Kernel#

Three tasks configure, build and clean a Linux tree with make. The tree is yours. They change no file it tracks, and write only in its build/.

host#
$ tasks/kernel/kconfig --directory ~/linux --target tinyconfig
$ tasks/kernel/build --directory ~/linux
$ tasks/kernel/mrproper --directory ~/linux

kconfig makes build/.config with one of make’s configuration targets, such as tinyconfig or defconfig. build builds what that .config says, with a job for each processor. mrproper removes what kbuild made in build/, the .config with it.

Requirements#

The tasks run make with GCC; the second line of each list is for Clang, under LLVM=1 (Requirements):

$ sudo apt install build-essential bc bison flex libelf-dev libssl-dev
$ sudo apt install clang lld llvm

$ sudo dnf install gcc make perl bc bison flex elfutils-libelf-devel \
    openssl-devel
$ sudo dnf install clang lld llvm

Clang is in universe:

$ sudo apt install build-essential bc bison flex libelf-dev libssl-dev
$ sudo add-apt-repository universe
$ sudo apt install clang lld llvm

The build directory#

kbuild keeps what it makes in build/ of the tree, its O=, apart from the sources.

A tree has one build. kbuild can keep several beside one tree, and the tasks do not: give each build a tree of its own, as git worktree adds one. systemd refuses a task a second run on a tree while the first lasts.

kbuild refuses to build apart from a tree that was built in place, and the mrproper task cleans build/ only. Clean such a tree yourself, with make mrproper in it: that removes your own .config, which no task should do for you.

The architecture and the compiler#

ARCH and LLVM come from the environment, and the log shows each one that is set:

$ LLVM=1 tasks/kernel/build --directory ~/linux
$ systemd-run --user --unit=kernel-build@… … --setenv=LLVM=1 … make O=build --jobs=16

The unit#

Each task runs make in a unit named for the task and the tree: kernel-build@home-user-linux.service builds /home/user/linux (The unit a task runs in). In the tree the unit may write build/ only. The three tasks take make’s line and kbuild’s variables from tasks/common/kbuild.