Buildroot Development Environment

August 7, 2024 - 2 mins read

Here are a few Buildroot tricks I use to develop and test my packages. This post will likely evolve over the years to come.

For the basics, please see my post Buildroot Development Checklist. It covers how to use the check-package and test-pkg tools shipped with Buildroot.

Tip: if stuck, always check the Buildroot documentation!

introduction

I often need to rebuild from scratch to verify fundamental changes to the structure of my embedded systems. So I don’t have the patience to wait for big chunks of code to be downloaded and rebuilt from scratch every time. Buildroot has two great options for this:

BR2_DL_DIR="$(TOPDIR)/dl"

and

BR2_CCACHE=y
BR2_CCACHE_DIR="$(TOPDIR)/.ccache"

The former is the default while the latter is not.

defconfig

Alright, the base configuration I use to test my packages in Qemu is called configs/troglobit_qemu_x86_64_defconfig:

BR2_x86_64=y
BR2_TOOLCHAIN_EXTERNAL=y
BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_X86_64_UCLIBC_BLEEDING_EDGE=y
BR2_CCACHE=y
BR2_CCACHE_DIR="$(TOPDIR)/.ccache"
BR2_TARGET_GENERIC_ISSUE="Buildroot Testing Ground"
BR2_ROOTFS_DEVICE_CREATION_STATIC=y
BR2_SYSTEM_DHCP="eth0"
BR2_TARGET_TZ_INFO=y
BR2_ROOTFS_POST_BUILD_SCRIPT="board/qemu/x86_64/post-build.sh"
BR2_ROOTFS_POST_IMAGE_SCRIPT="board/qemu/post-image.sh"
BR2_ROOTFS_POST_SCRIPT_ARGS="$(BR2_DEFCONFIG)"
BR2_LINUX_KERNEL=y
BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="linux.config"
BR2_LINUX_KERNEL_NEEDS_HOST_LIBELF=y
BR2_PACKAGE_BUSYBOX_CONFIG="busybox.config"
BR2_PACKAGE_BUSYBOX_SHOW_OTHERS=y
BR2_PACKAGE_PYTHON3=y
BR2_PACKAGE_PYTHON_TERMINALTABLES=y
BR2_PACKAGE_LIBXCRYPT=y
BR2_PACKAGE_EXPAT=y
BR2_PACKAGE_LINUX_PAM=y
BR2_PACKAGE_LINUX_PAM_LASTLOG=y
BR2_PACKAGE_OPENSSH=y
BR2_PACKAGE_SYSKLOGD=y
BR2_PACKAGE_SYSKLOGD_LOGGER=y
BR2_TARGET_ROOTFS_EXT2=y
BR2_TARGET_ROOTFS_EXT2_SIZE="384M"
BR2_TARGET_ROOTFS_SQUASHFS=y
# BR2_TARGET_ROOTFS_TAR is not set

You need the two .config files as well:

Apply and build from scratch with:

$ rm -rf output/
$ make troglobit_qemu_x86_64_defconfig
$ make

local.mk

Now, testing the resulting image has become substantially easier in Buildroot. They even ship their own qemu start script, provided you build the whole shebang (with host Qemu etc.), but we don’t have the patience for this so we’re using the Qemu packages provided on our Debian/Ubuntu or Linux Mint installation (not covered here either).

What I’ve done instead is to employ the local.mk trick to add run: build target:

#SSDP_RESPONDER_OVERRIDE_SRCDIR = /home/jocke/src/ssdp-responder
#SYSKLOGD_OVERRIDE_SRCDIR       = /home/jocke/src/sysklogd
#FINIT_OVERRIDE_SRCDIR          = /home/jocke/src/finit
#MG_OVERRIDE_SRCDIR             = /home/jocke/src/mg
#MROUTED_OVERRIDE_SRCDIR        = /home/jocke/src/mrouted
#LIBNL_OVERRIDE_SRCDIR          = /home/jocke/src/libnl

run:
	@line=`stty -g`; stty raw;																\
	qemu-system-x86_64 -nographic -M pc -cpu host -enable-kvm								\
			-kernel output/images/bzImage													\
			-drive file=output/images/rootfs.ext2,if=virtio,format=raw						\
			-append "rootwait root=/dev/vda console=tty1 console=ttyS0 net.ifnames=0 quiet" \
			-netdev tap,id=nd0,ifname=qtap0 -device virtio-net-pci,netdev=nd0				\
			-netdev tap,id=nd1,ifname=qtap1 -device virtio-net-pci,netdev=nd1				\
			-nic bridge,br=virbr0,model=virtio; stty $$line

Remember: makefiles need leading tabs!

So whenever I want to test any of my packages I run make menuconfig first to select it. Maybe uncomment one of them in my local.mk to build unreleased/patched code.

Then:

$ make foo-rebuild all run