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Learn more about bidirectional Unicode charactersOriginal file line number Diff line number Diff line change @@ -0,0 +1,519 @@ ## Common ```` export OPT=/opt export BUILDS=/some/where/mini_linux mkdir -p $BUILDS ```` ## Linux kernel ```` export LINUX=$OPT/linux export LINUX_BUILD=$BUILDS/linux mkdir -p $LINUX_BUILD cd $LINUX make O=$LINUX_BUILD allnoconfig cd $LINUX_BUILD make menuconfig ```` Configure the kernel according the following: ```` 64-bit kernel ---> yes General setup ---> Initial RAM filesystem and RAM disk (initramfs/initrd) support ---> yes General setup ---> Configure standard kernel features ---> Enable support for printk ---> yes Executable file formats / Emulations ---> Kernel support for ELF binaries ---> yes Executable file formats / Emulations ---> Kernel support for scripts starting with #! ---> yes Device Drivers ---> Generic Driver Options ---> Maintain a devtmpfs filesystem to mount at /dev ---> yes Device Drivers ---> Generic Driver Options ---> Automount devtmpfs at /dev, after the kernel mounted the rootfs ---> yes Device Drivers ---> Character devices ---> Enable TTY ---> yes Device Drivers ---> Character devices ---> Serial drivers ---> 8250/16550 and compatible serial support ---> yes Device Drivers ---> Character devices ---> Serial drivers ---> Console on 8250/16550 and compatible serial port ---> yes File systems ---> Pseudo filesystems ---> /proc file system support ---> yes File systems ---> Pseudo filesystems ---> sysfs file system support ---> yes ```` Build the kernel: ```` time make -j8 ```` ```` ... Kernel: arch/x86/boot/bzImage is ready (#1) real 2m37.247s user 1m58.541s sys 0m25.542s ```` ## Busybox ```` export BUSYBOX=$OPT/busybox export BUSYBOX_BUILD=$BUILDS/busybox mkdir -p $BUSYBOX_BUILD cd $BUSYBOX make O=$BUSYBOX_BUILD defconfig cd $BUSYBOX_BUILD make menuconfig ```` Configure Busybox according the following: ```` Busybox Settings ---> Build Options ---> Build BusyBox as a static binary (no shared libs) ---> yes ```` Build Busybox: ```` time make -j8 ```` ```` ... Final link with: m real 0m20.356s user 0m46.959s sys 0m10.628s ```` Install Busybox: ```` make install ```` Create an initramfs: ```` export INITRAMFS_BUILD=$BUILDS/initramfs mkdir -p $INITRAMFS_BUILD cd $INITRAMFS_BUILD mkdir -p bin sbin etc proc sys usr/bin usr/sbin cp -a $BUSYBOX_BUILD/_install/* . ```` Add a `$INITRAMFS_BUILD/init` script to the initramfs with the following content: ```` #!/bin/sh mount -t proc none /proc mount -t sysfs none /sys cat <<! Boot took $(cut -d' ' -f1 /proc/uptime) seconds _ _ __ _ /\/\ (_)_ __ (_) / /(_)_ __ _ ___ __ / \| | '_ \| | / / | | '_ \| | | \ \/ / / /\/\ \ | | | | | / /__| | | | | |_| |> < \/ \/_|_| |_|_| \____/_|_| |_|\__,_/_/\_\ Welcome to mini_linux ! exec /bin/sh ```` Create the initramfs archive: ```` chmod +x init find . -print0 | cpio --null -ov --format=newc \ | gzip -9 > $BUILDS/initramfs.cpio.gz ```` ## Run and see (`<CTRL>a x` to quit) ```` qemu-system-x86_64 -kernel $LINUX_BUILD/arch/x86_64/boot/bzImage \ -initrd $BUILDS/initramfs.cpio.gz -nographic \ -append "console=ttyS0" ```` Note: for better performance, add the `-enable-kvm` option if your host has KVM enabled: ```` qemu-system-x86_64 -kernel $LINUX_BUILD/arch/x86_64/boot/bzImage \ -initrd $BUILDS/initramfs.cpio.gz -nographic \ -append "console=ttyS0" -enable-kvm ```` ```` ... Boot took 0.45 seconds _ _ __ _ /\/\ (_)_ __ (_) / /(_)_ __ _ ___ __ / \| | '_ \| | / / | | '_ \| | | \ \/ / / /\/\ \ | | | | | / /__| | | | | |_| |> < \/ \/_|_| |_|_| \____/_|_| |_|\__,_/_/\_\ Welcome to mini_linux / # ls / bin etc linuxrc root sys dev init proc sbin usr / # QEMU: Terminated ```` ## Buildroot We assume that a toolchain is available in `/opt/toolchains/x86_64-unknown-linux-gnu` with prefix `x86_64-unknown-linux-gnu`, gcc version 5.x, kernel headers series 4.3.x, glibc C library and C++ support. These are reasonable defaults if you are using a toolchain generated by crosstool-NG. Adapt to your own situation. Notes: * You cannot use the native toolchain of your host computer (see Buildroot documentation to understand why). * If you do not have a toolchain already, you can build one using crosstool-NG (or Buildroot itself) and reuse it for other projects. * crosstool-NG is the recommended tool to build your own toolchain but avoid using uClibc (no IPV6 support), prefer uClibc-ng or glibc. * You can also use the built-in toolchain of Buildroot but be aware that it will take way longer than using an existing toolchain. Be also aware that in many cases you will have to re-build the toolchain after modifying the Buildroot configuration. * No yet convinced? Please use crosstool-NG, build and use your own toolchain. ```` export BUILDROOT=$OPT/buildroot export BUILDROOT_BUILD=$BUILDS/buildroot mkdir -p $BUILDROOT_BUILD cd $BUILDROOT_BUILD touch Config.in external.mk echo 'name: mini_linux' > external.desc echo 'desc: minimal linux system with buildroot' >> external.desc mkdir configs overlay cd $BUILDROOT make O=$BUILDROOT_BUILD BR2_EXTERNAL=$BUILDROOT_BUILD qemu_x86_64_defconfig cd $BUILDROOT_BUILD make menuconfig ```` Configure Buildroot according the following: ```` Build options ---> Location to save buildroot config ---> $(BR2_EXTERNAL)/configs/mini_linux_defconfig Build options ---> Download dir ---> /some/where/buildroot_dl Build options ---> Number of jobs to run simultaneously (0 for auto) ---> 8 Build options ---> Enable compiler cache ---> yes Build options ---> Compiler cache location ---> /some/where/buildroot_ccache Toolchain ---> Toolchain type ---> External toolchain Toolchain ---> Toolchain ---> Custom toolchain Toolchain ---> Toolchain origin ---> Pre-installed toolchain Toolchain ---> Toolchain path ---> /opt/toolchains/x86_64-unknown-linux-gnu Toolchain ---> Toolchain prefix ---> x86_64-unknown-linux-gnu Toolchain ---> External toolchain gcc version ---> 5.x Toolchain ---> External toolchain kernel headers series ---> 4.3.x Toolchain ---> External toolchain C library ---> glibc/eglibc Toolchain ---> Toolchain has C++ support? ---> yes System configuration ---> System hostname ---> mini_linux System configuration ---> System banner ---> Welcome to mini_linux System configuration ---> Run a getty (login prompt) after boot ---> TTY port ---> ttyS0 System configuration ---> Network interface to configure through DHCP ---> System configuration ---> Root filesystem overlay directories ---> $(BR2_EXTERNAL)/overlay Kernel ---> Linux Kernel ---> no Filesystem images ---> cpio the root filesystem (for use as an initial RAM filesystem) ---> yes Filesystem images ---> Compression method ---> gzip ```` Save the configuration and build: ```` make savedefconfig ```` Add a `$BUILDROOT_BUILD/overlay/init` script to the overlay with the following content: ```` #!/bin/sh /bin/mount -t devtmpfs devtmpfs /dev /bin/mount -t proc none /proc /bin/mount -t sysfs none /sys exec 0</dev/console exec 1>/dev/console exec 2>/dev/console cat <<! Boot took $(cut -d' ' -f1 /proc/uptime) seconds _ _ __ _ /\/\ (_)_ __ (_) / /(_)_ __ _ ___ __ / \| | '_ \| | / / | | '_ \| | | \ \/ / / /\/\ \ | | | | | / /__| | | | | |_| |> < \/ \/_|_| |_|_| \____/_|_| |_|\__,_/_/\_\ Welcome to mini_linux ! exec /bin/sh ```` Build the root filesystem: ```` chmod +x overlay/init time make ```` ```` ... real 1m52.905s user 0m50.682s sys 0m36.928s ```` ## Run and see (`<CTRL>a x` to quit) ```` qemu-system-x86_64 -kernel $LINUX_BUILD/arch/x86_64/boot/bzImage \ -initrd $BUILDROOT_BUILD/images/rootfs.cpio.gz -nographic \ -append "console=ttyS0" ```` Note: for better performance, add the `-enable-kvm` option if your host has KVM enabled. ```` ... Boot took 0.57 seconds _ _ __ _ /\/\ (_)_ __ (_) / /(_)_ __ _ ___ __ / \| | '_ \| | / / | | '_ \| | | \ \/ / / /\/\ \ | | | | | / /__| | | | | |_| |> < \/ \/_|_| |_|_| \____/_|_| |_|\__,_/_/\_\ Welcome to mini_linux / # ls / bin init linuxrc opt run tmp dev lib media proc sbin usr etc lib64 mnt root sys var / # QEMU: Terminated ```` ## Add and run a custom user application Create a new directory for the custom user applications: ```` export APPS=$BUILDS/apps mkdir -p $APPS cd $APPS ```` Add an application source file `$APPS/hello_world.c` with the following content: ```` #include <stdio.h> int main(int argc, char **argv) { printf("mini_linux says: Hello world!\n"); return 0; } ```` Add a `$APPS/Makefile` with the following content (replace the `CROSS_COMPILE` definition with whatever is appropriate in your specific case): ```` CROSS_COMPILE := /opt/toolchains/x86_64-unknown-linux-gnu/bin/x86_64-unknown-linux-gnu- CC := $(CROSS_COMPILE)gcc hello_world: hello_world.o $(CC) -o $@ $< hello_world.o: hello_world.c $(CC) -c -o $@ $< clean: rm -f hello_world hello_world.o ```` Compile the application, copy it in the Buildroot overlay directory and re-build the root filesystem: ```` make ... cp hello_world $BUILDROOT_BUILD/overlay ... cd $BUILDROOT_BUILD make ```` ## Run and see (`<CTRL>a x` to quit) ```` qemu-system-x86_64 -kernel $LINUX_BUILD/arch/x86_64/boot/bzImage \ -initrd $BUILDROOT_BUILD/images/rootfs.cpio.gz -nographic \ -append "console=ttyS0" ```` Note: for better performance, add the `-enable-kvm` option if your host has KVM enabled. ```` ... Boot took 0.57 seconds _ _ __ _ /\/\ (_)_ __ (_) / /(_)_ __ _ ___ __ / \| | '_ \| | / / | | '_ \| | | \ \/ / / /\/\ \ | | | | | / /__| | | | | |_| |> < \/ \/_|_| |_|_| \____/_|_| |_|\__,_/_/\_\ Welcome to mini_linux / # ls bin init media root tmp dev lib mnt run usr etc lib64 opt sbin var hello_world linuxrc proc sys / # ./hello_world mini_linux says: Hello world! / # QEMU: Terminated ```` ## Add loadable module support to the Linux kernel ```` cd $LINUX_BUILD make menuconfig ```` Change the kernel configuration according the following: ```` Enable loadable module support ---> yes ```` Re-build the kernel and its modules (none, in our case) and install the modules in the Buildroot overlay directory: ```` make -j8 make -j8 modules make modules_install INSTALL_MOD_PATH=$BUILDROOT_BUILD/overlay ```` ## Add a custom user module Create a new directory for the custom user modules: ```` export MODULES=$BUILDS/modules mkdir -p $MODULES cd $MODULES ```` Add a module source file `$MODULES/hello_world.c` with the following content: ```` /* hello_world.c */ #include <linux/init.h> #include <linux/module.h> #include <linux/kernel.h> static int __init first_init(void) { pr_info("mini_linux module says: Hello world!\n"); return 0; } static void __exit first_exit(void) { pr_info("Bye\n"); } module_init(first_init); module_exit(first_exit); MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("My first module"); MODULE_AUTHOR("The Doctor"); ```` Add a `$MODULES/Makefile` with the following content: ```` ifneq ($(KERNELRELEASE),) # kbuild part of makefile obj-m := hello_world.o else # normal makefile KDIR ?= $(LINUX_BUILD) default: $(MAKE) -C $(KDIR) M=$$PWD modules_install: $(MAKE) -C $(KDIR) M=$$PWD $@ clean: rm -rf *.o .*.cmd *.ko hello_world.mod.c modules.order Module.symvers .tmp_versions endif ```` Compile the module, install it in the Buildroot overlay directory and re-build the root filesystem: ```` make ... make modules_install INSTALL_MOD_PATH=$BUILDROOT_BUILD/overlay ... cd $BUILDROOT_BUILD make ```` ## Run and see (`<CTRL>a x` to quit) ```` qemu-system-x86_64 -kernel $LINUX_BUILD/arch/x86_64/boot/bzImage \ -initrd $BUILDROOT_BUILD/images/rootfs.cpio.gz -nographic \ -append "console=ttyS0" ```` Note: for better performance, add the `-enable-kvm` option if your host has KVM enabled. ```` ... Boot took 0.57 seconds _ _ __ _ /\/\ (_)_ __ (_) / /(_)_ __ _ ___ __ / \| | '_ \| | / / | | '_ \| | | \ \/ / / /\/\ \ | | | | | / /__| | | | | |_| |> < \/ \/_|_| |_|_| \____/_|_| |_|\__,_/_/\_\ Welcome to mini_linux / # ls lib/modules/4.8.0\+/extra hello_world.ko / # lsmod Module Size Used by Not tainted / # insmod lib/modules/4.8.0\+/extra/hello_world.ko hello_world: loading out-of-tree module taints kernel. mini_linux module says: Hello world! / # lsmod Module Size Used by Tainted: G hello_world 704 - / # QEMU: Terminated ````