arm-linux-gcc4.4.3编译busybox-1.25.0
系统环境：
1、操作系统：Ubuntu16.04
2、交叉编译工具链：arm-linux-gcc4.4.3
3、busybox源码包：busybox-1.25.0
一、修改Makefile配置
首先解压源码包：
tar -jxvf busybox-1.25.0.tar.bz2
进入busybox-1.25.0目录，修改Makefile文件如下：
ARCH ?= arm
CROSS_COMPILE ?= arm-linux-
二、修改配置文件
make menuconfig
选择Busybox Settings--->Build Options--->，选择[*] Build Busybox as a static binary（no shared libs）
三、编译
make
出现如下错误：
miscutils/nandwrite.c: In function 'nandwrite_main':
miscutils/nandwrite.c:151: error: 'MTD_FILE_MODE_RAW' undeclared (first use in this function)
miscutils/nandwrite.c:151: error: (Each undeclared identifier is reported only once
miscutils/nandwrite.c:151: error: for each function it appears in.)
scripts/Makefile.build:197: recipe for target 'miscutils/nandwrite.o' failed
make[1]: *** [miscutils/nandwrite.o] Error 1
Makefile:742: recipe for target 'miscutils' failed
make: *** [miscutils] Error 2
解决办法：
MTD_FILE_MODE_RAW在/usr/include/mtd/mtd-abi.h中定义，直接在nandwrite.c中包含<mtd/mtd-abi.h>编译仍无法通过。将/usr/include/mtd/mtd-abi.h拷贝到busybox的include文件中，然后包含该头文件：
#include "libbb.h"
#include "mtd-abi.h"
#include <mtd/mtd-user.h>
编译可以通过。
继续make，出现如下错误：
util-linux/blkdiscard.c: In function 'blkdiscard_main':
util-linux/blkdiscard.c:72: error: 'BLKSECDISCARD' undeclared (first use in this function)
util-linux/blkdiscard.c:72: error: (Each undeclared identifier is reported only once
util-linux/blkdiscard.c:72: error: for each function it appears in.)
scripts/Makefile.build:197: recipe for target 'util-linux/blkdiscard.o' failed
make[1]: *** [util-linux/blkdiscard.o] Error 1
Makefile:742: recipe for target 'util-linux' failed
make: *** [util-linux] Error 2
解决办法：
BLKSECDISCARD在/usr/include/linux/fs.h中定义，方法如上所述，将/usr/include/linux/fs.h拷贝到busybox的include文件中，然后修改blkdiscard.c中头文件包含：
修改：#include <linux/fs.h>为
#include "fs.h"
继续make，编译通过，但是在链接的时候出现问题：
networking/lib.a(nslookup.o): In function `print_host':
nslookup.c:(.text.print_host+0x44): warning: Using 'getaddrinfo' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
debianutils/lib.a(mktemp.o): In function `mktemp_main':
mktemp.c:(.text.mktemp_main+0x98): warning: the use of `mktemp' is dangerous, better use `mkstemp'
networking/lib.a(ipcalc.o): In function `ipcalc_main':
ipcalc.c:(.text.ipcalc_main+0x25c): warning: Using 'gethostbyaddr' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
libbb/lib.a(inet_common.o): In function `INET_resolve':
inet_common.c:(.text.INET_resolve+0x60): warning: Using 'gethostbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
networking/lib.a(inetd.o): In function `reread_config_file':
inetd.c:(.text.reread_config_file+0x230): warning: Using 'getservbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
networking/lib.a(netstat.o): In function `ip_port_str':
netstat.c:(.text.ip_port_str+0x50): warning: Using 'getservbyport' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
util-linux/lib.a(nsenter.o): In function `nsenter_main':
nsenter.c:(.text.nsenter_main+0x1b0): undefined reference to `setns'
collect2: ld returned 1 exit status
Note: if build needs additional libraries, put them in CONFIG_EXTRA_LDLIBS.
Example: CONFIG_EXTRA_LDLIBS="pthread dl tirpc audit pam"
Makefile:717: recipe for target 'busybox_unstripped' failed
make: *** [busybox_unstripped] Error 1
解决办法：
make menuconfig
Linux System Utilities--->nsenter，去掉该选项，重新编译make，又出现如下错误：
networking/lib.a(nslookup.o): In function `print_host':
nslookup.c:(.text.print_host+0x44): warning: Using 'getaddrinfo' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
debianutils/lib.a(mktemp.o): In function `mktemp_main':
mktemp.c:(.text.mktemp_main+0x98): warning: the use of `mktemp' is dangerous, better use `mkstemp'
networking/lib.a(ipcalc.o): In function `ipcalc_main':
ipcalc.c:(.text.ipcalc_main+0x25c): warning: Using 'gethostbyaddr' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
libbb/lib.a(inet_common.o): In function `INET_resolve':
inet_common.c:(.text.INET_resolve+0x60): warning: Using 'gethostbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
networking/lib.a(inetd.o): In function `reread_config_file':
inetd.c:(.text.reread_config_file+0x230): warning: Using 'getservbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
networking/lib.a(netstat.o): In function `ip_port_str':
netstat.c:(.text.ip_port_str+0x50): warning: Using 'getservbyport' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
coreutils/lib.a(sync.o): In function `sync_main':
sync.c:(.text.sync_main+0x7c): undefined reference to `syncfs'
collect2: ld returned 1 exit status
Note: if build needs additional libraries, put them in CONFIG_EXTRA_LDLIBS.
Example: CONFIG_EXTRA_LDLIBS="pthread dl tirpc audit pam"
Makefile:717: recipe for target 'busybox_unstripped' failed
make: *** [busybox_unstripped] Error 1
解决办法：
make menuconfig
Coreutils--->sync选项去掉，重新make编译通过，生成了busybox可执行文件。
具体选项是什么意思还不太清楚，需要进一步理解。
