What is an application binary interface (ABI)?

Question

I never clearly understood what an ABI is. Please don\'t point me to a Wikipedia article. If I could understand it, I wouldn\'t be here posting such a lengthy post.

Answer 1

ABI - Application Binary Interface is about a machine code communication in runtime between two binary parts like - application, library, OS... ABI describes how objects are saved in memory, how functions are called(calling convention), mangling...

A good example of API and ABI is iOS ecosystem with Swift language.

• Application layer - When you create an application using different languages. For example you can create application using Swift and Objective-C[Mixing Swift and Objective-C]

• Application - OS layer - runtime - Swift runtime and standard libraries are parts of OS and they should not be included into each bundle(e.g. app, framework). It is the same as like Objective-C uses

• Library layer - Module Stability case - compile time - you will be able to import a framework which was built with another version of Swift's compiler. It means that it is safety to create a closed-source(pre-build) binary which will be consumed by a different version of compiler( .swiftinterface is used with .swiftmodule) and you will not get

  Module compiled with _ cannot be imported by the _ compiler
  

• Library layer - Library Evolution case

1. Compile time - if a dependency was changed, a client has not to be recompiled.
2. Runtime - a system library or a dynamic framework can be hot-swapped by a new one.

[API vs ABI]
[Swift Module and Library stability]