利用 buildroot 與 Qemu 建構簡易 Embedded Linux 環境

tags: twlkh, qemu, buildroot

Embedded Linux development

Building Embedded Linux Full Tutorial for ARM

Building Embedded Linux Full Tutorial for ARM from Sherif Mousa

Components

• cross toolchain
  • libc: glibc / uclibc / musl
• bootloader
  • uboot / barebox
• kernel
• rootfs
  • busybox
  • applications
  • development toolkits

Some limitations

• Different sources download path
  • url
  • local
  • … and so on, one for each package
• Different download tools
  • tar ball / zip
  • git/svn/mercurial
  • copy (for local)
• Some patches might required for embedded environment
  • non-glibc
  • busybox
  • rootfs path
  • and so on
• Package dependency

builtroot

• (wiki) A set of Makefiles and patches that simplifies and automates the process of building a complete and bootable Linux environment for an embedded system
• menuconfig to select alternatives and versions of
  • board
  • bootloaders
  • compiler, binutils and libc
  • kernel version
  • supported packages
• How to support one package, e.g. foo
  • foo.mk (Makefile DSL). Commands for
    • download
    • configure
    • build
    • install
  • Config.in (menuconfig selection)
    
• Example mk for customized package, e.g. bpftest.mk
  ​​​ BPFTEST_VERSION = 1.0
  ​​​ BPFTEST_SITE = $(TOPDIR)/../bpftest
  ​​​ BPFTEST_SOURCE = "apps modules"
  ​​​ BPFTEST_SITE_METHOD = local
  ​​​ BPFTEST_LICENSE = GPLv3+
  ​​​ BPFTEST_LICENSE_FILES = COPYING
  
  ​​​ BPFTEST_MODULE_SUBDIRS = modules
  ​​​ BPF_MODULE_MAKE_OPTS = KVERSION=$(LINUX_VERSION_PROBED) KERNEL_DIR=$(LINUX_DIR)
  
  ​​​ define BPFTEST_EXTRACT_CMDS
  ​​​ 	cp -a $(TOPDIR)/$(BPFTEST_SOURCE) $(@D)
  ​​​ endef
  
  ​​​ define BPFTEST_BUILD_CMDS
  ​    $(MAKE) CC="$(TARGET_CC)" LD="$(TARGET_LD)" -C $(@D)/apps all
  ​​​ endef
  
  ​​​ define BPFTEST_INSTALL_TARGET_CMDS
  ​​​ 	$(INSTALL) -D -m 0755 $(@D)/apps/hello $(TARGET_DIR)/usr/bin
  ​​​ endef
  
  ​​​ $(eval $(kernel-module))
  ​​​ $(eval $(generic-package))
  

簡單的操作流程 - 以 qemu for ARM vexpress-a9 為例

git clone https://git.busybox.net/buildroot

cd buildroot

make qemu_arm_vexpress_defconfig

#這會跑很久，要下載新的 cross-toolchain, kernel, ... 並且把他全部 build起來
make

#接下來就可用 qemu跑了歐，簡單吧
# Ref:https://github.com/buildroot/buildroot/tree/master/board/qemu/arm-vexpress
qemu-system-arm -M vexpress-a9 -smp 1 -m 256 -kernel output/images/zImage -dtb output/images/vexpress-v2p-ca9.dtb -drive file=output/images/rootfs.ext2,if=sd,format=raw -append "console=ttyAMA0,115200 root=/dev/mmcblk0" -serial stdio -net nic,model=lan9118 -net user

參考資料:
Build Your ARM Image for QEMU
FicHugh blog - buildRoot study - 建立自己的作業系統

Qemu

• My target: arm vexpress
  • Supported by vanilla kernel
  • Supported by Qemu

Steps

• Build

$ configure --prefix=/path/to/install --target-list=arm-softmmu
$ make
$ make install

• Run

  • https://wiki.linaro.org/PeterMaydell/QemuVersatileExpress

    • target: -M vexpress-a15
      (Feedback) Can try virtio (?)
    • images:
      • kernel: -kernel /path/to/zImage
      • dtb: -dtb /path/to/dtb
      • disk: -drive ...
    • serial output to tty: -serial stdio
    • virtual NAT and port forwarding:-net nic,vlan=1 -net user,vlan=1,hostfwd=udp:127.0.0.1:6669-:69
      (Feedback) Can try tap
    • boot args: -append "root=/dev/mmcblk0 console=ttyAMA0,115200n8"
    • debug:-s or -gdb tcp::1234 / -S
    • CPU logging: -d op -D /path/to/qemu.log

  • example command

    ​​​$ /path/to/install/bin/qemu-system-arm \
    ​​​​​​-M vexpress-a15 \
    ​​​​​​-kernel buildroot/output/images/zImage \
    ​​​​​​-dtb buildroot/output/images/vexpress-v2p-ca15_a7.dtb \
    ​​​​​​-drive file=buildroot/output/images/rootfs.ext2,if=sd \
    ​​​​​​-smp 2 \
    ​​​​​​-s \
    ​​​​​​-serial stdio \
    ​​​​​​-append "root=/dev/mmcblk0 console=ttyAMA0,115200n8" \
    ​​​​​​-net nic,vlan=1 -net user,vlan=1,hostfwd=udp:127.0.0.1:6669-:69