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Programs

What is a program​

Code - Instructions that make up the program Data - Any data compiled into the program BBS - Any uninitialised data

Address​

Can put this anywhere in memory, as they are all just bytes

  • Code - Bytes that make up the opcodes for the programs instructions
  • Data - Bytes that represent the data
  • BSS - Bytes that we know will need to store things in at some point Providing the address are know the program would work fine, tend to be a little more structured when creating programs

Program Structure​

  • Find all the code is grouped together in one section (.text section)
  • Followed by all the data grouped into another section (.data section)
  • Followed by the BSS

Benefits​

  • Combining the sections enables the OS to do nice things
  • Code can be shared between multiple instances of the same program
  • Can make the code sections of memory read-only
  • Can make the data sections non-executable

Libraries​

  • Same approach is take with static libs
  • Code, data and BSS sections linked in which program code
  • Libraries are often just a collection of object files
  • Windows uses DLLs

Executable File​

  • Each section of the final linked program is then stored on disk
  • No need to store the BSS