Occasionally, I will forget to link something from the mailing list in this post. To see my full mailing list activity (patches, reviews, and reports), you can view it on lore.kernel.org.

Linux kernel patches

  • Build errors: These are patches to fix various build errors that I found through testing different configurations with LLVM or were exposed by our continuous integration setup. The kernel needs to build in order to be run :)

    • riscv: Move alternative length validation into subsection (v1)
    • riscv: Fix ALT_THEAD_PMA's asm parameters (v1)
    • ath6kl: Use cc-disable-warning to disable -Wdangling-pointer (v1)

  • Feature work: These patches focus on getting things that don’t currently work or happen but should. In this case, this series enables linking the PowerPC vDSO with ld.lld, which is necessary to avoid cryptic build failures when using Link Time Optimization (LTO), which is currently a work in progress.

    • Link the PowerPC vDSO with ld.lld (v1, v2)

  • Miscellaneous fixes: These are fixes that don’t fit into a particular category but are important to ClangBuiltLinux. In this case, this patch fixes a Control Flow Integrity (CFI) violation in the i915 driver, which I found while testing kCFI, a new CFI scheme specifically for the Linux kernel being developed in Clang/LLVM.

    • drm/i915: Fix CFI violation with show_dynamic_id() (v1)

  • Stable backports: These are patches It is important to make sure that the stable trees are as free from issues as possible, as those are the trees that devices and users use; for example, Android and Chrome OS regularly merge from stable, so if there is a problem that will impact those trees that we fixed in mainline, it should be backported.

  • Warning fixes: These are patches to fix various warnings that appear with LLVM. I used to go into detail about the different warnings and what they mean, but the important takeaway for this section is that the kernel should build warning free, as all developers should be using CONFIG_WERROR, which will turn these all into failures. Maybe these should be in the build failures section…

    • i2c: at91: Initialize dma_buf in at91_twi_xfer() (v1)
    • nvme: Ensure ret is always initialized in nvme_ns_head_chr_uring_cmd() (v1)
    • misc: rtsx: Fix clang -Wsometimes-uninitialized in rts5261_init_from_hw() (v1)
    • mailbox: qcom-ipcc: Fix -Wunused-function with CONFIG_PM_SLEEP=n (v1)

Patch review and input

For the next sections, I link directly to my first response in the thread when possible but there are times where the link is to the main post. My responses can be seen inline by going to the bottom of the thread and clicking on my name.

Reviewing patches that are submitted is incredibly important, as it helps ensure good code quality due to catching mistakes before the patches get accepted and it can help get patches accepted faster, as some maintainers will blindly pick up patches that have been reviewed by someone that they trust.

Issue triage and reporting

The unfortunate thing about working at the intersection of two projects is we will often find bugs that are not strictly related to the project, which require some triage and reporting back to the original author of the breakage so that they can be fixed and not impact our own testing. Some of these bugs fall into that category while others are issues strictly related to this project.

Tooling improvements

These are changes to various tools that we use, such as our continuous integration setup, booting utilities, toolchain building scripts, or other closely related projects such as AOSP’s distribution of LLVM and TuxMake.

Behind the scenes

  • Every day that there is a new linux-next release, I rebase and build a few different kernel trees then boot and runtime test them on several different machines, including a Windows Subsystem for Linux instance, a Raspberry Pi 3 and 4, an Intel-based desktop, an AMD-based desktop, and an Intel-based laptop. This is not always visible because I do not report anything unless there is something broken but it can take up to a few hours each day, depending on the amount of churn and issues uncovered.

  • I wrote a blog post as part of my work to get our llvm-project container builds self-hosted on GitHub Actions.

Special thanks to: