Linux Kernel Module Cheat

38.13.1. Linux kernel build variants

If you want to keep two builds around, one for the latest Linux version, and the other for Linux v4.16:

# Build master.
./build-linux

# Build another branch.
git -C "$(./getvar linux_source_dir)" fetch --tags --unshallow
git -C "$(./getvar linux_source_dir)" checkout v4.16
./build-linux --linux-build-id v4.16

# Restore master.
git -C "$(./getvar linux_source_dir)" checkout -

# Run master.
./run

# Run another branch.
./run --linux-build-id v4.16

The git fetch --unshallow is needed the first time because ./build --download-dependencies only does a shallow clone of the Linux kernel to save space and time, see also: https://stackoverflow.com/questions/6802145/how-to-convert-a-git-shallow-clone-to-a-full-clone

The --linux-build-id option should be passed to all scripts that support it, much like --arch for the CPU architecture, e.g. to step debug:

./run-gdb --linux-build-id v4.16

To run both kernels simultaneously, one on each QEMU instance, see: Section 38.12, “Simultaneous runs”.