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

/* Allocate size bytes of executable memory. */
unsigned char *alloc_exec_mem(size_t size)
{
        void *ptr;

        ptr = mmap(0, size, PROT_READ | PROT_WRITE | PROT_EXEC,
                   MAP_PRIVATE | MAP_ANON, -1, 0);

        if (ptr == MAP_FAILED) {
                perror("mmap");
                exit(1);
        }

        return ptr;
}

/* Read up to buffer_size bytes, encoded as 1's and 0's, into buffer. */
void read_ones_and_zeros(unsigned char *buffer, size_t buffer_size)
{
        unsigned char byte = 0;
        int bit_index = 0;
        int c;

        while ((c = getchar()) != EOF) {
                if (isspace(c)) {
                        continue;
                } else if (c != '0' && c != '1') {
                        fprintf(stderr, "error: expected 1 or 0!\n");
                        exit(1);
                }

                byte = (byte << 1) | (c == '1');
                bit_index++;

                if (bit_index == 8) {
                        if (buffer_size == 0) {
                                fprintf(stderr, "error: buffer full!\n");
                                exit(1);
                        }
                        *buffer++ = byte;
                        --buffer_size;
                        byte = 0;
                        bit_index = 0;
                }
        }

        if (bit_index != 0) {
                fprintf(stderr, "error: left-over bits!\n");
                exit(1);
        }
}

int main()
{
        typedef int (*func_ptr_t)(void);

        func_ptr_t func;
        unsigned char *mem;
        int x;

        mem = alloc_exec_mem(1024);
        func = (func_ptr_t) mem;

        read_ones_and_zeros(mem, 1024);

        x = (*func)();

        printf("function returned %d\n", x);

        return 0;
}