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Setting up a build machine

Everything here was built on a plain Debian 12 container: 6 cores, 8 GB RAM, 98 GB disk. Nothing about that is special. A VM, a container or a spare laptop all work; 4 GB RAM and 30 GB of free disk are enough. The build takes about seven minutes on six cores.

You do not need a build machine to install a prebuilt kernel. That runs on the KVM itself -- see device-only.md. This page is for changing the kernel.

Packages

sudo apt-get update
sudo apt-get install -y \
    build-essential git bc bison flex libssl-dev rsync unzip ccache \
    device-tree-compiler libncurses-dev python3-dev cpio file wget \
    libelf-dev kmod u-boot-tools pkg-config curl xz-utils
sudo apt-get install -y gcc-aarch64-linux-gnu g++-aarch64-linux-gnu

What the less obvious ones are for:

Package Why
u-boot-tools mkimage, which packs the FIT that goes into the boot partition
device-tree-compiler fdtget, used by build-fit.sh to read the FIT layout
libelf-dev, libssl-dev kernel build dependencies, missing them fails late and confusingly
bison, flex kconfig and the device-tree parser
cpio, kmod, bc, rsync used by the kernel build itself
ccache optional, but a rebuild drops from minutes to seconds
gcc-aarch64-linux-gnu the cross compiler; Debian 12 ships 12.2.0

Optional, only for specific jobs:

sudo apt-get install -y squashfs-tools    # unpacking vendor firmware images
sudo apt-get install -y sshpass           # only if you refuse to use SSH keys

SSH to the device

build-fit.sh, install-kernel.sh and revert-kernel.sh all reach the KVM over SSH and assume key-based login. Set that up once:

ssh-copy-id root@<device-ip>          # default password is 'admin'
ssh root@<device-ip> 'cat /proc/gl-hw-info/model'    # should print rm1pe

Without a key, every step stops to ask for the dropbear password.

ccache

Worth configuring if you expect to build more than once:

ccache --max-size=20G
ccache --set-config=compiler_check=content

compiler_check=content matters here: the default checks the compiler's mtime, which changes on a package upgrade even when the binary does not, throwing away the whole cache for no reason.

Toolchain notes

The vendor firmware was built with ARM GNU Toolchain 10.3-2021.07; we build with Debian's 12.2.0. That difference has caused no problems across every version in this repository. The modules the vendor ships have CONFIG_MODVERSIONS off, so only the vermagic string and the exported symbols have to line up -- not CRCs.

One trap: in a git tree, setlocalversion appends a + to the release string, kernel.release becomes 6.1.141+, and the vendor modules then refuse to load because vermagic no longer matches. Fix it with an empty .scmversion in the source root, as the build instructions do.

Disk
kernel source tree ~1.9 GB
out-of-tree build directory ~1.6 GB
ccache up to whatever you set, 1 GB after a few builds

Versions this was built and tested with

Debian            12.15
gcc               aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0
mkimage           2023.01
dtc               1.6.1
python3           3.11.2 (build machine) / 3.12.5 (device)

Nothing depends on these exact versions. They are recorded so that if a build misbehaves, you can tell whether you are somewhere we have been.

Next

build.md for bringing the tree to 6.1.141 and building it.