For example, if you want to assemble something that ends at ramtop you could do: .org RAMTOP-code_size code_start: ... ... code_end: code_size=code_end-code_start For now this will result in an error since none of the labels after the .org are known when .org will be assembled. So at least for this simple example we could flag that the .org address be modified before the fixups start, since hopefully by then all labels should have been resolved. And if not, then give an error.
Should be easy enough to add.