In computer software, an application binary interface (ABI) describes the low-level interface between an application (or any type of) program and the operating system or another application.
ABIs cover details such as data type, size, and alignment; the calling convention, which controls how functions' arguments are passed and return values retrieved; the system call numbers and how an application should make system calls to the operating system; and in the case of a complete operating system ABI, the binary format of object files, program libraries and so on. A complete ABI, such as the Intel Binary Compatibility Standard (iBCS), allows a program from one operating system supporting that ABI to run without modifications on any other such system, provided that necessary shared libraries are present, and similar prerequisites are fulfilled.
Other ABIs standardize details such as the C++ name mangling, exception propagation, and calling convention between compilers on the same platform, but do not require cross-platform compatibility.
An ABI should not be confused with an application programming interface (API) which defines a library of routines to call, data structures to manipulate, and/or object classes to use in the construction of an application using that particular (often language specific) API.
An embedded-application binary interface (EABI) specifies standard conventions for file formats, data types, register usage, stack frame organization, and function parameter passing of an embedded software program.
Compilers that support the EABI create object code that is compatible with code generated by other such compilers, thus allowing developers to link libraries generated with one compiler with object code generated with a different compiler. Developers writing their own assembly language code may also use the EABI to interface with assembly generated by a compliant compiler.
The main differences of an EABI with respect to an ABI for general purpose operating systems are that privileged instructions are allowed in application code, dynamic linking is not required (sometimes it is completely disallowed), and a more compact stack frame organization is used to save memory.
Widely used EABIs include PowerPC and ARM.
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