Mini_crt

It is a tiny implemetation of C runtime library for 64-bit Linux in 程序员的自我修养--链接、装载与库 (chapter 13.1), and it is programmed on Ubuntu 20.04.6 LTS (GNU/Linux 5.4.0-153-generic x86_64).

It does not support Windows or 32-bit Linux.

All system calls are implemeted by assembly: asm(""::).

entry.c

It calculates the argc and argv, and passes them to main().

malloc.c

It provides malloc and free by sys_brk(). It uses a linklist of struct heap_header to manage space.

stdio.c

It provieds fundamental file operations like fopen, fclose,fwrite, fread, fseek.

string.c

It provids fundamental string operations like strcpy, strcmp, strlen.

Build

$ cd study/mini_crt
$ make all
$ ./test {argc1} {argc2} ...
$ cat ./test1
$ make clean

Others

The original codes in the book can not run on 64-bit Linux.

1.I change the assembly code for 64-bit, like "movl %%eax" ->"movq %%rax".

2.All address-related or assembly-related variables should fit for 64-bit OS.

3.In the test.c, we need to use malloc for the integer len.Otherwise, it will not work on writing a integer in the file.