Всё, что вы хотели знать про SIGBUS, но так и не узнали

#include <stdlib.h>

int main(int argc, char **argv)
{
    int *iptr;
    char *cptr;

#if defined(__GNUC__)
# if defined(__i386__)
    /* Enable Alignment Checking on x86 */
    __asm__("pushf\norl $0x40000,(%esp)\npopf");
# elif defined(__x86_64__)
     /* Enable Alignment Checking on x86_64 */
    __asm__("pushf\norl $0x40000,(%rsp)\npopf");
# endif
#endif

    /* malloc() always provides aligned memory */
    cptr = malloc(sizeof(int) + 1);

    /* Increment the pointer by one, making it misaligned */
    iptr = (int *) ++cptr;

    /* Dereference it as an int pointer, causing an unaligned access */
    *iptr = 42;

    /*
       Following accesses will also result in sigbus error.
       short *sptr;
       int    i;

       sptr = (short *)&i;
       // For all odd value increments, it will result in sigbus.
       sptr = (short *)(((char *)sptr) + 1);
       *sptr = 100;

    */

    return 0;
}

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>

int main (int argc, char** argv) {
       	int fd = open("test", O_WRONLY | O_CREAT, 0644);
       	write(fd, "abcd\n", 5);
       	close(fd);

       	fd = open("test", O_RDONLY);
       	char* ptr = (char*)mmap(0, 102400, PROT_READ, MAP_SHARED, fd, 0);
       	char z = ptr[4097];
       	write(1, &z, 1);
       	return 0;
}

$ gcc t.c && ./a.out
Bus error (core dumped)