目标：在x86_64主机上(windows 10或ubuntu 20.04)上交叉编译arm架构的helloworld程序，然后通过scp将编译完的可执行文件传给树莓派4B，在树莓派上执行该程序。（树莓派运行的是官方32位Linux系统。）

1、执行arm-none-eabi-gcc test.c -o test报错

/home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld: /home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/lib/libc.a(lib_a-exit.o): in function `exit':
exit.c:(.text.exit+0x2c): undefined reference to `_exit'
/home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld: /home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/lib/libc.a(lib_a-sbrkr.o): in function `_sbrk_r':
sbrkr.c:(.text._sbrk_r+0x18): undefined reference to `_sbrk'
/home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld: /home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/lib/libc.a(lib_a-writer.o): in function `_write_r':
writer.c:(.text._write_r+0x24): undefined reference to `_write'
/home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld: /home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/lib/libc.a(lib_a-closer.o): in function `_close_r':
closer.c:(.text._close_r+0x18): undefined reference to `_close'
/home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld: /home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/lib/libc.a(lib_a-fstatr.o): in function `_fstat_r':
fstatr.c:(.text._fstat_r+0x1c): undefined reference to `_fstat'
/home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld: /home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/lib/libc.a(lib_a-isattyr.o): in function `_isatty_r':
isattyr.c:(.text._isatty_r+0x18): undefined reference to `_isatty'
/home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld: /home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/lib/libc.a(lib_a-lseekr.o): in function `_lseek_r':
lseekr.c:(.text._lseek_r+0x24): undefined reference to `_lseek'
/home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld: /home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/lib/libc.a(lib_a-readr.o): in function `_read_r':
readr.c:(.text._read_r+0x24): undefined reference to `_read'
/home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld: /home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/lib/libc.a(lib_a-abort.o): in function `abort':
abort.c:(.text.abort+0x10): undefined reference to `_exit'
/home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld: /home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/lib/libc.a(lib_a-signalr.o): in function `_kill_r':
signalr.c:(.text._kill_r+0x1c): undefined reference to `_kill'
/home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld: /home/sunch/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/lib/libc.a(lib_a-signalr.o): in function `_getpid_r':
signalr.c:(.text._getpid_r+0x4): undefined reference to `_getpid'
collect2: error: ld returned 1 exit status

2、在网上查找相关问题，解决方式是编译时添加--specs=nosys.specs

参考：https://www.freesion.com/article/1071345305/

所以编译命令改为 arm-none-eabi-gcc --specs=nosys.specs hello.c -o hello

这次可以成功编译，然后将生成的可执行文件scp到树莓派执行，报错：Segmentation fault

网上找到的解决方法都不适用：
1、segmentation fault 错误（运行一个简单的helloworld程序）
2、解决交叉编译产生的程序放到目标板上运行时出现Segmentation fault (core dumped)
3、嵌入式linux中遇到的segmentation fault问题

下面的网页解释了一部分原因，但是并没有解决问题：

https://www.coder.work/article/1516675

灵机一动，突然想到可能交叉编译器使用错误，arm-none-eabi从名字上就可以看出来是专门编译裸机程序的，可能不适合编译Linux应用程序。上网一查，果然，有专门交叉编译Linux应用程序的arm-linux-gnueabi-gcc。

3、解决方法：安装arm-linux-gnueabi-gcc工具链

在ubuntu上执行sudo apt install gcc-arm-linux-gnueabi就可以，在windows10上要下载：gcc-arm-10.3-2021.07-aarch64-arm-none-linux-gnueabihf.tar.xz （如果目标系统是arm32的）,下载链接：https://developer.arm.com/downloads/-/gnu-a

使用新安装的交叉编译工具链重新编译程序，然后scp到树莓派执行，都可以正常执行，问题解决。