一、交叉編譯
1. 建立交叉編譯環境
在使用buildroot對openwrt進行編譯之後，在buildroot目錄下會有一個名叫staging_dir的目錄，針對當前平臺的toolchain都在這個目錄下。
1.1增加toolchain的目錄到PATH目錄中
Vim ~/.bash_profile
添加代碼：
# add openWrt cross-compile path
PATH=$PATH:/home/jason/openWrt/trunk/staging_dir/toolchain-i386_gcc-4.6-linaro_uClibc-0.9.33.2/bin/
1.2 增加staging_dir的目錄到toolchain PATH
Vim ~/.bash_profile
添加代碼：
STAGING_DIR=/home/jason/openWrt/trunk/staging_dir/
exportSTAGING_DIR
1.3 保存退出
2. 編譯
2.1 configure
./configure--target=i486-openwrt-linux-uclibc
2.2 make
make CC=i486-openwrt-linux-uclibc-gcc LD=i486-openwrt-linux-uclibc-ld
二、編譯ipk包
1. 編譯SDK
在buildroot目錄下make menuconfig，然後選中SDK進行編譯
選中後，進行make編譯。
編譯完成後，對應生成的SDK會出現類似這樣的目錄：“openWrt/trunk/bin/x86”，進入SDK後，打印當前工作路徑如下：
“/openWrt/trunk/bin/x86/OpenWrt-SDK-x86-for-redhat-x86_64-gcc-4.6-linaro_uClibc-0.9.33.2”
2. 創建工程
在sdk的package目錄下創建我們的工程“helloworld”:
新建目錄中包含src目錄，這個目錄就是我們的源代碼所在地，另外一個非常重要的文件Makefile，這個Makefile的組成與GNU的有所不同，有點類似於製作rpm包時的spec文件。到後面會有更詳細的介紹。以下是具體文件的位置：
其中helloworld.c的內容如下：
Src目錄下的Makefile文件內容如下：
最後是helloworld目錄下的Makefile的內容：
##############################################
# OpenWrtMakefile for helloworld program
#
#
# Most ofthe variables used here are defined in
# theinclude directives below. We just need to
# specifya basic description of the package,
# whereto build our program, where to find
# thesource files, and where to install the
#compiled program on the router.
#
# Be verycareful of spacing in this file.
# Indentsshould be tabs, not spaces, and
# thereshould be no trailing whitespace in
# linesthat are not commented.
#
##############################################
include$(TOPDIR)/rules.mk
# Nameand release number of this package
PKG_NAME:=helloworld
PKG_RELEASE:=1
# Thisspecifies the directory where we're going to build the program.
# Theroot build directory, $(BUILD_DIR), is by default the build_mipsel
#directory in your OpenWrt SDK directory
PKG_BUILD_DIR:= $(BUILD_DIR)/$(PKG_NAME)
include$(INCLUDE_DIR)/package.mk
# Specifypackage information for this program.
# Thevariables defined here should be self explanatory.
# If youare running Kamikaze, delete the DESCRIPTION
#variable below and uncomment the Kamikaze define
# directivefor the description below
definePackage/helloworld
SECTION:=utils
CATEGORY:=Utilities
TITLE:=Helloworld-- prints a snarky message
endef
# Specifywhat needs to be done to prepare for building the package.
# In ourcase, we need to copy the source files to the build directory.
# This isNOT the default. The default uses thePKG_SOURCE_URL and the
#PKG_SOURCE which is not defined here to download the source from the web.
# Inorder to just build a simple program that we have just written, it is
# mucheasier to do it this way.
defineBuild/Prepare
mkdir -p $(PKG_BUILD_DIR)
$(CP) ./src/* $(PKG_BUILD_DIR)/
endef
# We donot need to define Build/Configure or Build/Compile directives
# Thedefaults are appropriate for compiling a simple program such as this one
# Specifywhere and how to install the program. Since we only have one file,
# thehelloworld executable, install it by copying it to the /bin directory on
# therouter. The $(1) variable represents the root directory on the router running
#OpenWrt. The $(INSTALL_DIR) variable contains a command to prepare the install
#directory if it does not already exist. Likewise $(INSTALL_BIN) contains the
# commandto copy the binary file from its current location (in our case the build
#directory) to the install directory.
definePackage/helloworld/install
$(INSTALL_DIR) $(1)/bin
$(INSTALL_BIN) $(PKG_BUILD_DIR)/helloworld$(1)/bin/
endef
# Thisline executes the necessary commands to compile our program.
# Theabove define directives specify all the information needed, but this
# linecalls BuildPackage which in turn actually uses this information to
# build apackage.
$(eval $(call BuildPackage,helloworld))
這個Makefile的語法規則還是參考官網吧：
http://wiki.openwrt.org/doc/devel/packages
3. 編譯
將當前目錄返回到SDK：
執行make進行編譯。如果一切順利，最後的結果會保存在SDK/bin/x86/packages目錄下，名稱爲helloword_1_x86.ipk。
4. 安裝最新編譯的包
通過scp將該包拷貝到目的機器上，通過opkg包管理工具進行安裝：
Opkg install helloworld_1_x86.ipk
一切順利，包安裝成功，在當前路徑下執行helloworld查看程序執行結果。