[[ building "Ultrix"-ABI binaries on non-Ultrix platforms, to test COMPAT_ULTRIX ]] I think x86 or arm makes a lot more sense than Sparc. All Ultrix platforms were little-endian. I don't recall ever making COMPAT_ULTRIX endian-neutral. Or whether any of the struct-copying code cares. You'd also have to create fake system headers with the Ultrix/4.3BSD-sized structs, and compile your userland test app using those headers. And all the ioctl codes, using the COMPAT struct sies. Not particularly hard, but tedious and error-prone.