Editing Application binary interface

{{short description|Interface to software defined in terms of in-process, machine code access}}
{{Use dmy dates|date=June 2020}}
[[File:Linux kernel interfaces.svg|thumb|300px|A high-level comparison of in-kernel and kernel-to-userspace APIs and ABIs]]
[[File:Linux API and Linux ABI.svg|thumb|300px|The [[Linux kernel]] and [[GNU C Library]] define the [[Linux kernel interfaces#Kernel–user space API|Linux API]]. After compilation, the binaries offer an ABI. Keeping this ABI stable over a long time is important for [[Independent software vendor|ISVs]].]]

An '''application binary interface''' ('''ABI''') is an [[interface (computing)|interface]] exposed by [[software]] that is defined for in-[[Process (computing)|process]] [[machine code]] access. Often, the exposing software is a [[Library (computing)|library]], and the consumer is a [[computer program|program]].

An ABI is at a relatively low-level of [[abstraction (computer science)|abstraction]]. Interface compatibility depends on the target [[computer hardware|hardware]] and the [[software build]] [[toolchain]]. In contrast, an [[application programming interface]] (API) defines access in [[source code]] which is a relatively high-level, hardware-independent, and [[human-readable]] format. An API defines interface at the source code level, before compilation, whereas an ABI defines an interface to compiled code.

API compatibility is generally the concern for [[system design]] and of the toolchain. However, a [[programmer]] may have to deal with an ABI directly when writing a program in a multiple [[programming language|languages]] or [[compiler]]s.

A complete ABI enables a program that supports an ABI to run without modification on multiple operating systems that provide the ABI. The target system must provide any required libraries (that implement the ABI), and there may be other prerequisites.

== Description ==
Interface aspects covered by an ABI include:
* [[Processor (computing)|Processor]] [[instruction set]], with details like register file structure, [[Computer memory|memory]] access types, etc.
* Size, layout, and [[Data structure alignment|alignment]] of basic [[data type]]s that the processor can directly access
* [[Calling convention]], which controls how the arguments of [[function (programming)|function]]s are passed, and return values retrieved; for example, it controls the following:
** How the [[call stack]] is organized
** Whether all parameters are passed on the call stack, or some are passed in registers
** Which registers are used for which function parameters
** Whether the first function parameter passed on the call stack is pushed first or last
** Whether the caller or callee is responsible for cleaning up the call stack after the function call
* [[Name mangling]]<ref>{{cite web|url=https://itanium-cxx-abi.github.io/cxx-abi/|title=Itanium C++ ABI}} (compatible with multiple architectures)</ref>
* [[exception handling|Exception]] propagation<ref>{{cite web|url=http://itanium-cxx-abi.github.io/cxx-abi/abi-eh.html|title=Itanium C++ ABI: Exception Handling}} (compatible with multiple architectures)</ref>
* How an application should make [[system call]]s to the operating system, and if the ABI specifies direct system calls rather than procedure calls to system call [[Method stub|stubs]], the system call numbers
* In the case of a complete operating system ABI, the binary format of [[object file]]s, program libraries, etc.

ABIs include the [[Intel Binary Compatibility Standard]] (iBCS)<ref>{{cite web |url=http://www.everything2.com/index.pl?node=iBCS |title=Intel Binary Compatibility Standard (iBCS)}}</ref> and the [[System V Release 4]] ABIs for various instruction sets.

== {{Anchor|EABI}}Embedded ABI ==
An '''embedded ABI''' (EABI), used on an [[embedded operating system]], specifies aspects such as [[file format]]s, data types, register usage, [[stack frame]] organization, and function parameter passing of an [[Embedded system|embedded]] software program.

Each compiler and [[assembly language|assembler]] that supports an EABI creates [[object code]] that is compatible with code generated by other such compilers and assemblers. This allows developers to link libraries generated by one compiler with object code generated by another.

Typically, an EABI is optimized for performance for the limited resources of the target embedded system. Therefore, an EABI may omit abstractions between [[User space and kernel space|kernel and user space]] typically found in [[desktop computer|desktop]] operating systems. For example, [[dynamic linking]] may be avoided to allow smaller executables and faster loading, fixed register usage allows more compact stacks and kernel calls, and running the application in privileged mode allows direct access to custom hardware operation without the indirection of calling a device driver.<ref name="ppc-eabi">{{cite book
 |     title = PowerPC Embedded Application Binary Interface: 32-Bit Implementation
 |      date = 1 October 1995
 |   edition = Version 1.0
 |   chapter = EABI Summary
 |     pages = 28&ndash;30
 | publisher = Freescale Semiconductor, Inc
 |       url = http://www.nxp.com/docs/en/application-note/PPCEABI.pdf
}}</ref>  The choice of EABI can affect performance.<ref>{{cite web
 |title=Debian ARM accelerates via EABI port
 |date=16 October 2016
 |publisher=Linuxdevices.com
 |url=http://linuxdevices.com/news/NS9048137234.html
 |access-date=11 October 2007
 |archive-url=https://web.archive.org/web/20070121183413/http://www.linuxdevices.com/news/NS9048137234.html
 |archive-date=21 January 2007
|url-status=dead
}}</ref><ref>{{cite web
 |author=Andrés Calderón and Nelson Castillo
 |title=Why ARM's EABI matters
 |date=14 March 2007
 |publisher=Linuxdevices.com
 |url=http://linuxdevices.com/articles/AT5920399313.html
 |access-date=11 October 2007
 |archive-url=https://web.archive.org/web/20070331193917/http://www.linuxdevices.com/articles/AT5920399313.html
 |archive-date=31 March 2007
|url-status=dead
}}</ref>

Widely used EABIs include the [[PowerPC]],<ref name="ppc-eabi"/> [[Arm architecture|Arm]],<ref>{{cite web|url=https://developer.arm.com/architectures/system-architectures/software-standards/abi |title=ABI for the Arm Architecture |publisher=Developer.arm.com |access-date=4 February 2020}}</ref> and [[MIPS architecture|MIPS]] EABIs.<ref>{{cite mailing list |url=https://sourceware.org/legacy-ml/binutils/2003-06/msg00436.html |author=Eric Christopher |title=mips eabi documentation |mailing-list=binutils@sources.redhat.com |date=11 June 2003 |access-date=19 June 2020}}</ref> Specific software implementations like the C library may impose additional limitations to form more concrete ABIs; one example is the GNU OABI and EABI for ARM, both of which are subsets of the ARM EABI.<ref>{{cite web |title=ArmEabiPort |url=https://wiki.debian.org/ArmEabiPort |website=Debian Wiki |quote=Strictly speaking, both the old and new ARM ABIs are subsets of the ARM EABI specification, but in everyday usage the term "EABI" is used to mean the new one described here and "OABI" or "old-ABI" to mean the old one.}}</ref>

== See also ==
{{Portal|Computer programming}}

* {{Annotated link|Binary-code compatibility}}
* {{Annotated link|Bytecode}}
* {{Annotated link|Comparison of application virtualization software}}
* {{Annotated link|Debug symbol}}
* {{Annotated link|Foreign function interface}}
* {{Annotated link|Language binding}}
* {{Annotated link|Native (computing)}}
* {{Annotated link|Opaque pointer}}
* {{Annotated link|PowerOpen Environment}}
* {{Annotated link|Symbol table}}
* {{Annotated link|SWIG}}
* [[Visual C++#Compatibility|Visual C++ Compatibility]]

==References==
{{Reflist|30em}}

== External links ==
* [https://community.kde.org/Policies/Binary_Compatibility_Issues_With_C%2B%2B Policies/Binary Compatibility Issues With C++]{{snd}} a compendium of development rules of thumb for not breaking binary compatibility between library releases
* [https://developer.apple.com/library/content/documentation/DeveloperTools/Conceptual/LowLevelABI/000-Introduction/introduction.html OS X ABI Function Call Guide]
* [http://wiki.debian.org/ArmEabiPort Debian ARM EABI port]
* [http://www.uclibc.org/ μClib: Motorola 8/16-bit embedded ABI]
* {{webarchive|url=https://web.archive.org/web/20080528070803/http://www.x86-64.org/documentation.html|title=AMD64 (x86-64) Application Binary Interface}}
* [http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ihi0036b/index.html Application Binary Interface (ABI) for the ARM Architecture]
* [https://sourceware.org/legacy-ml/binutils/2003-06/msg00436.html MIPS EABI documentation]
* {{webarchive|url=https://web.archive.org/web/20150114065444/http://www.oracle.com/technetwork/server-storage/solaris10/about-amd64-abi-141142.html|title=Sun Studio 10 Compilers and the AMD64 ABI}}{{snd}} a summary and comparison of some popular ABIs
* [https://www.nxp.com/docs/en/reference-manual/MCOREABISM.pdf M•CORE Applications Binary Interface Standards Manual] for the Freescale [[M·CORE]] processors

{{Application binary interface}}

[[Category:Application programming interfaces]]
[[Category:Operating system technology]]