---
tags:
- low-level
- dev
- How data structures & computational routines are accessed in machine code ([Code Types](Code%20Types.md))
- Machine code therefore hardware-dependent
- API defines this structure in source code
- Adherence usually responsibility of
- [Compilers](Compilers.md)
- 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](Calling%20Conventions.md)
- 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](Compilers.md) create object code compatible with code from other [compilers](Compilers.md)
- Link libraries from different [compilers](Compilers.md)
