What is a fixup?

An object file .o / .obj may 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.