create a tag locally, but don't push it to your remote.
3. Run the util/release_in_container.sh script. This script executes bazel run :release inside of an ubuntu-20.04 container.