Updates in April 2019

Lot’s of things changed in the Writing an OS in Rust series in the past month, both on the blog itself and in the tools behind the scenes. This post gives an overview of the most important updates.

This post is an experiment inspired by This Week in Rust and similar series. The goal is to provide a resource that allows following the project more closely and staying up-to-date with the changes in the tools/libraries behind the scenes. If enough people find this useful, I will try to turn this in a semi-regular series.

Bootloader

• The build system of the bootloader was rewritten to do a proper linking instead of appending the kernel executable manually like before. The relevant pull requests are Rewrite build system and Updates for new build system. These (breaking) changes were released as version 0.5.0 (changelog).
• To make the bootloader work with future versions of bootimage, a package.metadata.bootloader.target key was added to the Cargo.toml of the bootloader. This key specifies the name of the target JSON file, so that bootimage knows which --target argument to pass. This change was released as version 0.5.1 (changelog)
• In the Version 0.6.0 pull request, the #[cfg(not(test))] attribute was removed from the entry_point macro. This makes it possible to use the macro together with cargo xtest and a custom test framework. Since the change is breaking, it was released as version 0.6.0 (changelog).

Bootimage

• The Rewrite bootimage for new bootloader build system pull request completely revamped the implementation of the crate. This was released as version 0.7.0. See the changelog for a list of changes.
  • The rewrite had the unintended side-effect that bootimage run no longer ignored executables named test-*, so that an additional --bin argument was required for specifying which executable to run. To avoid breaking users of bootimage test, we yanked version 0.7.0. After fixing the issue, version 0.7.1 was released (changelog).
• The New features for bootimage runner pull request added support for additional arguments and various functionality for supporting cargo xtest. The changes were released as version 0.7.2 (changelog).
• An argument parsing bug that broke the new cargo bootimage subcommand on Windows was fixed. The fix was released as version 0.7.3.

Blog OS

• Performed an Update to new bootloader 0.5.1 and bootimage 0.7.2. Apart from requiring the llvm-tools-preview rustup component, this only changes version numbers.
• The Rewrite the linking section of “A Freestanding Rust Binary” pull request updated the first post to compile for the bare-metal thumbv7em-none-eabihf target instead of adding linker arguments for Linux/Windows/macOS.
• Since the blog came close to the free bandwidth limit of Netlify, we needed to Migrate from Netlify to Github Pages to avoid additional fees.
• With the Minimal Rust Kernel: Use a runner to make cargo xrun work pull request, we integrated the new bootimage runner into the blog.
  • The required updates to the post-02 and post-03 branches were performed in the Add .cargo/config file to post-02 branch and Merge the changes from #585 into the post-03 branch pull requests.
• In the New testing post pull request, we replaced the previous Unit Testing and Integration Tests with the new Testing post, which uses cargo xtest and a custom test framework for running tests.
  • The required updates for the post-04 branch were performed in the Implement code for new testing post in post-xx branches pull request. The updates for the other post-* branches were pushed manually to avoid spamming the repository with pull requests. You can find a list of the commits in the pull request description.
• The Avoid generic impl trait parameters in BootInfoFrameAllocator pull request made the BootInfoFrameAllocator non-generic by reconstructing the frame iterator on every allocation. This way, we avoid using a impl Trait type parameter, which makes it impossible to store the type in a static. See rust-lang/rust#60367 for the fundamental problem.