Why doesn't `-finstrument-functions` work for me?

Question

According to this answer,it should print all function names:

[root@ test]# cat hw.c
#include 

int func(void)
{  
  return 1;
}
int main(void)         


        

Answer 1

You didn't actually implement any instrumentation. The -finstrument-functions switch just tells gcc to call some function at entry and exit to each function. But you have to define these functions yourself (normally this is done by linking a profiler library in).