分类： LINUX
2011-10-27 08:39:31
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Terminology
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. However, there are one or two programs that sometimes describe an old ABI binary as "EABI".
To add to the confusion, powerpc has also had an ABI called "EABI" for some, which has nothing to do with this one.
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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
* gcc -dumpmachine: arm-unknown-linux
* objdump -x for compiled binary:
private flags = 2: [APCS-32] [FPA float format] [has entry point]* "file" on compiled Debian binary:
ELF 32-bit LSB executable, ARM, version 1 (ARM), for GNU/Linux 2.2.0, dynamically linked (uses shared libs), for GNU/Linux 2.2.0, stripped* "readelf -h | grep Flags""
Flags: 0x0
Arm EABI:
* ABI flags passed by gcc to binutils: -mabi=aapcs-linux -mfloat-abi=soft -meabi=4
* gcc -dumpmachine: arm-unknown-linux-gnueabi
* objdump -x for compiled binary:
private flags = 4000002: [Version4 EABI] [has entry point]* "file" on compiled binary (under Debian):
ELF 32-bit LSB executable, ARM, version 1 (SYSV), for GNU/Linux 2.4.17, dynamically linked (uses shared libs), for GNU/Linux 2.4.17, stripped* "readelf -h | grep Flags""
Flags: 0x4000002, has entry point, Version4 EABI
Furthermore, as well as the usual __arm__ and maybe also __thumb__ symbols, the C preprocessor symbol __ARM_EABI__ is also defined when compiling into EABI.
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Struct packing and alignment
With the new ABI, default structure packing changes, as do some default data sizes and alignment (which also have a knock-on effect on structure packing). In particular the minimum size and alignment of a structure was 4 bytes. Under the EABI there is no minimum and the alignment is determined by the types of the components it contains. This will break programs that know too much about the way structures are packed and can break code that writes binary files by dumping and reading structures.
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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.
For example, the POSIX standard defines an API that allows a wide range of common computing functions to be written such that they may operate on many different systems (Mac OS X, various BSDs and Microsoft Windows all implement this interface); however, making use of this requires re-compilation for each platform. A compatible ABI, on the other hand, allows compiled object code to function without any changes, on any system implementing that ABI. This is advantageous to both software providers (where they may distribute existing software on new systems without producing/distributing upgrades) and users (where they may install older software on their new systems without purchasing upgrades), although this generally requires various software libraries implementing the necessary APIs too.
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.
What is EABI?
GNU EABI is a new application binary interface (ABI) for Linux. It is part of a new family of ABI's from ARM
