ABI

• How data structures & computational routines are accessed in machine code (Code Types)
  • Machine code therefore hardware-dependent
• API defines this structure in source code
• Adherence usually responsibility of
  • Compilers
  • OS
  • Library author

Components

• Processor instruction set
  • Register file structure
  • Stack organisation
  • Memory access types
• Size, layouts and alignments of basic data types
• Calling Conventions
  • How function arguments are passed
    • Stack or register
    • Which registers for which function param
    • Parameter order
  • Return values retrieved
• How app makes sys calls to OS
  • If ABI specifies direct sys calls over procedure calls to sys call stubs then sys call numbers
• Binary format of object files, program files
  • For complete OS ABIs

Complete ABI

• Allows program from one OS to run on any other without change
  • Provided all shared libraries and prerequisites etc

Embedded ABI

• File format, data types, register usage, stack frame organisation, function parameter passing conventions
  • For embedded OS
• Compilers create object code compatible with code from other compilers
  • Link libraries from different compilers