Hi All, just wanted to report that as of Alien-eem.35 and https://github.com/OpenSmalltalk/vm/commit/da3fafdec9444754af104e0ed9f613f6e... we now have functional callbacks on all x86 platforms, ARM32 platforms and x86_64 platforms. There's a simple example Alien class>>exampleCqsort that shows how to use the system and tests the implementation using the C library's sort quick sort implementation that takes a function pointer as an argument to use for comparing pairs of elements. This is mapped onto a Smalltalk block by Alien's callback implementation. The example sorts 100 random double-precision floats using qsort and a callback into Smalltalk. _,,,^..^,,,_ best, Eliot