LD_DEBUG 是 glibc 中的 loader 为了方便自身调试而设置的一个环境变量。通过设置这个环境变量，可以方便的看到 loader 的加载过程。
LD_DEBUG=help ./main
Valid options for the LD_DEBUG environment variable are:
libs display library search paths
reloc display relocation processing
files display progress for input file
symbols display symbol table processing
bindings display information about symbol binding
versions display version dependencies
all all previous options combined
statistics display relocation statistics
unused determined unused DSOs
help display this help message and exit
To direct the debugging output into a file instead of standard output
a filename can be specified using the LD_DEBUG_OUTPUT environment variable.
用法 root@wshn$LD_DEBUG=libs ./main
4452:
find library=libc.so.6 [0]; searching
4452: search cache=/etc/ld.so.cache
4452: trying file=/lib/i386-Linux-gnu/libc.so.6
4452:
4452:
4452: calling init: /lib/i386-linux-gnu/libc.so.6
4452:
4452:
4452: initialize program: ./main
4452:
4452:
4452: transferring control: ./main
4452:
Hello
4452:
4452: calling fini: ./main [0]
4452:
4452:
4452: calling fini: /lib/i386-linux-gnu/libc.so.6 [0]
4452:
LD_DEBUG的可选参数在help里面可以看见其复用形式
LD_DEBUG=libs,symbols ./main
输出log保存可以使用LD_DEBUG=all LD_DEBUG_OUTPUT=log ./main 会生成一个output指定文件名加进程号结尾的文件