C语言也有一些标准的库，比如memcpy，属于标准库提供的内容

CRT可以理解为类似string.so这种东西（随便举的例子）

参考：runtime

https://en.wikipedia.org/wiki/Crt0

crt0 (also known as c0) is a set of execution startup routines linked into a C program that performs any initialization work required before calling the program's main function.

“crt” stands for “C runtime”, and the zero stands for “the very beginning”