Difference between API and ABI

api abi
Searock picture Searock · Sep 24, 2010 · Viewed 65.3k times · Source

I am new to linux system programming and I came across API and ABI while reading Linux System Programming.

Definition of API :

An API defines the interfaces by which one piece of software communicates with another at the source level.

Definition of ABI :

Whereas an API defines a source interface, an ABI defines the low-level binary interface between two or more pieces of software on a particular architecture. It defines how an application interacts with itself, how an application interacts with the kernel, and how an application interacts with libraries.

How can a program communicate at a source level ? What is a source level ? Is it related to source code in anyway? Or the source of the library gets included in the main program ?

The only difference I know is API is mostly used by programmers and ABI is mostly used by compiler.

Answer

Martin York picture Martin York · Sep 24, 2010

API: Application Program Interface

This is the set of public types/variables/functions that you expose from your application/library.

In C/C++ this is what you expose in the header files that you ship with the application.

ABI: Application Binary Interface

This is how the compiler builds an application.
It defines things (but is not limited to):

  • How parameters are passed to functions (registers/stack).
  • Who cleans parameters from the stack (caller/callee).
  • Where the return value is placed for return.
  • How exceptions propagate.

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