Redefining functions lin libC

Question

Assume the following simple C code:

file1.c

#include <stdio.h>

char* gets(char* i){
  return i;
}

which is redefining the libC native function gets.

This compiles fine with gcc file1.c.

My question is howcome the linker isn't complaining about duplicate symbols as this function is also defined in libC itself?

Answer 1

Because you can override functions from standard libraries in C, check this

Answer 2

add option -whole-archive in the link phase, as below:

gcc -c -ofile1.o file1.c
gcc -ofile1 -Wl,--whole-archive -lc file1.o -Wl,--no-whole-archive

result:

file1.o: In function `gets':
file1.c:(.text+0x0): multiple definition of `gets'
file1.o: In function `main':
file1.c:(.text+0x18): undefined reference to `gets@@GLIBC_2.2.5'
collect2: error: ld returned 1 exit status