ksh for 2.11BSD

[John D. Bruner]

In case anyone is interested, I've back-ported (pd)ksh from NetBSD-5.0.2 to 2.11BSD:

https://github.com/jdbruner/ksh

There is a prebuilt binary and formatted manpage in release v0.0.1   I've been using it as my login shell for a few months now, although I haven't really stressed it, so (as the version number implies) it's probably best to consider it as alpha quality.

I started with the NetBSD-5.0.2 version because it was closer in age to 2.11BSD, reducing the backport effort. One notable backporting issue was the use of pointers to static functions, which are an issue with overlays. For each non-static function there is a thunk in the common base area that handles the overlay switch. Pointers to these functions actually point to the thunk, so they work as expected. However, for static functions there is no thunk - so function pointers have unpredictable behavior when the called function is in a different overlay than the caller. The workaround is to declare any function invoked via a pointer as non-static. It's likely that I haven't found all of these yet.

--John