I am surprised by the number of comments that say the assembler is trivial - it is admittedly perhaps simpler than some other parts of the compiler chain, but it’s not trivial.

What you are doing is kinda serialising a self-referential graph structure of machine code entries that reference each others addresses, but you don’t know the addresses because the (x86) instructions are variable-length, so you can’t know them until you generate the machine code, chicken-and-egg problem.

Personally I find writing parsers much much simpler than writing assemblers.