Garbage collector needs to know

• reference roots
• reference fields

Need to generation information on

• global variables
• heap: tag each record with its type information, like class descriptors for dynamic method calls from Lecture 13
• stack: need stack map that determines for relevant points where references are on stack and registers

Note: sometimes compiler generates pointer arithmetic on references to access fields

• stack map must indicate those pointers, too, and indicate what their base pointers are