What is a fixup?
Anmay refer to some external it will output placeholder code like
“Put address some_symbollinks to non-existant zettel: some_symbol to register 5”.
And a note that says “Fill in that some_symnollinks to non-existant zettel: some_symnol with the actual address of symbol ‘foo’”.
Fixup refers to the process of using the above 2 information to update some_symbollinks to non-existant zettel: some_symbol to the actual correct address.
This information can be stored in the assembler.