[Dovecot] IMAP crashes with signal 10 (SIGBUS)

I wrote:

Any idea on what's causing this?

Description: imap process crashed with SIGBUS.

Versions: OS: Solaris 8, 9 Dovecot: 1.0-test57 Gcc: 3.2

same with 3.4.3

Backtrace: #0 mbox_file_seek (ibox=0x8d9b0, view=0x8dc38, seq=2, deleted_r=0xffbef40c) at mbox-file.c:119 ...

Subsequent versions still crashed and I looked into the problem further. Specifically it crashes at this line

offset = *((const uint64_t *)data);

when "data" assumes a non-64 bit aligned value. At first I thought that 64-bit ints should always be aligned on 64-bit boundaries, but when I isolated this code into a standalone executable to demonstrate it (no arguments to cause a crash, one argument is OK):

int main (int argc, char *argv[]) {
	int		a[]={1,2,3,4};
	long long int	i64;
	void 		*p=(void *) (&a[argc]);;

	printf("Pointer to 32-bit int = %x\n",p);
	i64 = *((long long int *)p);
	printf("Successful casting to 64-bit int: value=%016llx\n",i64);
}

I found out that the presence of any optimisation (-O, -O2, -O3) will cause this to crash, yet it will work if no optimisation is present even though a pointer being cast is still not aligned on a 64-bit boundary (but aligned on a 32-bit boundary).

I check the gcc bug web page page came up with this reference which may explain this behaviour.

http://gcc.gnu.org/bugs.html#known
	- see section "Casting does not work as expected when optimization is turned on"
http://mail-index.netbsd.org/tech-kern/2003/08/11/0001.html

They claim that this casting violates ISO aliasing rules and the results like crashing are to be expected. Maybe this statement ought to be rewritten

memcpy(&offset,data,sizeof(uint64_t));

There is one other statement at

mbox-synbc.c:319 (1.0-test59)

that may need this consideration.

Joseph Tam tam@math.ubc.ca