I have been testing hwloc on my macbook (OSX 10.6.8, Core 2 Duo, 4MB L2 Cache), and the 1.2 version of hwloc is unable to determine the cache sizes at all. I had initially used 1.0.3, which was doing fine, and I also tested 1.1.2, and that also appears to be fine. I attach screenshots from 1.0.3 and 1.2. Finally, I tested the trunk (rev 3551) and that is broken as well.
Just to let you know, in case this problem has not been already reported.
PS: I was unable to figure out if bug reports could be filed somewhere on the Trac system. I hope this mailing list is the correct destination. Otherwise I apologize in advance for spamming other users.