This document is a comprehensive tutorial on utilizing OpenWrt Buildroot for embedded systems, detailing the setup process and commands for building toolchains and packages. It covers how to manage OpenWrt feeds, create custom packages, and define build options, along with a sequence of make commands essential for compiling and installing components. Additionally, it provides guidance on configuring the environment and integrating packages, aimed at users developing for specific hardware platforms.

1. OpenWRT
Basic tutorial guide, memo.
by Antony.Wu
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2. OpenWRT builtroot
• It is a set of Makefiles and patches that allows users to generate
a cross-toolchain and a root filesystem for embeded system.
• It generates cross-compiler toolchain and use the toolchain to
build an image for your target board, such as AR-5387un router.
• It can also download packages (feeds), patches (using quilt) it
for you.
• # make toolchain/gdb/prepare QUILT=1
• <modify files in build_dir/>
• # make toolchain/gdb/updatevim
• It has modified make targets: component/name/action.
• # make toolchain/gdb/compile V=s
• V=s means “Verboase = stdout/stderror”
• # make toolchain/gdb/clean V=s
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V=?
s standard output/error
w shows only warning

3. 3
Get OpenWRT buildroot
Main repositories and feeds
− # git clone git://git.openwrt.org/openwrt.git
− # git clone git://git.openwrt.org/packages.git
Barrier Breaker
− # git clone git://git.openwrt.org/14.07/openwrt.git
− # git clone git://git.openwrt.org/14.07/packages.git
− # svn co -r 42990
svn://svn.openwrt.org/openwrt/branches/barrier_bre
aker

4. 4
Setup OpenWRT environment
Using Fedora distribution, you need the following
package ready.
− # yum install -y subversion binutils bzip2 gcc gcc-c++ gawk
gettext flex ncurses-devel zlib-devel make patch unzip perl-
ExtUtils-MakeMaker glibc glibc-devel glibc-static quilt
ncurses-lib sed sdcc intltool sharutils bison wget
Check environment variables
− # echo $SED # must be empty, or issue '# unset SED'
− # echo $GREP_OPTIONS # don't contain '--initial-tab'
Set the PATH:
− PATH=$PATH:<buildroot dir>/staging_dir/host/bin
− PATH=$PATH:<buildroot dir>/staging_dir/toolchain-
<platform>-<gcc_ver>-<libc_ver>/bin

5. 5
Understand OpenWRT Feeds
It is a set of packages, like a ‘yum repo’, or ‘apt-get repo’ on
desktop linux.
 The script downloads the packages info into ‘feeds/’ .
 The script installs packages into ‘package/feeds/’
 Packages in feeds selectable by CONFIG_PACKAGE_xxxx in .config
file.
The repo is configured in the feeds.conf or feeds.conf.default
(such as yum repo configured in /etc/yum.repos.d)
A script is used to control those packages
 # ./scripts/feeds update -a
 Package index (information) will be stored into feeds/
 # ./scripts/feeds install <package_name>
 Src will be checkouted into package/feeds/<package_name>

6. OpenWRT Make
• Clean
• # make clean # rm -rf bin build_dir
• # make dirclean # rm -rf bin build_dir staging_dir toolchain logs
• # make distclean # all above, rm all downloaded packages and .config
• Ignore errors
• #IGNORE_ERRORS=1 make <make options>
• component/name/action.
• Clean Linux objects
• # make target/linux/clean V=s
• Clean package luci.
• # make package/luci/clean
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7. OpenWRT Make sequence
1. # make tools/install
2. # make toolchain/install
3. # make target/compile
4. # make package/cleanup
5. # make package/compile
6. # make package/install
7. # make package/preconfig
8. # make target/install
9. # make package/index
You can issue them, one by
one, in order, so that you
can check and debug
each step.
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8. Create OpenWRT package
• Special Makefile template.
• Please refer to BuildPackage variables
PKG_NAME:=broadcom-wl
PKG_VERSION:=5.10.56.27.3
PKG_RELEASE:=5
PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION)_$(ARCH).tar.bz2
PKG_SOURCE_URL:=http://downloads.openwrt.org/sources
…
…
$(eval $(call KernelPackage,brcm-wl))
$(eval $(call KernelPackage,brcm-wl-mini))
$(eval $(call BuildPackage,wlc))
$(eval $(call BuildPackage,wl))
$(eval $(call BuildPackage,nas))
• BuildPackage only takes one argument directly – the
name of the package to be built, in this case “wlc".
# ls -l package/broadcom-wl/
files # default config.
Makefile
patches # patches from diff
src # source code
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9. Create OpenWRT package 2
• BuildPackage define ‘Package/’
• The following describe the ‘define’ you may need:
define Package/broadcom-wl/Default
<action>
endef
• Package/description : description
• Package/conffiles : config-files installed by this pkg.
• Build/Prepare (optional): How to unpack/patch src.
• Build/Configure (optional) : How to configure src.
• Build/Compile (optional) : How to compile src.
• Build/InstallDev (optoinal) : Lib. needed
• Please refer to BuildPackage defines
Note: ‘define’ in makefile is like
‘=‘ operator.
Define the action when calling
‘Package/broadcom/wl/Default ‘
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10. Create OpenWRT package 3
• Override Build option
• Autoconf
• Eg. CONFIGURE_VARS += ac_cv_header_regex_h=no
• Eg. CONFIGURE_ARGS += --disable-native-affinity
• Compiler flags
• Eg. TARGET_CFLAGS+= -Wall
• Make
• Eg. MAKE_VARS = CFLAGS="$(TARGET_CFLAGS) $(EXTRA_CFLAGS)
$(TARGET_CPPFLAGS) $(EXTRA_CPPFLAGS)" …
• Eg. MAKE_FLAGS = $(TARGET_CONFIGURE_OPTS) CROSS="$
(TARGET_CROSS)" ARCH="$(ARCH)“
• CMake and Scons
• CMAKE_OPTIONS, CMAKE_HOST_OPTIONS
• SCONS_VARS
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11. Create OpenWRT package 4
• Adding configuration options
• Add MENU:=1
• Add Config.in Package/<name>/config
Makefile:
define Package/mjpg-streamer/config source
"$(SOURCE)/Config.in“
endef
Config.in:
menu "Configuration" depends on PACKAGE_mjpg-streamer
config MJPEG_STREAMER_AUTOSTART
bool "Autostart enabled" default n
• How to check your configuration
Makefile:
ifeq ($(CONFIG_MJPEG_STREAMER_INPUT_UVC),y)
$(CP) $(PKG_BUILD_DIR)/input_uvc.so $(1)/usr/lib
endif
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12. Create OpenWRT package 5
• Working on local application source
• Using feeds to tracking your state-of-the-art
work.
# ln -s /path/to/local/awesome_app_tree/.git feeds/my_cool_feed/awesome_app/git-src
# make package/awesome_app/{clean,compile} V=s
• Using USE_SOURCE_DIR
# make package/awesome_app/clean V=s
# make package/awesome_app/prepare USE_SOURCE_DIR=~/src/awesome_src V=s
# make package/awesome_app/clean V=s
• make prepare needs to be run every time
• make package/awesome_app/{clean,compile}
USE_SOURCE_DIR=~blah doesn't work
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13. OpenWRT kernel package

Adding configuration options

Add .mk file
#vim package/kernel/modules/block.mk
define KernelPackage/loop
SUBMENU:=$(BLOCK_MENU)
TITLE:=Loopback device support
KCONFIG:= CONFIG_BLK_DEV_LOOP CONFIG_BLK_DEV_CRYPTOLOOP=n
FLES:=$(LINUX_DIR)/drivers/block/loop.ko
AUTOLOAD:=$(call AutoLoad,30,loop)
endef
$(eval $(call KernelPackage,loop))
 Announce to build system.
# touch package/kernel/linux/Makefile

Add a kernel module that is not part of kernel
distribution
 Please refer to ‘package/madwifi/Makefile’ 13

14. What’s in the following slides?
1. # make tools/install
2. # make toolchain/install
3. # make target/compile
4. # make package/cleanup
5. # make package/compile
6. # make package/install
7. # make package/preconfig
8. # make target/install
9. # make package/index
You can issue them, one by
one, in order, so that you
can check and debug
each step.
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15. External Toolchain
 Compile everything with the target board,
you will have a dir named toolchain, called
build1

Copy the .config-file from the build1 and
make menuconfig.
[*] Advanced configuration options (for developers)
[*] Use external toolchain
Target name: arm-openwrt-linux-uclibcgnueabi (in my case, yours may vary)
Toolchain prefix: arm-openwrt-linux-uclibcgnueabi- (mind the dash at the end)
Toolchain root: /path/to/toolchain/staging_dir/toolchain-arm_v5te_gcc-
linaro_uClibc-0.9.32_eabi
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16. Alter download procedure

$DL_DIR is the location for download

Through "include/download.mk“

Init in “rules.mk”

To share downloaded packages

Put them in a shared location /opt/…

Check them in download procedure “define
Download” in file “download.mk”

MEMO: we can use shell to do this.

Eg . test -e /opt/dl/$(FILE) && ln -s /opt/dl/$(FILE) $(DL_DIR)/$(FILE) || (
$(if $(DownloadMethod/$(call dl_method,$(URL),$(PROTO))),$
(DownloadMethod/$(call dl_method,$(URL),$(PROTO))),$
(DownloadMethod/unknown)) )
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17. What has been added?
dl/ # for downloaded src.
build_dir/ # source code location
├── host
├── target-mips_mips32_uClibc-0.9.33.2
└── toolchain-mips_mips32_gcc-4.8.3_uClibc-0.9.33.2
logs/ # for compile logs
├── target
├── toolchain
└── tools
staging_dir/ # built out binary files.
├── host
├── target-mips_mips32_uClibc-0.9.33.2
└── toolchain-mips_mips32_gcc-4.8.3_uClibc-0.9.33.2
tmp/
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18. What’s in the following slides?
1. # make tools/install
2. # make toolchain/install
3. # make target/compile
4. # make package/cleanup
5. # make package/compile
6. # make package/install
7. # make package/preconfig
8. # make target/install
9. # make package/index
You can issue them, one by
one, in order, so that you
can check and debug
each step.
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19. Add our own BSP in target

The makefile in target will go into each
subdir.

Create a dir <BSP> of yours in the target dir.

Create a Makefile contains the following target.
all, download, prepare,
compile, install, clean

This also apply to the general ruls
 Eg # make target/<BSP>/prepare
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20. Reference
1. http://wiki.openwrt.org/doc/start
2. http://wiki.openwrt.org/about/toolchain
3. http://wiki.openwrt.org/doc/devel/packages
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