Bazel C/C++ cross-compile example: RISC-V bare metal

This repository illustrates how to cross-compile C/C++ programs with Bazel through the toolchain and platforms mechanism. The concrete example used is building for bare metal RISC-V machine.

This repo is meant to accompany the article at http://popovicu.com/posts/cross-compiling-c-with-bazel

Hermeticity

The rules are not fully hermetic and they assume that your GCC tools for RISC-V are at /usr/bin/riscv64-linux-gnu-.... If the path prefix is something different on your system, make the relevant change in toolchain/rv64_bare_metal_toolchain.bzl file. This path is hardcoded for simplicity.

Building

To build, run the following command:

bazel build -s --platforms=//platform:riscv64_bare_metal //program

The -s flag ensures that you see the individual steps of the build (you may need to bazel clean first if there is some existing cache, so you can see the whole build from scratch).

Running on QEMU

Once built, the ELF file can be run on QEMU:

qemu-system-riscv64 -machine virt -bios bazel-bin/program/program -nographic

Output:

Hello world! Writing to UART from bare metal.