I can't seem to get the Garbage Collector to work properly on MacOS X. When a program triggers the Garbage Collector, it aborts with the following message: a.out: fatal error: scavenge_stack: weird activation record found on stack: 0 The same error happens both in unregistered mode and using my half-finished powerpc mangler (BTW, Hello World already works in registered mode!). In unregistered mode, I have also observed different numbers instead of zero in the error message. I'm positive that the problem is in the basic day-to-day workings of the STG machine. main = print $ length $ [1..5000000] -- aborts the first time GC is invoked It has nothing to do with the libs, I can replace length and the list generation with my own functions and print with a foreign import, and the result stays the same: crash on first GC, fine otherwise. Now I'm stuck. Are there any reasonably up-to-date docs on what a "normal" activation record should look like? The file GC.c is not exactly the kind of code that I understand the first time that I read it... One of my random guesses is that there is a problem with struct alignment, which has more padding on PPC than on Intel --- on the other hand, GHC is supposed to work on Sparc, and that doesn't use Intel alignment either, AFAIK (does the HEAD currently work on Sparc? The ghc-5.03 snapshot on the download page seems to have only intel versions). Can anyone give me any hints? Wolfgang