The profiling tool in GNU is called gprof. Here is a short, boring example of how to use it.

1) Write hello world in C (hello.c)

#include 
 
int foo() {
  int b = 54324;
  int j;
  for (j=0; j < 1000000; j++) {
    b = b^j;
  }
  return b;
}
 
int main() {
  int a = 321782;
  int i;
  for(i=0; i<1000; i++) {
    a = a ^ foo();
  }
  printf("Hello foo: %d\n", a);
  return 0;
}

}

2) Compile with -pg option

gcc -pg hello.c

3) Run the program to generate profiling information

./a.out # this generates gmon.out file

4) Run gprof on the program and read output in less:

gprof a.out gmon.out | less