Position Independent Code

• We want to maximize sharing of memory between processes

  • text (code) and read-only memory shouldn't change

  • ...even when the library or executable is loaded at a random location (ASLR)

  • generated code accesses variables and functions using relative addresses or by indirecting through a table

• the mappings needed by a program or library are packed into indirection tables

  • GOT: global offset table

    • stores final addresses of variables and functions

  • PLT: procedure linkage table

    • directly callable stub routines

• many architecture specific details