It's an awkward way to reserve memory. The important detail here is that both compiler phases do this, and the way the programs are linked guarantees that the reserved region has the same address in both phases. Therefore an expression tree involving pointers can be passed to the second phase very succinctly. Not pretty, no, but hardware limitations force you to do come up with strange solutions sometimes.
Here's the actual code that references the 'ospace' from before 'waste': https://github.com/mortdeus/legacy-cc/blob/936e12cfc756773cb...
Thank you! Is it relevant today at all, or is there an use-case for it today?
No, if you need fixed addresses i suppose a linker script would be the way to go? Or in this case you'd just serialize the data such that it doesn't contain any pointers in the first place.
There are better tools to do this these days—with the GNU toolchain, for example, you’d use a linker script and make sure you’re building a non-position-independent static executable. Alternatively, you could use self-relative pointers: instead of having foo_t *foo and putting p there, have ptrdiff_t foo and put ((char *)p - (char *)&foo) there.