I did not build busybox. It is in the aboriginal linux rootfs images I downloaded from landley.net. I was just planning to copy existing bits & pieces from aboriginal to my K1.
Though after those missing symbols, it looks like I may have to build aboriginal from source after all. No luck yet finding how to configure aboriginal to keep those symbols (uses a build script, not a configure script, and the missing symbol "enables" are only found in temp "do not edit" config files).
One of the armv4l binaries that runs on K1 and not K2+ is the
busybox-armv4l I mentioned previously, but it is stripped. Also, the binaries from aboriginal-ar4vl rootfs are stripped. So I compiled a non-stripped "hello world" (attached tarball). I tested it in multiple environments.
Working in aboriginal-arm4vl build environent, x86 linux mint with binfmt and qemu-arm-static, on the K1.
NOT working on K2 (hangs) or on PW3 (hangs). Well, this is new behavior -- no segfault or "Illegal instruction". Just a good old hung app. On earlier PW3 firmware, this armv4l "hello" program segfaulted as I recall. Same build environment, but fresh compile. New behavior. Never tested on the K2 before now. I expected a segfault on K2 and PW3, but just hanging instead.
EDIT: I read your edit. I browsed the download file. I see that you can also PIPE the name of a command into busybox, apparently (i.e. feed it a script file with it being the script handler). Interesting, and more interesting that it can build those symlink-replacement scripts for you too. Same idea I had (modelled on library loader scripts) but better execution.