How to get a "bus error"?

Question

I am trying very hard to get a bus error.

One way is misaligned access and I have tried the examples given here and here, but no error for me - the programs execute just fine.

Is there some situation which is sure to produce a bus error?

Answer 1

This should reliably result in a SIGBUS on a POSIX-compliant system.

#include <unistd.h>
#include <stdio.h>
#include <sys/mman.h>
int main() {
    FILE *f = tmpfile();
    int *m = mmap(0, 4, PROT_WRITE, MAP_PRIVATE, fileno(f), 0);
    *m = 0;
    return 0;
}

From the Single Unix Specification, mmap:

References within the address range starting at pa and continuing for len bytes to whole pages following the end of an object shall result in delivery of a SIGBUS signal.

Answer 2

Bus errors can only be invoked on hardware platforms that:

1. Require aligned access, and
2. Don't compensate for an unaligned access by performing two aligned accesses and combining the results.

You probably do not have access to such a system.

Answer 3

Try something along the lines of:

#include <signal.h>
int main(void)
{
    raise(SIGBUS);
    return 0;
}

(I know, probably not the answer you want, but it's almost sure to get you a "bus error"!)

Answer 4

As others have mentioned this is very platform specific. On the ARM system I'm working with (which doesn't have virtual memory) there are large portions of the address space which have no memory or peripheral assigned. If I read or write one of those addresses, I get a bus error.

You can also get a bus error if there's actually a hardware problem on the bus.

If you're running on a platform with virtual memory, you might not be able to intentionally generate a bus error with your program unless it's a device driver or other kernel mode software. An invalid memory access would likely be trapped as an access violation or similar by the memory manager (and it never even has a chance to hit the bus).