Labels are symbolic names for targets of branch instructions
- generate sequence of instructions with unknown destinations
- once lengths of code are known, resolve all labels
- emit the code
Two main kinds of jumps:
- absolute: indicate address from some fixed position
- relative: indicate address as an increment over current program counter
- positive increment: jumping forward
- negative increment: jumping backward
A minimal infrastructure for writing machine code
- allow ASCII names for instructions instead of operation codes
- avoid having to know labels for jumps (what we needed now)
- store constants for strings and other large data (give back the address of that data)
- Our cafebabe library enables Scala to be used as an assembler for Java bytecodes
- take small C file test.c, do 'gcc test.c -S'
- run the assembler by 'as test.s'