> The SIGBUS could be due to the buildbot running out of tmpfs.

I haven't been able to reproduce the crash by running the test on a tmpfs
on my own machine (Ubuntu AMD64; 8GB RAM; Linux 3.0.0-15-generic; zlib
1:1.2.3.4.dfsg-3ubuntu3), but maybe it's due to something specific about
the configuration of the buildbot machine?

I've temporarily changed the test to use a regular chunk of memory
instead of the mmap hack). If possible, I'd like to change back to the
old technique in the long run (since it allows the test to run on
machines with less RAM), but until we can figure out the problem, I'd
rather not have the test failing needlessly.