Linker Loader

Question : Can multiple programs share physical memory without hardware translation ?

• Yes : when program is copied into memory its addresses (loads, stores, branches, jumps) are changed to use the addresses of where program is placed in memory
• The linker-loader - which does the resolving
• Unix ld works this way : compiler generates a .o file with code that starts at location 0. How is an actual executable created from this ?
• Go through each .o file, and change addresses to point to where each module goes in the larger program (compiler oriented)
• With linker-loader no protection: one program's bugs can cause others to crash

  
Figure 8: Multiple User Programs in Memory

  
Figure 9: Use of Base and Bound Register

• Bound Register keeps check no unauthorised locations are referenced
• Base Register helps to determine virtual address