Cross compile iproute2 network management tool

The built-in ip command in busybox does not support netns and bridge, so I transplanted one by myself referring to the web document guide.

Reference: https://blog.csdn.net/u013401853/article/details/71126645

Release: May 03, 2017 17:04:58 Planck constant

1) Download the source code
- Official website:
- Lower version
  - http://pkgs.fedoraproject.org/repo/pkgs/iproute/iproute2-2.6.37.tar.bz2/9774ff9d74ebd301bf56bd8d74473786/iproute2-2.6.37.tar.bz2

2) Unzip and modify Makefile

Modify CC in Makefille as a cross compiler

CC = /usr/arm/toolchain/gcc-linaro-6.3.1-2017.05-x86_64_arm-linux-gnueabi/bin/arm-linux-gnueabi-gcc

Planck constants / PS : Because I only need the ip command, modify line 38 to compile only the ip tool SUBDIRS=ip

About 4.19.0 version

// 修改 Makefile --- 交叉编译器
CC = /usr/arm/toolchain/gcc-linaro-6.3.1-2017.05-x86_64_arm-linux-gnueabi/bin/arm-linux-gnueabi-gcc
// 修改config.mk --- 交叉编译器
AR:=/usr/arm/toolchain/gcc-linaro-6.3.1-2017.05-x86_64_arm-linux-gnueabi/bin/arm-linux-gnueabi-ar
CC:=/usr/arm/toolchain/gcc-linaro-6.3.1-2017.05-x86_64_arm-linux-gnueabi/bin/arm-linux-gnueabi-gcc
// 修改config.mk --- 去除对SELinux和CAP的支持
HAVE_SELINUX:=
#LDLIBS += -lselinux
#CFLAGS += -DHAVE_SELINUX
CFLAGS += -DNEED_STRLCPY
HAVE_CAP:=
#CFLAGS += -DHAVE_LIBCAP
#LDLIBS += -lcap

3）make
```
make LDFLAGS=-static  ## 静态连接，否则，运行时报缺少.so文件
```
PS:
- The make process will not be completely successful, but the required ip has been compiled, and the ip in the ip directory is the required ip executable program
- The downloaded version 4.19 requires the compiler to have selinux.h and capability.h (gcc-linaro-6.3.1-2017.05-x86_64_arm-linux-gnueabi does not support), so I downloaded version 4.13 and compiled it

4) Compile error resolution

Due to the gcc-linaro-6.3.1-2017.05-x86_64_arm-linux-gnueabi compiler, the function setns declaration conflicts, as follows:

In file included from utils.c:36:0:
../include/namespace.h:35:19: error: static declaration of ‘setns’ follows non-static declaration
static inline int setns(int fd, int nstype)
                  ^~~~~
In file included from /usr/arm/toolchain/gcc-linaro-6.3.1-2017.05-x86_64_arm-linux-gnueabi/arm-linux-gnueabi/libc/usr/include/sched.h:43:0,
                from ../include/namespace.h:4,
                from utils.c:36:
/usr/arm/toolchain/gcc-linaro-6.3.1-2017.05-x86_64_arm-linux-gnueabi/arm-linux-gnueabi/libc/usr/include/bits/sched.h:91:12: note: previous declaration of ‘setns’ was here
extern int setns (int __fd, int __nstype) __THROW;

Solution: Edit ./include/namespace.h and use the declaration of bits/sched.h

#ifndef HAVE_SETNS
extern int setns (int __fd, int __nstype) __THROW;
/*
static inline int setns(int fd, int nstype)
{
...
}
*/
#endif /* HAVE_SETNS */

libmnl required for error support
```
lib ## 编译 iproute2-4.19/lib目录
libnetlink.c:120:2: warning: #warning "libmnl required for error support" [-Wcpp]
#warning "libmnl required for error support"
```
Check the source code of lib/libnetlink.c. If the HAVE_LIBMNL macro is not defined, there will be the above warning. You can download libmnl from the official website http://ftp.netfilter.org/pub/libmnl/ and compile it. This test is not done here

When statically linked, execution ip link add veth0a type veth peer name veth0bfails

# 在 CentOS 7 中静态链接，出现同样问题，侧面佐证静态链接不可行；
# 在 ./ip/iplink.c 中加入跟踪代码，发现问题出在 dlh = BODY = dlopen(NULL, RTLD_LAZY) 时为（明显地，必须是动态链接）

Dynamically compile, copy libdl.so.2.23 to the target machine and ln -s as libdl.so.2, run ldd, as follows:

/root # ldd ./ip
        linux-vdso.so.1 (0x7ee1e000)
        libdl.so.2 => /lib/libdl.so.2 (0x76fa0000)
        libc.so.6 => /lib/libc.so.6 (0x76eb3000)
        /lib/ld-linux.so.3 (0x76fb3000)

Then, the execution is ip link add veth0a type veth peer name veth0bsuccessful

5) Put the ip program in the ip directory into the board to see if it can run

Can run directly

Planck Constants/ PS : I thought that I had to download the iproute2 version corresponding to the kernel to run normally, but I compiled the latest iiproute version and put it on the board to run it.
```
# 动态链接时，报告缺少.so文件
/root # ./ip --help
./ip: error while loading shared libraries: libdl.so.2: cannot open shared object file: No such file or directory  
```
reference:
- https://blog.csdn.net/hnyz1571048575/article/details/46290947
- https://www.cnblogs.com/hujianhua/p/8446291.html

Cross compile iproute2 network management tool

Cross compile iproute2 network management tool

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