Self modifing code in C.

smod.c

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

typedef int (*func_t)(void);

int main(int argc, char *argv[])
{
    char *fstart = "\x55\x48\x89\xe5\x48\x31\xc0";
    char *incrax = "\x48\xff\xc0";
    char *fend   = "\x5d\xc3";
    int icnt = 5;
    int i;
    char *text = mmap(NULL, 4096, PROT_READ|PROT_WRITE|PROT_EXEC
                                , MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
    if (argv[1]) {
        icnt = atoi(argv[1]);
    }
    strcpy(text, fstart);
    for (i = 0; i < icnt; i++) {
        strcat(text, incrax);
    }
    strcat(text, fend);
    func_t fn = (func_t)text;
    printf("%d\n", fn());
}