ABI,Legacy ABI, EABI

ABI,Legacy ABI, EABI

GCC view

New ABI is not only a new ABI field, it is also a new GCC target.

Legacy ABI:  * ABI flags passed to binutils: -mabi=apcs-gnu -mfpu=fpa

Arm EABI: * ABI flags passed by gcc to binutils: -mabi=aapcs-linux -mfloat-abi=soft -meabi=4

application binary interface (ABI) describes the low-level interface between an application program and the operating system, or the interface between an application and its libraries, or that between component parts of an application. An ABI is similar to an application programming interface (API); however, the latter defines a source code interface.[1] Simply put, ABIs enable binary compatibility, whereas APIs enable source code compatibility.

ABIs cover details such as 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),[2] allows a program from one operating system supporting that ABI to run without modifications on any other such system. 

Other ABIs standardize details such as the C++ name decoration,[3] exception propagation,[4] and calling convention between compilers on the same platform, but do not require cross-platform compatibility.