Build the kernel without Yocto

The standalone workflow lets you compile, test, and deploy kernel changes without building the full Yocto image. All required cross-compilation and image-packaging tools are bundled in the kmake-image Docker container.

Limitations and caveats

The standalone workflow builds and packages the kernel and modules only. It does not produce a root file system. To build or modify out-of-tree kernel modules that depend on the full Yocto BSP, use the Yocto-based workflow instead.

Toolchain: the kmake-image Docker image provides an aarch64 cross-toolchain, systemd ukify, and image-packaging scripts. No host toolchain installation is needed.
DTB packaging: when building standalone, you must package the DTB manually using a static ITS configuration from the qcom-dtb-metadata repository. The Yocto build handles this automatically via meta-qcom.
Source revision: to match the exact source used in a release build, check the SRCREV field in meta-qcom/recipes-kernel/linux/linux-qcom_6.18.bb.

Access kernel sources

Clone the kernel repository directly:

git clone --branch qcom-6.18.y \
    https://github.com/qualcomm-linux/kernel.git kernel

Table: Kernel branches

Branch	Use case
`qcom-6.18.y`	LTS production builds; recommended for SoC bring-up and integration
`qcom-next`	Upstream contribution and validation against the latest kernel

Set up the Docker toolchain

Clone and build the kmake-image container:

git clone https://github.com/qualcomm-linux/kmake-image.git
cd kmake-image
docker build --build-arg USER_ID=$(id -u) \
             --build-arg GROUP_ID=$(id -g) \
             --build-arg USER_NAME=$(whoami) \
             -t kmake-image .
cd ..

Set up shell aliases for convenience. Add these to your shell profile to persist across sessions:

alias kmake-image-run='docker run -it --rm \
  --user $(id -u):$(id -g) \
  --workdir="$PWD" \
  -v "$(dirname $PWD)":"$(dirname $PWD)" \
  kmake-image'
alias kmake='kmake-image-run make'

Gather build artifacts

Create an artifacts/ directory to hold the ramdisk, boot binaries, and DTB metadata required to assemble the final images:

mkdir artifacts

Get the initramfs ramdisk

wget -O artifacts/ramdisk.gz \
    http://storage.kernelci.org/images/rootfs/buildroot/buildroot-baseline/20230703.0/arm64/rootfs.cpio.gz

Get systemd-boot binaries

wget -O artifacts/systemd-boot-efi.deb \
    http://ports.ubuntu.com/pool/universe/s/systemd/systemd-boot-efi_255.4-1ubuntu8_arm64.deb
dpkg-deb -xv artifacts/systemd-boot-efi.deb artifacts/systemd

Get DTB metadata When building standalone, DTBs must be packaged manually using a static ITS configuration. Clone the qcom-dtb-metadata repository to get the required qcom-metadata.dts and qcom-next-fitimage.its files:

git clone https://github.com/qualcomm-linux/qcom-dtb-metadata.git \
    artifacts/qcom-dtb-metadata

Build the kernel and modules

Configure and build the kernel using the standard Qualcomm^® configuration fragments, then install modules into a staging directory:

cd kernel
mkdir -p ../kobj

env -u KCONFIG_CONFIG ./scripts/kconfig/merge_config.sh -m -O ../kobj \
    arch/arm64/configs/defconfig \
    arch/arm64/configs/prune.config \
    arch/arm64/configs/qcom.config

kmake O=../kobj olddefconfig
kmake O=../kobj -j$(nproc)
kmake O=../kobj -j$(nproc) dir-pkg INSTALL_MOD_STRIP=1

Package the built kernel modules (DLKMs) into the ramdisk:

(cd ../kobj/tar-install ; \
 find lib/modules | cpio -o -H newc -R +0:+0 | gzip -9 >> ../../artifacts/ramdisk.gz)

Package the boot images

Generate efi.bin (ESP partition) The efi.bin image contains systemd-boot, the kernel (packaged as a UKI type-2 image), and the initramfs:

cd ..
# Default command line matches the Yocto UKI_CMDLINE from esp-qcom-image.bb.
# Override CMDLINE if your rootfs partition label or console differs.
CMDLINE="root=PARTLABEL=rootfs rw rootwait console=ttyMSM0,115200"
kmake-image-run generate_boot_bins.sh efi \
    --ramdisk artifacts/ramdisk.gz \
    --systemd-boot artifacts/systemd/usr/lib/systemd/boot/efi/systemd-bootaa64.efi \
    --stub artifacts/systemd/usr/lib/systemd/boot/efi/linuxaa64.efi.stub \
    --linux kobj/arch/arm64/boot/Image \
    --cmdline "${CMDLINE}" \
    --output images

Generate dtb.bin (DTB partition) Build a FIT-based dtb.bin for all targets that support device tree:

kmake-image-run make_fitimage.sh \
    --metadata artifacts/qcom-dtb-metadata/qcom-metadata.dts \
    --its artifacts/qcom-dtb-metadata/qcom-next-fitimage.its \
    --kobj kobj \
    --output images

Both efi.bin and dtb.bin are placed in the images/ directory and are ready to flash.

Kernel Image Build Script

Above build and package steps are wrapped under a build.sh script which is part of docker, to automate building and packaging a bootable kernel image into efi.bin, dtb.bin, and boot.img. To use this alternative build.sh script run following:

kmake-image-run build.sh --dtb qcs6490-rb3gen2.dtb \
        --out kobj \
        --systemd artifacts/systemd/usr/lib/systemd/boot/efi \
        --ramdisk artifacts/ramdisk.gz \
        --images images \
        --cmdline "${CMDLINE}"

The —dtb argument is mandatory. It specifies the Device Tree Blob to be packed into the kernel image. Above command shows using qcs6490-rb3gen2.dtb as an example.
Initialize CMDLINE to set your kernel cmdline parameter else a default generic is used.

Flash and boot

Put the device into fastboot mode, then flash both images:

fastboot flash efi images/efi.bin
fastboot flash dtb_a images/dtb.bin
fastboot reboot

After the device reboots, verify the running kernel version as described in Install & boot the kernel.

Introduction

Architecture

Key Documents

Technologies

System

Release Notes

Limitations and caveats

Access kernel sources

Set up the Docker toolchain

Gather build artifacts

Build the kernel and modules

Package the boot images

Kernel Image Build Script

Flash and boot

Introduction

Architecture

Key Documents

Technologies

System

Release Notes

​Limitations and caveats

​Access kernel sources

​Set up the Docker toolchain

​Gather build artifacts

​Build the kernel and modules

​Package the boot images

​Kernel Image Build Script

​Flash and boot

Limitations and caveats

Access kernel sources

Set up the Docker toolchain

Gather build artifacts

Build the kernel and modules

Package the boot images

Kernel Image Build Script

Flash and boot