fc-kernels

Overview

This project builds custom Linux kernels for Firecracker microVMs from the same kernel sources as the official Firecracker repo, using the configuration files (and optional patches) that live in this repo.

Prerequisites

• Linux environment (for building kernels)

Building locally

1. Configure kernel versions:

   • Edit kernel_versions.txt to specify which kernel versions to build (one per line, e.g. 6.1.158).
   • Place the corresponding config(s) in configs/x86_64/<version>.config and configs/arm64/<version>.config.
   • (Optional) Drop *.patch files into patches/<version>/ to apply on top of the upstream tree before build.

2. Build:

   make build              # builds all versions in kernel_versions.txt for x86_64
   make build-arm64        # same, for arm64
   ./build.sh 6.1.158      # build a single version (x86_64)
   ./build.sh 6.1.158 arm64

   Output: builds/vmlinux-<version>/<arch>/vmlinux.bin where <arch> is amd64 or arm64 (Go/OCI convention). For x86_64 a legacy copy is also placed at builds/vmlinux-<version>/vmlinux.bin.

CI / Releasing

The Build & Release workflow runs in two modes:

• On every pull request: builds every (kernel version × arch) combination from kernel_versions.txt in parallel (one runner per pair) and uploads the binaries as workflow artifacts (downloadable from the PR's checks tab) so reviewers can inspect them. No release or GCS upload happens.
• Manually (workflow_dispatch): pick the branch in the GitHub UI and run. It does the same build as a PR and additionally creates a GitHub release tagged YYYY.MM.DD (with a .N suffix for additional runs the same day) containing every binary, and uploads them to GCS.

Release asset naming for that commit:

vmlinux-<version>-amd64.bin
vmlinux-<version>-arm64.bin
vmlinux-<version>.bin           # legacy (= amd64) for backwards compat

4. The same binaries are uploaded to GCS at gs://$GCP_BUCKET_NAME/kernels/vmlinux-<version>/<arch>/vmlinux.bin.

New kernel in E2B's infra

Note: these steps should give you a new kernel on your self-hosted E2B using https://github.com/e2b-dev/infra

• Run the release workflow on the branch with the new config/patch.
• Update DefaultKernelVersion in packages/api/internal/cfg/model.go if you changed the kernel version.
• Build and deploy api.

Architecture naming

Output directories use Go's runtime.GOARCH convention (amd64, arm64) so they match the infra orchestrator's TargetArch() path resolution. The build-time variable TARGET_ARCH (x86_64, arm64) is only used internally for config paths and cross-compilation flags.

License

This project is licensed under the Apache License 2.0. See LICENSE for details.