include <sys/mman.h>

include <err.h>

include <fcntl.h>

include <stdio.h>

include <stdlib.h>

include <string.h>

include <unistd.h>

typedef void (*fn)(int *); // NOTE the signature change!

define SLABSIZE 4096

int

main(int argc, char *argv[])

{

int value = 41;

unsigned char *slab = malloc(SLABSIZE);

if (!slab) err(1, "malloc");

memset(slab, 0xC3, SLABSIZE);

memcpy(slab, &(unsigned char[]){0xf3, 0xf,  0x1e, 0xfa, 0x55, 0x48,

                                0x89, 0xe5, 0x48, 0x89, 0x7d, 0xf8,

                                0x48, 0x8b, 0x45, 0xf8, 0x8b, 0x8,

                                0x83, 0xc1, 0x1,  0x89, 0x8,  0x5d},

       24);

int fd = open("slab", O_WRONLY | O_CREAT, 0666);

if (fd <= 0) err(1, "open");

write(fd, slab, SLABSIZE);

close(fd);

if (mprotect(slab, SLABSIZE, PROT_EXEC) != 0) err(1, "mprotect");

ifdef OpenBSD

if (pledge("stdio", NULL) == -1) err(1, "pledge");

endif

fn call = (fn) slab;

call(&value);

printf("%d\n", value);

}