Sample self-modifying code

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#include <stdint.h>

/*
f definition:
00000000004005e6 <f>:
    4005e6:     55          push   %rbp
    4005e7:     48 89 e5        mov    %rsp,%rbp
    4005ea:     be 01 00 00 00      mov    $0x1,%esi
               ^^^^^^^^^^^ this is what i change
so it's f+5
*/
uint32_t f() {
    printf("%d\n", 1);
}

int main() {
    uint32_t *p;
    /* I found that ready */
    void *page = (void *) ((unsigned long) (&f) & ~(getpagesize() - 1));

    p = malloc(sizeof(uint32_t));

    /* mark the code section we are going to overwrite as writable. */
    mprotect(page, getpagesize(), PROT_READ | PROT_WRITE | PROT_EXEC);

    while (*p < 100) {
        f();
        memcpy(p, (f+5), sizeof(uint32_t));
        *p += 1;
        memcpy((f+5), p, sizeof(uint32_t));
    }

    return 0;
}