我也试图理解ABI, JesperE的回答很有帮助。

从一个非常简单的角度来看，我们可以尝试通过考虑二进制兼容性来理解ABI。

KDE wiki将库定义为二进制兼容的，“如果动态链接到库的前版本的程序继续与库的新版本一起运行，而不需要重新编译”。有关动态链接的更多信息，请参阅静态链接与动态链接

现在，让我们试着看看一个库需要二进制兼容性的最基本方面(假设库没有源代码更改):

相同/向后兼容的指令集架构(处理器指令、寄存器文件结构、堆栈组织、内存访问类型，以及处理器可以直接访问的基本数据类型的大小、布局和对齐) 相同调用约定 同名混淆约定(如果Fortran程序需要调用一些c++库函数，这可能是需要的)。

当然，还有许多其他细节，但这主要是ABI所涵盖的内容。

更具体地回答你的问题，由以上，我们可以推断:

ABI功能:二进制兼容性 现有实体:现有程序/库/操作系统 消费者:库，操作系统

希望这能有所帮助!

调用方和被调用方之间的ABI需要一致，以确保调用成功。堆栈使用，寄存器使用，程序结束堆栈弹出。所有这些都是ABI中最重要的部分。

应用二进制接口(ABI)

ABI -应用二进制接口是关于运行时两个二进制部分之间的机器码通信，如应用程序，库，操作系统…ABI描述了如何将对象保存在内存中，如何调用函数(调用约定)，如何修改…

API和ABI的一个很好的例子是iOS生态系统从v5开始使用Swift语言。

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 Standard Library and Swift Run Time Library[About] 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. Available from iOS v12.2 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[About]) and you will not get Module compiled with _ cannot be imported by the _ compiler //or Compiled module was created by a newer version of the compiler Library layer - Library Evolution case Compile time - if a dependency was changed, a client has not to be recompiled. Runtime - a system library or a dynamic framework can be hot-swapped by a new one.

[API vs ABI] [Swift模块稳定性和库稳定性]

理解“ABI”的一个简单方法是将其与“API”进行比较。

您已经熟悉了API的概念。如果你想使用某些库或操作系统的特性，你将根据API进行编程。API由数据类型/结构、常量、函数等组成，您可以在代码中使用它们来访问外部组件的功能。

An ABI is very similar. Think of it as the compiled version of an API (or as an API on the machine-language level). When you write source code, you access the library through an API. Once the code is compiled, your application accesses the binary data in the library through the ABI. The ABI defines the structures and methods that your compiled application will use to access the external library (just like the API did), only on a lower level. Your API defines the order in which you pass arguments to a function. Your ABI defines the mechanics of how these arguments are passed (registers, stack, etc.). Your API defines which functions are part of your library. Your ABI defines how your code is stored inside the library file, so that any program using your library can locate the desired function and execute it.

ABIs are important when it comes to applications that use external libraries. Libraries are full of code and other resources, but your program has to know how to locate what it needs inside the library file. Your ABI defines how the contents of a library are stored inside the file, and your program uses the ABI to search through the file and find what it needs. If everything in your system conforms to the same ABI, then any program is able to work with any library file, no matter who created them. Linux and Windows use different ABIs, so a Windows program won't know how to access a library compiled for Linux.

有时，ABI更改是不可避免的。当这种情况发生时，任何使用该库的程序都将无法工作，除非它们被重新编译以使用新版本的库。如果ABI改变了，但API没有改变，那么新旧库版本有时被称为“源代码兼容”。这意味着，虽然为一个库版本编译的程序不能与另一个库版本一起工作，但为一个库版本编写的源代码如果重新编译，则可以与另一个库版本一起工作。

For this reason, developers tend to try to keep their ABI stable (to minimize disruption). Keeping an ABI stable means not changing function interfaces (return type and number, types, and order of arguments), definitions of data types or data structures, defined constants, etc. New functions and data types can be added, but existing ones must stay the same. If, for instance, your library uses 32-bit integers to indicate the offset of a function and you switch to 64-bit integers, then already-compiled code that uses that library will not be accessing that field (or any following it) correctly. Accessing data structure members gets converted into memory addresses and offsets during compilation and if the data structure changes, then these offsets will not point to what the code is expecting them to point to and the results are unpredictable at best.

除非您正在进行非常低级的系统设计工作，否则您不必显式地提供ABI。它也不是特定于语言的，因为(例如)C应用程序和Pascal应用程序在编译后可以使用相同的ABI。

Edit: Regarding your question about the chapters regarding the ELF file format in the SysV ABI docs: The reason this information is included is because the ELF format defines the interface between operating system and application. When you tell the OS to run a program, it expects the program to be formatted in a certain way and (for example) expects the first section of the binary to be an ELF header containing certain information at specific memory offsets. This is how the application communicates important information about itself to the operating system. If you build a program in a non-ELF binary format (such as a.out or PE), then an OS that expects ELF-formatted applications will not be able to interpret the binary file or run the application. This is one big reason why Windows apps cannot be run directly on a Linux machine (or vice versa) without being either re-compiled or run inside some type of emulation layer that can translate from one binary format to another.

IIRC, Windows目前使用可移植可执行文件(PE)格式。在维基百科页面的“外部链接”部分有关于PE格式的更多信息的链接。

Also, regarding your note about C++ name mangling: When locating a function in a library file, the function is typically looked up by name. C++ allows you to overload function names, so name alone is not sufficient to identify a function. C++ compilers have their own ways of dealing with this internally, called name mangling. An ABI can define a standard way of encoding the name of a function so that programs built with a different language or compiler can locate what they need. When you use extern "c" in a C++ program, you're instructing the compiler to use a standardized way of recording names that's understandable by other software.

如果您了解汇编以及操作系统级别的工作方式，那么您就符合特定的ABI。ABI控制参数的传递方式、返回值放置的位置等。对于许多平台来说，只有一种ABI可供选择，在这些情况下，ABI只是“事情如何工作”。

然而，ABI也控制着c++中类/对象的布局。如果您希望能够跨模块边界传递对象引用，或者如果您希望混合使用不同编译器编译的代码，这是必要的。

此外，如果您有一个可以执行32位二进制文件的64位操作系统，那么32位和64位代码将有不同的abi。

通常，链接到相同可执行文件中的任何代码都必须符合相同的ABI。如果希望在使用不同abi的代码之间进行通信，则必须使用某种形式的RPC或序列化协议。

我认为你过于努力地将不同类型的界面挤进一个固定的特征集。例如，一个界面不一定要分成消费者和生产者。接口只是两个实体交互的约定。

abi可以(部分地)与isa无关。有些方面(如调用约定)依赖于ISA，而其他方面(如c++类布局)则不依赖于ISA。

定义良好的ABI对于编写编译器的人来说非常重要。如果没有定义良好的ABI，就不可能生成可互操作的代码。

编辑:需要澄清的一些注释:

ABI中的“二进制”并不排除字符串或文本的使用。如果您想要链接一个导出c++类的DLL，则必须对其中的方法和类型签名进行编码。这就是c++名称破坏的用武之地。 您从未提供ABI的原因是绝大多数程序员都不会这样做。ABI是由设计平台(即操作系统)的人提供的，很少有程序员有特权设计一个广泛使用的ABI。

区分ABI和API的最好方法是了解它的用途和原因:

对于x86-64，通常有一个ABI(对于x86 32位，有另一组ABI):

http://www.x86-64.org/documentation/abi.pdf

https://developer.apple.com/library/mac/documentation/DeveloperTools/Conceptual/LowLevelABI/140-x86-64_Function_Calling_Conventions/x86_64.html

http://people.freebsd.org/~obrien/amd64-elf-abi.pdf

Linux + FreeBSD + MacOSX紧随其后，略有变化。Windows x64有自己的ABI:

http://eli.thegreenplace.net/2011/09/06/stack-frame-layout-on-x86-64/

Knowing the ABI and assuming other compiler follows it as well, then the binaries theoretically know how to call each other (libraries API in particular) and pass parameters over the stack or by registers etc. Or what registers will be changed upon calling the functions etc. Essentially these knowledge will help software to integrate with one another. Knowing the order of the registers / stack layout I can easily piece together different software written in assemblies together without much problem.

但是API是不同的:

它是一个定义了参数的高级函数名，这样如果不同的软件使用这些API构建，就可以相互调用。但是必须遵守SAME ABI的附加要求。

例如，Windows曾经是POSIX API兼容的:

https://en.wikipedia.org/wiki/Windows_Services_for_UNIX

https://en.wikipedia.org/wiki/POSIX

Linux也是POSIX兼容的。但是二进制文件不能被移动并立即运行。但是因为它们在POSIX兼容的API中使用了相同的NAMES，所以您可以在C语言中使用相同的软件，在不同的操作系统中重新编译它，并立即让它运行起来。

API是为了简化软件集成-预编译阶段。所以在编译之后，如果ABI不同的话，软件看起来会完全不同。

ABI的目的是在二进制/汇编级别定义软件的精确集成。